/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1982, 1986, 1989, 1991, 1993
 *      The Regents of the University of California. All Rights Reserved.
 * Copyright (c) 2004-2009 Robert N. M. Watson All Rights Reserved.
 * Copyright (c) 2018 Matthew Macy
 * Copyright (c) 2022-2025 Gleb Smirnoff <glebius@FreeBSD.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * UNIX Domain (Local) Sockets
 *
 * This is an implementation of UNIX (local) domain sockets.  Each socket has
 * an associated struct unpcb (UNIX protocol control block).  Stream sockets
 * may be connected to 0 or 1 other socket.  Datagram sockets may be
 * connected to 0, 1, or many other sockets.  Sockets may be created and
 * connected in pairs (socketpair(2)), or bound/connected to using the file
 * system name space.  For most purposes, only the receive socket buffer is
 * used, as sending on one socket delivers directly to the receive socket
 * buffer of a second socket.
 *
 * The implementation is substantially complicated by the fact that
 * "ancillary data", such as file descriptors or credentials, may be passed
 * across UNIX domain sockets.  The potential for passing UNIX domain sockets
 * over other UNIX domain sockets requires the implementation of a simple
 * garbage collector to find and tear down cycles of disconnected sockets.
 *
 * TODO:
 *      RDM
 *      rethink name space problems
 *      need a proper out-of-band
 */

#include "opt_ddb.h"

#include <sys/param.h>
#include <sys/capsicum.h>
#include <sys/domain.h>
#include <sys/eventhandler.h>
#include <sys/fcntl.h>
#include <sys/file.h>
#include <sys/filedesc.h>
#include <sys/jail.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/mount.h>
#include <sys/mutex.h>
#include <sys/namei.h>
#include <sys/poll.h>
#include <sys/proc.h>
#include <sys/protosw.h>
#include <sys/queue.h>
#include <sys/resourcevar.h>
#include <sys/rwlock.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/signalvar.h>
#include <sys/stat.h>
#include <sys/sx.h>
#include <sys/sysctl.h>
#include <sys/systm.h>
#include <sys/taskqueue.h>
#include <sys/un.h>
#include <sys/unpcb.h>
#include <sys/vnode.h>

#include <net/vnet.h>

#ifdef DDB
#include <ddb/ddb.h>
#endif

#include <security/mac/mac_framework.h>

#include <vm/uma.h>

MALLOC_DECLARE(M_FILECAPS);

static struct domain localdomain;

static uma_zone_t       unp_zone;
static unp_gen_t        unp_gencnt;     /* (l) */
static u_int            unp_count;      /* (l) Count of local sockets. */
static ino_t            unp_ino;        /* Prototype for fake inode numbers. */
static int              unp_rights;     /* (g) File descriptors in flight. */
static struct unp_head  unp_shead;      /* (l) List of stream sockets. */
static struct unp_head  unp_dhead;      /* (l) List of datagram sockets. */
static struct unp_head  unp_sphead;     /* (l) List of seqpacket sockets. */
static struct mtx_pool  *unp_vp_mtxpool;

struct unp_defer {
        SLIST_ENTRY(unp_defer) ud_link;
        struct file *ud_fp;
};
static SLIST_HEAD(, unp_defer) unp_defers;
static int unp_defers_count;

static const struct sockaddr    sun_noname = {
        .sa_len = sizeof(sun_noname),
        .sa_family = AF_LOCAL,
};

/*
 * Garbage collection of cyclic file descriptor/socket references occurs
 * asynchronously in a taskqueue context in order to avoid recursion and
 * reentrance in the UNIX domain socket, file descriptor, and socket layer
 * code.  See unp_gc() for a full description.
 */
static struct timeout_task unp_gc_task;

/*
 * The close of unix domain sockets attached as SCM_RIGHTS is
 * postponed to the taskqueue, to avoid arbitrary recursion depth.
 * The attached sockets might have another sockets attached.
 */
static struct task      unp_defer_task;

/*
 * SOCK_STREAM and SOCK_SEQPACKET unix(4) sockets fully bypass the send buffer,
 * however the notion of send buffer still makes sense with them.  Its size is
 * the amount of space that a send(2) syscall may copyin(9) before checking
 * with the receive buffer of a peer.  Although not linked anywhere yet,
 * pointed to by a stack variable, effectively it is a buffer that needs to be
 * sized.
 *
 * SOCK_DGRAM sockets really use the sendspace as the maximum datagram size,
 * and don't really want to reserve the sendspace.  Their recvspace should be
 * large enough for at least one max-size datagram plus address.
 */
static u_long   unpst_sendspace = 64*1024;
static u_long   unpst_recvspace = 64*1024;
static u_long   unpdg_maxdgram = 8*1024;        /* support 8KB syslog msgs */
static u_long   unpdg_recvspace = 16*1024;
static u_long   unpsp_sendspace = 64*1024;
static u_long   unpsp_recvspace = 64*1024;

static SYSCTL_NODE(_net, PF_LOCAL, local, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
    "Local domain");
static SYSCTL_NODE(_net_local, SOCK_STREAM, stream,
    CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
    "SOCK_STREAM");
static SYSCTL_NODE(_net_local, SOCK_DGRAM, dgram,
    CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
    "SOCK_DGRAM");
static SYSCTL_NODE(_net_local, SOCK_SEQPACKET, seqpacket,
    CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
    "SOCK_SEQPACKET");

SYSCTL_ULONG(_net_local_stream, OID_AUTO, sendspace, CTLFLAG_RW,
           &unpst_sendspace, 0, "Default stream send space.");
SYSCTL_ULONG(_net_local_stream, OID_AUTO, recvspace, CTLFLAG_RW,
           &unpst_recvspace, 0, "Default stream receive space.");
SYSCTL_ULONG(_net_local_dgram, OID_AUTO, maxdgram, CTLFLAG_RW,
           &unpdg_maxdgram, 0, "Maximum datagram size.");
SYSCTL_ULONG(_net_local_dgram, OID_AUTO, recvspace, CTLFLAG_RW,
           &unpdg_recvspace, 0, "Default datagram receive space.");
SYSCTL_ULONG(_net_local_seqpacket, OID_AUTO, maxseqpacket, CTLFLAG_RW,
           &unpsp_sendspace, 0, "Default seqpacket send space.");
SYSCTL_ULONG(_net_local_seqpacket, OID_AUTO, recvspace, CTLFLAG_RW,
           &unpsp_recvspace, 0, "Default seqpacket receive space.");
SYSCTL_INT(_net_local, OID_AUTO, inflight, CTLFLAG_RD, &unp_rights, 0,
    "File descriptors in flight.");
SYSCTL_INT(_net_local, OID_AUTO, deferred, CTLFLAG_RD,
    &unp_defers_count, 0,
    "File descriptors deferred to taskqueue for close.");

/*
 * Locking and synchronization:
 *
 * Several types of locks exist in the local domain socket implementation:
 * - a global linkage lock
 * - a global connection list lock
 * - the mtxpool lock
 * - per-unpcb mutexes
 *
 * The linkage lock protects the global socket lists, the generation number
 * counter and garbage collector state.
 *
 * The connection list lock protects the list of referring sockets in a datagram
 * socket PCB.  This lock is also overloaded to protect a global list of
 * sockets whose buffers contain socket references in the form of SCM_RIGHTS
 * messages.  To avoid recursion, such references are released by a dedicated
 * thread.
 *
 * The mtxpool lock protects the vnode from being modified while referenced.
 * Lock ordering rules require that it be acquired before any PCB locks.
 *
 * The unpcb lock (unp_mtx) protects the most commonly referenced fields in the
 * unpcb.  This includes the unp_conn field, which either links two connected
 * PCBs together (for connected socket types) or points at the destination
 * socket (for connectionless socket types).  The operations of creating or
 * destroying a connection therefore involve locking multiple PCBs.  To avoid
 * lock order reversals, in some cases this involves dropping a PCB lock and
 * using a reference counter to maintain liveness.
 *
 * UNIX domain sockets each have an unpcb hung off of their so_pcb pointer,
 * allocated in pr_attach() and freed in pr_detach().  The validity of that
 * pointer is an invariant, so no lock is required to dereference the so_pcb
 * pointer if a valid socket reference is held by the caller.  In practice,
 * this is always true during operations performed on a socket.  Each unpcb
 * has a back-pointer to its socket, unp_socket, which will be stable under
 * the same circumstances.
 *
 * This pointer may only be safely dereferenced as long as a valid reference
 * to the unpcb is held.  Typically, this reference will be from the socket,
 * or from another unpcb when the referring unpcb's lock is held (in order
 * that the reference not be invalidated during use).  For example, to follow
 * unp->unp_conn->unp_socket, you need to hold a lock on unp_conn to guarantee
 * that detach is not run clearing unp_socket.
 *
 * Blocking with UNIX domain sockets is a tricky issue: unlike most network
 * protocols, bind() is a non-atomic operation, and connect() requires
 * potential sleeping in the protocol, due to potentially waiting on local or
 * distributed file systems.  We try to separate "lookup" operations, which
 * may sleep, and the IPC operations themselves, which typically can occur
 * with relative atomicity as locks can be held over the entire operation.
 *
 * Another tricky issue is simultaneous multi-threaded or multi-process
 * access to a single UNIX domain socket.  These are handled by the flags
 * UNP_CONNECTING and UNP_BINDING, which prevent concurrent connecting or
 * binding, both of which involve dropping UNIX domain socket locks in order
 * to perform namei() and other file system operations.
 */
static struct rwlock    unp_link_rwlock;
static struct mtx       unp_defers_lock;

#define UNP_LINK_LOCK_INIT()            rw_init(&unp_link_rwlock,       \
                                            "unp_link_rwlock")

#define UNP_LINK_LOCK_ASSERT()          rw_assert(&unp_link_rwlock,     \
                                            RA_LOCKED)
#define UNP_LINK_UNLOCK_ASSERT()        rw_assert(&unp_link_rwlock,     \
                                            RA_UNLOCKED)

#define UNP_LINK_RLOCK()                rw_rlock(&unp_link_rwlock)
#define UNP_LINK_RUNLOCK()              rw_runlock(&unp_link_rwlock)
#define UNP_LINK_WLOCK()                rw_wlock(&unp_link_rwlock)
#define UNP_LINK_WUNLOCK()              rw_wunlock(&unp_link_rwlock)
#define UNP_LINK_WLOCK_ASSERT()         rw_assert(&unp_link_rwlock,     \
                                            RA_WLOCKED)
#define UNP_LINK_WOWNED()               rw_wowned(&unp_link_rwlock)

#define UNP_DEFERRED_LOCK_INIT()        mtx_init(&unp_defers_lock, \
                                            "unp_defer", NULL, MTX_DEF)
#define UNP_DEFERRED_LOCK()             mtx_lock(&unp_defers_lock)
#define UNP_DEFERRED_UNLOCK()           mtx_unlock(&unp_defers_lock)

#define UNP_REF_LIST_LOCK()             UNP_DEFERRED_LOCK();
#define UNP_REF_LIST_UNLOCK()           UNP_DEFERRED_UNLOCK();

#define UNP_PCB_LOCK_INIT(unp)          mtx_init(&(unp)->unp_mtx,       \
                                            "unp", "unp",       \
                                            MTX_DUPOK|MTX_DEF)
#define UNP_PCB_LOCK_DESTROY(unp)       mtx_destroy(&(unp)->unp_mtx)
#define UNP_PCB_LOCKPTR(unp)            (&(unp)->unp_mtx)
#define UNP_PCB_LOCK(unp)               mtx_lock(&(unp)->unp_mtx)
#define UNP_PCB_TRYLOCK(unp)            mtx_trylock(&(unp)->unp_mtx)
#define UNP_PCB_UNLOCK(unp)             mtx_unlock(&(unp)->unp_mtx)
#define UNP_PCB_OWNED(unp)              mtx_owned(&(unp)->unp_mtx)
#define UNP_PCB_LOCK_ASSERT(unp)        mtx_assert(&(unp)->unp_mtx, MA_OWNED)
#define UNP_PCB_UNLOCK_ASSERT(unp)      mtx_assert(&(unp)->unp_mtx, MA_NOTOWNED)

static int      uipc_connect2(struct socket *, struct socket *);
static int      uipc_ctloutput(struct socket *, struct sockopt *);
static int      unp_connect(struct socket *, struct sockaddr *,
                    struct thread *);
static int      unp_connectat(int, struct socket *, struct sockaddr *,
                    struct thread *, bool);
static void     unp_connect2(struct socket *, struct socket *, bool);
static void     unp_disconnect(struct unpcb *unp, struct unpcb *unp2);
static void     unp_dispose(struct socket *so);
static void     unp_drop(struct unpcb *);
static void     unp_gc(__unused void *, int);
static void     unp_scan(struct mbuf *, void (*)(struct filedescent **, int));
static void     unp_discard(struct file *);
static void     unp_freerights(struct filedescent **, int);
static int      unp_internalize(struct mbuf *, struct mchain *,
                    struct thread *);
static void     unp_internalize_fp(struct file *);
static int      unp_externalize(struct mbuf *, struct mbuf **, int);
static int      unp_externalize_fp(struct file *);
static void     unp_addsockcred(struct thread *, struct mchain *, int);
static void     unp_process_defers(void * __unused, int);

static void     uipc_wrknl_lock(void *);
static void     uipc_wrknl_unlock(void *);
static void     uipc_wrknl_assert_lock(void *, int);

static void
unp_pcb_hold(struct unpcb *unp)
{
        u_int old __unused;

        old = refcount_acquire(&unp->unp_refcount);
        KASSERT(old > 0, ("%s: unpcb %p has no references", __func__, unp));
}

static __result_use_check bool
unp_pcb_rele(struct unpcb *unp)
{
        bool ret;

        UNP_PCB_LOCK_ASSERT(unp);

        if ((ret = refcount_release(&unp->unp_refcount))) {
                UNP_PCB_UNLOCK(unp);
                UNP_PCB_LOCK_DESTROY(unp);
                uma_zfree(unp_zone, unp);
        }
        return (ret);
}

static void
unp_pcb_rele_notlast(struct unpcb *unp)
{
        bool ret __unused;

        ret = refcount_release(&unp->unp_refcount);
        KASSERT(!ret, ("%s: unpcb %p has no references", __func__, unp));
}

static void
unp_pcb_lock_pair(struct unpcb *unp, struct unpcb *unp2)
{
        UNP_PCB_UNLOCK_ASSERT(unp);
        UNP_PCB_UNLOCK_ASSERT(unp2);

        if (unp == unp2) {
                UNP_PCB_LOCK(unp);
        } else if ((uintptr_t)unp2 > (uintptr_t)unp) {
                UNP_PCB_LOCK(unp);
                UNP_PCB_LOCK(unp2);
        } else {
                UNP_PCB_LOCK(unp2);
                UNP_PCB_LOCK(unp);
        }
}

static void
unp_pcb_unlock_pair(struct unpcb *unp, struct unpcb *unp2)
{
        UNP_PCB_UNLOCK(unp);
        if (unp != unp2)
                UNP_PCB_UNLOCK(unp2);
}

/*
 * Try to lock the connected peer of an already locked socket.  In some cases
 * this requires that we unlock the current socket.  The pairbusy counter is
 * used to block concurrent connection attempts while the lock is dropped.  The
 * caller must be careful to revalidate PCB state.
 */
static struct unpcb *
unp_pcb_lock_peer(struct unpcb *unp)
{
        struct unpcb *unp2;

        UNP_PCB_LOCK_ASSERT(unp);
        unp2 = unp->unp_conn;
        if (unp2 == NULL)
                return (NULL);
        if (__predict_false(unp == unp2))
                return (unp);

        UNP_PCB_UNLOCK_ASSERT(unp2);

        if (__predict_true(UNP_PCB_TRYLOCK(unp2)))
                return (unp2);
        if ((uintptr_t)unp2 > (uintptr_t)unp) {
                UNP_PCB_LOCK(unp2);
                return (unp2);
        }
        unp->unp_pairbusy++;
        unp_pcb_hold(unp2);
        UNP_PCB_UNLOCK(unp);

        UNP_PCB_LOCK(unp2);
        UNP_PCB_LOCK(unp);
        KASSERT(unp->unp_conn == unp2 || unp->unp_conn == NULL,
            ("%s: socket %p was reconnected", __func__, unp));
        if (--unp->unp_pairbusy == 0 && (unp->unp_flags & UNP_WAITING) != 0) {
                unp->unp_flags &= ~UNP_WAITING;
                wakeup(unp);
        }
        if (unp_pcb_rele(unp2)) {
                /* unp2 is unlocked. */
                return (NULL);
        }
        if (unp->unp_conn == NULL) {
                UNP_PCB_UNLOCK(unp2);
                return (NULL);
        }
        return (unp2);
}

/*
 * Try to lock peer of our socket for purposes of sending data to it.
 */
static int
uipc_lock_peer(struct socket *so, struct unpcb **unp2)
{
        struct unpcb *unp;
        int error;

        unp = sotounpcb(so);
        UNP_PCB_LOCK(unp);
        *unp2 = unp_pcb_lock_peer(unp);
        if (__predict_false(so->so_error != 0)) {
                error = so->so_error;
                so->so_error = 0;
                UNP_PCB_UNLOCK(unp);
                if (*unp2 != NULL)
                        UNP_PCB_UNLOCK(*unp2);
                return (error);
        }
        if (__predict_false(*unp2 == NULL)) {
                /*
                 * Different error code for a previously connected socket and
                 * a never connected one.  The SS_ISDISCONNECTED is set in the
                 * unp_soisdisconnected() and is synchronized by the pcb lock.
                 */
                error = so->so_state & SS_ISDISCONNECTED ? EPIPE : ENOTCONN;
                UNP_PCB_UNLOCK(unp);
                return (error);
        }
        UNP_PCB_UNLOCK(unp);

        return (0);
}

static void
uipc_abort(struct socket *so)
{
        struct unpcb *unp, *unp2;

        unp = sotounpcb(so);
        KASSERT(unp != NULL, ("uipc_abort: unp == NULL"));
        UNP_PCB_UNLOCK_ASSERT(unp);

        UNP_PCB_LOCK(unp);
        unp2 = unp->unp_conn;
        if (unp2 != NULL) {
                unp_pcb_hold(unp2);
                UNP_PCB_UNLOCK(unp);
                unp_drop(unp2);
        } else
                UNP_PCB_UNLOCK(unp);
}

static int
uipc_attach(struct socket *so, int proto, struct thread *td)
{
        u_long sendspace, recvspace;
        struct unpcb *unp;
        int error, rcvmtxopts;
        bool locked;

        KASSERT(so->so_pcb == NULL, ("uipc_attach: so_pcb != NULL"));
        switch (so->so_type) {
        case SOCK_DGRAM:
                STAILQ_INIT(&so->so_rcv.uxdg_mb);
                STAILQ_INIT(&so->so_snd.uxdg_mb);
                TAILQ_INIT(&so->so_rcv.uxdg_conns);
                /*
                 * Since send buffer is either bypassed or is a part
                 * of one-to-many receive buffer, we assign both space
                 * limits to unpdg_recvspace.
                 */
                sendspace = recvspace = unpdg_recvspace;
                rcvmtxopts = 0;
                break;

        case SOCK_STREAM:
                sendspace = unpst_sendspace;
                recvspace = unpst_recvspace;
                goto common;

        case SOCK_SEQPACKET:
                sendspace = unpsp_sendspace;
                recvspace = unpsp_recvspace;
common:
                rcvmtxopts = MTX_DUPOK;
                knlist_init(&so->so_wrsel.si_note, so, uipc_wrknl_lock,
                    uipc_wrknl_unlock, uipc_wrknl_assert_lock);
                STAILQ_INIT(&so->so_rcv.uxst_mbq);
                break;
        default:
                panic("uipc_attach");
        }
        mtx_init(&so->so_rcv_mtx, "unix so_rcv", NULL, MTX_DEF | rcvmtxopts);
        mtx_init(&so->so_snd_mtx, "unix so_snd", NULL, MTX_DEF);
        error = soreserve(so, sendspace, recvspace);
        if (error)
                return (error);
        unp = uma_zalloc(unp_zone, M_NOWAIT | M_ZERO);
        if (unp == NULL)
                return (ENOBUFS);
        LIST_INIT(&unp->unp_refs);
        UNP_PCB_LOCK_INIT(unp);
        unp->unp_socket = so;
        so->so_pcb = unp;
        refcount_init(&unp->unp_refcount, 1);
        unp->unp_mode = ACCESSPERMS;

        if ((locked = UNP_LINK_WOWNED()) == false)
                UNP_LINK_WLOCK();

        unp->unp_gencnt = ++unp_gencnt;
        unp->unp_ino = ++unp_ino;
        unp_count++;
        switch (so->so_type) {
        case SOCK_STREAM:
                LIST_INSERT_HEAD(&unp_shead, unp, unp_link);
                break;

        case SOCK_DGRAM:
                LIST_INSERT_HEAD(&unp_dhead, unp, unp_link);
                break;

        case SOCK_SEQPACKET:
                LIST_INSERT_HEAD(&unp_sphead, unp, unp_link);
                break;

        default:
                panic("uipc_attach");
        }

        if (locked == false)
                UNP_LINK_WUNLOCK();

        return (0);
}

static int
uipc_bindat(int fd, struct socket *so, struct sockaddr *nam, struct thread *td)
{
        struct sockaddr_un *soun = (struct sockaddr_un *)nam;
        struct vattr vattr;
        int error, namelen;
        struct nameidata nd;
        struct unpcb *unp;
        struct vnode *vp;
        struct mount *mp;
        cap_rights_t rights;
        char *buf;
        mode_t mode;

        if (nam->sa_family != AF_UNIX)
                return (EAFNOSUPPORT);

        unp = sotounpcb(so);
        KASSERT(unp != NULL, ("uipc_bind: unp == NULL"));

        if (soun->sun_len > sizeof(struct sockaddr_un))
                return (EINVAL);
        namelen = soun->sun_len - offsetof(struct sockaddr_un, sun_path);
        if (namelen <= 0)
                return (EINVAL);

