FreeBSD/Linux Kernel Cross Reference
sys/sys/mbuf.h

     /*-
      * Copyright (c) 1982, 1986, 1988, 1993
      *      The Regents of the University of California.  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.
     * 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.
     *
     *      @(#)mbuf.h      8.5 (Berkeley) 2/19/95
     * $FreeBSD$
     */
    
    #ifndef _SYS_MBUF_H_
    #define _SYS_MBUF_H_
    
    /* XXX: These includes suck. Sorry! */
    #include <sys/queue.h>
    #ifdef _KERNEL
    #include <sys/systm.h>
    #include <vm/uma.h>
    #ifdef WITNESS
    #include <sys/lock.h>
    #endif
    #endif
    
    /*
     * Mbufs are of a single size, MSIZE (sys/param.h), which
     * includes overhead.  An mbuf may add a single "mbuf cluster" of size
     * MCLBYTES (also in sys/param.h), which has no additional overhead
     * and is used instead of the internal data area; this is done when
     * at least MINCLSIZE of data must be stored.  Additionally, it is possible
     * to allocate a separate buffer externally and attach it to the mbuf in
     * a way similar to that of mbuf clusters.
     */
    #define MLEN            (MSIZE - sizeof(struct m_hdr))  /* normal data len */
    #define MHLEN           (MLEN - sizeof(struct pkthdr))  /* data len w/pkthdr */
    #define MINCLSIZE       (MHLEN + 1)     /* smallest amount to put in cluster */
    #define M_MAXCOMPRESS   (MHLEN / 2)     /* max amount to copy for compression */
    
    #ifdef _KERNEL
    /*-
     * Macros for type conversion:
     * mtod(m, t)   -- Convert mbuf pointer to data pointer of correct type.
     * dtom(x)      -- Convert data pointer within mbuf to mbuf pointer (XXX).
     */
    #define mtod(m, t)      ((t)((m)->m_data))
    #define dtom(x)         ((struct mbuf *)((intptr_t)(x) & ~(MSIZE-1)))
    
    /*
     * Argument structure passed to UMA routines during mbuf and packet
     * allocations.
     */
    struct mb_args {
            int     flags;  /* Flags for mbuf being allocated */
            short   type;   /* Type of mbuf being allocated */
    };
    #endif /* _KERNEL */
    
    /*
     * Header present at the beginning of every mbuf.
     */
    struct m_hdr {
            struct  mbuf *mh_next;          /* next buffer in chain */
            struct  mbuf *mh_nextpkt;       /* next chain in queue/record */
            caddr_t mh_data;                /* location of data */
            int     mh_len;                 /* amount of data in this mbuf */
            int     mh_flags;               /* flags; see below */
            short   mh_type;                /* type of data in this mbuf */
    };
    
    /*
     * Packet tag structure (see below for details).
     */
    struct m_tag {
            SLIST_ENTRY(m_tag)      m_tag_link;     /* List of packet tags */
            u_int16_t               m_tag_id;       /* Tag ID */
            u_int16_t               m_tag_len;      /* Length of data */
            u_int32_t               m_tag_cookie;   /* ABI/Module ID */
            void                    (*m_tag_free)(struct m_tag *);
   };
   
   /*
    * Record/packet header in first mbuf of chain; valid only if M_PKTHDR is set.
    */
   struct pkthdr {
           struct  ifnet *rcvif;           /* rcv interface */
           int     len;                    /* total packet length */
           /* variables for ip and tcp reassembly */
           void    *header;                /* pointer to packet header */
           /* variables for hardware checksum */
           int     csum_flags;             /* flags regarding checksum */
           int     csum_data;              /* data field used by csum routines */
           SLIST_HEAD(packet_tags, m_tag) tags; /* list of packet tags */
   };
   
