FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_mbuf.c

     /*-
      * Copyright (c) 2004, 2005,
      *      Bosko Milekic <bmilekic@FreeBSD.org>.  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 unmodified, 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("$FreeBSD$");
    
    #include "opt_param.h"
    
    #include <sys/param.h>
    #include <sys/malloc.h>
    #include <sys/systm.h>
    #include <sys/mbuf.h>
    #include <sys/domain.h>
    #include <sys/eventhandler.h>
    #include <sys/kernel.h>
    #include <sys/protosw.h>
    #include <sys/smp.h>
    #include <sys/sysctl.h>
    
    #include <security/mac/mac_framework.h>
    
    #include <vm/vm.h>
    #include <vm/vm_extern.h>
    #include <vm/vm_kern.h>
    #include <vm/vm_page.h>
    #include <vm/vm_map.h>
    #include <vm/uma.h>
    #include <vm/uma_int.h>
    #include <vm/uma_dbg.h>
    
    /*
     * In FreeBSD, Mbufs and Mbuf Clusters are allocated from UMA
     * Zones.
     *
     * Mbuf Clusters (2K, contiguous) are allocated from the Cluster
     * Zone.  The Zone can be capped at kern.ipc.nmbclusters, if the
     * administrator so desires.
     *
     * Mbufs are allocated from a UMA Master Zone called the Mbuf
     * Zone.
     *
     * Additionally, FreeBSD provides a Packet Zone, which it
     * configures as a Secondary Zone to the Mbuf Master Zone,
     * thus sharing backend Slab kegs with the Mbuf Master Zone.
     *
     * Thus common-case allocations and locking are simplified:
     *
     *  m_clget()                m_getcl()
     *    |                         |
     *    |   .------------>[(Packet Cache)]    m_get(), m_gethdr()
     *    |   |             [     Packet   ]            |
     *  [(Cluster Cache)]   [    Secondary ]   [ (Mbuf Cache)     ]
     *  [ Cluster Zone  ]   [     Zone     ]   [ Mbuf Master Zone ]
     *        |                       \________         |
     *  [ Cluster Keg   ]                      \       /
     *        |                              [ Mbuf Keg   ]
     *  [ Cluster Slabs ]                         |
     *        |                              [ Mbuf Slabs ]
     *         \____________(VM)_________________/
     *
     *
     * Whenever an object is allocated with uma_zalloc() out of
     * one of the Zones its _ctor_ function is executed.  The same
     * for any deallocation through uma_zfree() the _dtor_ function
     * is executed.
     *
     * Caches are per-CPU and are filled from the Master Zone.
     *
     * Whenever an object is allocated from the underlying global
     * memory pool it gets pre-initialized with the _zinit_ functions.
     * When the Keg's are overfull objects get decommissioned with
     * _zfini_ functions and free'd back to the global memory pool.
     *
     */
    
   int nmbufs;                     /* limits number of mbufs */
   int nmbclusters;                /* limits number of mbuf clusters */
   int nmbjumbop;                  /* limits number of page size jumbo clusters */
   int nmbjumbo9;                  /* limits number of 9k jumbo clusters */
   int nmbjumbo16;                 /* limits number of 16k jumbo clusters */
   
   static quad_t maxmbufmem;       /* overall real memory limit for all mbufs */
   
   SYSCTL_QUAD(_kern_ipc, OID_AUTO, maxmbufmem, CTLFLAG_RDTUN, &maxmbufmem, 0,
       "Maximum real memory allocatable to various mbuf types");
   
   /*
    * tunable_mbinit() has to be run before any mbuf allocations are done.
    */
   static void
   tunable_mbinit(void *dummy)
   {
           quad_t realmem;
   