        /*
         * We don't allow simultaneous bind() calls on a single UNIX domain
         * socket, so flag in-progress operations, and return an error if an
         * operation is already in progress.
         *
         * Historically, we have not allowed a socket to be rebound, so this
         * also returns an error.  Not allowing re-binding simplifies the
         * implementation and avoids a great many possible failure modes.
         */
        UNP_PCB_LOCK(unp);
        if (unp->unp_vnode != NULL) {
                UNP_PCB_UNLOCK(unp);
                return (EINVAL);
        }
        if (unp->unp_flags & UNP_BINDING) {
                UNP_PCB_UNLOCK(unp);
                return (EALREADY);
        }
        unp->unp_flags |= UNP_BINDING;
        mode = unp->unp_mode & ~td->td_proc->p_pd->pd_cmask;
        UNP_PCB_UNLOCK(unp);

        buf = malloc(namelen + 1, M_TEMP, M_WAITOK);
        bcopy(soun->sun_path, buf, namelen);
        buf[namelen] = 0;

restart:
        NDINIT_ATRIGHTS(&nd, CREATE, NOFOLLOW | LOCKPARENT | NOCACHE,
            UIO_SYSSPACE, buf, fd, cap_rights_init_one(&rights, CAP_BINDAT));
/* SHOULD BE ABLE TO ADOPT EXISTING AND wakeup() ALA FIFO's */
        error = namei(&nd);
        if (error)
                goto error;
        vp = nd.ni_vp;
        if (vp != NULL || vn_start_write(nd.ni_dvp, &mp, V_NOWAIT) != 0) {
                NDFREE_PNBUF(&nd);
                if (nd.ni_dvp == vp)
                        vrele(nd.ni_dvp);
                else
                        vput(nd.ni_dvp);
                if (vp != NULL) {
                        vrele(vp);
                        error = EADDRINUSE;
                        goto error;
                }
                error = vn_start_write(NULL, &mp, V_XSLEEP | V_PCATCH);
                if (error)
                        goto error;
                goto restart;
        }
        VATTR_NULL(&vattr);
        vattr.va_type = VSOCK;
        vattr.va_mode = mode;
#ifdef MAC
        error = mac_vnode_check_create(td->td_ucred, nd.ni_dvp, &nd.ni_cnd,
            &vattr);
#endif
        if (error == 0) {
                /*
                 * The prior lookup may have left LK_SHARED in cn_lkflags,
                 * and VOP_CREATE technically only requires the new vnode to
                 * be locked shared. Most filesystems will return the new vnode
                 * locked exclusive regardless, but we should explicitly
                 * specify that here since we require it and assert to that
                 * effect below.
                 */
                nd.ni_cnd.cn_lkflags = (nd.ni_cnd.cn_lkflags & ~LK_SHARED) |
                    LK_EXCLUSIVE;
                error = VOP_CREATE(nd.ni_dvp, &nd.ni_vp, &nd.ni_cnd, &vattr);
        }
        NDFREE_PNBUF(&nd);
        if (error) {
                VOP_VPUT_PAIR(nd.ni_dvp, NULL, true);
                vn_finished_write(mp);
                if (error == ERELOOKUP)
                        goto restart;
                goto error;
        }
        vp = nd.ni_vp;
        ASSERT_VOP_ELOCKED(vp, "uipc_bind");
        soun = (struct sockaddr_un *)sodupsockaddr(nam, M_WAITOK);

        UNP_PCB_LOCK(unp);
        VOP_UNP_BIND(vp, unp);
        unp->unp_vnode = vp;
        unp->unp_addr = soun;
        unp->unp_flags &= ~UNP_BINDING;
        UNP_PCB_UNLOCK(unp);
        vref(vp);
        VOP_VPUT_PAIR(nd.ni_dvp, &vp, true);
        vn_finished_write(mp);
        free(buf, M_TEMP);
        return (0);

error:
        UNP_PCB_LOCK(unp);
        unp->unp_flags &= ~UNP_BINDING;
        UNP_PCB_UNLOCK(unp);
        free(buf, M_TEMP);
        return (error);
}

static int
uipc_bind(struct socket *so, struct sockaddr *nam, struct thread *td)
{

        return (uipc_bindat(AT_FDCWD, so, nam, td));
}

static int
uipc_connect(struct socket *so, struct sockaddr *nam, struct thread *td)
{
        int error;

        KASSERT(td == curthread, ("uipc_connect: td != curthread"));
        error = unp_connect(so, nam, td);
        return (error);
}

static int
uipc_connectat(int fd, struct socket *so, struct sockaddr *nam,
    struct thread *td)
{
        int error;

        KASSERT(td == curthread, ("uipc_connectat: td != curthread"));
        error = unp_connectat(fd, so, nam, td, false);
        return (error);
}

static void
uipc_close(struct socket *so)
{
        struct unpcb *unp, *unp2;
        struct vnode *vp = NULL;
        struct mtx *vplock;

        unp = sotounpcb(so);
        KASSERT(unp != NULL, ("uipc_close: unp == NULL"));

        vplock = NULL;
        if ((vp = unp->unp_vnode) != NULL) {
                vplock = mtx_pool_find(unp_vp_mtxpool, vp);
                mtx_lock(vplock);
        }
        UNP_PCB_LOCK(unp);
        if (vp && unp->unp_vnode == NULL) {
                mtx_unlock(vplock);
                vp = NULL;
        }
        if (vp != NULL) {
                VOP_UNP_DETACH(vp);
                unp->unp_vnode = NULL;
        }
        if ((unp2 = unp_pcb_lock_peer(unp)) != NULL)
                unp_disconnect(unp, unp2);
        else
                UNP_PCB_UNLOCK(unp);
        if (vp) {
                mtx_unlock(vplock);
                vrele(vp);
        }
}

static int
uipc_chmod(struct socket *so, mode_t mode, struct ucred *cred __unused,
    struct thread *td __unused)
{
        struct unpcb *unp;
        int error;

        if ((mode & ~ACCESSPERMS) != 0)
                return (EINVAL);

        error = 0;
        unp = sotounpcb(so);
        UNP_PCB_LOCK(unp);
        if (unp->unp_vnode != NULL || (unp->unp_flags & UNP_BINDING) != 0)
                error = EINVAL;
        else
                unp->unp_mode = mode;
        UNP_PCB_UNLOCK(unp);
        return (error);
}

static int
uipc_connect2(struct socket *so1, struct socket *so2)
{
        struct unpcb *unp, *unp2;

        if (so1->so_type != so2->so_type)
                return (EPROTOTYPE);

        unp = so1->so_pcb;
        KASSERT(unp != NULL, ("uipc_connect2: unp == NULL"));
        unp2 = so2->so_pcb;
        KASSERT(unp2 != NULL, ("uipc_connect2: unp2 == NULL"));
        unp_pcb_lock_pair(unp, unp2);
        unp_connect2(so1, so2, false);
        unp_pcb_unlock_pair(unp, unp2);

        return (0);
}

static void
maybe_schedule_gc(void)
{
        if (atomic_load_int(&unp_rights) != 0)
                taskqueue_enqueue_timeout(taskqueue_thread, &unp_gc_task, -1);
}

static void
uipc_detach(struct socket *so)
{
        struct unpcb *unp, *unp2;
        struct mtx *vplock;
        struct vnode *vp;

        unp = sotounpcb(so);
        KASSERT(unp != NULL, ("uipc_detach: unp == NULL"));

        vp = NULL;
        vplock = NULL;

        if (!SOLISTENING(so))
                unp_dispose(so);

        UNP_LINK_WLOCK();
        LIST_REMOVE(unp, unp_link);
        if (unp->unp_gcflag & UNPGC_DEAD)
                LIST_REMOVE(unp, unp_dead);
        unp->unp_gencnt = ++unp_gencnt;
        --unp_count;
        UNP_LINK_WUNLOCK();

        UNP_PCB_UNLOCK_ASSERT(unp);
 restart:
        if ((vp = unp->unp_vnode) != NULL) {
                vplock = mtx_pool_find(unp_vp_mtxpool, vp);
                mtx_lock(vplock);
        }
        UNP_PCB_LOCK(unp);
        if (unp->unp_vnode != vp && unp->unp_vnode != NULL) {
                if (vplock)
                        mtx_unlock(vplock);
                UNP_PCB_UNLOCK(unp);
                goto restart;
        }
        if ((vp = unp->unp_vnode) != NULL) {
                VOP_UNP_DETACH(vp);
                unp->unp_vnode = NULL;
        }
        if ((unp2 = unp_pcb_lock_peer(unp)) != NULL)
                unp_disconnect(unp, unp2);
        else
                UNP_PCB_UNLOCK(unp);

        UNP_REF_LIST_LOCK();
        while (!LIST_EMPTY(&unp->unp_refs)) {
                struct unpcb *ref = LIST_FIRST(&unp->unp_refs);

                unp_pcb_hold(ref);
                UNP_REF_LIST_UNLOCK();

                MPASS(ref != unp);
                UNP_PCB_UNLOCK_ASSERT(ref);
                unp_drop(ref);
                UNP_REF_LIST_LOCK();
        }
        UNP_REF_LIST_UNLOCK();

        UNP_PCB_LOCK(unp);
        unp->unp_socket->so_pcb = NULL;
        unp->unp_socket = NULL;
        free(unp->unp_addr, M_SONAME);
        unp->unp_addr = NULL;
        if (!unp_pcb_rele(unp))
                UNP_PCB_UNLOCK(unp);
        if (vp) {
                mtx_unlock(vplock);
                vrele(vp);
        }
        maybe_schedule_gc();

        switch (so->so_type) {
        case SOCK_STREAM:
        case SOCK_SEQPACKET:
                MPASS(SOLISTENING(so) || (STAILQ_EMPTY(&so->so_rcv.uxst_mbq) &&
                    so->so_rcv.uxst_peer == NULL));
                break;
        case SOCK_DGRAM:
                /*
                 * Everything should have been unlinked/freed by unp_dispose()
                 * and/or unp_disconnect().
                 */
                MPASS(so->so_rcv.uxdg_peeked == NULL);
                MPASS(STAILQ_EMPTY(&so->so_rcv.uxdg_mb));
                MPASS(TAILQ_EMPTY(&so->so_rcv.uxdg_conns));
                MPASS(STAILQ_EMPTY(&so->so_snd.uxdg_mb));
        }

        mtx_destroy(&so->so_snd_mtx);
        mtx_destroy(&so->so_rcv_mtx);
}

static int
uipc_disconnect(struct socket *so)
{
        struct unpcb *unp, *unp2;

        unp = sotounpcb(so);
        KASSERT(unp != NULL, ("uipc_disconnect: unp == NULL"));

        UNP_PCB_LOCK(unp);
        if ((unp2 = unp_pcb_lock_peer(unp)) != NULL)
                unp_disconnect(unp, unp2);
        else
                UNP_PCB_UNLOCK(unp);
        return (0);
}

static void
uipc_fdclose(struct socket *so __unused)
{
        /*
         * Ensure that userspace can't create orphaned file descriptors without
         * triggering garbage collection.  Triggering GC from uipc_detach() is
         * not sufficient, since that's only closed once a socket reference
         * count drops to zero.
         */
        maybe_schedule_gc();
}

static int
uipc_listen(struct socket *so, int backlog, struct thread *td)
{
        struct unpcb *unp;
        int error;

        MPASS(so->so_type != SOCK_DGRAM);

        /*
         * Synchronize with concurrent connection attempts.
         */
        error = 0;
        unp = sotounpcb(so);
        UNP_PCB_LOCK(unp);
        if (unp->unp_conn != NULL || (unp->unp_flags & UNP_CONNECTING) != 0)
                error = EINVAL;
        else if (unp->unp_vnode == NULL)
                error = EDESTADDRREQ;
        if (error != 0) {
                UNP_PCB_UNLOCK(unp);
                return (error);
        }

        SOCK_LOCK(so);
        error = solisten_proto_check(so);
        if (error == 0) {
                cru2xt(td, &unp->unp_peercred);
                if (!SOLISTENING(so)) {
                        (void)chgsbsize(so->so_cred->cr_uidinfo,
                            &so->so_snd.sb_hiwat, 0, RLIM_INFINITY);
                        (void)chgsbsize(so->so_cred->cr_uidinfo,
                            &so->so_rcv.sb_hiwat, 0, RLIM_INFINITY);
                }
                solisten_proto(so, backlog);
        }
        SOCK_UNLOCK(so);
        UNP_PCB_UNLOCK(unp);
        return (error);
}

static int
uipc_peeraddr(struct socket *so, struct sockaddr *ret)
{
        struct unpcb *unp, *unp2;
        const struct sockaddr *sa;

        unp = sotounpcb(so);
        KASSERT(unp != NULL, ("uipc_peeraddr: unp == NULL"));

        UNP_PCB_LOCK(unp);
        unp2 = unp_pcb_lock_peer(unp);
        if (unp2 != NULL) {
                if (unp2->unp_addr != NULL)
                        sa = (struct sockaddr *)unp2->unp_addr;
                else
                        sa = &sun_noname;
                bcopy(sa, ret, sa->sa_len);
                unp_pcb_unlock_pair(unp, unp2);
        } else {
                UNP_PCB_UNLOCK(unp);
                sa = &sun_noname;
                bcopy(sa, ret, sa->sa_len);
        }
        return (0);
}

/*
 * pr_sosend() called with mbuf instead of uio is a kernel thread.  NFS,
 * netgraph(4) and other subsystems can call into socket code.  The
 * function will condition the mbuf so that it can be safely put onto socket
 * buffer and calculate its char count and mbuf count.
 *
 * Note: we don't support receiving control data from a kernel thread.  Our
 * pr_sosend methods have MPASS() to check that.  This may change.
 */
static void
uipc_reset_kernel_mbuf(struct mbuf *m, struct mchain *mc)
{

        M_ASSERTPKTHDR(m);

        m_clrprotoflags(m);
        m_tag_delete_chain(m, NULL);
        m->m_pkthdr.rcvif = NULL;
        m->m_pkthdr.flowid = 0;
        m->m_pkthdr.csum_flags = 0;
        m->m_pkthdr.fibnum = 0;
        m->m_pkthdr.rsstype = 0;

        mc_init_m(mc, m);
        MPASS(m->m_pkthdr.len == mc->mc_len);
}

#ifdef SOCKBUF_DEBUG
static inline void
uipc_stream_sbcheck(struct sockbuf *sb)
{
        struct mbuf *d;
        u_int dacc, dccc, dctl, dmbcnt;
        bool notready = false;

        dacc = dccc = dctl = dmbcnt = 0;
        STAILQ_FOREACH(d, &sb->uxst_mbq, m_stailq) {
                if (d == sb->uxst_fnrdy) {
                        MPASS(d->m_flags & M_NOTREADY);
                        notready = true;
                }
                if (d->m_type == MT_CONTROL)
                        dctl += d->m_len;
                else if (d->m_type == MT_DATA) {
                        dccc +=  d->m_len;
                        if (!notready)
                                dacc += d->m_len;
                } else
                        MPASS(0);
                dmbcnt += MSIZE;
                if (d->m_flags & M_EXT)
                        dmbcnt += d->m_ext.ext_size;
                if (d->m_stailq.stqe_next == NULL)
                        MPASS(sb->uxst_mbq.stqh_last == &d->m_stailq.stqe_next);
        }
        MPASS(sb->uxst_fnrdy == NULL || notready);
        MPASS(dacc == sb->sb_acc);
        MPASS(dccc == sb->sb_ccc);
        MPASS(dctl == sb->sb_ctl);
        MPASS(dmbcnt == sb->sb_mbcnt);
        (void)STAILQ_EMPTY(&sb->uxst_mbq);
}
#define UIPC_STREAM_SBCHECK(sb) uipc_stream_sbcheck(sb)
#else
#define UIPC_STREAM_SBCHECK(sb) do {} while (0)
#endif

/*
 * uipc_stream_sbspace() returns how much a writer can send, limited by char
 * count or mbuf memory use, whatever ends first.
 *
 * An obvious and legitimate reason for a socket having more data than allowed,
 * is lowering the limit with setsockopt(SO_RCVBUF) on already full buffer.
 * Also, sb_mbcnt may overcommit sb_mbmax in case if previous write observed
 * 'space < mbspace', but mchain allocated to hold 'space' bytes of data ended
 * up with 'mc_mlen > mbspace'.  A typical scenario would be a full buffer with
 * writer trying to push in a large write, and a slow reader, that reads just
 * a few bytes at a time.  In that case writer will keep creating new mbufs
 * with mc_split().  These mbufs will carry little chars, but will all point at
 * the same cluster, thus each adding cluster size to sb_mbcnt.  This means we
 * will count same cluster many times potentially underutilizing socket buffer.
 * We aren't optimizing towards ineffective readers.  Classic socket buffer had
 * the same "feature".
 */
static inline u_int
uipc_stream_sbspace(struct sockbuf *sb)
{
        u_int space, mbspace;

        if (__predict_true(sb->sb_hiwat >= sb->sb_ccc + sb->sb_ctl))
                space = sb->sb_hiwat - sb->sb_ccc - sb->sb_ctl;
        else
                return (0);
        if (__predict_true(sb->sb_mbmax >= sb->sb_mbcnt))
                mbspace = sb->sb_mbmax - sb->sb_mbcnt;
        else
                return (0);

        return (min(space, mbspace));
}

/*
 * UNIX version of generic sbwait() for writes.  We wait on peer's receive
 * buffer, using our timeout.
 */
static int
uipc_stream_sbwait(struct socket *so, sbintime_t timeo)
{
        struct sockbuf *sb = &so->so_rcv;

        SOCK_RECVBUF_LOCK_ASSERT(so);
        sb->sb_flags |= SB_WAIT;
        return (msleep_sbt(&sb->sb_acc, SOCK_RECVBUF_MTX(so), PSOCK | PCATCH,
            "sbwait", timeo, 0, 0));
}

static int
uipc_sosend_stream_or_seqpacket(struct socket *so, struct sockaddr *addr,
    struct uio *uio0, struct mbuf *m, struct mbuf *c, int flags,
    struct thread *td)
{
        struct unpcb *unp2;
        struct socket *so2;
        struct sockbuf *sb;
        struct uio *uio;
        struct mchain mc, cmc;
        size_t resid, sent;
        bool nonblock, eor, aio;
        int error;