   /*
    * Description of external storage mapped into mbuf; valid only if M_EXT is set.
    */
   struct m_ext {
           caddr_t ext_buf;                /* start of buffer */
           void    (*ext_free)             /* free routine if not the usual */
                       (void *, void *);
           void    *ext_args;              /* optional argument pointer */
           u_int   ext_size;               /* size of buffer, for ext_free */
           volatile u_int *ref_cnt;        /* pointer to ref count info */
           int     ext_type;               /* type of external storage */
   };
   
   /*
    * The core of the mbuf object along with some shortcut defines for
    * practical purposes.
    */
   struct mbuf {
           struct  m_hdr m_hdr;
           union {
                   struct {
                           struct  pkthdr MH_pkthdr;       /* M_PKTHDR set */
                           union {
                                   struct  m_ext MH_ext;   /* M_EXT set */
                                   char    MH_databuf[MHLEN];
                           } MH_dat;
                   } MH;
                   char    M_databuf[MLEN];                /* !M_PKTHDR, !M_EXT */
           } M_dat;
   };
   #define m_next          m_hdr.mh_next
   #define m_len           m_hdr.mh_len
   #define m_data          m_hdr.mh_data
   #define m_type          m_hdr.mh_type
   #define m_flags         m_hdr.mh_flags
   #define m_nextpkt       m_hdr.mh_nextpkt
   #define m_act           m_nextpkt
   #define m_pkthdr        M_dat.MH.MH_pkthdr
   #define m_ext           M_dat.MH.MH_dat.MH_ext
   #define m_pktdat        M_dat.MH.MH_dat.MH_databuf
   #define m_dat           M_dat.M_databuf
   
   /*
    * mbuf flags.
    */
   #define M_EXT           0x0001  /* has associated external storage */
   #define M_PKTHDR        0x0002  /* start of record */
   #define M_EOR           0x0004  /* end of record */
   #define M_RDONLY        0x0008  /* associated data is marked read-only */
   #define M_PROTO1        0x0010  /* protocol-specific */
   #define M_PROTO2        0x0020  /* protocol-specific */
   #define M_PROTO3        0x0040  /* protocol-specific */
   #define M_PROTO4        0x0080  /* protocol-specific */
   #define M_PROTO5        0x0100  /* protocol-specific */
   #define M_SKIP_FIREWALL 0x4000  /* skip firewall processing */
   #define M_FREELIST      0x8000  /* mbuf is on the free list */
   
   /*
    * mbuf pkthdr flags (also stored in m_flags).
    */
   #define M_BCAST         0x0200  /* send/received as link-level broadcast */
   #define M_MCAST         0x0400  /* send/received as link-level multicast */
   #define M_FRAG          0x0800  /* packet is a fragment of a larger packet */
   #define M_FIRSTFRAG     0x1000  /* packet is first fragment */
   #define M_LASTFRAG      0x2000  /* packet is last fragment */
   #define M_VLANTAG       0x10000 /* packet has VLAN tag attached */
   
   /*
    * External buffer types: identify ext_buf type.
    */
   #define EXT_CLUSTER     1       /* mbuf cluster */
   #define EXT_SFBUF       2       /* sendfile(2)'s sf_bufs */
   #define EXT_PACKET      3       /* came out of Packet zone */
   #define EXT_JUMBOP      4       /* jumbo cluster 4096 bytes */
   #define EXT_JUMBO9      5       /* jumbo cluster 9216 bytes */
   #define EXT_JUMBO16     6       /* jumbo cluster 16184 bytes */
   #define EXT_NET_DRV     100     /* custom ext_buf provided by net driver(s) */
   #define EXT_MOD_TYPE    200     /* custom module's ext_buf type */
   #define EXT_DISPOSABLE  300     /* can throw this buffer away w/page flipping */
   #define EXT_EXTREF      400     /* has externally maintained ref_cnt ptr */
   
   /*
    * Flags copied when copying m_pkthdr.
    */
   #define M_COPYFLAGS     (M_PKTHDR|M_EOR|M_RDONLY|M_PROTO1|M_PROTO1|M_PROTO2|\
                               M_PROTO3|M_PROTO4|M_PROTO5|M_SKIP_FIREWALL|\
                               M_BCAST|M_MCAST|M_FRAG|M_FIRSTFRAG|M_LASTFRAG|\
                               M_VLANTAG)
   
