/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2004-2009 University of Zagreb
 * Copyright (c) 2006-2009 FreeBSD Foundation
 * All rights reserved.
 *
 * This software was developed by the University of Zagreb and the
 * FreeBSD Foundation under sponsorship by the Stichting NLnet and the
 * FreeBSD Foundation.
 *
 * Copyright (c) 2009 Jeffrey Roberson <jeff@freebsd.org>
 * Copyright (c) 2009 Robert N. M. Watson
 * All rights reserved.
 *
 * 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 AUTHOR 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 AUTHOR 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.
 */

#include <sys/cdefs.h>
#include "opt_ddb.h"
#include "opt_kdb.h"

#include <sys/param.h>
#include <sys/kdb.h>
#include <sys/kernel.h>
#include <sys/jail.h>
#include <sys/sdt.h>
#include <sys/stdarg.h>
#include <sys/systm.h>
#include <sys/sysctl.h>
#include <sys/eventhandler.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/proc.h>
#include <sys/socket.h>
#include <sys/sx.h>
#include <sys/sysctl.h>

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

#include <net/if.h>
#include <net/if_var.h>
#include <net/vnet.h>

/*-
 * This file implements core functions for virtual network stacks:
 *
 * - Virtual network stack management functions.
 *
 * - Virtual network stack memory allocator, which virtualizes global
 *   variables in the network stack
 *
 * - Virtualized SYSINIT's/SYSUNINIT's, which allow network stack subsystems
 *   to register startup/shutdown events to be run for each virtual network
 *   stack instance.
 */

FEATURE(vimage, "VIMAGE kernel virtualization");

static MALLOC_DEFINE(M_VNET, "vnet", "network stack control block");

/*
 * The virtual network stack list has two read-write locks, one sleepable and
 * the other not, so that the list can be stablized and walked in a variety
 * of network stack contexts.  Both must be acquired exclusively to modify
 * the list, but a read lock of either lock is sufficient to walk the list.
 */
struct rwlock           vnet_rwlock;
struct sx               vnet_sxlock;

#define VNET_LIST_WLOCK() do {                                          \
        sx_xlock(&vnet_sxlock);                                         \
        rw_wlock(&vnet_rwlock);                                         \
} while (0)

#define VNET_LIST_WUNLOCK() do {                                        \
        rw_wunlock(&vnet_rwlock);                                       \
        sx_xunlock(&vnet_sxlock);                                       \
} while (0)

struct vnet_list_head vnet_head = LIST_HEAD_INITIALIZER(vnet_head);
struct vnet *vnet0;

/*
 * The virtual network stack allocator provides storage for virtualized
 * global variables.  These variables are defined/declared using the
 * VNET_DEFINE()/VNET_DECLARE() macros, which place them in the 'set_vnet'
 * linker set.  The details of the implementation are somewhat subtle, but
 * allow the majority of most network subsystems to maintain
 * virtualization-agnostic.
 *
 * The virtual network stack allocator handles variables in the base kernel
 * vs. modules in similar but different ways.  In both cases, virtualized
 * global variables are marked as such by being declared to be part of the
 * vnet linker set.  These "master" copies of global variables serve two
 * functions:
 *
 * (1) They contain static initialization or "default" values for global
 *     variables which will be propagated to each virtual network stack
 *     instance when created.  As with normal global variables, they default
 *     to zero-filled.
 *
 * (2) They act as unique global names by which the variable can be referred
 *     to, regardless of network stack instance.  The single global symbol
 *     will be used to calculate the location of a per-virtual instance
 *     variable at run-time.
 *
 * Each virtual network stack instance has a complete copy of each
 * virtualized global variable, stored in a malloc'd block of memory
 * referred to by vnet->vnet_data_mem.  Critical to the design is that each
 * per-instance memory block is laid out identically to the master block so
 * that the offset of each global variable is the same across all blocks.  To
 * optimize run-time access, a precalculated 'base' address,
 * vnet->vnet_data_base, is stored in each vnet, and is the amount that can
 * be added to the address of a 'master' instance of a variable to get to the
 * per-vnet instance.
 *
 * Virtualized global variables are handled in a similar manner, but as each
 * module has its own 'set_vnet' linker set, and we want to keep all
 * virtualized globals togther, we reserve space in the kernel's linker set
 * for potential module variables using a per-vnet character array,
 * 'modspace'.  The virtual network stack allocator maintains a free list to
 * track what space in the array is free (all, initially) and as modules are
 * linked, allocates portions of the space to specific globals.  The kernel
 * module linker queries the virtual network stack allocator and will
 * bind references of the global to the location during linking.  It also
 * calls into the virtual network stack allocator, once the memory is
 * initialized, in order to propagate the new static initializations to all
 * existing virtual network stack instances so that the soon-to-be executing
 * module will find every network stack instance with proper default values.
 */