        MPASS((uio0 != NULL && m == NULL) || (m != NULL && uio0 == NULL));
        MPASS(m == NULL || c == NULL);

        if (__predict_false(flags & MSG_OOB))
                return (EOPNOTSUPP);

        nonblock = (so->so_state & SS_NBIO) ||
            (flags & (MSG_DONTWAIT | MSG_NBIO));
        eor = flags & MSG_EOR;

        mc = MCHAIN_INITIALIZER(&mc);
        cmc = MCHAIN_INITIALIZER(&cmc);
        sent = 0;
        aio = false;

        if (m == NULL) {
                if (c != NULL && (error = unp_internalize(c, &cmc, td)))
                        goto out;
                /*
                 * This function may read more data from the uio than it would
                 * then place on socket.  That would leave uio inconsistent
                 * upon return.  Normally uio is allocated on the stack of the
                 * syscall thread and we don't care about leaving it consistent.
                 * However, aio(9) will allocate a uio as part of job and will
                 * use it to track progress.  We detect aio(9) checking the
                 * SB_AIO_RUNNING flag.  It is safe to check it without lock
                 * cause it is set and cleared in the same taskqueue thread.
                 *
                 * This check can also produce a false positive: there is
                 * aio(9) job and also there is a syscall we are serving now.
                 * No sane software does that, it would leave to a mess in
                 * the socket buffer, as aio(9) doesn't grab the I/O sx(9).
                 * But syzkaller can create this mess.  For such false positive
                 * our goal is just don't panic or leak memory.
                 */
                if (__predict_false(so->so_snd.sb_flags & SB_AIO_RUNNING)) {
                        uio = cloneuio(uio0);
                        aio = true;
                } else {
                        uio = uio0;
                        resid = uio->uio_resid;
                }
                /*
                 * Optimization for a case when our send fits into the receive
                 * buffer - do the copyin before taking any locks, sized to our
                 * send buffer.  Later copyins will also take into account
                 * space in the peer's receive buffer.
                 */
                error = mc_uiotomc(&mc, uio, so->so_snd.sb_hiwat, 0, M_WAITOK,
                    eor ? M_EOR : 0);
                if (__predict_false(error))
                        goto out2;
        } else
                uipc_reset_kernel_mbuf(m, &mc);

        error = SOCK_IO_SEND_LOCK(so, SBLOCKWAIT(flags));
        if (error)
                goto out2;

        if (__predict_false((error = uipc_lock_peer(so, &unp2)) != 0))
                goto out3;

        if (unp2->unp_flags & UNP_WANTCRED_MASK) {
                /*
                 * Credentials are passed only once on SOCK_STREAM and
                 * SOCK_SEQPACKET (LOCAL_CREDS => WANTCRED_ONESHOT), or
                 * forever (LOCAL_CREDS_PERSISTENT => WANTCRED_ALWAYS).
                 */
                unp_addsockcred(td, &cmc, unp2->unp_flags);
                unp2->unp_flags &= ~UNP_WANTCRED_ONESHOT;
        }

        /*
         * Cycle through the data to send and available space in the peer's
         * receive buffer.  Put a reference on the peer socket, so that it
         * doesn't get freed while we sbwait().  If peer goes away, we will
         * observe the SBS_CANTRCVMORE and our sorele() will finalize peer's
         * socket destruction.
         */
        so2 = unp2->unp_socket;
        soref(so2);
        UNP_PCB_UNLOCK(unp2);
        sb = &so2->so_rcv;
        while (mc.mc_len + cmc.mc_len > 0) {
                struct mchain mcnext = MCHAIN_INITIALIZER(&mcnext);
                u_int space;

                SOCK_RECVBUF_LOCK(so2);
restart:
                UIPC_STREAM_SBCHECK(sb);
                if (__predict_false(cmc.mc_len > sb->sb_hiwat)) {
                        SOCK_RECVBUF_UNLOCK(so2);
                        error = EMSGSIZE;
                        goto out4;
                }
                if (__predict_false(sb->sb_state & SBS_CANTRCVMORE)) {
                        SOCK_RECVBUF_UNLOCK(so2);
                        error = EPIPE;
                        goto out4;
                }
                /*
                 * Wait on the peer socket receive buffer until we have enough
                 * space to put at least control.  The data is a stream and can
                 * be put partially, but control is really a datagram.
                 */
                space = uipc_stream_sbspace(sb);
                if (space < sb->sb_lowat || space < cmc.mc_len) {
                        if (nonblock) {
                                if (aio)
                                        sb->uxst_flags |= UXST_PEER_AIO;
                                SOCK_RECVBUF_UNLOCK(so2);
                                if (aio) {
                                        SOCK_SENDBUF_LOCK(so);
                                        so->so_snd.sb_ccc =
                                            so->so_snd.sb_hiwat - space;
                                        SOCK_SENDBUF_UNLOCK(so);
                                }
                                error = EWOULDBLOCK;
                                goto out4;
                        }
                        if ((error = uipc_stream_sbwait(so2,
                            so->so_snd.sb_timeo)) != 0) {
                                SOCK_RECVBUF_UNLOCK(so2);
                                goto out4;
                        } else
                                goto restart;
                }
                MPASS(space >= cmc.mc_len);
                space -= cmc.mc_len;
                if (space == 0) {
                        /* There is space only to send control. */
                        MPASS(!STAILQ_EMPTY(&cmc.mc_q));
                        mcnext = mc;
                        mc = MCHAIN_INITIALIZER(&mc);
                } else if (space < mc.mc_len) {
                        /* Not enough space. */
                        if (__predict_false(mc_split(&mc, &mcnext, space,
                            M_NOWAIT) == ENOMEM)) {
                                /*
                                 * If allocation failed use M_WAITOK and merge
                                 * the chain back.  Next time mc_split() will
                                 * easily split at the same place.  Only if we
                                 * race with setsockopt(SO_RCVBUF) shrinking
                                 * sb_hiwat can this happen more than once.
                                 */
                                SOCK_RECVBUF_UNLOCK(so2);
                                (void)mc_split(&mc, &mcnext, space, M_WAITOK);
                                mc_concat(&mc, &mcnext);
                                SOCK_RECVBUF_LOCK(so2);
                                goto restart;
                        }
                        MPASS(mc.mc_len == space);
                }
                if (!STAILQ_EMPTY(&cmc.mc_q)) {
                        STAILQ_CONCAT(&sb->uxst_mbq, &cmc.mc_q);
                        sb->sb_ctl += cmc.mc_len;
                        sb->sb_mbcnt += cmc.mc_mlen;
                        cmc.mc_len = 0;
                }
                sent += mc.mc_len;
                if (sb->uxst_fnrdy == NULL)
                        sb->sb_acc += mc.mc_len;
                sb->sb_ccc += mc.mc_len;
                sb->sb_mbcnt += mc.mc_mlen;
                STAILQ_CONCAT(&sb->uxst_mbq, &mc.mc_q);
                UIPC_STREAM_SBCHECK(sb);
                space = uipc_stream_sbspace(sb);
                sorwakeup_locked(so2);
                if (!STAILQ_EMPTY(&mcnext.mc_q)) {
                        /*
                         * Such assignment is unsafe in general, but it is
                         * safe with !STAILQ_EMPTY(&mcnext.mc_q).  In C++ we
                         * could reload = for STAILQs :)
                         */
                        mc = mcnext;
                } else if (uio != NULL && uio->uio_resid > 0) {
                        /*
                         * Copyin sum of peer's receive buffer space and our
                         * sb_hiwat, which is our virtual send buffer size.
                         * See comment above unpst_sendspace declaration.
                         * We are reading sb_hiwat locklessly, cause a) we
                         * don't care about an application that does send(2)
                         * and setsockopt(2) racing internally, and for an
                         * application that does this in sequence we will see
                         * the correct value cause sbsetopt() uses buffer lock
                         * and we also have already acquired it at least once.
                         */
                        error = mc_uiotomc(&mc, uio, space +
                            atomic_load_int(&so->so_snd.sb_hiwat), 0, M_WAITOK,
                            eor ? M_EOR : 0);
                        if (__predict_false(error))
                                goto out4;
                } else
                        mc = MCHAIN_INITIALIZER(&mc);
        }

        MPASS(STAILQ_EMPTY(&mc.mc_q));

        td->td_ru.ru_msgsnd++;
out4:
        sorele(so2);
out3:
        SOCK_IO_SEND_UNLOCK(so);
out2:
        if (aio) {
                freeuio(uio);
                uioadvance(uio0, sent);
        } else if (uio != NULL)
                uio->uio_resid = resid - sent;
        if (!mc_empty(&cmc))
                unp_scan(mc_first(&cmc), unp_freerights);
out:
        mc_freem(&mc);
        mc_freem(&cmc);

        return (error);
}

/*
 * Wakeup a writer, used by recv(2) and shutdown(2).
 *
 * @param so    Points to a connected stream socket with receive buffer locked
 *
 * In a blocking mode peer is sleeping on our receive buffer, and we need just
 * wakeup(9) on it.  But to wake up various event engines, we need to reach
 * over to peer's selinfo.  This can be safely done as the socket buffer
 * receive lock is protecting us from the peer going away.
 */
static void
uipc_wakeup_writer(struct socket *so)
{
        struct sockbuf *sb = &so->so_rcv;
        struct selinfo *sel;

        SOCK_RECVBUF_LOCK_ASSERT(so);
        MPASS(sb->uxst_peer != NULL);

        sel = &sb->uxst_peer->so_wrsel;

        if (sb->uxst_flags & UXST_PEER_SEL) {
                selwakeuppri(sel, PSOCK);
                /*
                 * XXXGL: sowakeup() does SEL_WAITING() without locks.
                 */
                if (!SEL_WAITING(sel))
                        sb->uxst_flags &= ~UXST_PEER_SEL;
        }
        if (sb->sb_flags & SB_WAIT) {
                sb->sb_flags &= ~SB_WAIT;
                wakeup(&sb->sb_acc);
        }
        KNOTE_LOCKED(&sel->si_note, 0);
        SOCK_RECVBUF_UNLOCK(so);
}

static void
uipc_cantrcvmore(struct socket *so)
{

        SOCK_RECVBUF_LOCK(so);
        so->so_rcv.sb_state |= SBS_CANTRCVMORE;
        selwakeuppri(&so->so_rdsel, PSOCK);
        KNOTE_LOCKED(&so->so_rdsel.si_note, 0);
        if (so->so_rcv.uxst_peer != NULL)
                uipc_wakeup_writer(so);
        else
                SOCK_RECVBUF_UNLOCK(so);
}

static int
uipc_soreceive_stream_or_seqpacket(struct socket *so, struct sockaddr **psa,
    struct uio *uio, struct mbuf **mp0, struct mbuf **controlp, int *flagsp)
{
        struct sockbuf *sb = &so->so_rcv;
        struct mbuf *control, *m, *first, *part, *next;
        u_int ctl, space, datalen, mbcnt, partlen;
        int error, flags;
        bool nonblock, waitall, peek;

        MPASS(mp0 == NULL);

        if (psa != NULL)
                *psa = NULL;
        if (controlp != NULL)
                *controlp = NULL;

        flags = flagsp != NULL ? *flagsp : 0;
        nonblock = (so->so_state & SS_NBIO) ||
            (flags & (MSG_DONTWAIT | MSG_NBIO));
        peek = flags & MSG_PEEK;
        waitall = (flags & MSG_WAITALL) && !peek;

        /*
         * This check may fail only on a socket that never went through
         * connect(2).  We can check this locklessly, cause: a) for a new born
         * socket we don't care about applications that may race internally
         * between connect(2) and recv(2), and b) for a dying socket if we
         * miss update by unp_sosidisconnected(), we would still get the check
         * correct.  For dying socket we would observe SBS_CANTRCVMORE later.
         */
        if (__predict_false((atomic_load_short(&so->so_state) &
            (SS_ISCONNECTED|SS_ISDISCONNECTED)) == 0))
                return (ENOTCONN);

        error = SOCK_IO_RECV_LOCK(so, SBLOCKWAIT(flags));
        if (__predict_false(error))
                return (error);

restart:
        SOCK_RECVBUF_LOCK(so);
        UIPC_STREAM_SBCHECK(sb);
        while (sb->sb_acc < sb->sb_lowat &&
            (sb->sb_ctl == 0 || controlp == NULL)) {
                if (so->so_error) {
                        error = so->so_error;
                        if (!peek)
                                so->so_error = 0;
                        SOCK_RECVBUF_UNLOCK(so);
                        SOCK_IO_RECV_UNLOCK(so);
                        return (error);
                }
                if (sb->sb_state & SBS_CANTRCVMORE) {
                        SOCK_RECVBUF_UNLOCK(so);
                        SOCK_IO_RECV_UNLOCK(so);
                        return (0);
                }
                if (nonblock) {
                        SOCK_RECVBUF_UNLOCK(so);
                        SOCK_IO_RECV_UNLOCK(so);
                        return (EWOULDBLOCK);
                }
                error = sbwait(so, SO_RCV);
                if (error) {
                        SOCK_RECVBUF_UNLOCK(so);
                        SOCK_IO_RECV_UNLOCK(so);
                        return (error);
                }
        }

        MPASS(STAILQ_FIRST(&sb->uxst_mbq));
        MPASS(sb->sb_acc > 0 || sb->sb_ctl > 0);

        mbcnt = 0;
        ctl = 0;
        first = STAILQ_FIRST(&sb->uxst_mbq);
        if (first->m_type == MT_CONTROL) {
                control = first;
                STAILQ_FOREACH_FROM(first, &sb->uxst_mbq, m_stailq) {
                        if (first->m_type != MT_CONTROL)
                                break;
                        ctl += first->m_len;
                        mbcnt += MSIZE;
                        if (first->m_flags & M_EXT)
                                mbcnt += first->m_ext.ext_size;
                }
        } else
                control = NULL;

        /*
         * Find split point for the next copyout.  On exit from the loop,
         * 'next' points to the new head of the buffer STAILQ and 'datalen'
         * contains the amount of data we will copy out at the end.  The
         * copyout is protected by the I/O lock only, as writers can only
         * append to the buffer.  We need to record the socket buffer state
         * and do all length adjustments before dropping the socket buffer lock.
         */
        for (space = uio->uio_resid, m = next = first, part = NULL, datalen = 0;
             space > 0 && m != sb->uxst_fnrdy && m->m_type == MT_DATA;
             m = STAILQ_NEXT(m, m_stailq)) {
                if (space >= m->m_len) {
                        space -= m->m_len;
                        datalen += m->m_len;
                        mbcnt += MSIZE;
                        if (m->m_flags & M_EXT)
                                mbcnt += m->m_ext.ext_size;
                        if (m->m_flags & M_EOR) {
                                flags |= MSG_EOR;
                                next = STAILQ_NEXT(m, m_stailq);
                                break;
                        }
                } else {
                        datalen += space;
                        partlen = space;
                        if (!peek) {
                                m->m_len -= partlen;
                                m->m_data += partlen;
                        }
                        next = part = m;
                        break;
                }
                next = STAILQ_NEXT(m, m_stailq);
        }

        if (!peek) {
                if (next == NULL)
                        STAILQ_INIT(&sb->uxst_mbq);
                else
                        STAILQ_FIRST(&sb->uxst_mbq) = next;
                MPASS(sb->sb_acc >= datalen);
                sb->sb_acc -= datalen;
                sb->sb_ccc -= datalen;
                MPASS(sb->sb_ctl >= ctl);
                sb->sb_ctl -= ctl;
                MPASS(sb->sb_mbcnt >= mbcnt);
                sb->sb_mbcnt -= mbcnt;
                UIPC_STREAM_SBCHECK(sb);
                if (__predict_true(sb->uxst_peer != NULL)) {
                        struct unpcb *unp2;
                        bool aio;

                        if ((aio = sb->uxst_flags & UXST_PEER_AIO))
                                sb->uxst_flags &= ~UXST_PEER_AIO;

                        uipc_wakeup_writer(so);
                        /*
                         * XXXGL: need to go through uipc_lock_peer() after
                         * the receive buffer lock dropped, it was protecting
                         * us from unp_soisdisconnected().  The aio workarounds
                         * should be refactored to the aio(4) side.
                         */
                        if (aio && uipc_lock_peer(so, &unp2) == 0) {
                                struct socket *so2 = unp2->unp_socket;

                                SOCK_SENDBUF_LOCK(so2);
                                so2->so_snd.sb_ccc -= datalen;
                                sowakeup_aio(so2, SO_SND);
                                SOCK_SENDBUF_UNLOCK(so2);
                                UNP_PCB_UNLOCK(unp2);
                        }
                } else
                        SOCK_RECVBUF_UNLOCK(so);
        } else
                SOCK_RECVBUF_UNLOCK(so);

        while (control != NULL && control->m_type == MT_CONTROL) {
                if (!peek) {
                        /*
                         * unp_externalize() failure must abort entire read(2).
                         * Such failure should also free the problematic
                         * control, but link back the remaining data to the head
                         * of the buffer, so that socket is not left in a state
                         * where it can't progress forward with reading.
                         * Probability of such a failure is really low, so it
                         * is fine that we need to perform pretty complex
                         * operation here to reconstruct the buffer.
                         */
                        error = unp_externalize(control, controlp, flags);
                        control = m_free(control);
                        if (__predict_false(error && control != NULL)) {
                                struct mchain cmc;

                                mc_init_m(&cmc, control);

                                SOCK_RECVBUF_LOCK(so);
                                if (__predict_false(
                                    (sb->sb_state & SBS_CANTRCVMORE) ||
                                    cmc.mc_len + sb->sb_ccc + sb->sb_ctl >
                                    sb->sb_hiwat)) {
                                        /*
                                         * While the lock was dropped and we
                                         * were failing in unp_externalize(),
                                         * the peer could has a) disconnected,
                                         * b) filled the buffer so that we
                                         * can't prepend data back.
                                         * These are two edge conditions that
                                         * we just can't handle, so lose the
                                         * data and return the error.
                                         */
                                        SOCK_RECVBUF_UNLOCK(so);
                                        SOCK_IO_RECV_UNLOCK(so);
                                        unp_scan(mc_first(&cmc),
                                            unp_freerights);
                                        mc_freem(&cmc);
                                        return (error);
                                }

                                UIPC_STREAM_SBCHECK(sb);
                                /* XXXGL: STAILQ_PREPEND */
                                STAILQ_CONCAT(&cmc.mc_q, &sb->uxst_mbq);
                                STAILQ_SWAP(&cmc.mc_q, &sb->uxst_mbq, mbuf);

                                sb->sb_ctl = sb->sb_acc = sb->sb_ccc =
                                    sb->sb_mbcnt = 0;
                                STAILQ_FOREACH(m, &sb->uxst_mbq, m_stailq) {
                                        if (m->m_type == MT_DATA) {
                                                sb->sb_acc += m->m_len;
                                                sb->sb_ccc += m->m_len;
                                        } else {
                                                sb->sb_ctl += m->m_len;
                                        }
                                        sb->sb_mbcnt += MSIZE;
                                        if (m->m_flags & M_EXT)
                                                sb->sb_mbcnt +=
                                                    m->m_ext.ext_size;
                                }
                                UIPC_STREAM_SBCHECK(sb);
                                SOCK_RECVBUF_UNLOCK(so);
                                SOCK_IO_RECV_UNLOCK(so);
                                return (error);
                        }
                        if (controlp != NULL) {
                                while (*controlp != NULL)
                                        controlp = &(*controlp)->m_next;
                        }
                } else {
                        /*
                         * XXXGL
                         *
                         * In MSG_PEEK case control is not externalized.  This
                         * means we are leaking some kernel pointers to the
                         * userland.  They are useless to a law-abiding
                         * application, but may be useful to a malware.  This
                         * is what the historical implementation in the
                         * soreceive_generic() did. To be improved?
                         */
                        if (controlp != NULL) {
                                *controlp = m_copym(control, 0, control->m_len,
                                    M_WAITOK);
                                controlp = &(*controlp)->m_next;
                        }
                        control = STAILQ_NEXT(control, m_stailq);
                }
        }

        for (m = first; datalen > 0; m = next) {
                void *data;
                u_int len;

                next = STAILQ_NEXT(m, m_stailq);
                if (m == part) {
                        data = peek ?
                            mtod(m, char *) : mtod(m, char *) - partlen;
                        len = partlen;
                } else {
                        data = mtod(m, char *);
                        len = m->m_len;
                }
                error = uiomove(data, len, uio);
                if (__predict_false(error)) {
                        if (!peek)
                                for (; m != part && datalen > 0; m = next) {
                                        next = STAILQ_NEXT(m, m_stailq);
                                        MPASS(datalen >= m->m_len);
                                        datalen -= m->m_len;
                                        m_free(m);
                                }
                        SOCK_IO_RECV_UNLOCK(so);
                        return (error);
                }
                datalen -= len;
                if (!peek && m != part)
                        m_free(m);
        }
        if (waitall && !(flags & MSG_EOR) && uio->uio_resid > 0)
                goto restart;
        SOCK_IO_RECV_UNLOCK(so);

        if (flagsp != NULL)
                *flagsp |= flags;

        uio->uio_td->td_ru.ru_msgrcv++;

        return (0);
}

static int
uipc_sopoll_stream_or_seqpacket(struct socket *so, int events,
    struct thread *td)
{
        struct unpcb *unp = sotounpcb(so);
        int revents;