           /*
            * The default limit for all mbuf related memory is 1/2 of all
            * available kernel memory (physical or kmem).
            * At most it can be 3/4 of available kernel memory.
            */
           realmem = qmin((quad_t)physmem * PAGE_SIZE, vm_kmem_size);
           maxmbufmem = realmem / 2;
           TUNABLE_QUAD_FETCH("kern.ipc.maxmbufmem", &maxmbufmem);
           if (maxmbufmem > realmem / 4 * 3)
                   maxmbufmem = realmem / 4 * 3;
   
           TUNABLE_INT_FETCH("kern.ipc.nmbclusters", &nmbclusters);
           if (nmbclusters == 0)
                   nmbclusters = maxmbufmem / MCLBYTES / 4;
   
           TUNABLE_INT_FETCH("kern.ipc.nmbjumbop", &nmbjumbop);
           if (nmbjumbop == 0)
                   nmbjumbop = maxmbufmem / MJUMPAGESIZE / 4;
   
           TUNABLE_INT_FETCH("kern.ipc.nmbjumbo9", &nmbjumbo9);
           if (nmbjumbo9 == 0)
                   nmbjumbo9 = maxmbufmem / MJUM9BYTES / 6;
   
           TUNABLE_INT_FETCH("kern.ipc.nmbjumbo16", &nmbjumbo16);
           if (nmbjumbo16 == 0)
                   nmbjumbo16 = maxmbufmem / MJUM16BYTES / 6;
   
           /*
            * We need at least as many mbufs as we have clusters of
            * the various types added together.
            */
           TUNABLE_INT_FETCH("kern.ipc.nmbufs", &nmbufs);
           if (nmbufs < nmbclusters + nmbjumbop + nmbjumbo9 + nmbjumbo16)
                   nmbufs = lmax(maxmbufmem / MSIZE / 5,
                       nmbclusters + nmbjumbop + nmbjumbo9 + nmbjumbo16);
   }
   SYSINIT(tunable_mbinit, SI_SUB_KMEM, SI_ORDER_MIDDLE, tunable_mbinit, NULL);
   
   static int
   sysctl_nmbclusters(SYSCTL_HANDLER_ARGS)
   {
           int error, newnmbclusters;
   
           newnmbclusters = nmbclusters;
           error = sysctl_handle_int(oidp, &newnmbclusters, 0, req);
           if (error == 0 && req->newptr && newnmbclusters != nmbclusters) {
                   if (newnmbclusters > nmbclusters &&
                       nmbufs >= nmbclusters + nmbjumbop + nmbjumbo9 + nmbjumbo16) {
                           nmbclusters = newnmbclusters;
                           nmbclusters = uma_zone_set_max(zone_clust, nmbclusters);
                           EVENTHANDLER_INVOKE(nmbclusters_change);
                   } else
                           error = EINVAL;
           }
           return (error);
   }
   SYSCTL_PROC(_kern_ipc, OID_AUTO, nmbclusters, CTLTYPE_INT|CTLFLAG_RW,
   &nmbclusters, 0, sysctl_nmbclusters, "IU",
       "Maximum number of mbuf clusters allowed");
   
   static int
   sysctl_nmbjumbop(SYSCTL_HANDLER_ARGS)
   {
           int error, newnmbjumbop;
   
           newnmbjumbop = nmbjumbop;
           error = sysctl_handle_int(oidp, &newnmbjumbop, 0, req);
           if (error == 0 && req->newptr && newnmbjumbop != nmbjumbop) {
                   if (newnmbjumbop > nmbjumbop &&
                       nmbufs >= nmbclusters + nmbjumbop + nmbjumbo9 + nmbjumbo16) {
                           nmbjumbop = newnmbjumbop;
                           nmbjumbop = uma_zone_set_max(zone_jumbop, nmbjumbop);
                   } else
                           error = EINVAL;
           }
           return (error);
   }
   SYSCTL_PROC(_kern_ipc, OID_AUTO, nmbjumbop, CTLTYPE_INT|CTLFLAG_RW,
   &nmbjumbop, 0, sysctl_nmbjumbop, "IU",
       "Maximum number of mbuf page size jumbo clusters allowed");
   