/*
 * Number of bytes of data in the 'set_vnet' linker set, and hence the total
 * size of all kernel virtualized global variables, and the malloc(9) type
 * that will be used to allocate it.
 */
#define VNET_BYTES      (VNET_STOP - VNET_START)

static MALLOC_DEFINE(M_VNET_DATA, "vnet_data", "VNET data");

/*
 * VNET_MODMIN is the minimum number of bytes we will reserve for the sum of
 * global variables across all loaded modules.  As this actually sizes an
 * array declared as a virtualized global variable in the kernel itself, and
 * we want the virtualized global variable space to be page-sized, we may
 * have more space than that in practice.
 */
#define VNET_MODMIN     (8 * PAGE_SIZE)
#define VNET_SIZE       roundup2(VNET_BYTES, PAGE_SIZE)

/*
 * Ensure space allocated by vnet_data_alloc() is suitably aligned for any
 * object.
 */
#define VNET_DATAALIGN  _Alignof(__max_align_t)

/*
 * Space to store virtualized global variables from loadable kernel modules,
 * and the free list to manage it.
 */
VNET_DEFINE_STATIC(char, modspace[VNET_MODMIN] __aligned(VNET_DATAALIGN));

/*
 * A copy of the initial values of all virtualized global variables.
 */
static uintptr_t vnet_init_var;

/*
 * Global lists of subsystem constructor and destructors for vnets.  They are
 * registered via VNET_SYSINIT() and VNET_SYSUNINIT().  Both lists are
 * protected by the vnet_sysinit_sxlock global lock.
 */
static TAILQ_HEAD(vnet_sysinit_head, vnet_sysinit) vnet_constructors =
        TAILQ_HEAD_INITIALIZER(vnet_constructors);
static TAILQ_HEAD(vnet_sysuninit_head, vnet_sysinit) vnet_destructors =
        TAILQ_HEAD_INITIALIZER(vnet_destructors);

struct sx               vnet_sysinit_sxlock;

#define VNET_SYSINIT_WLOCK()    sx_xlock(&vnet_sysinit_sxlock);
#define VNET_SYSINIT_WUNLOCK()  sx_xunlock(&vnet_sysinit_sxlock);
#define VNET_SYSINIT_RLOCK()    sx_slock(&vnet_sysinit_sxlock);
#define VNET_SYSINIT_RUNLOCK()  sx_sunlock(&vnet_sysinit_sxlock);

struct vnet_data_free {
        uintptr_t       vnd_start;
        int             vnd_len;
        TAILQ_ENTRY(vnet_data_free) vnd_link;
};

static MALLOC_DEFINE(M_VNET_DATA_FREE, "vnet_data_free",
    "VNET resource accounting");
static TAILQ_HEAD(, vnet_data_free) vnet_data_free_head =
    TAILQ_HEAD_INITIALIZER(vnet_data_free_head);
static struct sx vnet_data_free_lock;

SDT_PROVIDER_DEFINE(vnet);
SDT_PROBE_DEFINE1(vnet, functions, vnet_alloc, entry, "int");
SDT_PROBE_DEFINE2(vnet, functions, vnet_alloc, alloc, "int",
    "struct vnet *");
SDT_PROBE_DEFINE2(vnet, functions, vnet_alloc, return,
    "int", "struct vnet *");
SDT_PROBE_DEFINE2(vnet, functions, vnet_destroy, entry,
    "int", "struct vnet *");
SDT_PROBE_DEFINE1(vnet, functions, vnet_destroy, return,
    "int");

/*
 * Run per-vnet sysinits or sysuninits during vnet creation/destruction.
 */
static void vnet_sysinit(void);
static void vnet_sysuninit(void);