        UNP_PCB_LOCK(unp);
        if (SOLISTENING(so)) {
                /* The above check is safe, since conversion to listening uses
                 * both protocol and socket lock.
                 */
                SOCK_LOCK(so);
                if (!(events & (POLLIN | POLLRDNORM)))
                        revents = 0;
                else if (!TAILQ_EMPTY(&so->sol_comp))
                        revents = events & (POLLIN | POLLRDNORM);
                else if (so->so_error)
                        revents = (events & (POLLIN | POLLRDNORM)) | POLLHUP;
                else {
                        selrecord(td, &so->so_rdsel);
                        revents = 0;
                }
                SOCK_UNLOCK(so);
        } else {
                if (so->so_state & SS_ISDISCONNECTED)
                        revents = POLLHUP;
                else
                        revents = 0;
                if (events & (POLLIN | POLLRDNORM | POLLRDHUP)) {
                        SOCK_RECVBUF_LOCK(so);
                        if (sbavail(&so->so_rcv) >= so->so_rcv.sb_lowat ||
                            so->so_error || so->so_rerror)
                                revents |= events & (POLLIN | POLLRDNORM);
                        if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
                                revents |= events &
                                    (POLLIN | POLLRDNORM | POLLRDHUP);
                        if (!(revents & (POLLIN | POLLRDNORM | POLLRDHUP))) {
                                selrecord(td, &so->so_rdsel);
                                so->so_rcv.sb_flags |= SB_SEL;
                        }
                        SOCK_RECVBUF_UNLOCK(so);
                }
                if (events & (POLLOUT | POLLWRNORM)) {
                        struct socket *so2 = so->so_rcv.uxst_peer;

                        if (so2 != NULL) {
                                struct sockbuf *sb = &so2->so_rcv;

                                SOCK_RECVBUF_LOCK(so2);
                                if (uipc_stream_sbspace(sb) >= sb->sb_lowat)
                                        revents |= events &
                                            (POLLOUT | POLLWRNORM);
                                if (sb->sb_state & SBS_CANTRCVMORE)
                                        revents |= POLLHUP;
                                if (!(revents & (POLLOUT | POLLWRNORM))) {
                                        so2->so_rcv.uxst_flags |= UXST_PEER_SEL;
                                        selrecord(td, &so->so_wrsel);
                                }
                                SOCK_RECVBUF_UNLOCK(so2);
                        } else
                                selrecord(td, &so->so_wrsel);
                }
        }
        UNP_PCB_UNLOCK(unp);
        return (revents);
}

static void
uipc_wrknl_lock(void *arg)
{
        struct socket *so = arg;
        struct unpcb *unp = sotounpcb(so);

retry:
        if (SOLISTENING(so)) {
                SOLISTEN_LOCK(so);
        } else {
                UNP_PCB_LOCK(unp);
                if (__predict_false(SOLISTENING(so))) {
                        UNP_PCB_UNLOCK(unp);
                        goto retry;
                }
                if (so->so_rcv.uxst_peer != NULL)
                        SOCK_RECVBUF_LOCK(so->so_rcv.uxst_peer);
        }
}

static void
uipc_wrknl_unlock(void *arg)
{
        struct socket *so = arg;
        struct unpcb *unp = sotounpcb(so);

        if (SOLISTENING(so))
                SOLISTEN_UNLOCK(so);
        else {
                if (so->so_rcv.uxst_peer != NULL)
                        SOCK_RECVBUF_UNLOCK(so->so_rcv.uxst_peer);
                UNP_PCB_UNLOCK(unp);
        }
}

static void
uipc_wrknl_assert_lock(void *arg, int what)
{
        struct socket *so = arg;

        if (SOLISTENING(so)) {
                if (what == LA_LOCKED)
                        SOLISTEN_LOCK_ASSERT(so);
                else
                        SOLISTEN_UNLOCK_ASSERT(so);
        } else {
                /*
                 * The pr_soreceive method will put a note without owning the
                 * unp lock, so we can't assert it here.  But we can safely
                 * dereference uxst_peer pointer, since receive buffer lock
                 * is assumed to be held here.
                 */
                if (what == LA_LOCKED && so->so_rcv.uxst_peer != NULL)
                        SOCK_RECVBUF_LOCK_ASSERT(so->so_rcv.uxst_peer);
        }
}

static void
uipc_filt_sowdetach(struct knote *kn)
{
        struct socket *so = kn->kn_fp->f_data;

        uipc_wrknl_lock(so);
        knlist_remove(&so->so_wrsel.si_note, kn, 1);
        uipc_wrknl_unlock(so);
}

static int
uipc_filt_sowrite(struct knote *kn, long hint)
{
        struct socket *so = kn->kn_fp->f_data, *so2;
        struct unpcb *unp = sotounpcb(so), *unp2 = unp->unp_conn;

        if (SOLISTENING(so))
                return (0);

        if (unp2 == NULL) {
                if (so->so_state & SS_ISDISCONNECTED) {
                        kn->kn_flags |= EV_EOF;
                        kn->kn_fflags = so->so_error;
                        return (1);
                } else
                        return (0);
        }

        so2 = unp2->unp_socket;
        SOCK_RECVBUF_LOCK_ASSERT(so2);
        kn->kn_data = uipc_stream_sbspace(&so2->so_rcv);

        if (so2->so_rcv.sb_state & SBS_CANTRCVMORE) {
                kn->kn_flags |= EV_EOF;
                return (1);
        } else if (kn->kn_sfflags & NOTE_LOWAT)
                return (kn->kn_data >= kn->kn_sdata);
        else
                return (kn->kn_data >= so2->so_rcv.sb_lowat);
}

static int
uipc_filt_soempty(struct knote *kn, long hint)
{
        struct socket *so = kn->kn_fp->f_data, *so2;
        struct unpcb *unp = sotounpcb(so), *unp2 = unp->unp_conn;

        if (SOLISTENING(so) || unp2 == NULL)
                return (1);

        so2 = unp2->unp_socket;
        SOCK_RECVBUF_LOCK_ASSERT(so2);
        kn->kn_data = uipc_stream_sbspace(&so2->so_rcv);

        return (kn->kn_data == 0 ? 1 : 0);
}

static const struct filterops uipc_write_filtops = {
        .f_isfd = 1,
        .f_detach = uipc_filt_sowdetach,
        .f_event = uipc_filt_sowrite,
        .f_copy = knote_triv_copy,
};
static const struct filterops uipc_empty_filtops = {
        .f_isfd = 1,
        .f_detach = uipc_filt_sowdetach,
        .f_event = uipc_filt_soempty,
        .f_copy = knote_triv_copy,
};

static int
uipc_kqfilter_stream_or_seqpacket(struct socket *so, struct knote *kn)
{
        struct unpcb *unp = sotounpcb(so);
        struct knlist *knl;

        switch (kn->kn_filter) {
        case EVFILT_READ:
                return (sokqfilter_generic(so, kn));
        case EVFILT_WRITE:
                kn->kn_fop = &uipc_write_filtops;
                break;
        case EVFILT_EMPTY:
                kn->kn_fop = &uipc_empty_filtops;
                break;
        default:
                return (EINVAL);
        }

        knl = &so->so_wrsel.si_note;
        UNP_PCB_LOCK(unp);
        if (SOLISTENING(so)) {
                SOLISTEN_LOCK(so);
                knlist_add(knl, kn, 1);
                SOLISTEN_UNLOCK(so);
        } else {
                struct socket *so2 = so->so_rcv.uxst_peer;

                if (so2 != NULL)
                        SOCK_RECVBUF_LOCK(so2);
                knlist_add(knl, kn, 1);
                if (so2 != NULL)
                        SOCK_RECVBUF_UNLOCK(so2);
        }
        UNP_PCB_UNLOCK(unp);
        return (0);
}

/* PF_UNIX/SOCK_DGRAM version of sbspace() */
static inline bool
uipc_dgram_sbspace(struct sockbuf *sb, u_int cc, u_int mbcnt)
{
        u_int bleft, mleft;

        /*
         * Negative space may happen if send(2) is followed by
         * setsockopt(SO_SNDBUF/SO_RCVBUF) that shrinks maximum.
         */
        if (__predict_false(sb->sb_hiwat < sb->uxdg_cc ||
            sb->sb_mbmax < sb->uxdg_mbcnt))
                return (false);

        if (__predict_false(sb->sb_state & SBS_CANTRCVMORE))
                return (false);

        bleft = sb->sb_hiwat - sb->uxdg_cc;
        mleft = sb->sb_mbmax - sb->uxdg_mbcnt;

        return (bleft >= cc && mleft >= mbcnt);
}

/*
 * PF_UNIX/SOCK_DGRAM send
 *
 * Allocate a record consisting of 3 mbufs in the sequence of
 * from -> control -> data and append it to the socket buffer.
 *
 * The first mbuf carries sender's name and is a pkthdr that stores
 * overall length of datagram, its memory consumption and control length.
 */
#define ctllen  PH_loc.thirtytwo[1]
_Static_assert(offsetof(struct pkthdr, memlen) + sizeof(u_int) <=
    offsetof(struct pkthdr, ctllen), "unix/dgram can not store ctllen");
static int
uipc_sosend_dgram(struct socket *so, struct sockaddr *addr, struct uio *uio,
    struct mbuf *m, struct mbuf *c, int flags, struct thread *td)
{
        struct unpcb *unp, *unp2;
        const struct sockaddr *from;
        struct socket *so2;
        struct sockbuf *sb;
        struct mchain cmc = MCHAIN_INITIALIZER(&cmc);
        struct mbuf *f;
        u_int cc, ctl, mbcnt;
        u_int dcc __diagused, dctl __diagused, dmbcnt __diagused;
        int error;

        MPASS((uio != NULL && m == NULL) || (m != NULL && uio == NULL));

        error = 0;
        f = NULL;

        if (__predict_false(flags & MSG_OOB)) {
                error = EOPNOTSUPP;
                goto out;
        }
        if (m == NULL) {
                if (__predict_false(uio->uio_resid > unpdg_maxdgram)) {
                        error = EMSGSIZE;
                        goto out;
                }
                m = m_uiotombuf(uio, M_WAITOK, 0, max_hdr, M_PKTHDR);
                if (__predict_false(m == NULL)) {
                        error = EFAULT;
                        goto out;
                }
                f = m_gethdr(M_WAITOK, MT_SONAME);
                cc = m->m_pkthdr.len;
                mbcnt = MSIZE + m->m_pkthdr.memlen;
                if (c != NULL && (error = unp_internalize(c, &cmc, td)))
                        goto out;
        } else {
                struct mchain mc;

                uipc_reset_kernel_mbuf(m, &mc);
                cc = mc.mc_len;
                mbcnt = mc.mc_mlen;
                if (__predict_false(m->m_pkthdr.len > unpdg_maxdgram)) {
                        error = EMSGSIZE;
                        goto out;
                }
                if ((f = m_gethdr(M_NOWAIT, MT_SONAME)) == NULL) {
                        error = ENOBUFS;
                        goto out;
                }
        }

        unp = sotounpcb(so);
        MPASS(unp);

        /*
         * XXXGL: would be cool to fully remove so_snd out of the equation
         * and avoid this lock, which is not only extraneous, but also being
         * released, thus still leaving possibility for a race.  We can easily
         * handle SBS_CANTSENDMORE/SS_ISCONNECTED complement in unpcb, but it
         * is more difficult to invent something to handle so_error.
         */
        error = SOCK_IO_SEND_LOCK(so, SBLOCKWAIT(flags));
        if (error)
                goto out2;
        SOCK_SENDBUF_LOCK(so);
        if (so->so_snd.sb_state & SBS_CANTSENDMORE) {
                SOCK_SENDBUF_UNLOCK(so);
                error = EPIPE;
                goto out3;
        }
        if (so->so_error != 0) {
                error = so->so_error;
                so->so_error = 0;
                SOCK_SENDBUF_UNLOCK(so);
                goto out3;
        }
        if (((so->so_state & SS_ISCONNECTED) == 0) && addr == NULL) {
                SOCK_SENDBUF_UNLOCK(so);
                error = EDESTADDRREQ;
                goto out3;
        }
        SOCK_SENDBUF_UNLOCK(so);

        if (addr != NULL) {
                if ((error = unp_connectat(AT_FDCWD, so, addr, td, true)))
                        goto out3;
                UNP_PCB_LOCK_ASSERT(unp);
                unp2 = unp->unp_conn;
                UNP_PCB_LOCK_ASSERT(unp2);
        } else {
                UNP_PCB_LOCK(unp);
                unp2 = unp_pcb_lock_peer(unp);
                if (unp2 == NULL) {
                        UNP_PCB_UNLOCK(unp);
                        error = ENOTCONN;
                        goto out3;
                }
        }

        if (unp2->unp_flags & UNP_WANTCRED_MASK)
                unp_addsockcred(td, &cmc, unp2->unp_flags);
        if (unp->unp_addr != NULL)
                from = (struct sockaddr *)unp->unp_addr;
        else
                from = &sun_noname;
        f->m_len = from->sa_len;
        MPASS(from->sa_len <= MLEN);
        bcopy(from, mtod(f, void *), from->sa_len);

        /*
         * Concatenate mbufs: from -> control -> data.
         * Save overall cc and mbcnt in "from" mbuf.
         */
        if (!STAILQ_EMPTY(&cmc.mc_q)) {
                f->m_next = mc_first(&cmc);
                mc_last(&cmc)->m_next = m;
                /* XXXGL: This is dirty as well as rollback after ENOBUFS. */
                STAILQ_INIT(&cmc.mc_q);
        } else
                f->m_next = m;
        m = NULL;
        ctl = f->m_len + cmc.mc_len;
        mbcnt += cmc.mc_mlen;
#ifdef INVARIANTS
        dcc = dctl = dmbcnt = 0;
        for (struct mbuf *mb = f; mb != NULL; mb = mb->m_next) {
                if (mb->m_type == MT_DATA)
                        dcc += mb->m_len;
                else
                        dctl += mb->m_len;
                dmbcnt += MSIZE;
                if (mb->m_flags & M_EXT)
                        dmbcnt += mb->m_ext.ext_size;
        }
        MPASS(dcc == cc);
        MPASS(dctl == ctl);
        MPASS(dmbcnt == mbcnt);
#endif
        f->m_pkthdr.len = cc + ctl;
        f->m_pkthdr.memlen = mbcnt;
        f->m_pkthdr.ctllen = ctl;

        /*
         * Destination socket buffer selection.
         *
         * Unconnected sends, when !(so->so_state & SS_ISCONNECTED) and the
         * destination address is supplied, create a temporary connection for
         * the run time of the function (see call to unp_connectat() above and
         * to unp_disconnect() below).  We distinguish them by condition of
         * (addr != NULL).  We intentionally avoid adding 'bool connected' for
         * that condition, since, again, through the run time of this code we
         * are always connected.  For such "unconnected" sends, the destination
         * buffer would be the receive buffer of destination socket so2.
         *
         * For connected sends, data lands on the send buffer of the sender's
         * socket "so".  Then, if we just added the very first datagram
         * on this send buffer, we need to add the send buffer on to the
         * receiving socket's buffer list.  We put ourselves on top of the
         * list.  Such logic gives infrequent senders priority over frequent
         * senders.
         *
         * Note on byte count management. As long as event methods kevent(2),
         * select(2) are not protocol specific (yet), we need to maintain
         * meaningful values on the receive buffer.  So, the receive buffer
         * would accumulate counters from all connected buffers potentially
         * having sb_ccc > sb_hiwat or sb_mbcnt > sb_mbmax.
         */
        so2 = unp2->unp_socket;
        sb = (addr == NULL) ? &so->so_snd : &so2->so_rcv;
        SOCK_RECVBUF_LOCK(so2);
        if (uipc_dgram_sbspace(sb, cc + ctl, mbcnt)) {
                if (addr == NULL && STAILQ_EMPTY(&sb->uxdg_mb))
                        TAILQ_INSERT_HEAD(&so2->so_rcv.uxdg_conns, &so->so_snd,
                            uxdg_clist);
                STAILQ_INSERT_TAIL(&sb->uxdg_mb, f, m_stailqpkt);
                sb->uxdg_cc += cc + ctl;
                sb->uxdg_ctl += ctl;
                sb->uxdg_mbcnt += mbcnt;
                so2->so_rcv.sb_acc += cc + ctl;
                so2->so_rcv.sb_ccc += cc + ctl;
                so2->so_rcv.sb_ctl += ctl;
                so2->so_rcv.sb_mbcnt += mbcnt;
                sorwakeup_locked(so2);
                f = NULL;
        } else {
                soroverflow_locked(so2);
                error = ENOBUFS;
                if (f->m_next->m_type == MT_CONTROL) {
                        STAILQ_FIRST(&cmc.mc_q) = f->m_next;
                        f->m_next = NULL;
                }
        }

        if (addr != NULL)
                unp_disconnect(unp, unp2);
        else
                unp_pcb_unlock_pair(unp, unp2);

        td->td_ru.ru_msgsnd++;

out3:
        SOCK_IO_SEND_UNLOCK(so);
out2:
        if (!mc_empty(&cmc))
                unp_scan(mc_first(&cmc), unp_freerights);
out:
        if (f)
                m_freem(f);
        mc_freem(&cmc);
        if (m)
                m_freem(m);

        return (error);
}

/*
 * PF_UNIX/SOCK_DGRAM receive with MSG_PEEK.
 * The mbuf has already been unlinked from the uxdg_mb of socket buffer
 * and needs to be linked onto uxdg_peeked of receive socket buffer.
 */
static int
uipc_peek_dgram(struct socket *so, struct mbuf *m, struct sockaddr **psa,
    struct uio *uio, struct mbuf **controlp, int *flagsp)
{
        ssize_t len = 0;
        int error;

        so->so_rcv.uxdg_peeked = m;
        so->so_rcv.uxdg_cc += m->m_pkthdr.len;
        so->so_rcv.uxdg_ctl += m->m_pkthdr.ctllen;
        so->so_rcv.uxdg_mbcnt += m->m_pkthdr.memlen;
        SOCK_RECVBUF_UNLOCK(so);

        KASSERT(m->m_type == MT_SONAME, ("m->m_type == %d", m->m_type));
        if (psa != NULL)
                *psa = sodupsockaddr(mtod(m, struct sockaddr *), M_WAITOK);

        m = m->m_next;
        KASSERT(m, ("%s: no data or control after soname", __func__));

        /*
         * With MSG_PEEK the control isn't executed, just copied.
         */
        while (m != NULL && m->m_type == MT_CONTROL) {
                if (controlp != NULL) {
                        *controlp = m_copym(m, 0, m->m_len, M_WAITOK);
                        controlp = &(*controlp)->m_next;
                }
                m = m->m_next;
        }
        KASSERT(m == NULL || m->m_type == MT_DATA,
            ("%s: not MT_DATA mbuf %p", __func__, m));
        while (m != NULL && uio->uio_resid > 0) {
                len = uio->uio_resid;
                if (len > m->m_len)
                        len = m->m_len;
                error = uiomove(mtod(m, char *), (int)len, uio);
                if (error) {
                        SOCK_IO_RECV_UNLOCK(so);
                        return (error);
                }
                if (len == m->m_len)
                        m = m->m_next;
        }
        SOCK_IO_RECV_UNLOCK(so);

        if (flagsp != NULL) {
                if (m != NULL) {
                        if (*flagsp & MSG_TRUNC) {
                                /* Report real length of the packet */
                                uio->uio_resid -= m_length(m, NULL) - len;
                        }
                        *flagsp |= MSG_TRUNC;
                } else
                        *flagsp &= ~MSG_TRUNC;
        }

        return (0);
}

/*
 * PF_UNIX/SOCK_DGRAM receive
 */
static int
uipc_soreceive_dgram(struct socket *so, struct sockaddr **psa, struct uio *uio,
    struct mbuf **mp0, struct mbuf **controlp, int *flagsp)
{
        struct sockbuf *sb = NULL;
        struct mbuf *m;
        int flags, error;
        ssize_t len = 0;
        bool nonblock;

        MPASS(mp0 == NULL);

        if (psa != NULL)
                *psa = NULL;
        if (controlp != NULL)
                *controlp = NULL;

        flags = flagsp != NULL ? *flagsp : 0;
        nonblock = (so->so_state & SS_NBIO) ||
            (flags & (MSG_DONTWAIT | MSG_NBIO));

        error = SOCK_IO_RECV_LOCK(so, SBLOCKWAIT(flags));
        if (__predict_false(error))
                return (error);

        /*
         * Loop blocking while waiting for a datagram.  Prioritize connected
         * peers over unconnected sends.  Set sb to selected socket buffer
         * containing an mbuf on exit from the wait loop.  A datagram that
         * had already been peeked at has top priority.
         */
        SOCK_RECVBUF_LOCK(so);
        while ((m = so->so_rcv.uxdg_peeked) == NULL &&
            (sb = TAILQ_FIRST(&so->so_rcv.uxdg_conns)) == NULL &&
            (m = STAILQ_FIRST(&so->so_rcv.uxdg_mb)) == NULL) {
                if (so->so_error) {
                        error = so->so_error;
                        if (!(flags & MSG_PEEK))
                                so->so_error = 0;
                        SOCK_RECVBUF_UNLOCK(so);
                        SOCK_IO_RECV_UNLOCK(so);
                        return (error);
                }
                if (so->so_rcv.sb_state & SBS_CANTRCVMORE ||
                    uio->uio_resid == 0) {
                        SOCK_RECVBUF_UNLOCK(so);
                        SOCK_IO_RECV_UNLOCK(so);
                        return (0);
                }
                if (nonblock) {
                        SOCK_RECVBUF_UNLOCK(so);
                        SOCK_IO_RECV_UNLOCK(so);
                        return (EWOULDBLOCK);
                }
                error = sbwait(so, SO_RCV);
                if (error) {
                        SOCK_RECVBUF_UNLOCK(so);
                        SOCK_IO_RECV_UNLOCK(so);
                        return (error);
                }
        }

        if (sb == NULL)
                sb = &so->so_rcv;
        else if (m == NULL)
                m = STAILQ_FIRST(&sb->uxdg_mb);
        else
                MPASS(m == so->so_rcv.uxdg_peeked);