   static int
   sysctl_nmbjumbo9(SYSCTL_HANDLER_ARGS)
   {
           int error, newnmbjumbo9;
   
           newnmbjumbo9 = nmbjumbo9;
           error = sysctl_handle_int(oidp, &newnmbjumbo9, 0, req);
           if (error == 0 && req->newptr && newnmbjumbo9 != nmbjumbo9) {
                   if (newnmbjumbo9 > nmbjumbo9 &&
                       nmbufs >= nmbclusters + nmbjumbop + nmbjumbo9 + nmbjumbo16) {
                           nmbjumbo9 = newnmbjumbo9;
                           nmbjumbo9 = uma_zone_set_max(zone_jumbo9, nmbjumbo9);
                   } else
                           error = EINVAL;
           }
           return (error);
   }
   SYSCTL_PROC(_kern_ipc, OID_AUTO, nmbjumbo9, CTLTYPE_INT|CTLFLAG_RW,
   &nmbjumbo9, 0, sysctl_nmbjumbo9, "IU",
       "Maximum number of mbuf 9k jumbo clusters allowed");
   
   static int
   sysctl_nmbjumbo16(SYSCTL_HANDLER_ARGS)
   {
           int error, newnmbjumbo16;
   
           newnmbjumbo16 = nmbjumbo16;
           error = sysctl_handle_int(oidp, &newnmbjumbo16, 0, req);
           if (error == 0 && req->newptr && newnmbjumbo16 != nmbjumbo16) {
                   if (newnmbjumbo16 > nmbjumbo16 &&
                       nmbufs >= nmbclusters + nmbjumbop + nmbjumbo9 + nmbjumbo16) {
                           nmbjumbo16 = newnmbjumbo16;
                           nmbjumbo16 = uma_zone_set_max(zone_jumbo16, nmbjumbo16);
                   } else
                           error = EINVAL;
           }
           return (error);
   }
   SYSCTL_PROC(_kern_ipc, OID_AUTO, nmbjumbo16, CTLTYPE_INT|CTLFLAG_RW,
   &nmbjumbo16, 0, sysctl_nmbjumbo16, "IU",
       "Maximum number of mbuf 16k jumbo clusters allowed");
   
   static int
   sysctl_nmbufs(SYSCTL_HANDLER_ARGS)
   {
           int error, newnmbufs;
   
           newnmbufs = nmbufs;
           error = sysctl_handle_int(oidp, &newnmbufs, 0, req);
           if (error == 0 && req->newptr && newnmbufs != nmbufs) {
                   if (newnmbufs > nmbufs) {
                           nmbufs = newnmbufs;
                           nmbufs = uma_zone_set_max(zone_mbuf, nmbufs);
                           EVENTHANDLER_INVOKE(nmbufs_change);
                   } else
                           error = EINVAL;
           }
           return (error);
   }
   SYSCTL_PROC(_kern_ipc, OID_AUTO, nmbufs, CTLTYPE_INT|CTLFLAG_RW,
   &nmbufs, 0, sysctl_nmbufs, "IU",
       "Maximum number of mbufs allowed");
   
   /*
    * Zones from which we allocate.
    */
   uma_zone_t      zone_mbuf;
   uma_zone_t      zone_clust;
   uma_zone_t      zone_pack;
   uma_zone_t      zone_jumbop;
   uma_zone_t      zone_jumbo9;
   uma_zone_t      zone_jumbo16;
   uma_zone_t      zone_ext_refcnt;
   
   /*
    * Local prototypes.
    */
   static int      mb_ctor_mbuf(void *, int, void *, int);
   static int      mb_ctor_clust(void *, int, void *, int);
   static int      mb_ctor_pack(void *, int, void *, int);
   static void     mb_dtor_mbuf(void *, int, void *);
   static void     mb_dtor_clust(void *, int, void *);
   static void     mb_dtor_pack(void *, int, void *);
   static int      mb_zinit_pack(void *, int, int);
   static void     mb_zfini_pack(void *, int);
   
   static void     mb_reclaim(void *);
   static void    *mbuf_jumbo_alloc(uma_zone_t, vm_size_t, uint8_t *, int);
   