#ifdef DDB
static void db_show_vnet_print_vs(struct vnet_sysinit *, int);
#endif

/*
 * Allocate a virtual network stack.
 */
struct vnet *
vnet_alloc(void)
{
        struct vnet *vnet;

        SDT_PROBE1(vnet, functions, vnet_alloc, entry, __LINE__);
        vnet = malloc(sizeof(struct vnet), M_VNET, M_WAITOK | M_ZERO);
        vnet->vnet_magic_n = VNET_MAGIC_N;
        SDT_PROBE2(vnet, functions, vnet_alloc, alloc, __LINE__, vnet);

        /*
         * Allocate storage for virtualized global variables and copy in
         * initial values from our 'master' copy.
         */
        vnet->vnet_data_mem = malloc(VNET_SIZE, M_VNET_DATA, M_WAITOK);
        memcpy(vnet->vnet_data_mem, (void *)VNET_START, VNET_BYTES);

        /*
         * All use of vnet-specific data will immediately subtract VNET_START
         * from the base memory pointer, so pre-calculate that now to avoid
         * it on each use.
         */
        vnet->vnet_data_base = (uintptr_t)vnet->vnet_data_mem - VNET_START;

        /* Initialize / attach vnet module instances. */
        CURVNET_SET_QUIET(vnet);
        vnet_sysinit();
        CURVNET_RESTORE();

        VNET_LIST_WLOCK();
        LIST_INSERT_HEAD(&vnet_head, vnet, vnet_le);
        VNET_LIST_WUNLOCK();

        SDT_PROBE2(vnet, functions, vnet_alloc, return, __LINE__, vnet);
        return (vnet);
}

/*
 * Destroy a virtual network stack.
 */
void
vnet_destroy(struct vnet *vnet)
{

        SDT_PROBE2(vnet, functions, vnet_destroy, entry, __LINE__, vnet);
        KASSERT(vnet->vnet_sockcnt == 0,
            ("%s: vnet still has sockets", __func__));

        VNET_LIST_WLOCK();
        LIST_REMOVE(vnet, vnet_le);
        VNET_LIST_WUNLOCK();

        /* Signal that VNET is being shutdown. */
        vnet->vnet_shutdown = true;

        CURVNET_SET_QUIET(vnet);
        sx_xlock(&ifnet_detach_sxlock);
        vnet_sysuninit();
        sx_xunlock(&ifnet_detach_sxlock);
        CURVNET_RESTORE();

        /*
         * Release storage for the virtual network stack instance.
         */
        free(vnet->vnet_data_mem, M_VNET_DATA);
        vnet->vnet_data_mem = NULL;
        vnet->vnet_data_base = 0;
        vnet->vnet_magic_n = 0xdeadbeef;
        free(vnet, M_VNET);
        SDT_PROBE1(vnet, functions, vnet_destroy, return, __LINE__);
}

/*
 * Boot time initialization and allocation of virtual network stacks.
 */
static void
vnet_init_prelink(void *arg __unused)
{

        rw_init(&vnet_rwlock, "vnet_rwlock");
        sx_init(&vnet_sxlock, "vnet_sxlock");
        sx_init(&vnet_sysinit_sxlock, "vnet_sysinit_sxlock");
}
SYSINIT(vnet_init_prelink, SI_SUB_VNET_PRELINK, SI_ORDER_FIRST,
    vnet_init_prelink, NULL);

static void
vnet0_init(void *arg __unused)
{

        if (bootverbose)
                printf("VIMAGE (virtualized network stack) enabled\n");

        /*
         * We MUST clear curvnet in vi_init_done() before going SMP,
         * otherwise CURVNET_SET() macros would scream about unnecessary
         * curvnet recursions.
         */
        curvnet = prison0.pr_vnet = vnet0 = vnet_alloc();
}
SYSINIT(vnet0_init, SI_SUB_VNET, SI_ORDER_FIRST, vnet0_init, NULL);

static void
vnet_init_done(void *unused __unused)
{

        curvnet = NULL;
}
SYSINIT(vnet_init_done, SI_SUB_VNET_DONE, SI_ORDER_ANY, vnet_init_done,
    NULL);

