/*      $NetBSD: procfs_vnops.c,v 1.233 2024/07/01 01:35:53 christos Exp $      */

/*-
 * Copyright (c) 2006, 2007, 2008, 2020 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Andrew Doran.
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
 */

/*
 * Copyright (c) 1993, 1995
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Jan-Simon Pendry.
 *
 * 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.
 *
 *      @(#)procfs_vnops.c      8.18 (Berkeley) 5/21/95
 */

/*
 * Copyright (c) 1993 Jan-Simon Pendry
 *
 * This code is derived from software contributed to Berkeley by
 * Jan-Simon Pendry.
 *
 * 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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. 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.
 *
 *      @(#)procfs_vnops.c      8.18 (Berkeley) 5/21/95
 */

/*
 * procfs vnode interface
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: procfs_vnops.c,v 1.233 2024/07/01 01:35:53 christos Exp $");

#include <sys/param.h>
#include <sys/atomic.h>
#include <sys/systm.h>
#include <sys/time.h>
#include <sys/kernel.h>
#include <sys/file.h>
#include <sys/filedesc.h>
#include <sys/proc.h>
#include <sys/vnode.h>
#include <sys/namei.h>
#include <sys/malloc.h>
#include <sys/mount.h>
#include <sys/dirent.h>
#include <sys/resourcevar.h>
#include <sys/stat.h>
#include <sys/ptrace.h>
#include <sys/kauth.h>
#include <sys/exec.h>

#include <uvm/uvm_extern.h>     /* for PAGE_SIZE */

#include <machine/reg.h>

#include <miscfs/genfs/genfs.h>
#include <miscfs/procfs/procfs.h>

/*
 * Vnode Operations.
 *
 */

static int procfs_validfile_linux(struct lwp *, struct mount *);
static int procfs_root_readdir_callback(struct proc *, void *);
static void procfs_dir(pfstype, struct lwp *, struct proc *, char **, char *,
    size_t);

/*
 * This is a list of the valid names in the
 * process-specific sub-directories.  It is
 * used in procfs_lookup and procfs_readdir
 */
static const struct proc_target {
        u_char  pt_type;
        u_char  pt_namlen;
        const char      *pt_name;
        pfstype pt_pfstype;
        int     (*pt_valid)(struct lwp *, struct mount *);
} proc_targets[] = {
#define N(s) sizeof(s)-1, s
        /*        name          type            validp */
        { DT_DIR, N("."),       PFSproc,        NULL },
        { DT_DIR, N(".."),      PFSroot,        NULL },
        { DT_DIR, N("fd"),      PFSfd,          NULL },
        { DT_DIR, N("task"),    PFStask,        procfs_validfile_linux },
        { DT_LNK, N("cwd"),     PFScwd,         NULL },
        { DT_REG, N("emul"),    PFSemul,        NULL },
        { DT_LNK, N("root"),    PFSchroot,      NULL },
        { DT_REG, N("auxv"),    PFSauxv,        procfs_validauxv },
        { DT_REG, N("cmdline"), PFScmdline,     NULL },
        { DT_REG, N("environ"), PFSenviron,     NULL },
        { DT_LNK, N("exe"),     PFSexe,         procfs_validfile },
        { DT_REG, N("file"),    PFSfile,        procfs_validfile },
        { DT_REG, N("fpregs"),  PFSfpregs,      procfs_validfpregs },
        { DT_REG, N("limit"),   PFSlimit,       NULL },
        { DT_REG, N("limits"),  PFSlimits,      procfs_validfile_linux },
        { DT_REG, N("map"),     PFSmap,         procfs_validmap },
        { DT_REG, N("maps"),    PFSmaps,        procfs_validmap },
        { DT_REG, N("mem"),     PFSmem,         NULL },
        { DT_REG, N("note"),    PFSnote,        NULL },
        { DT_REG, N("notepg"),  PFSnotepg,      NULL },
        { DT_REG, N("regs"),    PFSregs,        procfs_validregs },
        { DT_REG, N("stat"),    PFSstat,        procfs_validfile_linux },
        { DT_REG, N("statm"),   PFSstatm,       procfs_validfile_linux },
        { DT_REG, N("status"),  PFSstatus,      NULL },
#ifdef __HAVE_PROCFS_MACHDEP
        PROCFS_MACHDEP_NODETYPE_DEFNS
#endif
#undef N
};
static const int nproc_targets = sizeof(proc_targets) / sizeof(proc_targets[0]);

/*
 * List of files in the root directory. Note: the validate function will
 * be called with p == NULL for these ones.
 */
static const struct proc_target proc_root_targets[] = {
#define N(s) sizeof(s)-1, s
        /*        name              type            validp */
        { DT_REG, N("meminfo"),     PFSmeminfo,        procfs_validfile_linux },
        { DT_REG, N("cpuinfo"),     PFScpuinfo,        procfs_validfile_linux },
        { DT_REG, N("uptime"),      PFSuptime,         procfs_validfile_linux },
        { DT_REG, N("mounts"),      PFSmounts,         procfs_validfile_linux },
        { DT_REG, N("devices"),     PFSdevices,        procfs_validfile_linux },
        { DT_REG, N("stat"),        PFScpustat,        procfs_validfile_linux },
        { DT_REG, N("loadavg"),     PFSloadavg,        procfs_validfile_linux },
        { DT_REG, N("version"),     PFSversion,        procfs_validfile_linux },
        { DT_DIR, N("sys"),         PFSsys,            procfs_validfile_linux },
        { DT_DIR, N("sysvipc"),     PFSsysvipc,        procfs_validfile_linux },
#undef N
};
static const int nproc_root_targets =
    sizeof(proc_root_targets) / sizeof(proc_root_targets[0]);

/*
 * List of files in the sys directory
 */
static const struct proc_target proc_sys_targets[] = {
#define N(s) sizeof(s)-1, s
        /*        name              type            validp */
        { DT_DIR, N("."),       PFSsys,         procfs_validfile_linux },
        { DT_DIR, N(".."),      PFSroot,        NULL },
        { DT_REG, N("fs"),      PFSsysfs,       procfs_validfile_linux },
#undef N
};
static const int nproc_sys_targets =
    sizeof(proc_sys_targets) / sizeof(proc_sys_targets[0]);

/*
 * List of files in the sys/fs directory
 */
static const struct proc_target proc_sysfs_targets[] = {
#define N(s) sizeof(s)-1, s
        /*        name              type            validp */
        { DT_DIR, N("."),       PFSsysfs,       procfs_validfile_linux },
        { DT_DIR, N(".."),      PFSsys,         procfs_validfile_linux },
        { DT_REG, N("mqueue"),  PFSmqueue,      procfs_validfile_linux },
#undef N
};
static const int nproc_sysfs_targets =
    sizeof(proc_sysfs_targets) / sizeof(proc_sysfs_targets[0]);

/*
 * List of files in the sys/fs/mqueue directory
 */
static const struct proc_target proc_mqueue_targets[] = {
#define N(s) sizeof(s)-1, s
        /*        name                  type            validp */
        { DT_DIR, N("."),               PFSmqueue,      procfs_validfile_linux },
        { DT_DIR, N(".."),              PFSsysfs,       procfs_validfile_linux },
        { DT_REG, N("msg_default"),     PFSmq_msg_def,  procfs_validfile_linux },
        { DT_REG, N("msg_max"),         PFSmq_msg_max,  procfs_validfile_linux },
        { DT_REG, N("msgsize_default"), PFSmq_siz_def,  procfs_validfile_linux },
        { DT_REG, N("msgsize_max"),     PFSmq_siz_max,  procfs_validfile_linux },
        { DT_REG, N("queues_max"),      PFSmq_qmax,     procfs_validfile_linux },
#undef N
};
static const int nproc_mqueue_targets =
    sizeof(proc_mqueue_targets) / sizeof(proc_mqueue_targets[0]);