   /* Ensure that MSIZE is a power of 2. */
   CTASSERT((((MSIZE - 1) ^ MSIZE) + 1) >> 1 == MSIZE);
   
   /*
    * Initialize FreeBSD Network buffer allocation.
    */
   static void
   mbuf_init(void *dummy)
   {
   
           /*
            * Configure UMA zones for Mbufs, Clusters, and Packets.
            */
           zone_mbuf = uma_zcreate(MBUF_MEM_NAME, MSIZE,
               mb_ctor_mbuf, mb_dtor_mbuf,
   #ifdef INVARIANTS
               trash_init, trash_fini,
   #else
               NULL, NULL,
   #endif
               MSIZE - 1, UMA_ZONE_MAXBUCKET);
           if (nmbufs > 0)
                   nmbufs = uma_zone_set_max(zone_mbuf, nmbufs);
           uma_zone_set_warning(zone_mbuf, "kern.ipc.nmbufs limit reached");
   
           zone_clust = uma_zcreate(MBUF_CLUSTER_MEM_NAME, MCLBYTES,
               mb_ctor_clust, mb_dtor_clust,
   #ifdef INVARIANTS
               trash_init, trash_fini,
   #else
               NULL, NULL,
   #endif
               UMA_ALIGN_PTR, UMA_ZONE_REFCNT);
           if (nmbclusters > 0)
                   nmbclusters = uma_zone_set_max(zone_clust, nmbclusters);
           uma_zone_set_warning(zone_clust, "kern.ipc.nmbclusters limit reached");
   
           zone_pack = uma_zsecond_create(MBUF_PACKET_MEM_NAME, mb_ctor_pack,
               mb_dtor_pack, mb_zinit_pack, mb_zfini_pack, zone_mbuf);
   
           /* Make jumbo frame zone too. Page size, 9k and 16k. */
           zone_jumbop = uma_zcreate(MBUF_JUMBOP_MEM_NAME, MJUMPAGESIZE,
               mb_ctor_clust, mb_dtor_clust,
   #ifdef INVARIANTS
               trash_init, trash_fini,
   #else
               NULL, NULL,
   #endif
               UMA_ALIGN_PTR, UMA_ZONE_REFCNT);
           if (nmbjumbop > 0)
                   nmbjumbop = uma_zone_set_max(zone_jumbop, nmbjumbop);
           uma_zone_set_warning(zone_jumbop, "kern.ipc.nmbjumbop limit reached");
   
           zone_jumbo9 = uma_zcreate(MBUF_JUMBO9_MEM_NAME, MJUM9BYTES,
               mb_ctor_clust, mb_dtor_clust,
   #ifdef INVARIANTS
               trash_init, trash_fini,
   #else
               NULL, NULL,
   #endif
               UMA_ALIGN_PTR, UMA_ZONE_REFCNT);
           uma_zone_set_allocf(zone_jumbo9, mbuf_jumbo_alloc);
           if (nmbjumbo9 > 0)
                   nmbjumbo9 = uma_zone_set_max(zone_jumbo9, nmbjumbo9);
           uma_zone_set_warning(zone_jumbo9, "kern.ipc.nmbjumbo9 limit reached");
   
           zone_jumbo16 = uma_zcreate(MBUF_JUMBO16_MEM_NAME, MJUM16BYTES,
               mb_ctor_clust, mb_dtor_clust,
   #ifdef INVARIANTS
               trash_init, trash_fini,
   #else
               NULL, NULL,
   #endif
               UMA_ALIGN_PTR, UMA_ZONE_REFCNT);
           uma_zone_set_allocf(zone_jumbo16, mbuf_jumbo_alloc);
           if (nmbjumbo16 > 0)
                   nmbjumbo16 = uma_zone_set_max(zone_jumbo16, nmbjumbo16);
           uma_zone_set_warning(zone_jumbo16, "kern.ipc.nmbjumbo16 limit reached");
   