        MPASS(sb->uxdg_cc > 0);
        M_ASSERTPKTHDR(m);
        KASSERT(m->m_type == MT_SONAME, ("m->m_type == %d", m->m_type));

        if (uio->uio_td)
                uio->uio_td->td_ru.ru_msgrcv++;

        if (__predict_true(m != so->so_rcv.uxdg_peeked)) {
                STAILQ_REMOVE_HEAD(&sb->uxdg_mb, m_stailqpkt);
                if (STAILQ_EMPTY(&sb->uxdg_mb) && sb != &so->so_rcv)
                        TAILQ_REMOVE(&so->so_rcv.uxdg_conns, sb, uxdg_clist);
        } else
                so->so_rcv.uxdg_peeked = NULL;

        sb->uxdg_cc -= m->m_pkthdr.len;
        sb->uxdg_ctl -= m->m_pkthdr.ctllen;
        sb->uxdg_mbcnt -= m->m_pkthdr.memlen;

        if (__predict_false(flags & MSG_PEEK))
                return (uipc_peek_dgram(so, m, psa, uio, controlp, flagsp));

        so->so_rcv.sb_acc -= m->m_pkthdr.len;
        so->so_rcv.sb_ccc -= m->m_pkthdr.len;
        so->so_rcv.sb_ctl -= m->m_pkthdr.ctllen;
        so->so_rcv.sb_mbcnt -= m->m_pkthdr.memlen;
        SOCK_RECVBUF_UNLOCK(so);

        if (psa != NULL)
                *psa = sodupsockaddr(mtod(m, struct sockaddr *), M_WAITOK);
        m = m_free(m);
        KASSERT(m, ("%s: no data or control after soname", __func__));

        /*
         * Packet to copyout() is now in 'm' and it is disconnected from the
         * queue.
         *
         * Process one or more MT_CONTROL mbufs present before any data mbufs
         * in the first mbuf chain on the socket buffer.  We call into the
         * unp_externalize() to perform externalization (or freeing if
         * controlp == NULL). In some cases there can be only MT_CONTROL mbufs
         * without MT_DATA mbufs.
         */
        while (m != NULL && m->m_type == MT_CONTROL) {
                error = unp_externalize(m, controlp, flags);
                m = m_free(m);
                if (error != 0) {
                        SOCK_IO_RECV_UNLOCK(so);
                        unp_scan(m, unp_freerights);
                        m_freem(m);
                        return (error);
                }
                if (controlp != NULL) {
                        while (*controlp != NULL)
                                controlp = &(*controlp)->m_next;
                }
        }
        KASSERT(m == NULL || m->m_type == MT_DATA,
            ("%s: not MT_DATA mbuf %p", __func__, m));
        while (m != NULL && uio->uio_resid > 0) {
                len = uio->uio_resid;
                if (len > m->m_len)
                        len = m->m_len;
                error = uiomove(mtod(m, char *), (int)len, uio);
                if (error) {
                        SOCK_IO_RECV_UNLOCK(so);
                        m_freem(m);
                        return (error);
                }
                if (len == m->m_len)
                        m = m_free(m);
                else {
                        m->m_data += len;
                        m->m_len -= len;
                }
        }
        SOCK_IO_RECV_UNLOCK(so);

        if (m != NULL) {
                if (flagsp != NULL) {
                        if (flags & MSG_TRUNC) {
                                /* Report real length of the packet */
                                uio->uio_resid -= m_length(m, NULL);
                        }
                        *flagsp |= MSG_TRUNC;
                }
                m_freem(m);
        } else if (flagsp != NULL)
                *flagsp &= ~MSG_TRUNC;

        return (0);
}

static int
uipc_sendfile_wait(struct socket *so, off_t need, int *space)
{
        struct unpcb *unp2;
        struct socket *so2;
        struct sockbuf *sb;
        bool nonblock, sockref;
        int error;

        MPASS(so->so_type == SOCK_STREAM);
        MPASS(need > 0);
        MPASS(space != NULL);

        nonblock = so->so_state & SS_NBIO;
        sockref = false;

        if (__predict_false((so->so_state & SS_ISCONNECTED) == 0))
                return (ENOTCONN);

        if (__predict_false((error = uipc_lock_peer(so, &unp2)) != 0))
                return (error);

        so2 = unp2->unp_socket;
        sb = &so2->so_rcv;
        SOCK_RECVBUF_LOCK(so2);
        UNP_PCB_UNLOCK(unp2);
        while ((*space = uipc_stream_sbspace(sb)) < need &&
            (*space < so->so_snd.sb_hiwat / 2)) {
                UIPC_STREAM_SBCHECK(sb);
                if (nonblock) {
                        SOCK_RECVBUF_UNLOCK(so2);
                        return (EAGAIN);
                }
                if (!sockref)
                        soref(so2);
                error = uipc_stream_sbwait(so2, so->so_snd.sb_timeo);
                if (error == 0 &&
                    __predict_false(sb->sb_state & SBS_CANTRCVMORE))
                        error = EPIPE;
                if (error) {
                        SOCK_RECVBUF_UNLOCK(so2);
                        sorele(so2);
                        return (error);
                }
        }
        UIPC_STREAM_SBCHECK(sb);
        SOCK_RECVBUF_UNLOCK(so2);
        if (sockref)
                sorele(so2);

        return (0);
}

/*
 * Although this is a pr_send method, for unix(4) it is called only via
 * sendfile(2) path.  This means we can be sure that mbufs are clear of
 * any extra flags and don't require any conditioning.
 */
static int
uipc_sendfile(struct socket *so, int flags, struct mbuf *m,
    struct sockaddr *from, struct mbuf *control, struct thread *td)
{
        struct mchain mc;
        struct unpcb *unp2;
        struct socket *so2;
        struct sockbuf *sb;
        bool notready, wakeup;
        int error;

        MPASS(so->so_type == SOCK_STREAM);
        MPASS(from == NULL && control == NULL);
        KASSERT(!(m->m_flags & M_EXTPG),
            ("unix(4): TLS sendfile(2) not supported"));

        notready = flags & PRUS_NOTREADY;

        if (__predict_false((so->so_state & SS_ISCONNECTED) == 0)) {
                error = ENOTCONN;
                goto out;
        }

        if (__predict_false((error = uipc_lock_peer(so, &unp2)) != 0))
                goto out;

        mc_init_m(&mc, m);

        so2 = unp2->unp_socket;
        sb = &so2->so_rcv;
        SOCK_RECVBUF_LOCK(so2);
        UNP_PCB_UNLOCK(unp2);
        UIPC_STREAM_SBCHECK(sb);
        sb->sb_ccc += mc.mc_len;
        sb->sb_mbcnt += mc.mc_mlen;
        if (sb->uxst_fnrdy == NULL) {
                if (notready) {
                        wakeup = false;
                        STAILQ_FOREACH(m, &mc.mc_q, m_stailq) {
                                if (m->m_flags & M_NOTREADY) {
                                        sb->uxst_fnrdy = m;
                                        break;
                                } else {
                                        sb->sb_acc += m->m_len;
                                        wakeup = true;
                                }
                        }
                } else {
                        wakeup = true;
                        sb->sb_acc += mc.mc_len;
                }
        } else {
                wakeup = false;
        }
        STAILQ_CONCAT(&sb->uxst_mbq, &mc.mc_q);
        UIPC_STREAM_SBCHECK(sb);
        if (wakeup)
                sorwakeup_locked(so2);
        else
                SOCK_RECVBUF_UNLOCK(so2);

        return (0);
out:
        /*
         * In case of not ready data, uipc_ready() is responsible
         * for freeing memory.
         */
        if (m != NULL && !notready)
                m_freem(m);

        return (error);
}

static int
uipc_sbready(struct sockbuf *sb, struct mbuf *m, int count)
{
        bool blocker;

        /* assert locked */

        blocker = (sb->uxst_fnrdy == m);
        STAILQ_FOREACH_FROM(m, &sb->uxst_mbq, m_stailq) {
                if (count > 0) {
                        MPASS(m->m_flags & M_NOTREADY);
                        m->m_flags &= ~M_NOTREADY;
                        if (blocker)
                                sb->sb_acc += m->m_len;
                        count--;
                } else if (m->m_flags & M_NOTREADY)
                        break;
                else if (blocker)
                        sb->sb_acc += m->m_len;
        }
        if (blocker) {
                sb->uxst_fnrdy = m;
                return (0);
        } else
                return (EINPROGRESS);
}

static bool
uipc_ready_scan(struct socket *so, struct mbuf *m, int count, int *errorp)
{
        struct mbuf *mb;
        struct sockbuf *sb;

        SOCK_LOCK(so);
        if (SOLISTENING(so)) {
                SOCK_UNLOCK(so);
                return (false);
        }
        mb = NULL;
        sb = &so->so_rcv;
        SOCK_RECVBUF_LOCK(so);
        if (sb->uxst_fnrdy != NULL) {
                STAILQ_FOREACH(mb, &sb->uxst_mbq, m_stailq) {
                        if (mb == m) {
                                *errorp = uipc_sbready(sb, m, count);
                                break;
                        }
                }
        }
        SOCK_RECVBUF_UNLOCK(so);
        SOCK_UNLOCK(so);
        return (mb != NULL);
}

static int
uipc_ready(struct socket *so, struct mbuf *m, int count)
{
        struct unpcb *unp, *unp2;
        int error;

        MPASS(so->so_type == SOCK_STREAM);

        if (__predict_true(uipc_lock_peer(so, &unp2) == 0)) {
                struct socket *so2;
                struct sockbuf *sb;

                so2 = unp2->unp_socket;
                sb = &so2->so_rcv;
                SOCK_RECVBUF_LOCK(so2);
                UNP_PCB_UNLOCK(unp2);
                UIPC_STREAM_SBCHECK(sb);
                error = uipc_sbready(sb, m, count);
                UIPC_STREAM_SBCHECK(sb);
                if (error == 0)
                        sorwakeup_locked(so2);
                else
                        SOCK_RECVBUF_UNLOCK(so2);
        } else {
                /*
                 * The receiving socket has been disconnected, but may still
                 * be valid.  In this case, the not-ready mbufs are still
                 * present in its socket buffer, so perform an exhaustive
                 * search before giving up and freeing the mbufs.
                 */
                UNP_LINK_RLOCK();
                LIST_FOREACH(unp, &unp_shead, unp_link) {
                        if (uipc_ready_scan(unp->unp_socket, m, count, &error))
                                break;
                }
                UNP_LINK_RUNLOCK();

                if (unp == NULL) {
                        for (int i = 0; i < count; i++)
                                m = m_free(m);
                        return (ECONNRESET);
                }
        }
        return (error);
}

static int
uipc_sense(struct socket *so, struct stat *sb)
{
        struct unpcb *unp;

        unp = sotounpcb(so);
        KASSERT(unp != NULL, ("uipc_sense: unp == NULL"));

        sb->st_blksize = so->so_snd.sb_hiwat;
        sb->st_dev = NODEV;
        sb->st_ino = unp->unp_ino;
        return (0);
}

static int
uipc_shutdown(struct socket *so, enum shutdown_how how)
{
        struct unpcb *unp = sotounpcb(so);
        int error;

        SOCK_LOCK(so);
        if (SOLISTENING(so)) {
                if (how != SHUT_WR) {
                        so->so_error = ECONNABORTED;
                        solisten_wakeup(so);    /* unlocks so */
                } else
                        SOCK_UNLOCK(so);
                return (ENOTCONN);
        } else if ((so->so_state &
            (SS_ISCONNECTED | SS_ISCONNECTING | SS_ISDISCONNECTING)) == 0) {
                /*
                 * POSIX mandates us to just return ENOTCONN when shutdown(2) is
                 * invoked on a datagram sockets, however historically we would
                 * actually tear socket down.  This is known to be leveraged by
                 * some applications to unblock process waiting in recv(2) by
                 * other process that it shares that socket with.  Try to meet
                 * both backward-compatibility and POSIX requirements by forcing
                 * ENOTCONN but still flushing buffers and performing wakeup(9).
                 *
                 * XXXGL: it remains unknown what applications expect this
                 * behavior and is this isolated to unix/dgram or inet/dgram or
                 * both.  See: D10351, D3039.
                 */
                error = ENOTCONN;
                if (so->so_type != SOCK_DGRAM) {
                        SOCK_UNLOCK(so);
                        return (error);
                }
        } else
                error = 0;
        SOCK_UNLOCK(so);

        switch (how) {
        case SHUT_RD:
                if (so->so_type == SOCK_DGRAM)
                        socantrcvmore(so);
                else
                        uipc_cantrcvmore(so);
                unp_dispose(so);
                break;
        case SHUT_RDWR:
                if (so->so_type == SOCK_DGRAM)
                        socantrcvmore(so);
                else
                        uipc_cantrcvmore(so);
                unp_dispose(so);
                /* FALLTHROUGH */
        case SHUT_WR:
                if (so->so_type == SOCK_DGRAM) {
                        socantsendmore(so);
                } else {
                        UNP_PCB_LOCK(unp);
                        if (unp->unp_conn != NULL)
                                uipc_cantrcvmore(unp->unp_conn->unp_socket);
                        UNP_PCB_UNLOCK(unp);
                }
        }
        wakeup(&so->so_timeo);

        return (error);
}

static int
uipc_sockaddr(struct socket *so, struct sockaddr *ret)
{
        struct unpcb *unp;
        const struct sockaddr *sa;

        unp = sotounpcb(so);
        KASSERT(unp != NULL, ("uipc_sockaddr: unp == NULL"));

        UNP_PCB_LOCK(unp);
        if (unp->unp_addr != NULL)
                sa = (struct sockaddr *) unp->unp_addr;
        else
                sa = &sun_noname;
        bcopy(sa, ret, sa->sa_len);
        UNP_PCB_UNLOCK(unp);
        return (0);
}

static int
uipc_ctloutput(struct socket *so, struct sockopt *sopt)
{
        struct unpcb *unp;
        struct xucred xu;
        int error, optval;

        if (sopt->sopt_level != SOL_LOCAL)
                return (EINVAL);

        unp = sotounpcb(so);
        KASSERT(unp != NULL, ("uipc_ctloutput: unp == NULL"));
        error = 0;
        switch (sopt->sopt_dir) {
        case SOPT_GET:
                switch (sopt->sopt_name) {
                case LOCAL_PEERCRED:
                        UNP_PCB_LOCK(unp);
                        if (unp->unp_flags & UNP_HAVEPC)
                                xu = unp->unp_peercred;
                        else {
                                if (so->so_proto->pr_flags & PR_CONNREQUIRED)
                                        error = ENOTCONN;
                                else
                                        error = EINVAL;
                        }
                        UNP_PCB_UNLOCK(unp);
                        if (error == 0)
                                error = sooptcopyout(sopt, &xu, sizeof(xu));
                        break;

                case LOCAL_CREDS:
                        /* Unlocked read. */
                        optval = unp->unp_flags & UNP_WANTCRED_ONESHOT ? 1 : 0;
                        error = sooptcopyout(sopt, &optval, sizeof(optval));
                        break;

                case LOCAL_CREDS_PERSISTENT:
                        /* Unlocked read. */
                        optval = unp->unp_flags & UNP_WANTCRED_ALWAYS ? 1 : 0;
                        error = sooptcopyout(sopt, &optval, sizeof(optval));
                        break;

                default:
                        error = EOPNOTSUPP;
                        break;
                }
                break;

        case SOPT_SET:
                switch (sopt->sopt_name) {
                case LOCAL_CREDS:
                case LOCAL_CREDS_PERSISTENT:
                        error = sooptcopyin(sopt, &optval, sizeof(optval),
                                            sizeof(optval));
                        if (error)
                                break;

#define OPTSET(bit, exclusive) do {                                     \
        UNP_PCB_LOCK(unp);                                              \
        if (optval) {                                                   \
                if ((unp->unp_flags & (exclusive)) != 0) {              \
                        UNP_PCB_UNLOCK(unp);                            \
                        error = EINVAL;                                 \
                        break;                                          \
                }                                                       \
                unp->unp_flags |= (bit);                                \
        } else                                                          \
                unp->unp_flags &= ~(bit);                               \
        UNP_PCB_UNLOCK(unp);                                            \
} while (0)

                        switch (sopt->sopt_name) {
                        case LOCAL_CREDS:
                                OPTSET(UNP_WANTCRED_ONESHOT, UNP_WANTCRED_ALWAYS);
                                break;

                        case LOCAL_CREDS_PERSISTENT:
                                OPTSET(UNP_WANTCRED_ALWAYS, UNP_WANTCRED_ONESHOT);
                                break;

                        default:
                                break;
                        }
                        break;
#undef  OPTSET
                default:
                        error = ENOPROTOOPT;
                        break;
                }
                break;

        default:
                error = EOPNOTSUPP;
                break;
        }
        return (error);
}

static int
unp_connect(struct socket *so, struct sockaddr *nam, struct thread *td)
{

        return (unp_connectat(AT_FDCWD, so, nam, td, false));
}

static int
unp_connectat(int fd, struct socket *so, struct sockaddr *nam,
    struct thread *td, bool return_locked)
{
        struct mtx *vplock;
        struct sockaddr_un *soun;
        struct vnode *vp;
        struct socket *so2;
        struct unpcb *unp, *unp2, *unp3;
        struct nameidata nd;
        char buf[SOCK_MAXADDRLEN];
        struct sockaddr *sa;
        cap_rights_t rights;
        int error, len;
        bool connreq;

        CURVNET_ASSERT_SET();

        if (nam->sa_family != AF_UNIX)
                return (EAFNOSUPPORT);
        if (nam->sa_len > sizeof(struct sockaddr_un))
                return (EINVAL);
        len = nam->sa_len - offsetof(struct sockaddr_un, sun_path);
        if (len <= 0)
                return (EINVAL);
        soun = (struct sockaddr_un *)nam;
        bcopy(soun->sun_path, buf, len);
        buf[len] = 0;

        error = 0;
        unp = sotounpcb(so);
        UNP_PCB_LOCK(unp);
        for (;;) {
                /*
                 * Wait for connection state to stabilize.  If a connection
                 * already exists, give up.  For datagram sockets, which permit
                 * multiple consecutive connect(2) calls, upper layers are
                 * responsible for disconnecting in advance of a subsequent
                 * connect(2), but this is not synchronized with PCB connection
                 * state.
                 *
                 * Also make sure that no threads are currently attempting to
                 * lock the peer socket, to ensure that unp_conn cannot
                 * transition between two valid sockets while locks are dropped.
                 */
                if (SOLISTENING(so))
                        error = EOPNOTSUPP;
                else if (unp->unp_conn != NULL)
                        error = EISCONN;
                else if ((unp->unp_flags & UNP_CONNECTING) != 0) {
                        error = EALREADY;
                }
                if (error != 0) {
                        UNP_PCB_UNLOCK(unp);
                        return (error);
                }
                if (unp->unp_pairbusy > 0) {
                        unp->unp_flags |= UNP_WAITING;
                        mtx_sleep(unp, UNP_PCB_LOCKPTR(unp), 0, "unpeer", 0);
                        continue;
                }
                break;
        }
        unp->unp_flags |= UNP_CONNECTING;
        UNP_PCB_UNLOCK(unp);

        connreq = (so->so_proto->pr_flags & PR_CONNREQUIRED) != 0;
        if (connreq)
                sa = malloc(sizeof(struct sockaddr_un), M_SONAME, M_WAITOK);
        else
                sa = NULL;
        NDINIT_ATRIGHTS(&nd, LOOKUP, FOLLOW | LOCKSHARED | LOCKLEAF,
            UIO_SYSSPACE, buf, fd, cap_rights_init_one(&rights, CAP_CONNECTAT));
        error = namei(&nd);
        if (error)
                vp = NULL;
        else
                vp = nd.ni_vp;
        ASSERT_VOP_LOCKED(vp, "unp_connect");
        if (error)
                goto bad;
        NDFREE_PNBUF(&nd);

        if (vp->v_type != VSOCK) {
                error = ENOTSOCK;
                goto bad;
        }
#ifdef MAC
        error = mac_vnode_check_open(td->td_ucred, vp, VWRITE | VREAD);
        if (error)
                goto bad;
#endif
        error = VOP_ACCESS(vp, VWRITE, td->td_ucred, td);
        if (error)
                goto bad;

        unp = sotounpcb(so);
        KASSERT(unp != NULL, ("unp_connect: unp == NULL"));

        vplock = mtx_pool_find(unp_vp_mtxpool, vp);
        mtx_lock(vplock);
        VOP_UNP_CONNECT(vp, &unp2);
        if (unp2 == NULL) {
                error = ECONNREFUSED;
                goto bad2;
        }
        so2 = unp2->unp_socket;
        if (so->so_type != so2->so_type) {
                error = EPROTOTYPE;
                goto bad2;
        }
        if (connreq) {
                if (SOLISTENING(so2))
                        so2 = solisten_clone(so2);
                else
                        so2 = NULL;
                if (so2 == NULL) {
                        error = ECONNREFUSED;
                        goto bad2;
                }
                if ((error = uipc_attach(so2, 0, NULL)) != 0) {
                        sodealloc(so2);
                        goto bad2;
                }
                unp3 = sotounpcb(so2);
                unp_pcb_lock_pair(unp2, unp3);
                if (unp2->unp_addr != NULL) {
                        bcopy(unp2->unp_addr, sa, unp2->unp_addr->sun_len);
                        unp3->unp_addr = (struct sockaddr_un *) sa;
                        sa = NULL;
                }

                unp_copy_peercred(td, unp3, unp, unp2);