/*
 * List of files in the sysvipc directory
 */
static const struct proc_target proc_sysvipc_targets[] = {
#define N(s) sizeof(s)-1, s
        /*        name              type            validp */
        { DT_DIR, N("."),       PFSsysvipc,     NULL },
        { DT_DIR, N(".."),      PFSroot,        NULL },
        { DT_REG, N("msg"),     PFSsysvipc_msg, procfs_validfile_linux },
        { DT_REG, N("sem"),     PFSsysvipc_sem, procfs_validfile_linux },
        { DT_REG, N("shm"),     PFSsysvipc_shm, procfs_validfile_linux },
#undef N
};
static const int nproc_sysvipc_targets =
    sizeof(proc_sysvipc_targets) / sizeof(proc_sysvipc_targets[0]);

int     procfs_lookup(void *);
int     procfs_open(void *);
int     procfs_close(void *);
int     procfs_access(void *);
int     procfs_getattr(void *);
int     procfs_setattr(void *);
int     procfs_readdir(void *);
int     procfs_readlink(void *);
int     procfs_inactive(void *);
int     procfs_reclaim(void *);
int     procfs_print(void *);
int     procfs_pathconf(void *);
int     procfs_getpages(void *);

static uint8_t fttodt(file_t *);
static int atoi(const char *, size_t);

/*
 * procfs vnode operations.
 */
int (**procfs_vnodeop_p)(void *);
const struct vnodeopv_entry_desc procfs_vnodeop_entries[] = {
        { &vop_default_desc, vn_default_error },
        { &vop_parsepath_desc, genfs_parsepath },       /* parsepath */
        { &vop_lookup_desc, procfs_lookup },            /* lookup */
        { &vop_create_desc, genfs_eopnotsupp },         /* create */
        { &vop_mknod_desc, genfs_eopnotsupp },          /* mknod */
        { &vop_open_desc, procfs_open },                /* open */
        { &vop_close_desc, procfs_close },              /* close */
        { &vop_access_desc, procfs_access },            /* access */
        { &vop_accessx_desc, genfs_accessx },           /* accessx */
        { &vop_getattr_desc, procfs_getattr },          /* getattr */
        { &vop_setattr_desc, procfs_setattr },          /* setattr */
        { &vop_read_desc, procfs_rw },                  /* read */
        { &vop_write_desc, procfs_rw },                 /* write */
        { &vop_fallocate_desc, genfs_eopnotsupp },      /* fallocate */
        { &vop_fdiscard_desc, genfs_eopnotsupp },       /* fdiscard */
        { &vop_fcntl_desc, genfs_fcntl },               /* fcntl */
        { &vop_ioctl_desc, genfs_enoioctl },            /* ioctl */
        { &vop_poll_desc, genfs_poll },                 /* poll */
        { &vop_kqfilter_desc, genfs_kqfilter },         /* kqfilter */
        { &vop_revoke_desc, genfs_revoke },             /* revoke */
        { &vop_fsync_desc, genfs_nullop },              /* fsync */
        { &vop_seek_desc, genfs_nullop },               /* seek */
        { &vop_remove_desc, genfs_eopnotsupp },         /* remove */
        { &vop_link_desc, genfs_erofs_link },           /* link */
        { &vop_rename_desc, genfs_eopnotsupp },         /* rename */
        { &vop_mkdir_desc, genfs_eopnotsupp },          /* mkdir */
        { &vop_rmdir_desc, genfs_eopnotsupp },          /* rmdir */
        { &vop_symlink_desc, genfs_erofs_symlink },     /* symlink */
        { &vop_readdir_desc, procfs_readdir },          /* readdir */
        { &vop_readlink_desc, procfs_readlink },        /* readlink */
        { &vop_abortop_desc, genfs_abortop },           /* abortop */
        { &vop_inactive_desc, procfs_inactive },        /* inactive */
        { &vop_reclaim_desc, procfs_reclaim },          /* reclaim */
        { &vop_lock_desc, genfs_lock },                 /* lock */
        { &vop_unlock_desc, genfs_unlock },             /* unlock */
        { &vop_bmap_desc, genfs_eopnotsupp },           /* bmap */
        { &vop_strategy_desc, genfs_badop },            /* strategy */
        { &vop_print_desc, procfs_print },              /* print */
        { &vop_islocked_desc, genfs_islocked },         /* islocked */
        { &vop_pathconf_desc, procfs_pathconf },        /* pathconf */
        { &vop_advlock_desc, genfs_einval },            /* advlock */
        { &vop_getpages_desc, procfs_getpages },        /* getpages */
        { &vop_putpages_desc, genfs_null_putpages },    /* putpages */
        { NULL, NULL }
};
const struct vnodeopv_desc procfs_vnodeop_opv_desc =
        { &procfs_vnodeop_p, procfs_vnodeop_entries };
/*
 * set things up for doing i/o on
 * the pfsnode (vp).  (vp) is locked
 * on entry, and should be left locked
 * on exit.
 *
 * for procfs we don't need to do anything
 * in particular for i/o.  all that is done
 * is to support exclusive open on process
 * memory images.
 */
int
procfs_open(void *v)
{
        struct vop_open_args /* {
                struct vnode *a_vp;
                int  a_mode;
                kauth_cred_t a_cred;
        } */ *ap = v;
        struct vnode *vp = ap->a_vp;
        struct pfsnode *pfs = VTOPFS(vp);
        struct lwp *l1;
        struct proc *p2;
        int error;

        if ((error =
             procfs_proc_lock(vp->v_mount, pfs->pfs_pid, &p2, ENOENT)) != 0)
                return error;

        l1 = curlwp;                            /* tracer */

#define M2K(m)  (((m) & FREAD) && ((m) & FWRITE) ? \
                 KAUTH_REQ_PROCESS_PROCFS_RW : \
                 (m) & FWRITE ? KAUTH_REQ_PROCESS_PROCFS_WRITE : \
                 KAUTH_REQ_PROCESS_PROCFS_READ)

        mutex_enter(p2->p_lock);
        error = kauth_authorize_process(l1->l_cred, KAUTH_PROCESS_PROCFS,
            p2, pfs, KAUTH_ARG(M2K(ap->a_mode)), NULL);
        mutex_exit(p2->p_lock);
        if (error) {
                procfs_proc_unlock(p2);
                return (error);
        }

#undef M2K

        switch (pfs->pfs_type) {
        case PFSmem:
                if (((pfs->pfs_flags & FWRITE) && (ap->a_mode & O_EXCL)) ||
                    ((pfs->pfs_flags & O_EXCL) && (ap->a_mode & FWRITE))) {
                        error = EBUSY;
                        break;
                }

                if (!proc_isunder(p2, l1)) {
                        error = EPERM;
                        break;
                }

                if (ap->a_mode & FWRITE)
                        pfs->pfs_flags = ap->a_mode & (FWRITE|O_EXCL);

                break;

        case PFSregs:
        case PFSfpregs:
                if (!proc_isunder(p2, l1)) {
                        error = EPERM;
                        break;
                }
                break;

        default:
                break;
        }

        procfs_proc_unlock(p2);
        return (error);
}

/*
 * close the pfsnode (vp) after doing i/o.
 * (vp) is not locked on entry or exit.
 *
 * nothing to do for procfs other than undo
 * any exclusive open flag (see _open above).
 */
int
procfs_close(void *v)
{
        struct vop_close_args /* {
                struct vnode *a_vp;
                int  a_fflag;
                kauth_cred_t a_cred;
        } */ *ap = v;
        struct pfsnode *pfs = VTOPFS(ap->a_vp);

        switch (pfs->pfs_type) {
        case PFSmem:
                if ((ap->a_fflag & FWRITE) && (pfs->pfs_flags & O_EXCL))
                        pfs->pfs_flags &= ~(FWRITE|O_EXCL);
                break;

        default:
                break;
        }

        return (0);
}

/*
 * _inactive is called when the pfsnode
 * is vrele'd and the reference count goes
 * to zero.  (vp) will be on the vnode free
 * list, so to get it back vget() must be
 * used.
 *
 * (vp) is locked on entry, but must be unlocked on exit.
 */
int
procfs_inactive(void *v)
{
        struct vop_inactive_v2_args /* {
                struct vnode *a_vp;
                bool *a_recycle;
        } */ *ap = v;
        struct vnode *vp = ap->a_vp;
        struct pfsnode *pfs = VTOPFS(vp);

        mutex_enter(&proc_lock);
        *ap->a_recycle = (procfs_proc_find(vp->v_mount, pfs->pfs_pid) == NULL);
        mutex_exit(&proc_lock);

        return (0);
}

/*
 * _reclaim is called when getnewvnode()
 * wants to make use of an entry on the vnode
 * free list.  at this time the filesystem needs
 * to free any private data and remove the node
 * from any private lists.
 */
int
procfs_reclaim(void *v)
{
        struct vop_reclaim_v2_args /* {
                struct vnode *a_vp;
        } */ *ap = v;
        struct vnode *vp = ap->a_vp;
        struct pfsnode *pfs = VTOPFS(vp);