           zone_ext_refcnt = uma_zcreate(MBUF_EXTREFCNT_MEM_NAME, sizeof(u_int),
               NULL, NULL,
               NULL, NULL,
               UMA_ALIGN_PTR, UMA_ZONE_ZINIT);
   
           /* uma_prealloc() goes here... */
   
           /*
            * Hook event handler for low-memory situation, used to
            * drain protocols and push data back to the caches (UMA
            * later pushes it back to VM).
            */
           EVENTHANDLER_REGISTER(vm_lowmem, mb_reclaim, NULL,
               EVENTHANDLER_PRI_FIRST);
   }
   SYSINIT(mbuf, SI_SUB_MBUF, SI_ORDER_FIRST, mbuf_init, NULL);
   
   /*
    * UMA backend page allocator for the jumbo frame zones.
    *
    * Allocates kernel virtual memory that is backed by contiguous physical
    * pages.
    */
   static void *
   mbuf_jumbo_alloc(uma_zone_t zone, vm_size_t bytes, uint8_t *flags, int wait)
   {
   
           /* Inform UMA that this allocator uses kernel_map/object. */
           *flags = UMA_SLAB_KERNEL;
           return ((void *)kmem_alloc_contig(kernel_arena, bytes, wait,
               (vm_paddr_t)0, ~(vm_paddr_t)0, 1, 0, VM_MEMATTR_DEFAULT));
   }
   
   /*
    * Constructor for Mbuf master zone.
    *
    * The 'arg' pointer points to a mb_args structure which
    * contains call-specific information required to support the
    * mbuf allocation API.  See mbuf.h.
    */
   static int
   mb_ctor_mbuf(void *mem, int size, void *arg, int how)
   {
           struct mbuf *m;
           struct mb_args *args;
           int error;
           int flags;
           short type;
   
   #ifdef INVARIANTS
           trash_ctor(mem, size, arg, how);
   #endif
           args = (struct mb_args *)arg;
           type = args->type;
   
           /*
            * The mbuf is initialized later.  The caller has the
            * responsibility to set up any MAC labels too.
            */
           if (type == MT_NOINIT)
                   return (0);
   
           m = (struct mbuf *)mem;
           flags = args->flags;
           MPASS((flags & M_NOFREE) == 0);
   
           error = m_init(m, NULL, size, how, type, flags);
   
           return (error);
   }
   
   /*
    * The Mbuf master zone destructor.
    */
   static void
   mb_dtor_mbuf(void *mem, int size, void *arg)
   {
           struct mbuf *m;
           unsigned long flags;
   
           m = (struct mbuf *)mem;
           flags = (unsigned long)arg;
   
           if ((m->m_flags & M_PKTHDR) && !SLIST_EMPTY(&m->m_pkthdr.tags))
                   m_tag_delete_chain(m, NULL);
           KASSERT((m->m_flags & M_EXT) == 0, ("%s: M_EXT set", __func__));
           KASSERT((m->m_flags & M_NOFREE) == 0, ("%s: M_NOFREE set", __func__));
   #ifdef INVARIANTS
           trash_dtor(mem, size, arg);
   #endif
   }
   
   /*
    * The Mbuf Packet zone destructor.
    */
   static void
   mb_dtor_pack(void *mem, int size, void *arg)
   {
           struct mbuf *m;
   
           m = (struct mbuf *)mem;
           if ((m->m_flags & M_PKTHDR) != 0)
                   m_tag_delete_chain(m, NULL);
   