/*
 * Once on boot, initialize the modspace freelist to entirely cover modspace.
 */
static void
vnet_data_startup(void *dummy __unused)
{
        struct vnet_data_free *df;

        df = malloc(sizeof(*df), M_VNET_DATA_FREE, M_WAITOK | M_ZERO);
        df->vnd_start = (uintptr_t)&VNET_NAME(modspace);
        df->vnd_len = VNET_MODMIN;
        TAILQ_INSERT_HEAD(&vnet_data_free_head, df, vnd_link);
        sx_init(&vnet_data_free_lock, "vnet_data alloc lock");
        vnet_init_var = (uintptr_t)malloc(VNET_BYTES, M_VNET_DATA, M_WAITOK);
}
SYSINIT(vnet_data, SI_SUB_KLD, SI_ORDER_FIRST, vnet_data_startup, NULL);

/* Dummy VNET_SYSINIT to make sure we always reach the final end state. */
static void
vnet_sysinit_done(void *unused __unused)
{

        return;
}
VNET_SYSINIT(vnet_sysinit_done, SI_SUB_VNET_DONE, SI_ORDER_ANY,
    vnet_sysinit_done, NULL);

/*
 * When a module is loaded and requires storage for a virtualized global
 * variable, allocate space from the modspace free list.  This interface
 * should be used only by the kernel linker.
 */
void *
vnet_data_alloc(int size)
{
        struct vnet_data_free *df;
        void *s;

        s = NULL;
        size = roundup2(size, VNET_DATAALIGN);
        sx_xlock(&vnet_data_free_lock);
        TAILQ_FOREACH(df, &vnet_data_free_head, vnd_link) {
                if (df->vnd_len < size)
                        continue;
                if (df->vnd_len == size) {
                        s = (void *)df->vnd_start;
                        TAILQ_REMOVE(&vnet_data_free_head, df, vnd_link);
                        free(df, M_VNET_DATA_FREE);
                        break;
                }
                s = (void *)df->vnd_start;
                df->vnd_len -= size;
                df->vnd_start = df->vnd_start + size;
                break;
        }
        sx_xunlock(&vnet_data_free_lock);

        KASSERT(((uintptr_t)s & (VNET_DATAALIGN - 1)) == 0,
            ("unaligned vnet alloc %p", s));
        return (s);
}

/*
 * Free space for a virtualized global variable on module unload.
 */
void
vnet_data_free(void *start_arg, int size)
{
        struct vnet_data_free *df;
        struct vnet_data_free *dn;
        uintptr_t start;
        uintptr_t end;

        size = roundup2(size, VNET_DATAALIGN);
        start = (uintptr_t)start_arg;
        end = start + size;
        /*
         * Free a region of space and merge it with as many neighbors as
         * possible.  Keeping the list sorted simplifies this operation.
         */
        sx_xlock(&vnet_data_free_lock);
        TAILQ_FOREACH(df, &vnet_data_free_head, vnd_link) {
                if (df->vnd_start > end)
                        break;
                /*
                 * If we expand at the end of an entry we may have to merge
                 * it with the one following it as well.
                 */
                if (df->vnd_start + df->vnd_len == start) {
                        df->vnd_len += size;
                        dn = TAILQ_NEXT(df, vnd_link);
                        if (df->vnd_start + df->vnd_len == dn->vnd_start) {
                                df->vnd_len += dn->vnd_len;
                                TAILQ_REMOVE(&vnet_data_free_head, dn,
                                    vnd_link);
                                free(dn, M_VNET_DATA_FREE);
                        }
                        sx_xunlock(&vnet_data_free_lock);
                        return;
                }
                if (df->vnd_start == end) {
                        df->vnd_start = start;
                        df->vnd_len += size;
                        sx_xunlock(&vnet_data_free_lock);
                        return;
                }
        }
        dn = malloc(sizeof(*df), M_VNET_DATA_FREE, M_WAITOK | M_ZERO);
        dn->vnd_start = start;
        dn->vnd_len = size;
        if (df)
                TAILQ_INSERT_BEFORE(df, dn, vnd_link);
        else
                TAILQ_INSERT_TAIL(&vnet_data_free_head, dn, vnd_link);
        sx_xunlock(&vnet_data_free_lock);
}

/*
 * When a new virtualized global variable has been allocated, propagate its
 * initial value to each already-allocated virtual network stack instance.
 */
void
vnet_data_copy(void *start, int size)
{
        struct vnet *vnet;