        VOP_UNLOCK(vp);

        /*
         * To interlock with procfs_revoke_vnodes().
         */
        mutex_enter(vp->v_interlock);
        vp->v_data = NULL;
        mutex_exit(vp->v_interlock);
        procfs_hashrem(pfs);
        kmem_free(pfs, sizeof(*pfs));
        return 0;
}

/*
 * Return POSIX pathconf information applicable to special devices.
 */
int
procfs_pathconf(void *v)
{
        struct vop_pathconf_args /* {
                struct vnode *a_vp;
                int a_name;
                register_t *a_retval;
        } */ *ap = v;

        switch (ap->a_name) {
        case _PC_LINK_MAX:
                *ap->a_retval = LINK_MAX;
                return (0);
        case _PC_MAX_CANON:
                *ap->a_retval = MAX_CANON;
                return (0);
        case _PC_MAX_INPUT:
                *ap->a_retval = MAX_INPUT;
                return (0);
        case _PC_PIPE_BUF:
                *ap->a_retval = PIPE_BUF;
                return (0);
        case _PC_CHOWN_RESTRICTED:
                *ap->a_retval = 1;
                return (0);
        case _PC_VDISABLE:
                *ap->a_retval = _POSIX_VDISABLE;
                return (0);
        case _PC_SYNC_IO:
                *ap->a_retval = 1;
                return (0);
        default:
                return genfs_pathconf(ap);
        }
        /* NOTREACHED */
}

/*
 * _print is used for debugging.
 * just print a readable description
 * of (vp).
 */
int
procfs_print(void *v)
{
        struct vop_print_args /* {
                struct vnode *a_vp;
        } */ *ap = v;
        struct pfsnode *pfs = VTOPFS(ap->a_vp);

        printf("tag VT_PROCFS, type %d, pid %d, mode %x, flags %lx\n",
            pfs->pfs_type, pfs->pfs_pid, pfs->pfs_mode, pfs->pfs_flags);
        return 0;
}

/*
 * Works out the path to the target process's current
 * working directory or chroot.  If the caller is in a chroot and
 * can't "reach" the target's cwd or root (or some other error
 * occurs), a "/" is returned for the path.
 */
static void
procfs_dir(pfstype t, struct lwp *caller, struct proc *target, char **bpp,
    char *path, size_t len)
{
        struct cwdinfo *cwdi;
        struct vnode *vp, *rvp;
        char *bp;

        /*
         * Lock target cwdi and take a reference to the vnode
         * we are interested in to prevent it from disappearing
         * before getcwd_common() below.
         */
        rw_enter(&target->p_cwdi->cwdi_lock, RW_READER);
        switch (t) {
        case PFScwd:
                vp = target->p_cwdi->cwdi_cdir;
                break;
        case PFSchroot:
                vp = target->p_cwdi->cwdi_rdir;
                break;
        default:
                rw_exit(&target->p_cwdi->cwdi_lock);
                return;
        }
        if (vp != NULL)
                vref(vp);
        rw_exit(&target->p_cwdi->cwdi_lock);

        cwdi = caller->l_proc->p_cwdi;
        rw_enter(&cwdi->cwdi_lock, RW_READER);

        rvp = cwdi->cwdi_rdir;
        bp = bpp ? *bpp : NULL;

        /*
         * XXX: this horrible kludge avoids locking panics when
         * attempting to lookup links that point to within procfs
         */
        if (vp != NULL && vp->v_tag == VT_PROCFS) {
                if (bpp) {
                        *--bp = '/';
                        *bpp = bp;
                }
                vrele(vp);
                rw_exit(&cwdi->cwdi_lock);
                return;
        }

        if (rvp == NULL)
                rvp = rootvnode;
        if (vp == NULL || getcwd_common(vp, rvp, bp ? &bp : NULL, path,
            len / 2, 0, caller) != 0) {
                if (bpp) {
                        bp = *bpp;
                        *--bp = '/';
                }
        }

        if (bpp)
                *bpp = bp;

        if (vp != NULL)
                vrele(vp);
        rw_exit(&cwdi->cwdi_lock);
}

/*
 * Invent attributes for pfsnode (vp) and store
 * them in (vap).
 * Directories lengths are returned as zero since
 * any real length would require the genuine size
 * to be computed, and nothing cares anyway.
 *
 * this is relatively minimal for procfs.
 */
int
procfs_getattr(void *v)
{
        struct vop_getattr_args /* {
                struct vnode *a_vp;
                struct vattr *a_vap;
                kauth_cred_t a_cred;
        } */ *ap = v;
        struct vnode *vp = ap->a_vp;
        struct pfsnode *pfs = VTOPFS(vp);
        struct vattr *vap = ap->a_vap;
        struct proc *procp;
        char *path, *bp, bf[16];
        int error;

        /* first check the process still exists */
        switch (pfs->pfs_type) {
        case PFSroot:
        case PFScurproc:
        case PFSself:
                procp = NULL;
                break;

        default:
                error =
                    procfs_proc_lock(vp->v_mount, pfs->pfs_pid, &procp, ENOENT);
                if (error != 0)
                        return (error);
                break;
        }

        switch (pfs->pfs_type) {
        case PFStask:
                if (pfs->pfs_fd == -1) {
                        path = NULL;
                        break;
                }
                /*FALLTHROUGH*/
        case PFScwd:
        case PFSchroot:
                path = malloc(MAXPATHLEN + 4, M_TEMP, M_WAITOK);
                if (path == NULL && procp != NULL) {
                        procfs_proc_unlock(procp);
                        return (ENOMEM);
                }
                break;

        default:
                path = NULL;
                break;
        }

        if (procp != NULL) {
                mutex_enter(procp->p_lock);
                error = kauth_authorize_process(kauth_cred_get(),
                    KAUTH_PROCESS_CANSEE, procp,
                    KAUTH_ARG(KAUTH_REQ_PROCESS_CANSEE_ENTRY), NULL, NULL);
                mutex_exit(procp->p_lock);
                if (error != 0) {
                        procfs_proc_unlock(procp);
                        if (path != NULL)
                                free(path, M_TEMP);
                        return (ENOENT);
                }
        }

        error = 0;

        /* start by zeroing out the attributes */
        vattr_null(vap);

        /* next do all the common fields */
        vap->va_type = ap->a_vp->v_type;
        vap->va_mode = pfs->pfs_mode;
        vap->va_fileid = pfs->pfs_fileno;
        vap->va_flags = 0;
        vap->va_blocksize = PAGE_SIZE;