   /*
    * Flags indicating hw checksum support and sw checksum requirements.
    */
   #define CSUM_IP                 0x0001          /* will csum IP */
   #define CSUM_TCP                0x0002          /* will csum TCP */
   #define CSUM_UDP                0x0004          /* will csum UDP */
   #define CSUM_IP_FRAGS           0x0008          /* will csum IP fragments */
   #define CSUM_FRAGMENT           0x0010          /* will do IP fragmentation */
   
   #define CSUM_IP_CHECKED         0x0100          /* did csum IP */
   #define CSUM_IP_VALID           0x0200          /*   ... the csum is valid */
   #define CSUM_DATA_VALID         0x0400          /* csum_data field is valid */
   #define CSUM_PSEUDO_HDR         0x0800          /* csum_data has pseudo hdr */
   
   #define CSUM_DELAY_DATA         (CSUM_TCP | CSUM_UDP)
   #define CSUM_DELAY_IP           (CSUM_IP)       /* XXX add ipv6 here too? */
   
   /*
    * mbuf types.
    */
   #define MT_NOTMBUF      0       /* USED INTERNALLY ONLY! Object is not mbuf */
   #define MT_DATA         1       /* dynamic (data) allocation */
   #define MT_HEADER       2       /* packet header */
   #if 0
   #define MT_SOCKET       3       /* socket structure */
   #define MT_PCB          4       /* protocol control block */
   #define MT_RTABLE       5       /* routing tables */
   #define MT_HTABLE       6       /* IMP host tables */
   #define MT_ATABLE       7       /* address resolution tables */
   #endif
   #define MT_SONAME       8       /* socket name */
   #if 0
   #define MT_SOOPTS       10      /* socket options */
   #endif
   #define MT_FTABLE       11      /* fragment reassembly header */
   #if 0
   #define MT_RIGHTS       12      /* access rights */
   #define MT_IFADDR       13      /* interface address */
   #endif
   #define MT_CONTROL      14      /* extra-data protocol message */
   #define MT_OOBDATA      15      /* expedited data  */
   #define MT_NTYPES       16      /* number of mbuf types for mbtypes[] */
   
   #define MT_NOINIT       255     /* Not a type but a flag to allocate
                                      a non-initialized mbuf */
   
   /*
    * General mbuf allocator statistics structure.
    */
   struct mbstat {
           u_long  m_mbufs;        /* XXX */
           u_long  m_mclusts;      /* XXX */
   
           u_long  m_drain;        /* times drained protocols for space */
           u_long  m_mcfail;       /* XXX: times m_copym failed */
           u_long  m_mpfail;       /* XXX: times m_pullup failed */
           u_long  m_msize;        /* length of an mbuf */
           u_long  m_mclbytes;     /* length of an mbuf cluster */
           u_long  m_minclsize;    /* min length of data to allocate a cluster */
           u_long  m_mlen;         /* length of data in an mbuf */
           u_long  m_mhlen;        /* length of data in a header mbuf */
   
           /* Number of mbtypes (gives # elems in mbtypes[] array: */
           short   m_numtypes;
   
           /* XXX: Sendfile stats should eventually move to their own struct */
           u_long  sf_iocnt;       /* times sendfile had to do disk I/O */
           u_long  sf_allocfail;   /* times sfbuf allocation failed */
           u_long  sf_allocwait;   /* times sfbuf allocation had to wait */
   };
   