           /* Make sure we've got a clean cluster back. */
           KASSERT((m->m_flags & M_EXT) == M_EXT, ("%s: M_EXT not set", __func__));
           KASSERT(m->m_ext.ext_buf != NULL, ("%s: ext_buf == NULL", __func__));
           KASSERT(m->m_ext.ext_free == NULL, ("%s: ext_free != NULL", __func__));
           KASSERT(m->m_ext.ext_arg1 == NULL, ("%s: ext_arg1 != NULL", __func__));
           KASSERT(m->m_ext.ext_arg2 == NULL, ("%s: ext_arg2 != NULL", __func__));
           KASSERT(m->m_ext.ext_size == MCLBYTES, ("%s: ext_size != MCLBYTES", __func__));
           KASSERT(m->m_ext.ext_type == EXT_PACKET, ("%s: ext_type != EXT_PACKET", __func__));
           KASSERT(*m->m_ext.ref_cnt == 1, ("%s: ref_cnt != 1", __func__));
   #ifdef INVARIANTS
           trash_dtor(m->m_ext.ext_buf, MCLBYTES, arg);
   #endif
           /*
            * If there are processes blocked on zone_clust, waiting for pages
            * to be freed up, * cause them to be woken up by draining the
            * packet zone.  We are exposed to a race here * (in the check for
            * the UMA_ZFLAG_FULL) where we might miss the flag set, but that
            * is deliberate. We don't want to acquire the zone lock for every
            * mbuf free.
            */
           if (uma_zone_exhausted_nolock(zone_clust))
                   zone_drain(zone_pack);
   }
   
   /*
    * The Cluster and Jumbo[PAGESIZE|9|16] zone constructor.
    *
    * Here the 'arg' pointer points to the Mbuf which we
    * are configuring cluster storage for.  If 'arg' is
    * empty we allocate just the cluster without setting
    * the mbuf to it.  See mbuf.h.
    */
   static int
   mb_ctor_clust(void *mem, int size, void *arg, int how)
   {
           struct mbuf *m;
           u_int *refcnt;
           int type;
           uma_zone_t zone;
   
   #ifdef INVARIANTS
           trash_ctor(mem, size, arg, how);
   #endif
           switch (size) {
           case MCLBYTES:
                   type = EXT_CLUSTER;
                   zone = zone_clust;
                   break;
   #if MJUMPAGESIZE != MCLBYTES
           case MJUMPAGESIZE:
                   type = EXT_JUMBOP;
                   zone = zone_jumbop;
                   break;
   #endif
           case MJUM9BYTES:
                   type = EXT_JUMBO9;
                   zone = zone_jumbo9;
                   break;
           case MJUM16BYTES:
                   type = EXT_JUMBO16;
                   zone = zone_jumbo16;
                   break;
           default:
                   panic("unknown cluster size");
                   break;
           }
   
           m = (struct mbuf *)arg;
           refcnt = uma_find_refcnt(zone, mem);
           *refcnt = 1;
           if (m != NULL) {
                   m->m_ext.ext_buf = (caddr_t)mem;
                   m->m_data = m->m_ext.ext_buf;
                   m->m_flags |= M_EXT;
                   m->m_ext.ext_free = NULL;
                   m->m_ext.ext_arg1 = NULL;
                   m->m_ext.ext_arg2 = NULL;
                   m->m_ext.ext_size = size;
                   m->m_ext.ext_type = type;
                   m->m_ext.ext_flags = 0;
                   m->m_ext.ref_cnt = refcnt;
           }
   
           return (0);
   }
   
   /*
    * The Mbuf Cluster zone destructor.
    */
   static void
   mb_dtor_clust(void *mem, int size, void *arg)
   {
   #ifdef INVARIANTS
           uma_zone_t zone;
   
           zone = m_getzone(size);
           KASSERT(*(uma_find_refcnt(zone, mem)) <= 1,
                   ("%s: refcnt incorrect %u", __func__,
                    *(uma_find_refcnt(zone, mem))) );
   