        /*
         * Make all times be current TOD.
         *
         * It would be possible to get the process start
         * time from the p_stats structure, but there's
         * no "file creation" time stamp anyway, and the
         * p_stats structure is not addressable if u. gets
         * swapped out for that process.
         */
        getnanotime(&vap->va_ctime);
        vap->va_atime = vap->va_mtime = vap->va_ctime;
        if (procp)
                TIMEVAL_TO_TIMESPEC(&procp->p_stats->p_start,
                    &vap->va_birthtime);
        else
                getnanotime(&vap->va_birthtime);

        switch (pfs->pfs_type) {
        case PFSmem:
        case PFSregs:
        case PFSfpregs:
#if defined(__HAVE_PROCFS_MACHDEP) && defined(PROCFS_MACHDEP_PROTECT_CASES)
        PROCFS_MACHDEP_PROTECT_CASES
#endif
                /*
                 * If the process has exercised some setuid or setgid
                 * privilege, then rip away read/write permission so
                 * that only root can gain access.
                 */
                if (procp->p_flag & PK_SUGID)
                        vap->va_mode &= ~(S_IRUSR|S_IWUSR);
                /* FALLTHROUGH */
        case PFSstatus:
        case PFSstat:
        case PFSnote:
        case PFSnotepg:
        case PFScmdline:
        case PFSenviron:
        case PFSemul:
        case PFSstatm:

        case PFSmap:
        case PFSmaps:
        case PFSlimit:
        case PFSlimits:
        case PFSauxv:
                vap->va_nlink = 1;
                vap->va_uid = kauth_cred_geteuid(procp->p_cred);
                vap->va_gid = kauth_cred_getegid(procp->p_cred);
                break;
        case PFScwd:
        case PFSchroot:
        case PFSmeminfo:
        case PFSdevices:
        case PFScpuinfo:
        case PFSuptime:
        case PFSmounts:
        case PFScpustat:
        case PFSloadavg:
        case PFSversion:
        case PFSexe:
        case PFSself:
        case PFScurproc:
        case PFSroot:
        case PFSmq_msg_def:
        case PFSmq_msg_max:
        case PFSmq_siz_def:
        case PFSmq_siz_max:
        case PFSmq_qmax:
        case PFSsysvipc_msg:
        case PFSsysvipc_sem:
        case PFSsysvipc_shm:
                vap->va_nlink = 1;
                vap->va_uid = vap->va_gid = 0;
                break;

        case PFSsysvipc:
                vap->va_nlink = 5;
                vap->va_uid = vap->va_gid = 0;
                break;

        case PFSsys:    /* proc/sys only contains "fs" */
        case PFSsysfs:  /* proc/sys/fs only contains "mqueue" */
                vap->va_nlink = 3;
                vap->va_uid = vap->va_gid = 0;
                break;

        case PFSmqueue:
                vap->va_nlink = 7;
                vap->va_uid = vap->va_gid = 0;
                break;

        case PFSproc:
        case PFStask:
        case PFSfile:
        case PFSfd:
                break;

        default:
                panic("%s: %d/1", __func__, pfs->pfs_type);
        }

        /*
         * now do the object specific fields
         *
         * The size could be set from struct reg, but it's hardly
         * worth the trouble, and it puts some (potentially) machine
         * dependent data into this machine-independent code.  If it
         * becomes important then this function should break out into
         * a per-file stat function in the corresponding .c file.
         */

        switch (pfs->pfs_type) {
        case PFSroot:
                vap->va_bytes = vap->va_size = DEV_BSIZE;
                break;

        case PFSself:
        case PFScurproc:
                vap->va_bytes = vap->va_size =
                    snprintf(bf, sizeof(bf), "%ld", (long)curproc->p_pid);
                break;
        case PFStask:
                if (pfs->pfs_fd != -1) {
                        vap->va_nlink = 1;
                        vap->va_uid = 0;
                        vap->va_gid = 0;
                        vap->va_bytes = vap->va_size =
                            snprintf(bf, sizeof(bf), "..");
                        break;
                }
                /*FALLTHROUGH*/
        case PFSfd:
                if (pfs->pfs_fd != -1) {
                        file_t *fp;

                        fp = fd_getfile2(procp, pfs->pfs_fd);
                        if (fp == NULL) {
                                error = EBADF;
                                break;
                        }
                        vap->va_nlink = 1;
                        vap->va_uid = kauth_cred_geteuid(fp->f_cred);
                        vap->va_gid = kauth_cred_getegid(fp->f_cred);
                        switch (fp->f_type) {
                        case DTYPE_VNODE:
                                vap->va_bytes = vap->va_size =
                                    fp->f_vnode->v_size;
                                break;
                        default:
                                vap->va_bytes = vap->va_size = 0;
                                break;
                        }
                        closef(fp);
                        break;
                }
                /*FALLTHROUGH*/
        case PFSproc:
                vap->va_nlink = 2;
                vap->va_uid = kauth_cred_geteuid(procp->p_cred);
                vap->va_gid = kauth_cred_getegid(procp->p_cred);
                vap->va_bytes = vap->va_size = DEV_BSIZE;
                break;

        case PFSfile:
                error = EOPNOTSUPP;
                break;

        case PFSmem:
                vap->va_bytes = vap->va_size =
                        ctob(procp->p_vmspace->vm_tsize +
                                    procp->p_vmspace->vm_dsize +
                                    procp->p_vmspace->vm_ssize);
                break;

        case PFSauxv:
                vap->va_bytes = vap->va_size = procp->p_execsw->es_arglen;
                break;

#if defined(PT_GETREGS) || defined(PT_SETREGS)
        case PFSregs:
                vap->va_bytes = vap->va_size = sizeof(struct reg);
                break;
#endif

#if defined(PT_GETFPREGS) || defined(PT_SETFPREGS)
        case PFSfpregs:
                vap->va_bytes = vap->va_size = sizeof(struct fpreg);
                break;
#endif

        case PFSstatus:
        case PFSstat:
        case PFSnote:
        case PFSnotepg:
        case PFScmdline:
        case PFSenviron:
        case PFSmeminfo:
        case PFSdevices:
        case PFScpuinfo:
        case PFSuptime:
        case PFSmounts:
        case PFScpustat:
        case PFSloadavg:
        case PFSstatm:
        case PFSversion:
        case PFSsys:
        case PFSsysfs:
        case PFSmqueue:
        case PFSmq_msg_def:
        case PFSmq_msg_max:
        case PFSmq_siz_def:
        case PFSmq_siz_max:
        case PFSmq_qmax:
        case PFSsysvipc:
        case PFSsysvipc_msg:
        case PFSsysvipc_sem:
        case PFSsysvipc_shm:
                vap->va_bytes = vap->va_size = 0;
                break;
        case PFSlimit:
        case PFSlimits:
        case PFSmap:
        case PFSmaps:
                /*
                 * Advise a larger blocksize for the map files, so that
                 * they may be read in one pass.
                 */
                vap->va_blocksize = 4 * PAGE_SIZE;
                vap->va_bytes = vap->va_size = 0;
                break;

        case PFScwd:
        case PFSchroot:
                bp = path + MAXPATHLEN;
                *--bp = '\0';
                procfs_dir(pfs->pfs_type, curlwp, procp, &bp, path,
                     MAXPATHLEN);
                vap->va_bytes = vap->va_size = strlen(bp);
                break;

        case PFSexe:
                vap->va_bytes = vap->va_size = strlen(procp->p_path);
                break;

        case PFSemul:
                vap->va_bytes = vap->va_size = strlen(procp->p_emul->e_name);
                break;