        VNET_LIST_RLOCK();
        LIST_FOREACH(vnet, &vnet_head, vnet_le)
                memcpy((void *)((uintptr_t)vnet->vnet_data_base +
                    (uintptr_t)start), start, size);
        VNET_LIST_RUNLOCK();
}

/*
 * Save a copy of the initial values of virtualized global variables.
 */
void
vnet_save_init(void *start, size_t size)
{
        MPASS(vnet_init_var != 0);
        MPASS(VNET_START <= (uintptr_t)start &&
            (uintptr_t)start + size <= VNET_STOP);
        memcpy((void *)(vnet_init_var + ((uintptr_t)start - VNET_START)),
            start, size);
}

/*
 * Restore the 'master' copies of virtualized global variables to theirs
 * initial values.
 */
void
vnet_restore_init(void *start, size_t size)
{
        MPASS(vnet_init_var != 0);
        MPASS(VNET_START <= (uintptr_t)start &&
            (uintptr_t)start + size <= VNET_STOP);
        memcpy(start,
            (void *)(vnet_init_var + ((uintptr_t)start - VNET_START)), size);
}

/*
 * Support for special SYSINIT handlers registered via VNET_SYSINIT()
 * and VNET_SYSUNINIT().
 */
void
vnet_register_sysinit(void *arg)
{
        struct vnet_sysinit *vs, *vs2;
        struct vnet *vnet;

        vs = arg;
        KASSERT(vs->subsystem > SI_SUB_VNET, ("vnet sysinit too early"));

        /* Add the constructor to the global list of vnet constructors. */
        VNET_SYSINIT_WLOCK();
        TAILQ_FOREACH(vs2, &vnet_constructors, link) {
                if (vs2->subsystem > vs->subsystem)
                        break;
                if (vs2->subsystem == vs->subsystem && vs2->order > vs->order)
                        break;
        }
        if (vs2 != NULL)
                TAILQ_INSERT_BEFORE(vs2, vs, link);
        else
                TAILQ_INSERT_TAIL(&vnet_constructors, vs, link);

        /*
         * Invoke the constructor on all the existing vnets when it is
         * registered.
         */
        VNET_LIST_RLOCK();
        VNET_FOREACH(vnet) {
                CURVNET_SET_QUIET(vnet);
                vs->func(vs->arg);
                CURVNET_RESTORE();
        }
        VNET_LIST_RUNLOCK();
        VNET_SYSINIT_WUNLOCK();
}

void
vnet_deregister_sysinit(void *arg)
{
        struct vnet_sysinit *vs;

        vs = arg;

        /* Remove the constructor from the global list of vnet constructors. */
        VNET_SYSINIT_WLOCK();
        TAILQ_REMOVE(&vnet_constructors, vs, link);
        VNET_SYSINIT_WUNLOCK();
}

void
vnet_register_sysuninit(void *arg)
{
        struct vnet_sysinit *vs, *vs2;

        vs = arg;

        /* Add the destructor to the global list of vnet destructors. */
        VNET_SYSINIT_WLOCK();
        TAILQ_FOREACH(vs2, &vnet_destructors, link) {
                if (vs2->subsystem > vs->subsystem)
                        break;
                if (vs2->subsystem == vs->subsystem && vs2->order > vs->order)
                        break;
        }
        if (vs2 != NULL)
                TAILQ_INSERT_BEFORE(vs2, vs, link);
        else
                TAILQ_INSERT_TAIL(&vnet_destructors, vs, link);
        VNET_SYSINIT_WUNLOCK();
}

void
vnet_deregister_sysuninit(void *arg)
{
        struct vnet_sysinit *vs;
        struct vnet *vnet;

        vs = arg;

        /*
         * Invoke the destructor on all the existing vnets when it is
         * deregistered.
         */
        VNET_SYSINIT_WLOCK();
        VNET_LIST_RLOCK();
        VNET_FOREACH(vnet) {
                CURVNET_SET_QUIET(vnet);
                vs->func(vs->arg);
                CURVNET_RESTORE();
        }

        /* Remove the destructor from the global list of vnet destructors. */
        TAILQ_REMOVE(&vnet_destructors, vs, link);
        VNET_SYSINIT_WUNLOCK();
        VNET_LIST_RUNLOCK();
}