           trash_dtor(mem, size, arg);
   #endif
   }
   
   /*
    * The Packet secondary zone's init routine, executed on the
    * object's transition from mbuf keg slab to zone cache.
    */
   static int
   mb_zinit_pack(void *mem, int size, int how)
   {
           struct mbuf *m;
   
           m = (struct mbuf *)mem;         /* m is virgin. */
           if (uma_zalloc_arg(zone_clust, m, how) == NULL ||
               m->m_ext.ext_buf == NULL)
                   return (ENOMEM);
           m->m_ext.ext_type = EXT_PACKET; /* Override. */
   #ifdef INVARIANTS
           trash_init(m->m_ext.ext_buf, MCLBYTES, how);
   #endif
           return (0);
   }
   
   /*
    * The Packet secondary zone's fini routine, executed on the
    * object's transition from zone cache to keg slab.
    */
   static void
   mb_zfini_pack(void *mem, int size)
   {
           struct mbuf *m;
   
           m = (struct mbuf *)mem;
   #ifdef INVARIANTS
           trash_fini(m->m_ext.ext_buf, MCLBYTES);
   #endif
           uma_zfree_arg(zone_clust, m->m_ext.ext_buf, NULL);
   #ifdef INVARIANTS
           trash_dtor(mem, size, NULL);
   #endif
   }
   
   /*
    * The "packet" keg constructor.
    */
   static int
   mb_ctor_pack(void *mem, int size, void *arg, int how)
   {
           struct mbuf *m;
           struct mb_args *args;
           int error, flags;
           short type;
   
           m = (struct mbuf *)mem;
           args = (struct mb_args *)arg;
           flags = args->flags;
           type = args->type;
           MPASS((flags & M_NOFREE) == 0);
   
   #ifdef INVARIANTS
           trash_ctor(m->m_ext.ext_buf, MCLBYTES, arg, how);
   #endif
   
           error = m_init(m, NULL, size, how, type, flags);
   
           /* m_ext is already initialized. */
           m->m_data = m->m_ext.ext_buf;
           m->m_flags = (flags | M_EXT);
   
           return (error);
   }
   
   int
   m_pkthdr_init(struct mbuf *m, int how)
   {
   #ifdef MAC
           int error;
   #endif
           m->m_data = m->m_pktdat;
           m->m_pkthdr.rcvif = NULL;
           SLIST_INIT(&m->m_pkthdr.tags);
           m->m_pkthdr.len = 0;
           m->m_pkthdr.flowid = 0;
           m->m_pkthdr.csum_flags = 0;
           m->m_pkthdr.fibnum = 0;
           m->m_pkthdr.cosqos = 0;
           m->m_pkthdr.rsstype = 0;
           m->m_pkthdr.l2hlen = 0;
           m->m_pkthdr.l3hlen = 0;
           m->m_pkthdr.l4hlen = 0;
           m->m_pkthdr.l5hlen = 0;
           m->m_pkthdr.PH_per.sixtyfour[0] = 0;
           m->m_pkthdr.PH_loc.sixtyfour[0] = 0;
   #ifdef MAC
           /* If the label init fails, fail the alloc */
           error = mac_mbuf_init(m, how);
           if (error)
                   return (error);
   #endif
   
           return (0);
   }
   
   /*
    * This is the protocol drain routine.
    *
    * No locks should be held when this is called.  The drain routines have to
    * presently acquire some locks which raises the possibility of lock order
    * reversal.
    */
   static void
   mb_reclaim(void *junk)
   {
           struct domain *dp;
           struct protosw *pr;
   
           WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK | WARN_PANIC, NULL,
               "mb_reclaim()");
   
           for (dp = domains; dp != NULL; dp = dp->dom_next)
                   for (pr = dp->dom_protosw; pr < dp->dom_protoswNPROTOSW; pr++)
                           if (pr->pr_drain != NULL)
                                   (*pr->pr_drain)();
   }

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