#ifdef __HAVE_PROCFS_MACHDEP
        PROCFS_MACHDEP_NODETYPE_CASES
                error = procfs_machdep_getattr(ap->a_vp, vap, procp);
                break;
#endif

        default:
                panic("%s: %d/2", __func__, pfs->pfs_type);
        }

        if (procp != NULL)
                procfs_proc_unlock(procp);
        if (path != NULL)
                free(path, M_TEMP);

        return (error);
}

/*ARGSUSED*/
int
procfs_setattr(void *v)
{
        /*
         * just fake out attribute setting
         * it's not good to generate an error
         * return, otherwise things like creat()
         * will fail when they try to set the
         * file length to 0.  worse, this means
         * that echo $note > /proc/$pid/note will fail.
         */

        return (0);
}

/*
 * implement access checking.
 *
 * actually, the check for super-user is slightly
 * broken since it will allow read access to write-only
 * objects.  this doesn't cause any particular trouble
 * but does mean that the i/o entry points need to check
 * that the operation really does make sense.
 */
int
procfs_access(void *v)
{
        struct vop_access_args /* {
                struct vnode *a_vp;
                accmode_t a_accmode;
                kauth_cred_t a_cred;
        } */ *ap = v;
        struct vattr va;
        int error;

        if ((error = VOP_GETATTR(ap->a_vp, &va, ap->a_cred)) != 0)
                return (error);

        return kauth_authorize_vnode(ap->a_cred,
            KAUTH_ACCESS_ACTION(ap->a_accmode, ap->a_vp->v_type, va.va_mode),
            ap->a_vp, NULL, genfs_can_access(ap->a_vp, ap->a_cred,
            va.va_uid, va.va_gid, va.va_mode, NULL, ap->a_accmode));
}

/*
 * lookup.  this is incredibly complicated in the
 * general case, however for most pseudo-filesystems
 * very little needs to be done.
 *
 * Locking isn't hard here, just poorly documented.
 *
 * If we're looking up ".", just vref the parent & return it.
 *
 * If we're looking up "..", unlock the parent, and lock "..". If everything
 * went ok, and we're on the last component and the caller requested the
 * parent locked, try to re-lock the parent. We do this to prevent lock
 * races.
 *
 * For anything else, get the needed node. Then unlock the parent if not
 * the last component or not LOCKPARENT (i.e. if we wouldn't re-lock the
 * parent in the .. case).
 *
 * We try to exit with the parent locked in error cases.
 */
int
procfs_lookup(void *v)
{
        struct vop_lookup_v2_args /* {
                struct vnode * a_dvp;
                struct vnode ** a_vpp;
                struct componentname * a_cnp;
        } */ *ap = v;
        struct componentname *cnp = ap->a_cnp;
        struct vnode **vpp = ap->a_vpp;
        struct vnode *dvp = ap->a_dvp;
        const char *pname = cnp->cn_nameptr;
        const struct proc_target *pt = NULL;
        struct vnode *fvp;
        pid_t pid, vnpid;
        struct pfsnode *pfs;
        struct proc *p = NULL;
        struct lwp *plwp;
        int i, error;
        pfstype type;

        *vpp = NULL;

        if ((error = VOP_ACCESS(dvp, VEXEC, cnp->cn_cred)) != 0)
                return (error);

        if (cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME)
                return (EROFS);

        if (cnp->cn_namelen == 1 && *pname == '.') {
                *vpp = dvp;
                vref(dvp);
                return (0);
        }

        pfs = VTOPFS(dvp);
        switch (pfs->pfs_type) {
        case PFSroot:
                /*
                 * Shouldn't get here with .. in the root node.
                 */
                if (cnp->cn_flags & ISDOTDOT)
                        return (EIO);

                for (i = 0; i < nproc_root_targets; i++) {
                        pt = &proc_root_targets[i];
                        /*
                         * check for node match.  proc is always NULL here,
                         * so call pt_valid with constant NULL lwp.
                         */
                        if (cnp->cn_namelen == pt->pt_namlen &&
                            memcmp(pt->pt_name, pname, cnp->cn_namelen) == 0 &&
                            (pt->pt_valid == NULL ||
                             (*pt->pt_valid)(NULL, dvp->v_mount)))
                                break;
                }

                if (i != nproc_root_targets) {
                        error = procfs_allocvp(dvp->v_mount, vpp, 0,
                            pt->pt_pfstype, -1);
                        return (error);
                }

                if (CNEQ(cnp, "curproc", 7)) {
                        pid = curproc->p_pid;
                        vnpid = 0;
                        type = PFScurproc;
                } else if (CNEQ(cnp, "self", 4)) {
                        pid = curproc->p_pid;
                        vnpid = 0;
                        type = PFSself;
                } else {
                        pid = (pid_t)atoi(pname, cnp->cn_namelen);
                        vnpid = pid;
                        type = PFSproc;
                }

                if (procfs_proc_lock(dvp->v_mount, pid, &p, ESRCH) != 0)
                        break;
                error = procfs_allocvp(dvp->v_mount, vpp, vnpid, type, -1);
                procfs_proc_unlock(p);
                return (error);

        case PFSproc:
                if (cnp->cn_flags & ISDOTDOT) {
                        error = procfs_allocvp(dvp->v_mount, vpp, 0, PFSroot,
                            -1);
                        return (error);
                }

                if (procfs_proc_lock(dvp->v_mount, pfs->pfs_pid, &p,
                                     ESRCH) != 0)
                        break;

                mutex_enter(p->p_lock);
                LIST_FOREACH(plwp, &p->p_lwps, l_sibling) {
                        if (plwp->l_stat != LSZOMB)
                                break;
                }
                /* Process is exiting if no-LWPS or all LWPs are LSZOMB */
                if (plwp == NULL) {
                        mutex_exit(p->p_lock);
                        procfs_proc_unlock(p);
                        return ESRCH;
                }

                lwp_addref(plwp);
                mutex_exit(p->p_lock);

                for (pt = proc_targets, i = 0; i < nproc_targets; pt++, i++) {
                        int found;

                        found = cnp->cn_namelen == pt->pt_namlen &&
                            memcmp(pt->pt_name, pname, cnp->cn_namelen) == 0 &&
                            (pt->pt_valid == NULL
                              || (*pt->pt_valid)(plwp, dvp->v_mount));
                        if (found)
                                break;
                }
                lwp_delref(plwp);

                if (i == nproc_targets) {
                        procfs_proc_unlock(p);
                        break;
                }
                if (pt->pt_pfstype == PFSfile) {
                        fvp = p->p_textvp;
                        /* We already checked that it exists. */
                        vref(fvp);
                        procfs_proc_unlock(p);
                        *vpp = fvp;
                        return (0);
                }

                error = procfs_allocvp(dvp->v_mount, vpp, pfs->pfs_pid,
                    pt->pt_pfstype, -1);
                procfs_proc_unlock(p);
                return (error);

        case PFSfd: {
                int fd;
                file_t *fp;

                if ((error = procfs_proc_lock(dvp->v_mount, pfs->pfs_pid, &p,
                                              ENOENT)) != 0)
                        return error;

                if (cnp->cn_flags & ISDOTDOT) {
                        error = procfs_allocvp(dvp->v_mount, vpp, pfs->pfs_pid,
                            PFSproc, -1);
                        procfs_proc_unlock(p);
                        return (error);
                }
                fd = atoi(pname, cnp->cn_namelen);

                fp = fd_getfile2(p, fd);
                if (fp == NULL) {
                        procfs_proc_unlock(p);
                        return ENOENT;
                }
                fvp = fp->f_vnode;