   /*
    * Flags specifying how an allocation should be made.
    *
    * The flag to use is as follows:
    * - M_DONTWAIT or M_NOWAIT from an interrupt handler to not block allocation.
    * - M_WAIT or M_WAITOK or M_TRYWAIT from wherever it is safe to block.
    *
    * M_DONTWAIT/M_NOWAIT means that we will not block the thread explicitly
    * and if we cannot allocate immediately we may return NULL,
    * whereas M_WAIT/M_WAITOK/M_TRYWAIT means that if we cannot allocate
    * resources we will block until they are available, and thus never
    * return NULL.
    *
    * XXX Eventually just phase this out to use M_WAITOK/M_NOWAIT.
    */
   #define MBTOM(how)      (how)
   #define M_DONTWAIT      M_NOWAIT
   #define M_TRYWAIT       M_WAITOK
   #define M_WAIT          M_WAITOK
   
   /*
    * String names of mbuf-related UMA(9) and malloc(9) types.  Exposed to
    * !_KERNEL so that monitoring tools can look up the zones with
    * libmemstat(3).
    */
   #define MBUF_MEM_NAME           "mbuf"
   #define MBUF_CLUSTER_MEM_NAME   "mbuf_cluster"
   #define MBUF_JUMBOP_MEM_NAME    "mbuf_jumbo_pagesize"
   #define MBUF_JUMBO9_MEM_NAME    "mbuf_jumbo_9k"
   #define MBUF_JUMBO16_MEM_NAME   "mbuf_jumbo_16k"
   #define MBUF_PACKET_MEM_NAME    "mbuf_packet"
   #define MBUF_TAG_MEM_NAME       "mbuf_tag"
   
   #ifdef _KERNEL
   /*-
    * mbuf external reference count management macros.
    *
    * MEXT_IS_REF(m): true if (m) is not the only mbuf referencing
    *     the external buffer ext_buf.
    *
    * MEXT_REM_REF(m): remove reference to m_ext object.
    *
    * MEXT_ADD_REF(m): add reference to m_ext object already
    *     referred to by (m).  XXX Note that it is VERY important that you
    *     always set the second mbuf's m_ext.ref_cnt to point to the first
    *     one's (i.e., n->m_ext.ref_cnt = m->m_ext.ref_cnt) AFTER you run
    *     MEXT_ADD_REF(m).  This is because m might have a lazy initialized
    *     ref_cnt (NULL) before this is run and it will only be looked up
    *     from here.  We should make MEXT_ADD_REF() always take two mbufs
    *     as arguments so that it can take care of this itself.
    */
   #define MEXT_IS_REF(m)  (((m)->m_ext.ref_cnt != NULL)                   \
       && (*((m)->m_ext.ref_cnt) > 1))
   
   #define MEXT_REM_REF(m) do {                                            \
           KASSERT((m)->m_ext.ref_cnt != NULL, ("m_ext refcnt lazy NULL")); \
           KASSERT(*((m)->m_ext.ref_cnt) > 0, ("m_ext refcnt < 0"));       \
           atomic_subtract_int((m)->m_ext.ref_cnt, 1);                     \
   } while(0)
   
   #define MEXT_ADD_REF(m) do {                                            \
           if ((m)->m_ext.ref_cnt == NULL) {                               \
                   KASSERT((m)->m_ext.ext_type == EXT_CLUSTER ||           \
                       (m)->m_ext.ext_type == EXT_PACKET,                  \
                       ("Unexpected mbuf type has lazy refcnt"));          \
                   (m)->m_ext.ref_cnt = (u_int *)uma_find_refcnt(          \
                       zone_clust, (m)->m_ext.ext_buf);                    \
                   *((m)->m_ext.ref_cnt) = 2;                              \
           } else                                                          \
                   atomic_add_int((m)->m_ext.ref_cnt, 1);                  \
   } while (0)
   
   #ifdef WITNESS
   #define MBUF_CHECKSLEEP(how) do {                                       \
           if (how == M_WAITOK)                                            \
                   WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,         \
                       "Sleeping in \"%s\"", __func__);                    \
   } while(0)
   #else
   #define MBUF_CHECKSLEEP(how)
   #endif
   