                UNP_PCB_UNLOCK(unp2);
                unp2 = unp3;

                /*
                 * It is safe to block on the PCB lock here since unp2 is
                 * nascent and cannot be connected to any other sockets.
                 */
                UNP_PCB_LOCK(unp);
#ifdef MAC
                mac_socketpeer_set_from_socket(so, so2);
                mac_socketpeer_set_from_socket(so2, so);
#endif
        } else {
                unp_pcb_lock_pair(unp, unp2);
        }
        KASSERT(unp2 != NULL && so2 != NULL && unp2->unp_socket == so2 &&
            sotounpcb(so2) == unp2,
            ("%s: unp2 %p so2 %p", __func__, unp2, so2));
        unp_connect2(so, so2, connreq);
        if (connreq)
                (void)solisten_enqueue(so2, SS_ISCONNECTED);
        KASSERT((unp->unp_flags & UNP_CONNECTING) != 0,
            ("%s: unp %p has UNP_CONNECTING clear", __func__, unp));
        unp->unp_flags &= ~UNP_CONNECTING;
        if (!return_locked)
                unp_pcb_unlock_pair(unp, unp2);
bad2:
        mtx_unlock(vplock);
bad:
        if (vp != NULL) {
                /*
                 * If we are returning locked (called via uipc_sosend_dgram()),
                 * we need to be sure that vput() won't sleep.  This is
                 * guaranteed by VOP_UNP_CONNECT() call above and unp2 lock.
                 * SOCK_STREAM/SEQPACKET can't request return_locked (yet).
                 */
                MPASS(!(return_locked && connreq));
                vput(vp);
        }
        free(sa, M_SONAME);
        if (__predict_false(error)) {
                UNP_PCB_LOCK(unp);
                KASSERT((unp->unp_flags & UNP_CONNECTING) != 0,
                    ("%s: unp %p has UNP_CONNECTING clear", __func__, unp));
                unp->unp_flags &= ~UNP_CONNECTING;
                UNP_PCB_UNLOCK(unp);
        }
        return (error);
}

/*
 * Set socket peer credentials at connection time.
 *
 * The client's PCB credentials are copied from its process structure.  The
 * server's PCB credentials are copied from the socket on which it called
 * listen(2).  uipc_listen cached that process's credentials at the time.
 */
void
unp_copy_peercred(struct thread *td, struct unpcb *client_unp,
    struct unpcb *server_unp, struct unpcb *listen_unp)
{
        cru2xt(td, &client_unp->unp_peercred);
        client_unp->unp_flags |= UNP_HAVEPC;

        memcpy(&server_unp->unp_peercred, &listen_unp->unp_peercred,
            sizeof(server_unp->unp_peercred));
        server_unp->unp_flags |= UNP_HAVEPC;
        client_unp->unp_flags |= (listen_unp->unp_flags & UNP_WANTCRED_MASK);
}

/*
 * unix/stream & unix/seqpacket version of soisconnected().
 *
 * The crucial thing we are doing here is setting up the uxst_peer linkage,
 * holding unp and receive buffer locks of the both sockets.  The disconnect
 * procedure does the same.  This gives as a safe way to access the peer in the
 * send(2) and recv(2) during the socket lifetime.
 *
 * The less important thing is event notification of the fact that a socket is
 * now connected.  It is unusual for a software to put a socket into event
 * mechanism before connect(2), but is supposed to be supported.  Note that
 * there can not be any sleeping I/O on the socket, yet, only presence in the
 * select/poll/kevent.
 *
 * This function can be called via two call paths:
 * 1) socketpair(2) - in this case socket has not been yet reported to userland
 *    and just can't have any event notifications mechanisms set up.  The
 *    'wakeup' boolean is always false.
 * 2) connect(2) of existing socket to a recent clone of a listener:
 *   2.1) Socket that connect(2)s will have 'wakeup' true.  An application
 *        could have already put it into event mechanism, is it shall be
 *        reported as readable and as writable.
 *   2.2) Socket that was just cloned with solisten_clone().  Same as 1).
 */
static void
unp_soisconnected(struct socket *so, bool wakeup)
{
        struct socket *so2 = sotounpcb(so)->unp_conn->unp_socket;
        struct sockbuf *sb;

        SOCK_LOCK_ASSERT(so);
        UNP_PCB_LOCK_ASSERT(sotounpcb(so));
        UNP_PCB_LOCK_ASSERT(sotounpcb(so2));
        SOCK_RECVBUF_LOCK_ASSERT(so);
        SOCK_RECVBUF_LOCK_ASSERT(so2);

        MPASS(so->so_type == SOCK_STREAM || so->so_type == SOCK_SEQPACKET);
        MPASS((so->so_state & (SS_ISCONNECTED | SS_ISCONNECTING |
            SS_ISDISCONNECTING)) == 0);
        MPASS(so->so_qstate == SQ_NONE);

        so->so_state &= ~SS_ISDISCONNECTED;
        so->so_state |= SS_ISCONNECTED;

        sb = &so2->so_rcv;
        sb->uxst_peer = so;

        if (wakeup) {
                KNOTE_LOCKED(&sb->sb_sel->si_note, 0);
                sb = &so->so_rcv;
                selwakeuppri(sb->sb_sel, PSOCK);
                SOCK_SENDBUF_LOCK_ASSERT(so);
                sb = &so->so_snd;
                selwakeuppri(sb->sb_sel, PSOCK);
                SOCK_SENDBUF_UNLOCK(so);
        }
}

static void
unp_connect2(struct socket *so, struct socket *so2, bool wakeup)
{
        struct unpcb *unp;
        struct unpcb *unp2;

        MPASS(so2->so_type == so->so_type);
        unp = sotounpcb(so);
        KASSERT(unp != NULL, ("unp_connect2: unp == NULL"));
        unp2 = sotounpcb(so2);
        KASSERT(unp2 != NULL, ("unp_connect2: unp2 == NULL"));

        UNP_PCB_LOCK_ASSERT(unp);
        UNP_PCB_LOCK_ASSERT(unp2);
        KASSERT(unp->unp_conn == NULL,
            ("%s: socket %p is already connected", __func__, unp));

        unp->unp_conn = unp2;
        unp_pcb_hold(unp2);
        unp_pcb_hold(unp);
        switch (so->so_type) {
        case SOCK_DGRAM:
                UNP_REF_LIST_LOCK();
                LIST_INSERT_HEAD(&unp2->unp_refs, unp, unp_reflink);
                UNP_REF_LIST_UNLOCK();
                soisconnected(so);
                break;

        case SOCK_STREAM:
        case SOCK_SEQPACKET:
                KASSERT(unp2->unp_conn == NULL,
                    ("%s: socket %p is already connected", __func__, unp2));
                unp2->unp_conn = unp;
                SOCK_LOCK(so);
                SOCK_LOCK(so2);
                if (wakeup)     /* Avoid LOR with receive buffer lock. */
                        SOCK_SENDBUF_LOCK(so);
                SOCK_RECVBUF_LOCK(so);
                SOCK_RECVBUF_LOCK(so2);
                unp_soisconnected(so, wakeup);  /* Will unlock send buffer. */
                unp_soisconnected(so2, false);
                SOCK_RECVBUF_UNLOCK(so);
                SOCK_RECVBUF_UNLOCK(so2);
                SOCK_UNLOCK(so);
                SOCK_UNLOCK(so2);
                break;

        default:
                panic("unp_connect2");
        }
}

static void
unp_soisdisconnected(struct socket *so)
{
        SOCK_LOCK_ASSERT(so);
        SOCK_RECVBUF_LOCK_ASSERT(so);
        MPASS(so->so_type == SOCK_STREAM || so->so_type == SOCK_SEQPACKET);
        MPASS(!SOLISTENING(so));
        MPASS((so->so_state & (SS_ISCONNECTING | SS_ISDISCONNECTING |
            SS_ISDISCONNECTED)) == 0);
        MPASS(so->so_state & SS_ISCONNECTED);

        so->so_state |= SS_ISDISCONNECTED;
        so->so_state &= ~SS_ISCONNECTED;
        so->so_rcv.uxst_peer = NULL;
        socantrcvmore_locked(so);
}

static void
unp_disconnect(struct unpcb *unp, struct unpcb *unp2)
{
        struct socket *so, *so2;
        struct mbuf *m = NULL;
#ifdef INVARIANTS
        struct unpcb *unptmp;
#endif

        UNP_PCB_LOCK_ASSERT(unp);
        UNP_PCB_LOCK_ASSERT(unp2);
        KASSERT(unp->unp_conn == unp2,
            ("%s: unpcb %p is not connected to %p", __func__, unp, unp2));

        unp->unp_conn = NULL;
        so = unp->unp_socket;
        so2 = unp2->unp_socket;
        switch (unp->unp_socket->so_type) {
        case SOCK_DGRAM:
                /*
                 * Remove our send socket buffer from the peer's receive buffer.
                 * Move the data to the receive buffer only if it is empty.
                 * This is a protection against a scenario where a peer
                 * connects, floods and disconnects, effectively blocking
                 * sendto() from unconnected sockets.
                 */
                SOCK_RECVBUF_LOCK(so2);
                if (!STAILQ_EMPTY(&so->so_snd.uxdg_mb)) {
                        TAILQ_REMOVE(&so2->so_rcv.uxdg_conns, &so->so_snd,
                            uxdg_clist);
                        if (__predict_true((so2->so_rcv.sb_state &
                            SBS_CANTRCVMORE) == 0) &&
                            STAILQ_EMPTY(&so2->so_rcv.uxdg_mb)) {
                                STAILQ_CONCAT(&so2->so_rcv.uxdg_mb,
                                    &so->so_snd.uxdg_mb);
                                so2->so_rcv.uxdg_cc += so->so_snd.uxdg_cc;
                                so2->so_rcv.uxdg_ctl += so->so_snd.uxdg_ctl;
                                so2->so_rcv.uxdg_mbcnt += so->so_snd.uxdg_mbcnt;
                        } else {
                                m = STAILQ_FIRST(&so->so_snd.uxdg_mb);
                                STAILQ_INIT(&so->so_snd.uxdg_mb);
                                so2->so_rcv.sb_acc -= so->so_snd.uxdg_cc;
                                so2->so_rcv.sb_ccc -= so->so_snd.uxdg_cc;
                                so2->so_rcv.sb_ctl -= so->so_snd.uxdg_ctl;
                                so2->so_rcv.sb_mbcnt -= so->so_snd.uxdg_mbcnt;
                        }
                        /* Note: so may reconnect. */
                        so->so_snd.uxdg_cc = 0;
                        so->so_snd.uxdg_ctl = 0;
                        so->so_snd.uxdg_mbcnt = 0;
                }
                SOCK_RECVBUF_UNLOCK(so2);
                UNP_REF_LIST_LOCK();
#ifdef INVARIANTS
                LIST_FOREACH(unptmp, &unp2->unp_refs, unp_reflink) {
                        if (unptmp == unp)
                                break;
                }
                KASSERT(unptmp != NULL,
                    ("%s: %p not found in reflist of %p", __func__, unp, unp2));
#endif
                LIST_REMOVE(unp, unp_reflink);
                UNP_REF_LIST_UNLOCK();
                SOCK_LOCK(so);
                so->so_state &= ~SS_ISCONNECTED;
                SOCK_UNLOCK(so);
                break;

        case SOCK_STREAM:
        case SOCK_SEQPACKET:
                SOCK_LOCK(so);
                SOCK_LOCK(so2);
                SOCK_RECVBUF_LOCK(so);
                SOCK_RECVBUF_LOCK(so2);
                unp_soisdisconnected(so);
                MPASS(unp2->unp_conn == unp);
                unp2->unp_conn = NULL;
                unp_soisdisconnected(so2);
                SOCK_UNLOCK(so);
                SOCK_UNLOCK(so2);
                break;
        }

        if (unp == unp2) {
                unp_pcb_rele_notlast(unp);
                if (!unp_pcb_rele(unp))
                        UNP_PCB_UNLOCK(unp);
        } else {
                if (!unp_pcb_rele(unp))
                        UNP_PCB_UNLOCK(unp);
                if (!unp_pcb_rele(unp2))
                        UNP_PCB_UNLOCK(unp2);
        }

        if (m != NULL) {
                unp_scan(m, unp_freerights);
                m_freemp(m);
        }
}

/*
 * unp_pcblist() walks the global list of struct unpcb's to generate a
 * pointer list, bumping the refcount on each unpcb.  It then copies them out
 * sequentially, validating the generation number on each to see if it has
 * been detached.  All of this is necessary because copyout() may sleep on
 * disk I/O.
 */
static int
unp_pcblist(SYSCTL_HANDLER_ARGS)
{
        struct unpcb *unp, **unp_list;
        unp_gen_t gencnt;
        struct xunpgen *xug;
        struct unp_head *head;
        struct xunpcb *xu;
        u_int i;
        int error, n;

        switch ((intptr_t)arg1) {
        case SOCK_STREAM:
                head = &unp_shead;
                break;

        case SOCK_DGRAM:
                head = &unp_dhead;
                break;

        case SOCK_SEQPACKET:
                head = &unp_sphead;
                break;

        default:
                panic("unp_pcblist: arg1 %d", (int)(intptr_t)arg1);
        }

        /*
         * The process of preparing the PCB list is too time-consuming and
         * resource-intensive to repeat twice on every request.
         */
        if (req->oldptr == NULL) {
                n = unp_count;
                req->oldidx = 2 * (sizeof *xug)
                        + (n + n/8) * sizeof(struct xunpcb);
                return (0);
        }

        if (req->newptr != NULL)
                return (EPERM);

        /*
         * OK, now we're committed to doing something.
         */
        xug = malloc(sizeof(*xug), M_TEMP, M_WAITOK | M_ZERO);
        UNP_LINK_RLOCK();
        gencnt = unp_gencnt;
        n = unp_count;
        UNP_LINK_RUNLOCK();

        xug->xug_len = sizeof *xug;
        xug->xug_count = n;
        xug->xug_gen = gencnt;
        xug->xug_sogen = so_gencnt;
        error = SYSCTL_OUT(req, xug, sizeof *xug);
        if (error) {
                free(xug, M_TEMP);
                return (error);
        }

        unp_list = malloc(n * sizeof *unp_list, M_TEMP, M_WAITOK);

        UNP_LINK_RLOCK();
        for (unp = LIST_FIRST(head), i = 0; unp && i < n;
             unp = LIST_NEXT(unp, unp_link)) {
                UNP_PCB_LOCK(unp);
                if (unp->unp_gencnt <= gencnt) {
                        if (cr_cansee(req->td->td_ucred,
                            unp->unp_socket->so_cred)) {
                                UNP_PCB_UNLOCK(unp);
                                continue;
                        }
                        unp_list[i++] = unp;
                        unp_pcb_hold(unp);
                }
                UNP_PCB_UNLOCK(unp);
        }
        UNP_LINK_RUNLOCK();
        n = i;                  /* In case we lost some during malloc. */

        error = 0;
        xu = malloc(sizeof(*xu), M_TEMP, M_WAITOK | M_ZERO);
        for (i = 0; i < n; i++) {
                unp = unp_list[i];
                UNP_PCB_LOCK(unp);
                if (unp_pcb_rele(unp))
                        continue;

                if (unp->unp_gencnt <= gencnt) {
                        xu->xu_len = sizeof *xu;
                        xu->xu_unpp = (uintptr_t)unp;
                        /*
                         * XXX - need more locking here to protect against
                         * connect/disconnect races for SMP.
                         */
                        if (unp->unp_addr != NULL)
                                bcopy(unp->unp_addr, &xu->xu_addr,
                                      unp->unp_addr->sun_len);
                        else
                                bzero(&xu->xu_addr, sizeof(xu->xu_addr));
                        if (unp->unp_conn != NULL &&
                            unp->unp_conn->unp_addr != NULL)
                                bcopy(unp->unp_conn->unp_addr,
                                      &xu->xu_caddr,
                                      unp->unp_conn->unp_addr->sun_len);
                        else
                                bzero(&xu->xu_caddr, sizeof(xu->xu_caddr));
                        xu->unp_vnode = (uintptr_t)unp->unp_vnode;
                        xu->unp_conn = (uintptr_t)unp->unp_conn;
                        xu->xu_firstref = (uintptr_t)LIST_FIRST(&unp->unp_refs);
                        xu->xu_nextref = (uintptr_t)LIST_NEXT(unp, unp_reflink);
                        xu->unp_gencnt = unp->unp_gencnt;
                        sotoxsocket(unp->unp_socket, &xu->xu_socket);
                        UNP_PCB_UNLOCK(unp);
                        error = SYSCTL_OUT(req, xu, sizeof *xu);
                } else {
                        UNP_PCB_UNLOCK(unp);
                }
        }
        free(xu, M_TEMP);
        if (!error) {
                /*
                 * Give the user an updated idea of our state.  If the
                 * generation differs from what we told her before, she knows
                 * that something happened while we were processing this
                 * request, and it might be necessary to retry.
                 */
                xug->xug_gen = unp_gencnt;
                xug->xug_sogen = so_gencnt;
                xug->xug_count = unp_count;
                error = SYSCTL_OUT(req, xug, sizeof *xug);
        }
        free(unp_list, M_TEMP);
        free(xug, M_TEMP);
        return (error);
}

SYSCTL_PROC(_net_local_dgram, OID_AUTO, pcblist,
    CTLTYPE_OPAQUE | CTLFLAG_RD | CTLFLAG_MPSAFE,
    (void *)(intptr_t)SOCK_DGRAM, 0, unp_pcblist, "S,xunpcb",
    "List of active local datagram sockets");
SYSCTL_PROC(_net_local_stream, OID_AUTO, pcblist,
    CTLTYPE_OPAQUE | CTLFLAG_RD | CTLFLAG_MPSAFE,
    (void *)(intptr_t)SOCK_STREAM, 0, unp_pcblist, "S,xunpcb",
    "List of active local stream sockets");
SYSCTL_PROC(_net_local_seqpacket, OID_AUTO, pcblist,
    CTLTYPE_OPAQUE | CTLFLAG_RD | CTLFLAG_MPSAFE,
    (void *)(intptr_t)SOCK_SEQPACKET, 0, unp_pcblist, "S,xunpcb",
    "List of active local seqpacket sockets");

static void
unp_drop(struct unpcb *unp)
{
        struct socket *so;
        struct unpcb *unp2;

        /*
         * Regardless of whether the socket's peer dropped the connection
         * with this socket by aborting or disconnecting, POSIX requires
         * that ECONNRESET is returned on next connected send(2) in case of
         * a SOCK_DGRAM socket and EPIPE for SOCK_STREAM.
         */
        UNP_PCB_LOCK(unp);
        if ((so = unp->unp_socket) != NULL)
                so->so_error =
                    so->so_proto->pr_type == SOCK_DGRAM ? ECONNRESET : EPIPE;
        if ((unp2 = unp_pcb_lock_peer(unp)) != NULL) {
                /* Last reference dropped in unp_disconnect(). */
                unp_pcb_rele_notlast(unp);
                unp_disconnect(unp, unp2);
        } else if (!unp_pcb_rele(unp)) {
                UNP_PCB_UNLOCK(unp);
        }
}

static void
unp_freerights(struct filedescent **fdep, int fdcount)
{
        struct file *fp;
        int i;