                /* Don't show directories */
                if (fp->f_type == DTYPE_VNODE && fvp->v_type != VDIR &&
                    !procfs_proc_is_linux_compat()) {
                        vref(fvp);
                        closef(fp);
                        procfs_proc_unlock(p);
                        *vpp = fvp;
                        return 0;
                }

                closef(fp);
                error = procfs_allocvp(dvp->v_mount, vpp, pfs->pfs_pid,
                    PFSfd, fd);
                procfs_proc_unlock(p);
                return error;
        }
        case PFStask: {
                int xpid;

                if ((error = procfs_proc_lock(dvp->v_mount, pfs->pfs_pid, &p,
                                              ENOENT)) != 0)
                        return error;

                if (cnp->cn_flags & ISDOTDOT) {
                        error = procfs_allocvp(dvp->v_mount, vpp, pfs->pfs_pid,
                            PFSproc, -1);
                        procfs_proc_unlock(p);
                        return (error);
                }
                xpid = atoi(pname, cnp->cn_namelen);

                if (xpid != pfs->pfs_pid) {
                        procfs_proc_unlock(p);
                        return ENOENT;
                }
                error = procfs_allocvp(dvp->v_mount, vpp, pfs->pfs_pid,
                    PFStask, 0);
                procfs_proc_unlock(p);
                return error;
        }
        case PFSsys:
        case PFSsysfs:
        case PFSmqueue:
        case PFSsysvipc: {
                const struct proc_target *targets;
                int ntargets;
                pfstype parent;

                switch (pfs->pfs_type) {
                case PFSsys:
                        targets = proc_sys_targets;
                        ntargets = nproc_sys_targets;
                        parent = PFSroot;
                        break;
                case PFSsysfs:
                        targets = proc_sysfs_targets;
                        ntargets = nproc_sysfs_targets;
                        parent = PFSsys;
                        break;
                case PFSmqueue:
                        targets = proc_mqueue_targets;
                        ntargets = nproc_mqueue_targets;
                        parent = PFSsysfs;
                        break;
                case PFSsysvipc:
                        targets = proc_sysvipc_targets;
                        ntargets = nproc_sysvipc_targets;
                        parent = PFSroot;
                        break;
                default:
                        return (EINVAL);
                }

                if (cnp->cn_flags & ISDOTDOT) {
                        error = procfs_allocvp(dvp->v_mount, vpp, 0, parent,
                            -1);
                        return (error);
                }

                for (i = 0; i < ntargets; i++) {
                        pt = &targets[i];
                        /*
                         * check for node match.  proc is always NULL here,
                         * so call pt_valid with constant NULL lwp.
                         */
                        if (cnp->cn_namelen == pt->pt_namlen &&
                            memcmp(pt->pt_name, pname, cnp->cn_namelen) == 0 &&
                            (pt->pt_valid == NULL ||
                             (*pt->pt_valid)(NULL, dvp->v_mount)))
                                break;
                }

                if (i != ntargets) {
                        error = procfs_allocvp(dvp->v_mount, vpp, 0,
                            pt->pt_pfstype, -1);
                        return (error);
                }

                return (ENOENT);
        }

        default:
                return (ENOTDIR);
        }

        return (cnp->cn_nameiop == LOOKUP ? ENOENT : EROFS);
}

int
procfs_validfile(struct lwp *l, struct mount *mp)
{
        return l != NULL && l->l_proc != NULL && l->l_proc->p_textvp != NULL;
}

static int
procfs_validfile_linux(struct lwp *l, struct mount *mp)
{
        return procfs_use_linux_compat(mp) &&
            (l == NULL || l->l_proc == NULL || procfs_validfile(l, mp));
}

struct procfs_root_readdir_ctx {
        struct uio *uiop;
        off_t *cookies;
        int ncookies;
        off_t off;
        off_t startoff;
        int error;
};

static int
procfs_root_readdir_callback(struct proc *p, void *arg)
{
        struct procfs_root_readdir_ctx *ctxp = arg;
        struct dirent d;
        struct uio *uiop;
        int error;

        uiop = ctxp->uiop;
        if (uiop->uio_resid < UIO_MX)
                return -1; /* no space */

        if (kauth_authorize_process(kauth_cred_get(),
            KAUTH_PROCESS_CANSEE, p,
            KAUTH_ARG(KAUTH_REQ_PROCESS_CANSEE_ENTRY), NULL, NULL) != 0)
                return 0;

        if (ctxp->off < ctxp->startoff) {
                ctxp->off++;
                return 0;
        }

        memset(&d, 0, UIO_MX);
        d.d_reclen = UIO_MX;
        d.d_fileno = PROCFS_FILENO(p->p_pid, PFSproc, -1);
        d.d_namlen = snprintf(d.d_name,
            UIO_MX - offsetof(struct dirent, d_name), "%ld", (long)p->p_pid);
        d.d_type = DT_DIR;

        mutex_exit(&proc_lock);
        error = uiomove(&d, UIO_MX, uiop);
        mutex_enter(&proc_lock);
        if (error) {
                ctxp->error = error;
                return -1;
        }

        ctxp->ncookies++;
        if (ctxp->cookies)
                *(ctxp->cookies)++ = ctxp->off + 1;
        ctxp->off++;

        return 0;
}

/*
 * readdir returns directory entries from pfsnode (vp).
 *
 * the strategy here with procfs is to generate a single
 * directory entry at a time (struct dirent) and then
 * copy that out to userland using uiomove.  a more efficient
 * though more complex implementation, would try to minimize
 * the number of calls to uiomove().  for procfs, this is
 * hardly worth the added code complexity.
 *
 * this should just be done through read()
 */
int
procfs_readdir(void *v)
{
        struct vop_readdir_args /* {
                struct vnode *a_vp;
                struct uio *a_uio;
                kauth_cred_t a_cred;
                int *a_eofflag;
                off_t **a_cookies;
                int *a_ncookies;
        } */ *ap = v;
        struct uio *uio = ap->a_uio;
        struct dirent d;
        struct pfsnode *pfs;
        off_t i;
        int error;
        off_t *cookies = NULL;
        int ncookies;
        struct vnode *vp;
        const struct proc_target *pt;
        struct procfs_root_readdir_ctx ctx;
        struct proc *p = NULL;
        struct lwp *l;
        int nfd;
        int nc = 0;

        vp = ap->a_vp;
        pfs = VTOPFS(vp);

        if (uio->uio_resid < UIO_MX)
                return (EINVAL);
        if (uio->uio_offset < 0)
                return (EINVAL);

        error = 0;
        i = uio->uio_offset;
        memset(&d, 0, UIO_MX);
        d.d_reclen = UIO_MX;
        ncookies = uio->uio_resid / UIO_MX;

        switch (pfs->pfs_type) {
        /*
         * this is for the process-specific sub-directories.
         * all that is needed to is copy out all the entries
         * from the procent[] table (top of this file).
         */
        case PFSproc: {

                if (i >= nproc_targets)
                        return 0;

                if (procfs_proc_lock(vp->v_mount, pfs->pfs_pid, &p, ESRCH) != 0)
                        break;

                if (ap->a_ncookies) {
                        ncookies = uimin(ncookies, (nproc_targets - i));
                        cookies = malloc(ncookies * sizeof (off_t),
                            M_TEMP, M_WAITOK);
                        *ap->a_cookies = cookies;
                }

                for (pt = &proc_targets[i];
                     uio->uio_resid >= UIO_MX && i < nproc_targets; pt++, i++) {
                        if (pt->pt_valid) {
                                /* XXXSMP LWP can disappear */
                                mutex_enter(p->p_lock);
                                l = LIST_FIRST(&p->p_lwps);
                                KASSERT(l != NULL);
                                mutex_exit(p->p_lock);
                                if ((*pt->pt_valid)(l, vp->v_mount) == 0)
                                        continue;
                        }

                        d.d_fileno = PROCFS_FILENO(pfs->pfs_pid,
                            pt->pt_pfstype, -1);
                        d.d_namlen = pt->pt_namlen;
                        memcpy(d.d_name, pt->pt_name, pt->pt_namlen + 1);
                        d.d_type = pt->pt_type;

                        if ((error = uiomove(&d, UIO_MX, uio)) != 0)
                                break;
                        if (cookies)
                                *cookies++ = i + 1;
                }

                procfs_proc_unlock(p);
                break;
        }
        case PFSfd: {
                file_t *fp;
                int lim;

                if ((error = procfs_proc_lock(vp->v_mount, pfs->pfs_pid, &p,
                                              ESRCH)) != 0)
                        return error;