/*
 * Invoke all registered vnet constructors on the current vnet.  Used during
 * vnet construction.  The caller is responsible for ensuring the new vnet is
 * the current vnet and that the vnet_sysinit_sxlock lock is locked.
 */
static void
vnet_sysinit(void)
{
        struct vnet_sysinit *vs;

        VNET_SYSINIT_RLOCK();
        TAILQ_FOREACH(vs, &vnet_constructors, link) {
                curvnet->vnet_state = vs->subsystem;
                vs->func(vs->arg);
        }
        VNET_SYSINIT_RUNLOCK();
}

/*
 * Invoke all registered vnet destructors on the current vnet.  Used during
 * vnet destruction.  The caller is responsible for ensuring the dying vnet
 * the current vnet and that the vnet_sysinit_sxlock lock is locked.
 */
static void
vnet_sysuninit(void)
{
        struct vnet_sysinit *vs;

        VNET_SYSINIT_RLOCK();
        TAILQ_FOREACH_REVERSE(vs, &vnet_destructors, vnet_sysuninit_head,
            link) {
                curvnet->vnet_state = vs->subsystem;
                vs->func(vs->arg);
        }
        VNET_SYSINIT_RUNLOCK();
}

/*
 * EVENTHANDLER(9) extensions.
 */
/*
 * Invoke the eventhandler function originally registered with the possibly
 * registered argument for all virtual network stack instances.
 *
 * This iterator can only be used for eventhandlers that do not take any
 * additional arguments, as we do ignore the variadic arguments from the
 * EVENTHANDLER_INVOKE() call.
 */
void
vnet_global_eventhandler_iterator_func(void *arg, ...)
{
        VNET_ITERATOR_DECL(vnet_iter);
        struct eventhandler_entry_vimage *v_ee;

        /*
         * There is a bug here in that we should actually cast things to
         * (struct eventhandler_entry_ ## name *)  but that's not easily
         * possible in here so just re-using the variadic version we
         * defined for the generic vimage case.
         */
        v_ee = arg;
        VNET_LIST_RLOCK();
        VNET_FOREACH(vnet_iter) {
                CURVNET_SET(vnet_iter);
                ((vimage_iterator_func_t)v_ee->func)(v_ee->ee_arg);
                CURVNET_RESTORE();
        }
        VNET_LIST_RUNLOCK();
}

#ifdef VNET_DEBUG
struct vnet_recursion {
        SLIST_ENTRY(vnet_recursion)      vnr_le;
        const char                      *prev_fn;
        const char                      *where_fn;
        int                              where_line;
        struct vnet                     *old_vnet;
        struct vnet                     *new_vnet;
};

static SLIST_HEAD(, vnet_recursion) vnet_recursions =
    SLIST_HEAD_INITIALIZER(vnet_recursions);

static void
vnet_print_recursion(struct vnet_recursion *vnr, int brief)
{

        if (!brief)
                printf("CURVNET_SET() recursion in ");
        printf("%s() line %d, prev in %s()", vnr->where_fn, vnr->where_line,
            vnr->prev_fn);
        if (brief)
                printf(", ");
        else
                printf("\n    ");
        printf("%p -> %p\n", vnr->old_vnet, vnr->new_vnet);
}

void
vnet_log_recursion(struct vnet *old_vnet, const char *old_fn, int line)
{
        struct vnet_recursion *vnr;

        /* Skip already logged recursion events. */
        SLIST_FOREACH(vnr, &vnet_recursions, vnr_le)
                if (vnr->prev_fn == old_fn &&
                    vnr->where_fn == curthread->td_vnet_lpush &&
                    vnr->where_line == line &&
                    (vnr->old_vnet == vnr->new_vnet) == (curvnet == old_vnet))
                        return;

        vnr = malloc(sizeof(*vnr), M_VNET, M_NOWAIT | M_ZERO);
        if (vnr == NULL)
                panic("%s: malloc failed", __func__);
        vnr->prev_fn = old_fn;
        vnr->where_fn = curthread->td_vnet_lpush;
        vnr->where_line = line;
        vnr->old_vnet = old_vnet;
        vnr->new_vnet = curvnet;

        SLIST_INSERT_HEAD(&vnet_recursions, vnr, vnr_le);

        vnet_print_recursion(vnr, 0);
#ifdef KDB
        kdb_backtrace();
#endif
}
#endif /* VNET_DEBUG */