        KASSERT(fdcount > 0, ("%s: fdcount %d", __func__, fdcount));

        for (i = 0; i < fdcount; i++) {
                fp = fdep[i]->fde_file;
                filecaps_free(&fdep[i]->fde_caps);
                unp_discard(fp);
        }
        free(fdep[0], M_FILECAPS);
}

static bool
restrict_rights(struct file *fp, struct thread *td)
{
        struct prison *prison1, *prison2;

        prison1 = fp->f_cred->cr_prison;
        prison2 = td->td_ucred->cr_prison;
        return (prison1 != prison2 && prison1->pr_root != prison2->pr_root &&
            prison2 != &prison0);
}

static int
unp_externalize(struct mbuf *control, struct mbuf **controlp, int flags)
{
        struct thread *td = curthread;          /* XXX */
        struct cmsghdr *cm = mtod(control, struct cmsghdr *);
        int *fdp;
        struct filedesc *fdesc = td->td_proc->p_fd;
        struct filedescent **fdep;
        void *data;
        socklen_t clen = control->m_len, datalen;
        int error, fdflags, newfds;
        u_int newlen;

        UNP_LINK_UNLOCK_ASSERT();

        fdflags = ((flags & MSG_CMSG_CLOEXEC) ? O_CLOEXEC : 0) |
            ((flags & MSG_CMSG_CLOFORK) ? O_CLOFORK : 0);

        error = 0;
        if (controlp != NULL) /* controlp == NULL => free control messages */
                *controlp = NULL;
        while (cm != NULL) {
                MPASS(clen >= sizeof(*cm) && clen >= cm->cmsg_len);

                data = CMSG_DATA(cm);
                datalen = (caddr_t)cm + cm->cmsg_len - (caddr_t)data;
                if (cm->cmsg_level == SOL_SOCKET
                    && cm->cmsg_type == SCM_RIGHTS) {
                        newfds = datalen / sizeof(*fdep);
                        if (newfds == 0)
                                goto next;
                        fdep = data;

                        /* If we're not outputting the descriptors free them. */
                        if (error || controlp == NULL) {
                                unp_freerights(fdep, newfds);
                                goto next;
                        }
                        FILEDESC_XLOCK(fdesc);

                        /*
                         * Now change each pointer to an fd in the global
                         * table to an integer that is the index to the local
                         * fd table entry that we set up to point to the
                         * global one we are transferring.
                         */
                        newlen = newfds * sizeof(int);
                        *controlp = sbcreatecontrol(NULL, newlen,
                            SCM_RIGHTS, SOL_SOCKET, M_WAITOK);

                        fdp = (int *)
                            CMSG_DATA(mtod(*controlp, struct cmsghdr *));
                        if ((error = fdallocn(td, 0, fdp, newfds))) {
                                FILEDESC_XUNLOCK(fdesc);
                                unp_freerights(fdep, newfds);
                                m_freem(*controlp);
                                *controlp = NULL;
                                goto next;
                        }
                        for (int i = 0; i < newfds; i++, fdp++) {
                                struct file *fp;

                                fp = fdep[i]->fde_file;
                                _finstall(fdesc, fp, *fdp, fdflags |
                                    (restrict_rights(fp, td) ?
                                    O_RESOLVE_BENEATH : 0), &fdep[i]->fde_caps);
                                unp_externalize_fp(fp);
                        }

                        /*
                         * The new type indicates that the mbuf data refers to
                         * kernel resources that may need to be released before
                         * the mbuf is freed.
                         */
                        m_chtype(*controlp, MT_EXTCONTROL);
                        FILEDESC_XUNLOCK(fdesc);
                        free(fdep[0], M_FILECAPS);
                } else {
                        /* We can just copy anything else across. */
                        if (error || controlp == NULL)
                                goto next;
                        *controlp = sbcreatecontrol(NULL, datalen,
                            cm->cmsg_type, cm->cmsg_level, M_WAITOK);
                        bcopy(data,
                            CMSG_DATA(mtod(*controlp, struct cmsghdr *)),
                            datalen);
                }
                controlp = &(*controlp)->m_next;

next:
                if (CMSG_SPACE(datalen) < clen) {
                        clen -= CMSG_SPACE(datalen);
                        cm = (struct cmsghdr *)
                            ((caddr_t)cm + CMSG_SPACE(datalen));
                } else {
                        clen = 0;
                        cm = NULL;
                }
        }

        return (error);
}

static void
unp_zone_change(void *tag)
{

        uma_zone_set_max(unp_zone, maxsockets);
}

#ifdef INVARIANTS
static void
unp_zdtor(void *mem, int size __unused, void *arg __unused)
{
        struct unpcb *unp;

        unp = mem;

        KASSERT(LIST_EMPTY(&unp->unp_refs),
            ("%s: unpcb %p has lingering refs", __func__, unp));
        KASSERT(unp->unp_socket == NULL,
            ("%s: unpcb %p has socket backpointer", __func__, unp));
        KASSERT(unp->unp_vnode == NULL,
            ("%s: unpcb %p has vnode references", __func__, unp));
        KASSERT(unp->unp_conn == NULL,
            ("%s: unpcb %p is still connected", __func__, unp));
        KASSERT(unp->unp_addr == NULL,
            ("%s: unpcb %p has leaked addr", __func__, unp));
}
#endif

static void
unp_init(void *arg __unused)
{
        uma_dtor dtor;

#ifdef INVARIANTS
        dtor = unp_zdtor;
#else
        dtor = NULL;
#endif
        unp_zone = uma_zcreate("unpcb", sizeof(struct unpcb), NULL, dtor,
            NULL, NULL, UMA_ALIGN_CACHE, 0);
        uma_zone_set_max(unp_zone, maxsockets);
        uma_zone_set_warning(unp_zone, "kern.ipc.maxsockets limit reached");
        EVENTHANDLER_REGISTER(maxsockets_change, unp_zone_change,
            NULL, EVENTHANDLER_PRI_ANY);
        LIST_INIT(&unp_dhead);
        LIST_INIT(&unp_shead);
        LIST_INIT(&unp_sphead);
        SLIST_INIT(&unp_defers);
        TIMEOUT_TASK_INIT(taskqueue_thread, &unp_gc_task, 0, unp_gc, NULL);
        TASK_INIT(&unp_defer_task, 0, unp_process_defers, NULL);
        UNP_LINK_LOCK_INIT();
        UNP_DEFERRED_LOCK_INIT();
        unp_vp_mtxpool = mtx_pool_create("unp vp mtxpool", 32, MTX_DEF);
}
SYSINIT(unp_init, SI_SUB_PROTO_DOMAIN, SI_ORDER_SECOND, unp_init, NULL);

static void
unp_internalize_cleanup_rights(struct mbuf *control)
{
        struct cmsghdr *cp;
        struct mbuf *m;
        void *data;
        socklen_t datalen;

        for (m = control; m != NULL; m = m->m_next) {
                cp = mtod(m, struct cmsghdr *);
                if (cp->cmsg_level != SOL_SOCKET ||
                    cp->cmsg_type != SCM_RIGHTS)
                        continue;
                data = CMSG_DATA(cp);
                datalen = (caddr_t)cp + cp->cmsg_len - (caddr_t)data;
                unp_freerights(data, datalen / sizeof(struct filedesc *));
        }
}

static int
unp_internalize(struct mbuf *control, struct mchain *mc, struct thread *td)
{
        struct proc *p;
        struct filedesc *fdesc;
        struct bintime *bt;
        struct cmsghdr *cm;
        struct cmsgcred *cmcred;
        struct mbuf *m;
        struct filedescent *fde, **fdep, *fdev;
        struct file *fp;
        struct timeval *tv;
        struct timespec *ts;
        void *data;
        socklen_t clen, datalen;
        int i, j, error, *fdp, oldfds;
        u_int newlen;

        MPASS(control->m_next == NULL); /* COMPAT_OLDSOCK may violate */
        UNP_LINK_UNLOCK_ASSERT();

        p = td->td_proc;
        fdesc = p->p_fd;
        error = 0;
        *mc = MCHAIN_INITIALIZER(mc);
        for (clen = control->m_len, cm = mtod(control, struct cmsghdr *),
            data = CMSG_DATA(cm);

            clen >= sizeof(*cm) && cm->cmsg_level == SOL_SOCKET &&
            clen >= cm->cmsg_len && cm->cmsg_len >= sizeof(*cm) &&
            (char *)cm + cm->cmsg_len >= (char *)data;

            clen -= min(CMSG_SPACE(datalen), clen),
            cm = (struct cmsghdr *) ((char *)cm + CMSG_SPACE(datalen)),
            data = CMSG_DATA(cm)) {
                datalen = (char *)cm + cm->cmsg_len - (char *)data;
                switch (cm->cmsg_type) {
                case SCM_CREDS:
                        m = sbcreatecontrol(NULL, sizeof(*cmcred), SCM_CREDS,
                            SOL_SOCKET, M_WAITOK);
                        cmcred = (struct cmsgcred *)
                            CMSG_DATA(mtod(m, struct cmsghdr *));
                        cmcred->cmcred_pid = p->p_pid;
                        cmcred->cmcred_uid = td->td_ucred->cr_ruid;
                        cmcred->cmcred_gid = td->td_ucred->cr_rgid;
                        cmcred->cmcred_euid = td->td_ucred->cr_uid;
                        _Static_assert(CMGROUP_MAX >= 1,
                            "Room needed for the effective GID.");
                        cmcred->cmcred_ngroups = MIN(td->td_ucred->cr_ngroups + 1,
                            CMGROUP_MAX);
                        cmcred->cmcred_groups[0] = td->td_ucred->cr_gid;
                        for (i = 1; i < cmcred->cmcred_ngroups; i++)
                                cmcred->cmcred_groups[i] =
                                    td->td_ucred->cr_groups[i - 1];
                        break;

                case SCM_RIGHTS:
                        oldfds = datalen / sizeof (int);
                        if (oldfds == 0)
                                continue;
                        /* On some machines sizeof pointer is bigger than
                         * sizeof int, so we need to check if data fits into
                         * single mbuf.  We could allocate several mbufs, and
                         * unp_externalize() should even properly handle that.
                         * But it is not worth to complicate the code for an
                         * insane scenario of passing over 200 file descriptors
                         * at once.
                         */
                        newlen = oldfds * sizeof(fdep[0]);
                        if (CMSG_SPACE(newlen) > MCLBYTES) {
                                error = EMSGSIZE;
                                goto out;
                        }
                        /*
                         * Check that all the FDs passed in refer to legal
                         * files.  If not, reject the entire operation.
                         */
                        fdp = data;
                        FILEDESC_SLOCK(fdesc);
                        for (i = 0; i < oldfds; i++, fdp++) {
                                fp = fget_noref(fdesc, *fdp);
                                if (fp == NULL) {
                                        FILEDESC_SUNLOCK(fdesc);
                                        error = EBADF;
                                        goto out;
                                }
                                if (!(fp->f_ops->fo_flags & DFLAG_PASSABLE)) {
                                        FILEDESC_SUNLOCK(fdesc);
                                        error = EOPNOTSUPP;
                                        goto out;
                                }
                        }

                        /*
                         * Now replace the integer FDs with pointers to the
                         * file structure and capability rights.
                         */
                        m = sbcreatecontrol(NULL, newlen, SCM_RIGHTS,
                            SOL_SOCKET, M_WAITOK);
                        fdp = data;
                        for (i = 0; i < oldfds; i++, fdp++) {
                                if (!fhold(fdesc->fd_ofiles[*fdp].fde_file)) {
                                        fdp = data;
                                        for (j = 0; j < i; j++, fdp++) {
                                                fdrop(fdesc->fd_ofiles[*fdp].
                                                    fde_file, td);
                                        }
                                        FILEDESC_SUNLOCK(fdesc);
                                        error = EBADF;
                                        goto out;
                                }
                        }
                        fdp = data;
                        fdep = (struct filedescent **)
                            CMSG_DATA(mtod(m, struct cmsghdr *));
                        fdev = malloc(sizeof(*fdev) * oldfds, M_FILECAPS,
                            M_WAITOK);
                        for (i = 0; i < oldfds; i++, fdev++, fdp++) {
                                fde = &fdesc->fd_ofiles[*fdp];
                                fdep[i] = fdev;
                                fdep[i]->fde_file = fde->fde_file;
                                filecaps_copy(&fde->fde_caps,
                                    &fdep[i]->fde_caps, true);
                                unp_internalize_fp(fdep[i]->fde_file);
                        }
                        FILEDESC_SUNLOCK(fdesc);
                        break;

                case SCM_TIMESTAMP:
                        m = sbcreatecontrol(NULL, sizeof(*tv), SCM_TIMESTAMP,
                            SOL_SOCKET, M_WAITOK);
                        tv = (struct timeval *)
                            CMSG_DATA(mtod(m, struct cmsghdr *));
                        microtime(tv);
                        break;

                case SCM_BINTIME:
                        m = sbcreatecontrol(NULL, sizeof(*bt), SCM_BINTIME,
                            SOL_SOCKET, M_WAITOK);
                        bt = (struct bintime *)
                            CMSG_DATA(mtod(m, struct cmsghdr *));
                        bintime(bt);
                        break;

                case SCM_REALTIME:
                        m = sbcreatecontrol(NULL, sizeof(*ts), SCM_REALTIME,
                            SOL_SOCKET, M_WAITOK);
                        ts = (struct timespec *)
                            CMSG_DATA(mtod(m, struct cmsghdr *));
                        nanotime(ts);
                        break;

                case SCM_MONOTONIC:
                        m = sbcreatecontrol(NULL, sizeof(*ts), SCM_MONOTONIC,
                            SOL_SOCKET, M_WAITOK);
                        ts = (struct timespec *)
                            CMSG_DATA(mtod(m, struct cmsghdr *));
                        nanouptime(ts);
                        break;

                default:
                        error = EINVAL;
                        goto out;
                }

                mc_append(mc, m);
        }
        if (clen > 0)
                error = EINVAL;

out:
        if (error != 0)
                unp_internalize_cleanup_rights(mc_first(mc));
        m_freem(control);
        return (error);
}

static void
unp_addsockcred(struct thread *td, struct mchain *mc, int mode)
{
        struct mbuf *m, *n, *n_prev;
        const struct cmsghdr *cm;
        int ngroups, i, cmsgtype;
        size_t ctrlsz;

        ngroups = MIN(td->td_ucred->cr_ngroups, CMGROUP_MAX);
        if (mode & UNP_WANTCRED_ALWAYS) {
                ctrlsz = SOCKCRED2SIZE(ngroups);
                cmsgtype = SCM_CREDS2;
        } else {
                ctrlsz = SOCKCREDSIZE(ngroups);
                cmsgtype = SCM_CREDS;
        }

        /* XXXGL: uipc_sosend_*() need to be improved so that we can M_WAITOK */
        m = sbcreatecontrol(NULL, ctrlsz, cmsgtype, SOL_SOCKET, M_NOWAIT);
        if (m == NULL)
                return;
        MPASS((m->m_flags & M_EXT) == 0 && m->m_next == NULL);

        if (mode & UNP_WANTCRED_ALWAYS) {
                struct sockcred2 *sc;

                sc = (void *)CMSG_DATA(mtod(m, struct cmsghdr *));
                sc->sc_version = 0;
                sc->sc_pid = td->td_proc->p_pid;
                sc->sc_uid = td->td_ucred->cr_ruid;
                sc->sc_euid = td->td_ucred->cr_uid;
                sc->sc_gid = td->td_ucred->cr_rgid;
                sc->sc_egid = td->td_ucred->cr_gid;
                sc->sc_ngroups = ngroups;
                for (i = 0; i < sc->sc_ngroups; i++)
                        sc->sc_groups[i] = td->td_ucred->cr_groups[i];
        } else {
                struct sockcred *sc;

                sc = (void *)CMSG_DATA(mtod(m, struct cmsghdr *));
                sc->sc_uid = td->td_ucred->cr_ruid;
                sc->sc_euid = td->td_ucred->cr_uid;
                sc->sc_gid = td->td_ucred->cr_rgid;
                sc->sc_egid = td->td_ucred->cr_gid;
                sc->sc_ngroups = ngroups;
                for (i = 0; i < sc->sc_ngroups; i++)
                        sc->sc_groups[i] = td->td_ucred->cr_groups[i];
        }

        /*
         * Unlink SCM_CREDS control messages (struct cmsgcred), since just
         * created SCM_CREDS control message (struct sockcred) has another
         * format.
         */
        if (!STAILQ_EMPTY(&mc->mc_q) && cmsgtype == SCM_CREDS)
                STAILQ_FOREACH_SAFE(n, &mc->mc_q, m_stailq, n_prev) {
                        cm = mtod(n, struct cmsghdr *);
                        if (cm->cmsg_level == SOL_SOCKET &&
                            cm->cmsg_type == SCM_CREDS) {
                                mc_remove(mc, n);
                                m_free(n);
                        }
                }

        /* Prepend it to the head. */
        mc_prepend(mc, m);
}

static struct unpcb *
fptounp(struct file *fp)
{
        struct socket *so;

        if (fp->f_type != DTYPE_SOCKET)
                return (NULL);
        if ((so = fp->f_data) == NULL)
                return (NULL);
        if (so->so_proto->pr_domain != &localdomain)
                return (NULL);
        return sotounpcb(so);
}

static void
unp_discard(struct file *fp)
{
        struct unp_defer *dr;

        if (unp_externalize_fp(fp)) {
                dr = malloc(sizeof(*dr), M_TEMP, M_WAITOK);
                dr->ud_fp = fp;
                UNP_DEFERRED_LOCK();
                SLIST_INSERT_HEAD(&unp_defers, dr, ud_link);
                UNP_DEFERRED_UNLOCK();
                atomic_add_int(&unp_defers_count, 1);
                taskqueue_enqueue(taskqueue_thread, &unp_defer_task);
        } else
                closef_nothread(fp);
}

static void
unp_process_defers(void *arg __unused, int pending)
{
        struct unp_defer *dr;
        SLIST_HEAD(, unp_defer) drl;
        int count;

        SLIST_INIT(&drl);
        for (;;) {
                UNP_DEFERRED_LOCK();
                if (SLIST_FIRST(&unp_defers) == NULL) {
                        UNP_DEFERRED_UNLOCK();
                        break;
                }
                SLIST_SWAP(&unp_defers, &drl, unp_defer);
                UNP_DEFERRED_UNLOCK();
                count = 0;
                while ((dr = SLIST_FIRST(&drl)) != NULL) {
                        SLIST_REMOVE_HEAD(&drl, ud_link);
                        closef_nothread(dr->ud_fp);
                        free(dr, M_TEMP);
                        count++;
                }
                atomic_add_int(&unp_defers_count, -count);
        }
}

static void
unp_internalize_fp(struct file *fp)
{
        struct unpcb *unp;

        UNP_LINK_WLOCK();
        if ((unp = fptounp(fp)) != NULL) {
                unp->unp_file = fp;
                unp->unp_msgcount++;
        }
        unp_rights++;
        UNP_LINK_WUNLOCK();
}

static int
unp_externalize_fp(struct file *fp)
{
        struct unpcb *unp;
        int ret;

        UNP_LINK_WLOCK();
        if ((unp = fptounp(fp)) != NULL) {
                unp->unp_msgcount--;
                ret = 1;
        } else
                ret = 0;
        unp_rights--;
        UNP_LINK_WUNLOCK();
        return (ret);
}

/*
 * unp_defer indicates whether additional work has been defered for a future
 * pass through unp_gc().  It is thread local and does not require explicit
 * synchronization.
 */
static int      unp_marked;

static void
unp_remove_dead_ref(struct filedescent **fdep, int fdcount)
{
        struct unpcb *unp;
        struct file *fp;
        int i;

        /*
         * This function can only be called from the gc task.
         */
        KASSERT(taskqueue_member(taskqueue_thread, curthread) != 0,
            ("%s: not on gc callout", __func__));
        UNP_LINK_LOCK_ASSERT();

        for (i = 0; i < fdcount; i++) {
                fp = fdep[i]->fde_file;
                if ((unp = fptounp(fp)) == NULL)
                        continue;
                if ((unp->unp_gcflag & UNPGC_DEAD) == 0)
                        continue;
                unp->unp_gcrefs--;
        }
}

static void
unp_restore_undead_ref(struct filedescent **fdep, int fdcount)
{
        struct unpcb *unp;
        struct file *fp;
        int i;

        /*
         * This function can only be called from the gc task.
         */
        KASSERT(taskqueue_member(taskqueue_thread, curthread) != 0,
            ("%s: not on gc callout", __func__));
        UNP_LINK_LOCK_ASSERT();

        for (i = 0; i < fdcount; i++) {
                fp = fdep[i]->fde_file;
                if ((unp = fptounp(fp)) == NULL)
                        continue;
                if ((unp->unp_gcflag & UNPGC_DEAD) == 0)
                        continue;
                unp->unp_gcrefs++;
                unp_marked++;
        }
}

static void
unp_scan_socket(struct socket *so, void (*op)(struct filedescent **, int))
{
        struct sockbuf *sb;