                /* XXX Should this be by file as well? */
                if (kauth_authorize_process(kauth_cred_get(),
                    KAUTH_PROCESS_CANSEE, p,
                    KAUTH_ARG(KAUTH_REQ_PROCESS_CANSEE_OPENFILES), NULL,
                    NULL) != 0) {
                        procfs_proc_unlock(p);
                        return ESRCH;
                }

                nfd = atomic_load_consume(&p->p_fd->fd_dt)->dt_nfiles;

                lim = uimin((int)p->p_rlimit[RLIMIT_NOFILE].rlim_cur, maxfiles);
                if (i >= lim) {
                        procfs_proc_unlock(p);
                        return 0;
                }

                if (ap->a_ncookies) {
                        ncookies = uimin(ncookies, (nfd + 2 - i));
                        cookies = malloc(ncookies * sizeof (off_t),
                            M_TEMP, M_WAITOK);
                        *ap->a_cookies = cookies;
                }

                for (; i < 2 && uio->uio_resid >= UIO_MX; i++) {
                        pt = &proc_targets[i];
                        d.d_namlen = pt->pt_namlen;
                        d.d_fileno = PROCFS_FILENO(pfs->pfs_pid,
                            pt->pt_pfstype, -1);
                        (void)memcpy(d.d_name, pt->pt_name, pt->pt_namlen + 1);
                        d.d_type = pt->pt_type;
                        if ((error = uiomove(&d, UIO_MX, uio)) != 0)
                                break;
                        if (cookies)
                                *cookies++ = i + 1;
                        nc++;
                }
                if (error)
                        goto out;
                for (; uio->uio_resid >= UIO_MX && i < nfd; i++) {
                        /* check the descriptor exists */
                        if ((fp = fd_getfile2(p, i - 2)) == NULL)
                                continue;
                        closef(fp);

                        d.d_fileno = PROCFS_FILENO(pfs->pfs_pid, PFSfd, i - 2);
                        d.d_namlen = snprintf(d.d_name, sizeof(d.d_name),
                            "%lld", (long long)(i - 2));
                        d.d_type = fttodt(fp);
                        if ((error = uiomove(&d, UIO_MX, uio)) != 0)
                                break;
                        if (cookies)
                                *cookies++ = i + 1;
                        nc++;
                }
                goto out;
        }
        case PFStask: {

                if ((error = procfs_proc_lock(vp->v_mount, pfs->pfs_pid, &p,
                                              ESRCH)) != 0)
                        return error;

                nfd = 3;        /* ., .., pid */

                if (ap->a_ncookies) {
                        ncookies = uimin(ncookies, (nfd + 2 - i));
                        cookies = malloc(ncookies * sizeof (off_t),
                            M_TEMP, M_WAITOK);
                        *ap->a_cookies = cookies;
                }

                for (; i < 2 && uio->uio_resid >= UIO_MX; i++) {
                        pt = &proc_targets[i];
                        d.d_namlen = pt->pt_namlen;
                        d.d_fileno = PROCFS_FILENO(pfs->pfs_pid,
                            pt->pt_pfstype, -1);
                        (void)memcpy(d.d_name, pt->pt_name, pt->pt_namlen + 1);
                        d.d_type = pt->pt_type;
                        if ((error = uiomove(&d, UIO_MX, uio)) != 0)
                                break;
                        if (cookies)
                                *cookies++ = i + 1;
                        nc++;
                }
                if (error)
                        goto out;
                for (; uio->uio_resid >= UIO_MX && i < nfd; i++) {
                        /* check the descriptor exists */
                        d.d_fileno = PROCFS_FILENO(pfs->pfs_pid, PFStask,
                            i - 2);
                        d.d_namlen = snprintf(d.d_name, sizeof(d.d_name),
                            "%ld", (long)pfs->pfs_pid);
                        d.d_type = DT_LNK;
                        if ((error = uiomove(&d, UIO_MX, uio)) != 0)
                                break;
                        if (cookies)
                                *cookies++ = i + 1;
                        nc++;
                }
                goto out;
        }

        /*
         * misc subdirectories
         */
        case PFSsys:
        case PFSsysfs:
        case PFSmqueue:
        case PFSsysvipc: {
                const struct proc_target *targets;
                int ntargets;

                switch (pfs->pfs_type) {
                case PFSsys:
                        targets = proc_sys_targets;
                        ntargets = nproc_sys_targets;
                        break;
                case PFSsysfs:
                        targets = proc_sysfs_targets;
                        ntargets = nproc_sysfs_targets;
                        break;
                case PFSmqueue:
                        targets = proc_mqueue_targets;
                        ntargets = nproc_mqueue_targets;
                        break;
                case PFSsysvipc:
                        targets = proc_sysvipc_targets;
                        ntargets = nproc_sysvipc_targets;
                        break;
                default:
                        return (EINVAL);
                }

                if ((error = procfs_proc_lock(vp->v_mount, pfs->pfs_pid, &p,
                                              ESRCH)) != 0)
                        return error;
                if (ap->a_ncookies) {
                        ncookies = uimin(ncookies, (ntargets - i));
                        cookies = malloc(ncookies * sizeof (off_t),
                            M_TEMP, M_WAITOK);
                        *ap->a_cookies = cookies;
                }

                for (pt = &targets[i];
                     uio->uio_resid >= UIO_MX && i < ntargets; pt++, i++) {
                        if (pt->pt_valid &&
                            (*pt->pt_valid)(NULL, vp->v_mount) == 0)
                                continue;
                        d.d_fileno = PROCFS_FILENO(pfs->pfs_pid,
                            pt->pt_pfstype, -1);
                        d.d_namlen = pt->pt_namlen;
                        memcpy(d.d_name, pt->pt_name, pt->pt_namlen + 1);
                        d.d_type = pt->pt_type;

                        if ((error = uiomove(&d, UIO_MX, uio)) != 0)
                                break;
                        if (cookies)
                                *cookies++ = i + 1;
                }

                goto out;
        }

        /*
         * this is for the root of the procfs filesystem
         * what is needed are special entries for "curproc"
         * and "self" followed by an entry for each process
         * on allproc.
         */

        case PFSroot: {

                if (ap->a_ncookies) {
                        /*
                         * XXX Potentially allocating too much space here,
                         * but I'm lazy. This loop needs some work.
                         */
                        cookies = malloc(ncookies * sizeof (off_t),
                            M_TEMP, M_WAITOK);
                        *ap->a_cookies = cookies;
                }

                /* 0 ... 3 are static entries. */
                for (; i <= 3 && uio->uio_resid >= UIO_MX; i++) {
                        switch (i) {
                        case 0:         /* `.' */
                        case 1:         /* `..' */
                                d.d_fileno = PROCFS_FILENO(0, PFSroot, -1);
                                d.d_namlen = i + 1;
                                memcpy(d.d_name, "..", d.d_namlen);
                                d.d_name[i + 1] = '\0';
                                d.d_type = DT_DIR;
                                break;

                        case 2:
                                d.d_fileno = PROCFS_FILENO(0, PFScurproc, -1);
                                d.d_namlen = sizeof("curproc") - 1;
                                memcpy(d.d_name, "curproc", sizeof("curproc"));
                                d.d_type = DT_LNK;
                                break;

                        case 3:
                                d.d_fileno = PROCFS_FILENO(0, PFSself, -1);
                                d.d_namlen = sizeof("self") - 1;
                                memcpy(d.d_name, "self", sizeof("self"));
                                d.d_type = DT_LNK;
                                break;
                        }

                        if ((error = uiomove(&d, UIO_MX, uio)) != 0)
                                break;
                        nc++;
                        if (cookies)
                                *cookies++ = i + 1;
                }
                if (error)
                        break;
                /* 4 ... are process entries. */
                ctx.uiop = uio;
                ctx.error = 0;
                ctx.off = 4;
                ctx.startoff = i;
                ctx.cookies = cookies;
                ctx.ncookies = nc;
                proclist_foreach_call(&allproc,
                    procfs_root_readdir_callback, &ctx);
                cookies = ctx.cookies;
                nc = ctx.ncookies;
                error = ctx.error;
                if (error)
                        break;