   /*
    * Network buffer allocation API
    *
    * The rest of it is defined in kern/kern_mbuf.c
    */
   
   extern uma_zone_t       zone_mbuf;
   extern uma_zone_t       zone_clust;
   extern uma_zone_t       zone_pack;
   extern uma_zone_t       zone_jumbop;
   extern uma_zone_t       zone_jumbo9;
   extern uma_zone_t       zone_jumbo16;
   
   static __inline struct mbuf     *m_get(int how, short type);
   static __inline struct mbuf     *m_gethdr(int how, short type);
   static __inline struct mbuf     *m_getcl(int how, short type, int flags);
   static __inline struct mbuf     *m_getjcl(int how, short type, int flags, int size);
   static __inline struct mbuf     *m_getclr(int how, short type); /* XXX */
   static __inline struct mbuf     *m_free(struct mbuf *m);
   static __inline void             m_clget(struct mbuf *m, int how);
   static __inline void            *m_cljget(struct mbuf *m, int how, int size);
   static __inline void             m_chtype(struct mbuf *m, short new_type);
   void                             mb_free_ext(struct mbuf *);
   
   static __inline
   struct mbuf *
   m_get(int how, short type)
   {
           struct mb_args args;
   
           args.flags = 0;
           args.type = type;
           return (uma_zalloc_arg(zone_mbuf, &args, how));
   }
   
   /* XXX This should be depracated, very little use */
   static __inline
   struct mbuf *
   m_getclr(int how, short type)
   {
           struct mbuf *m;
           struct mb_args args;
   
           args.flags = 0;
           args.type = type;
           m = uma_zalloc_arg(zone_mbuf, &args, how);
           if (m != NULL)
                   bzero(m->m_data, MLEN);
           return m;
   }
   
   static __inline
   struct mbuf *
   m_gethdr(int how, short type)
   {
           struct mb_args args;
   
           args.flags = M_PKTHDR;
           args.type = type;
           return (uma_zalloc_arg(zone_mbuf, &args, how));
   }
   
   static __inline
   struct mbuf *
   m_getcl(int how, short type, int flags)
   {
           struct mb_args args;
   
           args.flags = flags;
           args.type = type;
           return (uma_zalloc_arg(zone_pack, &args, how));
   }
   
   /*
    * m_getjcl() returns an mbuf with a cluster of the specified size attached.
    * For size it takes MCLBYTES, MJUMPAGESIZE, MJUM9BYTES, MJUM16BYTES.
    */
   static __inline /* XXX: This is rather large, should be real function maybe. */
   struct mbuf *
   m_getjcl(int how, short type, int flags, int size)
   {
           struct mb_args args;
           struct mbuf *m, *n;
           uma_zone_t zone;
   
           args.flags = flags;
           args.type = type;
   
           m = uma_zalloc_arg(zone_mbuf, &args, how);
           if (m == NULL)
                   return NULL;
   
           switch (size) {
           case MCLBYTES:
                   zone = zone_clust;
                   break;
   #if MJUMPAGESIZE != MCLBYTES
           case MJUMPAGESIZE:
                   zone = zone_jumbop;
                   break;
   #endif
           case MJUM9BYTES:
                   zone = zone_jumbo9;
                   break;
           case MJUM16BYTES:
                   zone = zone_jumbo16;
                   break;
           default:
                   panic("%s: m_getjcl: invalid cluster type", __func__);
           }
           n = uma_zalloc_arg(zone, m, how);
           if (n == NULL) {
                   uma_zfree(zone_mbuf, m);
                   return NULL;
           }
           return m;
   }
   
   static __inline
   struct mbuf *
   m_free(struct mbuf *m)
   {
           struct mbuf *n = m->m_next;
   
   #ifdef INVARIANTS
           m->m_flags |= M_FREELIST;
   #endif
           if (m->m_flags & M_EXT)
                   mb_free_ext(m);
           else
                   uma_zfree(zone_mbuf, m);
           return n;
   }
   
   static __inline
   void
   m_clget(struct mbuf *m, int how)
   {
   
           m->m_ext.ext_buf = NULL;
           uma_zalloc_arg(zone_clust, m, how);
           /*
            * On a cluster allocation failure, drain the packet zone and retry,
            * we might be able to loosen a few clusters up on the drain.
            */
           if ((how & M_NOWAIT) && (m->m_ext.ext_buf == NULL)) {
                   zone_drain(zone_pack);
                   uma_zalloc_arg(zone_clust, m, how);
           }
   }
   