        SOCK_LOCK_ASSERT(so);

        if (sotounpcb(so)->unp_gcflag & UNPGC_IGNORE_RIGHTS)
                return;

        SOCK_RECVBUF_LOCK(so);
        switch (so->so_type) {
        case SOCK_DGRAM:
                unp_scan(STAILQ_FIRST(&so->so_rcv.uxdg_mb), op);
                unp_scan(so->so_rcv.uxdg_peeked, op);
                TAILQ_FOREACH(sb, &so->so_rcv.uxdg_conns, uxdg_clist)
                        unp_scan(STAILQ_FIRST(&sb->uxdg_mb), op);
                break;
        case SOCK_STREAM:
        case SOCK_SEQPACKET:
                unp_scan(STAILQ_FIRST(&so->so_rcv.uxst_mbq), op);
                break;
        }
        SOCK_RECVBUF_UNLOCK(so);
}

static void
unp_gc_scan(struct unpcb *unp, void (*op)(struct filedescent **, int))
{
        struct socket *so, *soa;

        so = unp->unp_socket;
        SOCK_LOCK(so);
        if (SOLISTENING(so)) {
                /*
                 * Mark all sockets in our accept queue.
                 */
                TAILQ_FOREACH(soa, &so->sol_comp, so_list)
                        unp_scan_socket(soa, op);
        } else {
                /*
                 * Mark all sockets we reference with RIGHTS.
                 */
                unp_scan_socket(so, op);
        }
        SOCK_UNLOCK(so);
}

static int unp_recycled;
SYSCTL_INT(_net_local, OID_AUTO, recycled, CTLFLAG_RD, &unp_recycled, 0, 
    "Number of unreachable sockets claimed by the garbage collector.");

static int unp_taskcount;
SYSCTL_INT(_net_local, OID_AUTO, taskcount, CTLFLAG_RD, &unp_taskcount, 0, 
    "Number of times the garbage collector has run.");

SYSCTL_UINT(_net_local, OID_AUTO, sockcount, CTLFLAG_RD, &unp_count, 0, 
    "Number of active local sockets.");

static void
unp_gc(__unused void *arg, int pending)
{
        struct unp_head *heads[] = { &unp_dhead, &unp_shead, &unp_sphead,
                                    NULL };
        struct unp_head **head;
        struct unp_head unp_deadhead;   /* List of potentially-dead sockets. */
        struct file *f, **unref;
        struct unpcb *unp, *unptmp;
        int i, total, unp_unreachable;

        LIST_INIT(&unp_deadhead);
        unp_taskcount++;
        UNP_LINK_RLOCK();
        /*
         * First determine which sockets may be in cycles.
         */
        unp_unreachable = 0;

        for (head = heads; *head != NULL; head++)
                LIST_FOREACH(unp, *head, unp_link) {
                        KASSERT((unp->unp_gcflag & ~UNPGC_IGNORE_RIGHTS) == 0,
                            ("%s: unp %p has unexpected gc flags 0x%x",
                            __func__, unp, (unsigned int)unp->unp_gcflag));

                        f = unp->unp_file;

                        /*
                         * Check for an unreachable socket potentially in a
                         * cycle.  It must be in a queue as indicated by
                         * msgcount, and this must equal the file reference
                         * count.  Note that when msgcount is 0 the file is
                         * NULL.
                         */
                        if (f != NULL && unp->unp_msgcount != 0 &&
                            refcount_load(&f->f_count) == unp->unp_msgcount) {
                                LIST_INSERT_HEAD(&unp_deadhead, unp, unp_dead);
                                unp->unp_gcflag |= UNPGC_DEAD;
                                unp->unp_gcrefs = unp->unp_msgcount;
                                unp_unreachable++;
                        }
                }

        /*
         * Scan all sockets previously marked as potentially being in a cycle
         * and remove the references each socket holds on any UNPGC_DEAD
         * sockets in its queue.  After this step, all remaining references on
         * sockets marked UNPGC_DEAD should not be part of any cycle.
         */
        LIST_FOREACH(unp, &unp_deadhead, unp_dead)
                unp_gc_scan(unp, unp_remove_dead_ref);

        /*
         * If a socket still has a non-negative refcount, it cannot be in a
         * cycle.  In this case increment refcount of all children iteratively.
         * Stop the scan once we do a complete loop without discovering
         * a new reachable socket.
         */
        do {
                unp_marked = 0;
                LIST_FOREACH_SAFE(unp, &unp_deadhead, unp_dead, unptmp)
                        if (unp->unp_gcrefs > 0) {
                                unp->unp_gcflag &= ~UNPGC_DEAD;
                                LIST_REMOVE(unp, unp_dead);
                                KASSERT(unp_unreachable > 0,
                                    ("%s: unp_unreachable underflow.",
                                    __func__));
                                unp_unreachable--;
                                unp_gc_scan(unp, unp_restore_undead_ref);
                        }
        } while (unp_marked);

        UNP_LINK_RUNLOCK();

        if (unp_unreachable == 0)
                return;

        /*
         * Allocate space for a local array of dead unpcbs.
         * TODO: can this path be simplified by instead using the local
         * dead list at unp_deadhead, after taking out references
         * on the file object and/or unpcb and dropping the link lock?
         */
        unref = malloc(unp_unreachable * sizeof(struct file *),
            M_TEMP, M_WAITOK);

        /*
         * Iterate looking for sockets which have been specifically marked
         * as unreachable and store them locally.
         */
        UNP_LINK_RLOCK();
        total = 0;
        LIST_FOREACH(unp, &unp_deadhead, unp_dead) {
                KASSERT((unp->unp_gcflag & UNPGC_DEAD) != 0,
                    ("%s: unp %p not marked UNPGC_DEAD", __func__, unp));
                unp->unp_gcflag &= ~UNPGC_DEAD;
                f = unp->unp_file;
                if (unp->unp_msgcount == 0 || f == NULL ||
                    refcount_load(&f->f_count) != unp->unp_msgcount ||
                    !fhold(f))
                        continue;
                unref[total++] = f;
                KASSERT(total <= unp_unreachable,
                    ("%s: incorrect unreachable count.", __func__));
        }
        UNP_LINK_RUNLOCK();

        /*
         * Now flush all sockets, free'ing rights.  This will free the
         * struct files associated with these sockets but leave each socket
         * with one remaining ref.
         */
        for (i = 0; i < total; i++) {
                struct socket *so;

                so = unref[i]->f_data;
                if (!SOLISTENING(so)) {
                        CURVNET_SET(so->so_vnet);
                        socantrcvmore(so);
                        unp_dispose(so);
                        CURVNET_RESTORE();
                }
        }

        /*
         * And finally release the sockets so they can be reclaimed.
         */
        for (i = 0; i < total; i++)
                fdrop(unref[i], NULL);
        unp_recycled += total;
        free(unref, M_TEMP);
}

/*
 * Synchronize against unp_gc, which can trip over data as we are freeing it.
 */
static void
unp_dispose(struct socket *so)
{
        struct sockbuf *sb;
        struct unpcb *unp;
        struct mbuf *m;
        int error __diagused;

        MPASS(!SOLISTENING(so));

        unp = sotounpcb(so);
        UNP_LINK_WLOCK();
        unp->unp_gcflag |= UNPGC_IGNORE_RIGHTS;
        UNP_LINK_WUNLOCK();

        /*
         * Grab our special mbufs before calling sbrelease().
         */
        error = SOCK_IO_RECV_LOCK(so, SBL_WAIT | SBL_NOINTR);
        MPASS(!error);
        SOCK_RECVBUF_LOCK(so);
        switch (so->so_type) {
        case SOCK_DGRAM:
                while ((sb = TAILQ_FIRST(&so->so_rcv.uxdg_conns)) != NULL) {
                        STAILQ_CONCAT(&so->so_rcv.uxdg_mb, &sb->uxdg_mb);
                        TAILQ_REMOVE(&so->so_rcv.uxdg_conns, sb, uxdg_clist);
                        /* Note: socket of sb may reconnect. */
                        sb->uxdg_cc = sb->uxdg_ctl = sb->uxdg_mbcnt = 0;
                }
                sb = &so->so_rcv;
                if (sb->uxdg_peeked != NULL) {
                        STAILQ_INSERT_HEAD(&sb->uxdg_mb, sb->uxdg_peeked,
                            m_stailqpkt);
                        sb->uxdg_peeked = NULL;
                }
                m = STAILQ_FIRST(&sb->uxdg_mb);
                STAILQ_INIT(&sb->uxdg_mb);
                break;
        case SOCK_STREAM:
        case SOCK_SEQPACKET:
                sb = &so->so_rcv;
                m = STAILQ_FIRST(&sb->uxst_mbq);
                STAILQ_INIT(&sb->uxst_mbq);
                sb->sb_acc = sb->sb_ccc = sb->sb_ctl = sb->sb_mbcnt = 0;
                /*
                 * Trim M_NOTREADY buffers from the free list.  They are
                 * referenced by the I/O thread.
                 */
                if (sb->uxst_fnrdy != NULL) {
                        struct mbuf *n, *prev;

                        while (m != NULL && m->m_flags & M_NOTREADY)
                                m = m->m_next;
                        for (prev = n = m; n != NULL; n = n->m_next) {
                                if (n->m_flags & M_NOTREADY)
                                        prev->m_next = n->m_next;
                                else
                                        prev = n;
                        }
                        sb->uxst_fnrdy = NULL;
                }
                break;
        }
        /*
         * Mark sb with SBS_CANTRCVMORE.  This is needed to prevent
         * uipc_sosend_*() or unp_disconnect() adding more data to the socket.
         * We came here either through shutdown(2) or from the final sofree().
         * The sofree() case is simple as it guarantees that no more sends will
         * happen, however we can race with unp_disconnect() from our peer.
         * The shutdown(2) case is more exotic.  It would call into
         * unp_dispose() only if socket is SS_ISCONNECTED.  This is possible if
         * we did connect(2) on this socket and we also had it bound with
         * bind(2) and receive connections from other sockets.  Because
         * uipc_shutdown() violates POSIX (see comment there) this applies to
         * SOCK_DGRAM as well.  For SOCK_DGRAM this SBS_CANTRCVMORE will have
         * affect not only on the peer we connect(2)ed to, but also on all of
         * the peers who had connect(2)ed to us.  Their sends would end up
         * with ENOBUFS.
         */
        sb->sb_state |= SBS_CANTRCVMORE;
        (void)chgsbsize(so->so_cred->cr_uidinfo, &sb->sb_hiwat, 0,
            RLIM_INFINITY);
        SOCK_RECVBUF_UNLOCK(so);
        SOCK_IO_RECV_UNLOCK(so);

        if (m != NULL) {
                unp_scan(m, unp_freerights);
                m_freemp(m);
        }
}

static void
unp_scan(struct mbuf *m0, void (*op)(struct filedescent **, int))
{
        struct mbuf *m;
        struct cmsghdr *cm;
        void *data;
        socklen_t clen, datalen;

        while (m0 != NULL) {
                for (m = m0; m; m = m->m_next) {
                        if (m->m_type != MT_CONTROL)
                                continue;

                        cm = mtod(m, struct cmsghdr *);
                        clen = m->m_len;

                        while (cm != NULL) {
                                if (sizeof(*cm) > clen || cm->cmsg_len > clen)
                                        break;

                                data = CMSG_DATA(cm);
                                datalen = (caddr_t)cm + cm->cmsg_len
                                    - (caddr_t)data;

                                if (cm->cmsg_level == SOL_SOCKET &&
                                    cm->cmsg_type == SCM_RIGHTS) {
                                        (*op)(data, datalen /
                                            sizeof(struct filedescent *));
                                }

                                if (CMSG_SPACE(datalen) < clen) {
                                        clen -= CMSG_SPACE(datalen);
                                        cm = (struct cmsghdr *)
                                            ((caddr_t)cm + CMSG_SPACE(datalen));
                                } else {
                                        clen = 0;
                                        cm = NULL;
                                }
                        }
                }
                m0 = m0->m_nextpkt;
        }
}

/*
 * Definitions of protocols supported in the LOCAL domain.
 */
static struct protosw streamproto = {
        .pr_type =              SOCK_STREAM,
        .pr_flags =             PR_CONNREQUIRED | PR_CAPATTACH | PR_SOCKBUF,
        .pr_ctloutput =         &uipc_ctloutput,
        .pr_abort =             uipc_abort,
        .pr_accept =            uipc_peeraddr,
        .pr_attach =            uipc_attach,
        .pr_bind =              uipc_bind,
        .pr_bindat =            uipc_bindat,
        .pr_connect =           uipc_connect,
        .pr_connectat =         uipc_connectat,
        .pr_connect2 =          uipc_connect2,
        .pr_detach =            uipc_detach,
        .pr_disconnect =        uipc_disconnect,
        .pr_fdclose =           uipc_fdclose,
        .pr_listen =            uipc_listen,
        .pr_peeraddr =          uipc_peeraddr,
        .pr_send =              uipc_sendfile,
        .pr_sendfile_wait =     uipc_sendfile_wait,
        .pr_ready =             uipc_ready,
        .pr_sense =             uipc_sense,
        .pr_shutdown =          uipc_shutdown,
        .pr_sockaddr =          uipc_sockaddr,
        .pr_sosend =            uipc_sosend_stream_or_seqpacket,
        .pr_soreceive =         uipc_soreceive_stream_or_seqpacket,
        .pr_sopoll =            uipc_sopoll_stream_or_seqpacket,
        .pr_kqfilter =          uipc_kqfilter_stream_or_seqpacket,
        .pr_close =             uipc_close,
        .pr_chmod =             uipc_chmod,
};

static struct protosw dgramproto = {
        .pr_type =              SOCK_DGRAM,
        .pr_flags =             PR_ATOMIC | PR_ADDR | PR_CAPATTACH | PR_SOCKBUF,
        .pr_ctloutput =         &uipc_ctloutput,
        .pr_abort =             uipc_abort,
        .pr_accept =            uipc_peeraddr,
        .pr_attach =            uipc_attach,
        .pr_bind =              uipc_bind,
        .pr_bindat =            uipc_bindat,
        .pr_connect =           uipc_connect,
        .pr_connectat =         uipc_connectat,
        .pr_connect2 =          uipc_connect2,
        .pr_detach =            uipc_detach,
        .pr_disconnect =        uipc_disconnect,
        .pr_fdclose =           uipc_fdclose,
        .pr_peeraddr =          uipc_peeraddr,
        .pr_sosend =            uipc_sosend_dgram,
        .pr_sense =             uipc_sense,
        .pr_shutdown =          uipc_shutdown,
        .pr_sockaddr =          uipc_sockaddr,
        .pr_soreceive =         uipc_soreceive_dgram,
        .pr_close =             uipc_close,
        .pr_chmod =             uipc_chmod,
};

static struct protosw seqpacketproto = {
        .pr_type =              SOCK_SEQPACKET,
        .pr_flags =             PR_CONNREQUIRED | PR_CAPATTACH | PR_SOCKBUF,
        .pr_ctloutput =         &uipc_ctloutput,
        .pr_abort =             uipc_abort,
        .pr_accept =            uipc_peeraddr,
        .pr_attach =            uipc_attach,
        .pr_bind =              uipc_bind,
        .pr_bindat =            uipc_bindat,
        .pr_connect =           uipc_connect,
        .pr_connectat =         uipc_connectat,
        .pr_connect2 =          uipc_connect2,
        .pr_detach =            uipc_detach,
        .pr_disconnect =        uipc_disconnect,
        .pr_fdclose =           uipc_fdclose,
        .pr_listen =            uipc_listen,
        .pr_peeraddr =          uipc_peeraddr,
        .pr_sense =             uipc_sense,
        .pr_shutdown =          uipc_shutdown,
        .pr_sockaddr =          uipc_sockaddr,
        .pr_sosend =            uipc_sosend_stream_or_seqpacket,
        .pr_soreceive =         uipc_soreceive_stream_or_seqpacket,
        .pr_sopoll =            uipc_sopoll_stream_or_seqpacket,
        .pr_kqfilter =          uipc_kqfilter_stream_or_seqpacket,
        .pr_close =             uipc_close,
        .pr_chmod =             uipc_chmod,
};

static struct domain localdomain = {
        .dom_family =           AF_LOCAL,
        .dom_name =             "local",
        .dom_nprotosw =         3,
        .dom_protosw =          {
                &streamproto,
                &dgramproto,
                &seqpacketproto,
        }
};
DOMAIN_SET(local);

/*
 * A helper function called by VFS before socket-type vnode reclamation.
 * For an active vnode it clears unp_vnode pointer and decrements unp_vnode
 * use count.
 */
void
vfs_unp_reclaim(struct vnode *vp)
{
        struct unpcb *unp;
        int active;
        struct mtx *vplock;

        ASSERT_VOP_ELOCKED(vp, "vfs_unp_reclaim");
        KASSERT(vp->v_type == VSOCK,
            ("vfs_unp_reclaim: vp->v_type != VSOCK"));

        active = 0;
        vplock = mtx_pool_find(unp_vp_mtxpool, vp);
        mtx_lock(vplock);
        VOP_UNP_CONNECT(vp, &unp);
        if (unp == NULL)
                goto done;
        UNP_PCB_LOCK(unp);
        if (unp->unp_vnode == vp) {
                VOP_UNP_DETACH(vp);
                unp->unp_vnode = NULL;
                active = 1;
        }
        UNP_PCB_UNLOCK(unp);
 done:
        mtx_unlock(vplock);
        if (active)
                vunref(vp);
}

#ifdef DDB
static void
db_print_indent(int indent)
{
        int i;

        for (i = 0; i < indent; i++)
                db_printf(" ");
}

static void
db_print_unpflags(int unp_flags)
{
        int comma;

        comma = 0;
        if (unp_flags & UNP_HAVEPC) {
                db_printf("%sUNP_HAVEPC", comma ? ", " : "");
                comma = 1;
        }
        if (unp_flags & UNP_WANTCRED_ALWAYS) {
                db_printf("%sUNP_WANTCRED_ALWAYS", comma ? ", " : "");
                comma = 1;
        }
        if (unp_flags & UNP_WANTCRED_ONESHOT) {
                db_printf("%sUNP_WANTCRED_ONESHOT", comma ? ", " : "");
                comma = 1;
        }
        if (unp_flags & UNP_CONNECTING) {
                db_printf("%sUNP_CONNECTING", comma ? ", " : "");
                comma = 1;
        }
        if (unp_flags & UNP_BINDING) {
                db_printf("%sUNP_BINDING", comma ? ", " : "");
                comma = 1;
        }
}

static void
db_print_xucred(int indent, struct xucred *xu)
{
        int comma, i;

        db_print_indent(indent);
        db_printf("cr_version: %u   cr_uid: %u   cr_pid: %d   cr_ngroups: %d\n",
            xu->cr_version, xu->cr_uid, xu->cr_pid, xu->cr_ngroups);
        db_print_indent(indent);
        db_printf("cr_groups: ");
        comma = 0;
        for (i = 0; i < xu->cr_ngroups; i++) {
                db_printf("%s%u", comma ? ", " : "", xu->cr_groups[i]);
                comma = 1;
        }
        db_printf("\n");
}

static void
db_print_unprefs(int indent, struct unp_head *uh)
{
        struct unpcb *unp;
        int counter;

        counter = 0;
        LIST_FOREACH(unp, uh, unp_reflink) {
                if (counter % 4 == 0)
                        db_print_indent(indent);
                db_printf("%p  ", unp);
                if (counter % 4 == 3)
                        db_printf("\n");
                counter++;
        }
        if (counter != 0 && counter % 4 != 0)
                db_printf("\n");
}

DB_SHOW_COMMAND(unpcb, db_show_unpcb)
{
        struct unpcb *unp;

        if (!have_addr) {
                db_printf("usage: show unpcb <addr>\n");
                return;
        }
        unp = (struct unpcb *)addr;

        db_printf("unp_socket: %p   unp_vnode: %p\n", unp->unp_socket,
            unp->unp_vnode);

        db_printf("unp_ino: %ju   unp_conn: %p\n", (uintmax_t)unp->unp_ino,
            unp->unp_conn);

        db_printf("unp_refs:\n");
        db_print_unprefs(2, &unp->unp_refs);

        /* XXXRW: Would be nice to print the full address, if any. */
        db_printf("unp_addr: %p\n", unp->unp_addr);

        db_printf("unp_gencnt: %llu\n",
            (unsigned long long)unp->unp_gencnt);

        db_printf("unp_flags: %x (", unp->unp_flags);
        db_print_unpflags(unp->unp_flags);
        db_printf(")\n");

        db_printf("unp_peercred:\n");
        db_print_xucred(2, &unp->unp_peercred);

        db_printf("unp_refcount: %u\n", unp->unp_refcount);
}
#endif