                /* misc entries. */
                if (i < ctx.off)
                        i = ctx.off;
                if (i >= ctx.off + nproc_root_targets)
                        break;
                error = procfs_proc_lock(vp->v_mount, pfs->pfs_pid, &p, ESRCH);
                if (error)
                        break;
                for (pt = &proc_root_targets[i - ctx.off];
                    uio->uio_resid >= UIO_MX &&
                    pt < &proc_root_targets[nproc_root_targets];
                    pt++, i++) {
                        if (pt->pt_valid &&
                            (*pt->pt_valid)(NULL, vp->v_mount) == 0)
                                continue;
                        if (kauth_authorize_process(kauth_cred_get(),
                            KAUTH_PROCESS_CANSEE, p,
                            KAUTH_ARG(KAUTH_REQ_PROCESS_CANSEE_ENTRY),
                            NULL, NULL) != 0)
                                continue;
                        d.d_fileno = PROCFS_FILENO(0, pt->pt_pfstype, -1);
                        d.d_namlen = pt->pt_namlen;
                        memcpy(d.d_name, pt->pt_name, pt->pt_namlen + 1);
                        d.d_type = pt->pt_type;

                        if ((error = uiomove(&d, UIO_MX, uio)) != 0)
                                break;
                        nc++;
                        if (cookies)
                                *cookies++ = i + 1;
                }
out:
                KASSERT(p != NULL);
                ncookies = nc;
                procfs_proc_unlock(p);
                break;
        }

        default:
                error = ENOTDIR;
                break;
        }

        if (ap->a_ncookies) {
                if (error) {
                        if (cookies)
                                free(*ap->a_cookies, M_TEMP);
                        *ap->a_ncookies = 0;
                        *ap->a_cookies = NULL;
                } else
                        *ap->a_ncookies = ncookies;
        }
        uio->uio_offset = i;
        return (error);
}

/*
 * readlink reads the link of `curproc' and others
 */
int
procfs_readlink(void *v)
{
        struct vop_readlink_args *ap = v;
        char bf[16];            /* should be enough */
        char *bp = bf;
        char *path = NULL;
        int len = 0;
        int error = 0;
        struct vnode *vp = ap->a_vp;
        struct pfsnode *pfs = VTOPFS(vp);
        struct proc *pown = NULL;

        if (pfs->pfs_fileno == PROCFS_FILENO(0, PFScurproc, -1))
                len = snprintf(bf, sizeof(bf), "%ld", (long)curproc->p_pid);
        else if (pfs->pfs_fileno == PROCFS_FILENO(0, PFSself, -1))
                len = snprintf(bf, sizeof(bf), "%s", "curproc");
        else if (pfs->pfs_fileno == PROCFS_FILENO(pfs->pfs_pid, PFStask, 0))
                len = snprintf(bf, sizeof(bf), "..");
        else if (pfs->pfs_fileno == PROCFS_FILENO(pfs->pfs_pid, PFSexe, -1)) {
                if ((error = procfs_proc_lock(vp->v_mount, pfs->pfs_pid, &pown,
                                              ESRCH)) != 0)
                        return error;
                bp = pown->p_path;
                len = strlen(bp);
        } else if (pfs->pfs_fileno == PROCFS_FILENO(pfs->pfs_pid, PFScwd, -1) ||
            pfs->pfs_fileno == PROCFS_FILENO(pfs->pfs_pid, PFSchroot, -1)) {
                if ((error = procfs_proc_lock(vp->v_mount, pfs->pfs_pid, &pown,
                                              ESRCH)) != 0)
                        return error;
                path = malloc(MAXPATHLEN + 4, M_TEMP, M_WAITOK);
                if (path == NULL) {
                        procfs_proc_unlock(pown);
                        return (ENOMEM);
                }
                bp = path + MAXPATHLEN;
                *--bp = '\0';
                procfs_dir(PROCFS_TYPE(pfs->pfs_fileno), curlwp, pown,
                    &bp, path, MAXPATHLEN);
                len = strlen(bp);
        } else {
                file_t *fp;
                struct vnode *vxp;

                if ((error = procfs_proc_lock(vp->v_mount, pfs->pfs_pid, &pown,
                                              ESRCH)) != 0)
                        return error;

                fp = fd_getfile2(pown, pfs->pfs_fd);
                if (fp == NULL) {
                        procfs_proc_unlock(pown);
                        return EBADF;
                }

                switch (fp->f_type) {
                case DTYPE_VNODE:
                        vxp = fp->f_vnode;
                        if (vxp->v_type != VDIR &&
                            !procfs_proc_is_linux_compat()) {
                                error = EINVAL;
                                break;
                        }
                        if ((path = malloc(MAXPATHLEN, M_TEMP, M_WAITOK))
                            == NULL) {
                                error = ENOMEM;
                                break;
                        }
                        bp = path + MAXPATHLEN;
                        *--bp = '\0';

                        /*
                         * XXX: kludge to avoid locking against ourselves
                         * in getcwd()
                         */
                        if (vxp->v_tag == VT_PROCFS) {
                                *--bp = '/';
                        } else {
                                rw_enter(&curproc->p_cwdi->cwdi_lock,
                                    RW_READER);
                                vp = curproc->p_cwdi->cwdi_rdir;
                                if (vp == NULL)
                                        vp = rootvnode;
                                error = getcwd_common(vxp, vp, &bp, path,
                                    MAXPATHLEN / 2, 0, curlwp);
                                rw_exit(&curproc->p_cwdi->cwdi_lock);
                        }
                        if (error)
                                break;
                        len = strlen(bp);
                        break;

                case DTYPE_MISC:
                        len = snprintf(bf, sizeof(bf), "%s", "[misc]");
                        break;

                case DTYPE_KQUEUE:
                        len = snprintf(bf, sizeof(bf), "%s", "[kqueue]");
                        break;

                case DTYPE_SEM:
                        len = snprintf(bf, sizeof(bf), "%s", "[ksem]");
                        break;

                default:
                        error = EINVAL;
                        break;
                }       
                closef(fp);
        }

        if (error == 0)
                error = uiomove(bp, len, ap->a_uio);
        if (pown)
                procfs_proc_unlock(pown);
        if (path)
                free(path, M_TEMP);
        return error;
}

int
procfs_getpages(void *v)
{
        struct vop_getpages_args /* {
                struct vnode *a_vp;
                voff_t a_offset;
                struct vm_page **a_m;
                int *a_count;
                int a_centeridx;
                vm_prot_t a_access_type;
                int a_advice;
                int a_flags;
        } */ *ap = v;

        if ((ap->a_flags & PGO_LOCKED) == 0)
                rw_exit(ap->a_vp->v_uobj.vmobjlock);

        return (EFAULT);
}

/*
 * convert decimal ascii to int
 */
static int
atoi(const char *b, size_t len)
{
        int p = 0;

        while (len--) {
                char c = *b++;
                if (c < '0' || c > '9')
                        return -1;
                p = 10 * p + (c - '0');
        }

        return p;
}

/**
 * convert DTYPE_XXX to corresponding DT_XXX
 * matching what procfs_loadvnode() does.
 */
static uint8_t
fttodt(file_t *fp)
{
        switch (fp->f_type) {
        case DTYPE_VNODE:
                switch (fp->f_vnode->v_type) {
                case VREG:      return DT_REG;
                case VDIR:      return DT_LNK;  /* symlink */
                case VBLK:      return DT_BLK;
                case VCHR:      return DT_CHR;
                case VLNK:      return DT_LNK;
                case VSOCK:     return DT_SOCK;
                case VFIFO:     return DT_FIFO;
                default:        return DT_UNKNOWN;
                }
        case DTYPE_PIPE:        return DT_FIFO;
        case DTYPE_SOCKET:      return DT_SOCK;
        case DTYPE_KQUEUE:      /*FALLTHROUGH*/
        case DTYPE_MISC:        /*FALLTHROUGH*/
        case DTYPE_SEM:         return DT_LNK;  /* symlinks */
        default:                return DT_UNKNOWN;
        }
}