   /*
    * m_cljget() is different from m_clget() as it can allocate clusters
    * without attaching them to an mbuf.  In that case the return value
    * is the pointer to the cluster of the requested size.  If an mbuf was
    * specified, it gets the cluster attached to it and the return value
    * can be safely ignored.
    * For size it takes MCLBYTES, MJUMPAGESIZE, MJUM9BYTES, MJUM16BYTES.
    */
   static __inline
   void *
   m_cljget(struct mbuf *m, int how, int size)
   {
           uma_zone_t zone;
   
           if (m && m->m_flags & M_EXT)
                   printf("%s: %p mbuf already has cluster\n", __func__, m);
           if (m != NULL)
                   m->m_ext.ext_buf = NULL;
   
           switch (size) {
           case MCLBYTES:
                   zone = zone_clust;
                   break;
   #if MJUMPAGESIZE != MCLBYTES
           case MJUMPAGESIZE:
                   zone = zone_jumbop;
                   break;
   #endif
           case MJUM9BYTES:
                   zone = zone_jumbo9;
                   break;
           case MJUM16BYTES:
                   zone = zone_jumbo16;
                   break;
           default:
                   panic("%s: m_getjcl: invalid cluster type", __func__);
           }
           
           return (uma_zalloc_arg(zone, m, how));
   }
   
   static __inline
   void
   m_chtype(struct mbuf *m, short new_type)
   {
           m->m_type = new_type;
   }
   
   static __inline struct mbuf *
   m_last(struct mbuf *m)
   {
   
           while (m->m_next)
                   m = m->m_next;
           return (m);
   }
   
   /*
    * mbuf, cluster, and external object allocation macros
    * (for compatibility purposes).
    */
   /* NB: M_COPY_PKTHDR is deprecated.  Use M_MOVE_PKTHDR or m_dup_pktdr. */
   #define M_MOVE_PKTHDR(to, from) m_move_pkthdr((to), (from))
   #define MGET(m, how, type)      ((m) = m_get((how), (type)))
   #define MGETHDR(m, how, type)   ((m) = m_gethdr((how), (type)))
   #define MCLGET(m, how)          m_clget((m), (how))
   #define MEXTADD(m, buf, size, free, args, flags, type)                  \
       m_extadd((m), (caddr_t)(buf), (size), (free), (args), (flags), (type))
   
   /*
    * Evaluate TRUE if it's safe to write to the mbuf m's data region (this
    * can be both the local data payload, or an external buffer area,
    * depending on whether M_EXT is set).
    */
   #define M_WRITABLE(m)   (!((m)->m_flags & M_RDONLY) && (!((m)->m_flags  \
                               & M_EXT) || !MEXT_IS_REF(m)))
   
   /* Check if the supplied mbuf has a packet header, or else panic. */
   #define M_ASSERTPKTHDR(m)                                               \
           KASSERT(m != NULL && m->m_flags & M_PKTHDR,                     \
               ("%s: no mbuf packet header!", __func__))
   
   /* Ensure that the supplied mbuf is a valid, non-free mbuf. */
   #define M_ASSERTVALID(m)                                                \
           KASSERT((((struct mbuf *)m)->m_flags & M_FREELIST) == 0,        \
               ("%s: attempted use of a free mbuf!", __func__))
   
   /*
    * Set the m_data pointer of a newly-allocated mbuf (m_get/MGET) to place
    * an object of the specified size at the end of the mbuf, longword aligned.
    */
   #define M_ALIGN(m, len) do {                                            \
           (m)->m_data += (MLEN - (len)) & ~(sizeof(long) - 1);            \
   } while (0)
   
