FreeBSD/Linux Kernel Cross Reference
sys/net/vnet.c

     /*-
      * 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>
    __FBSDID("$FreeBSD: releng/11.0/sys/net/vnet.c 302054 2016-06-21 13:48:49Z bz $");
    
    #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/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>
    
    #include <machine/stdarg.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;
   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     8192
   #define VNET_SIZE       roundup2(VNET_BYTES, PAGE_SIZE)
   
   /*
    * Space to store virtualized global variables from loadable kernel modules,
    * and the free list to manage it.
    */
   static VNET_DEFINE(char, modspace[VNET_MODMIN]);
   
   /*
    * 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");
   
   #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;
           vnet->vnet_state = 0;
           SDT_PROBE2(vnet, functions, vnet_alloc, alloc, __LINE__, vnet);
   
           /*
            * Allocate storage for virtualized global variables and copy in
            * initial values form 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();
   
           CURVNET_SET_QUIET(vnet);
           vnet_sysuninit();
           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");
           LIST_INIT(&vnet_head);
   }
   SYSINIT(vnet_init_prelink, SI_SUB_VNET_PRELINK, SI_ORDER_FIRST,
       vnet_init_prelink, NULL);
   
   static void
   vnet0_init(void *arg __unused)
   {
   
           /* Warn people before take off - in case we crash early. */
           printf("WARNING: VIMAGE (virtualized network stack) is a highly "
               "experimental feature.\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");
   }
   SYSINIT(vnet_data, SI_SUB_KLD, SI_ORDER_FIRST, vnet_data_startup, 0);
   
   /* 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, sizeof(void *));
           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);
   
           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, sizeof(void *));
           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();
   }
   
   /*
    * 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_FOREACH(vnet) {
                   CURVNET_SET_QUIET(vnet);
                   vs->func(vs->arg);
                   CURVNET_RESTORE();
           }
           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_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();
   }
   
   /*
    * 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.
    */
   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.
    */
   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("\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(...)                                                     \
           if (ddb)                                                        \
                   db_printf(__VA_ARGS__);                                 \
           else                                                            \
                   printf(__VA_ARGS__)
   
           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(vnet_sysinit, db_show_vnet_sysinit)
   {
           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(vnet_sysuninit, db_show_vnet_sysuninit)
   {
           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(vnetrcrs, db_show_vnetrcrs)
   {
           struct vnet_recursion *vnr;
   
           SLIST_FOREACH(vnr, &vnet_recursions, vnr_le)
                   vnet_print_recursion(vnr, 1);
   }
   #endif
   #endif /* DDB */

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