/*
 * DDB(4).
 */
#ifdef DDB
static void
db_vnet_print(struct vnet *vnet)
{

        db_printf("vnet            = %p\n", vnet);
        db_printf(" vnet_magic_n   = %#08x (%s, orig %#08x)\n",
            vnet->vnet_magic_n,
            (vnet->vnet_magic_n == VNET_MAGIC_N) ?
                "ok" : "mismatch", VNET_MAGIC_N);
        db_printf(" vnet_ifcnt     = %u\n", vnet->vnet_ifcnt);
        db_printf(" vnet_sockcnt   = %u\n", vnet->vnet_sockcnt);
        db_printf(" vnet_data_mem  = %p\n", vnet->vnet_data_mem);
        db_printf(" vnet_data_base = %#jx\n",
            (uintmax_t)vnet->vnet_data_base);
        db_printf(" vnet_state     = %#08x\n", vnet->vnet_state);
        db_printf(" vnet_shutdown  = %#03x\n", vnet->vnet_shutdown);
        db_printf("\n");
}

DB_SHOW_ALL_COMMAND(vnets, db_show_all_vnets)
{
        VNET_ITERATOR_DECL(vnet_iter);

        VNET_FOREACH(vnet_iter) {
                db_vnet_print(vnet_iter);
                if (db_pager_quit)
                        break;
        }
}

DB_SHOW_COMMAND(vnet, db_show_vnet)
{

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

        db_vnet_print((struct vnet *)addr);
}

static void
db_show_vnet_print_vs(struct vnet_sysinit *vs, int ddb)
{
        const char *vsname, *funcname;
        c_db_sym_t sym;
        db_expr_t  offset;

#define xprint(...) do {                                                \
        if (ddb)                                                        \
                db_printf(__VA_ARGS__);                                 \
        else                                                            \
                printf(__VA_ARGS__);                                    \
} while (0)

        if (vs == NULL) {
                xprint("%s: no vnet_sysinit * given\n", __func__);
                return;
        }

        sym = db_search_symbol((vm_offset_t)vs, DB_STGY_ANY, &offset);
        db_symbol_values(sym, &vsname, NULL);
        sym = db_search_symbol((vm_offset_t)vs->func, DB_STGY_PROC, &offset);
        db_symbol_values(sym, &funcname, NULL);
        xprint("%s(%p)\n", (vsname != NULL) ? vsname : "", vs);
        xprint("  %#08x %#08x\n", vs->subsystem, vs->order);
        xprint("  %p(%s)(%p)\n",
            vs->func, (funcname != NULL) ? funcname : "", vs->arg);
#undef xprint
}

DB_SHOW_COMMAND_FLAGS(vnet_sysinit, db_show_vnet_sysinit, DB_CMD_MEMSAFE)
{
        struct vnet_sysinit *vs;

        db_printf("VNET_SYSINIT vs Name(Ptr)\n");
        db_printf("  Subsystem  Order\n");
        db_printf("  Function(Name)(Arg)\n");
        TAILQ_FOREACH(vs, &vnet_constructors, link) {
                db_show_vnet_print_vs(vs, 1);
                if (db_pager_quit)
                        break;
        }
}

DB_SHOW_COMMAND_FLAGS(vnet_sysuninit, db_show_vnet_sysuninit, DB_CMD_MEMSAFE)
{
        struct vnet_sysinit *vs;

        db_printf("VNET_SYSUNINIT vs Name(Ptr)\n");
        db_printf("  Subsystem  Order\n");
        db_printf("  Function(Name)(Arg)\n");
        TAILQ_FOREACH_REVERSE(vs, &vnet_destructors, vnet_sysuninit_head,
            link) {
                db_show_vnet_print_vs(vs, 1);
                if (db_pager_quit)
                        break;
        }
}

#ifdef VNET_DEBUG
DB_SHOW_COMMAND_FLAGS(vnetrcrs, db_show_vnetrcrs, DB_CMD_MEMSAFE)
{
        struct vnet_recursion *vnr;

        SLIST_FOREACH(vnr, &vnet_recursions, vnr_le)
                vnet_print_recursion(vnr, 1);
}
#endif
#endif /* DDB */