   /*
    * As above, for mbufs allocated with m_gethdr/MGETHDR
    * or initialized by M_COPY_PKTHDR.
    */
   #define MH_ALIGN(m, len) do {                                           \
           (m)->m_data += (MHLEN - (len)) & ~(sizeof(long) - 1);           \
   } while (0)
   
   /*
    * Compute the amount of space available
    * before the current start of data in an mbuf.
    *
    * The M_WRITABLE() is a temporary, conservative safety measure: the burden
    * of checking writability of the mbuf data area rests solely with the caller.
    */
   #define M_LEADINGSPACE(m)                                               \
           ((m)->m_flags & M_EXT ?                                         \
               (M_WRITABLE(m) ? (m)->m_data - (m)->m_ext.ext_buf : 0):     \
               (m)->m_flags & M_PKTHDR ? (m)->m_data - (m)->m_pktdat :     \
               (m)->m_data - (m)->m_dat)
   
   /*
    * Compute the amount of space available
    * after the end of data in an mbuf.
    *
    * The M_WRITABLE() is a temporary, conservative safety measure: the burden
    * of checking writability of the mbuf data area rests solely with the caller.
    */
   #define M_TRAILINGSPACE(m)                                              \
           ((m)->m_flags & M_EXT ?                                         \
               (M_WRITABLE(m) ? (m)->m_ext.ext_buf + (m)->m_ext.ext_size   \
                   - ((m)->m_data + (m)->m_len) : 0) :                     \
               &(m)->m_dat[MLEN] - ((m)->m_data + (m)->m_len))
   
   /*
    * Arrange to prepend space of size plen to mbuf m.
    * If a new mbuf must be allocated, how specifies whether to wait.
    * If the allocation fails, the original mbuf chain is freed and m is
    * set to NULL.
    */
   #define M_PREPEND(m, plen, how) do {                                    \
           struct mbuf **_mmp = &(m);                                      \
           struct mbuf *_mm = *_mmp;                                       \
           int _mplen = (plen);                                            \
           int __mhow = (how);                                             \
                                                                           \
           MBUF_CHECKSLEEP(how);                                           \
           if (M_LEADINGSPACE(_mm) >= _mplen) {                            \
                   _mm->m_data -= _mplen;                                  \
                   _mm->m_len += _mplen;                                   \
           } else                                                          \
                   _mm = m_prepend(_mm, _mplen, __mhow);                   \
           if (_mm != NULL && _mm->m_flags & M_PKTHDR)                     \
                   _mm->m_pkthdr.len += _mplen;                            \
           *_mmp = _mm;                                                    \
   } while (0)
   
   /*
    * Change mbuf to new type.
    * This is a relatively expensive operation and should be avoided.
    */
   #define MCHTYPE(m, t)   m_chtype((m), (t))
   
   /* Length to m_copy to copy all. */
   #define M_COPYALL       1000000000
   
   /* Compatibility with 4.3. */
   #define m_copy(m, o, l) m_copym((m), (o), (l), M_DONTWAIT)
   
   extern  int max_datalen;                /* MHLEN - max_hdr */
   extern  int max_hdr;                    /* Largest link + protocol header */
   extern  int max_linkhdr;                /* Largest link-level header */
   extern  int max_protohdr;               /* Largest protocol header */
   extern  struct mbstat mbstat;           /* General mbuf stats/infos */
   extern  int nmbclusters;                /* Maximum number of clusters */
   
   struct uio;
   
   void             m_adj(struct mbuf *, int);
   void             m_align(struct mbuf *, int);
   int              m_apply(struct mbuf *, int, int,
                       int (*)(void *, void *, u_int), void *);
   int              m_append(struct mbuf *, int, c_caddr_t);
   void             m_cat(struct mbuf *, struct mbuf *);
   void             m_extadd(struct mbuf *, caddr_t, u_int,
                       void (*)(void *, void *), void *, int, int);
   void             m_copyback(struct mbuf *, int, int, c_caddr_t);
   void             m_copydata(const struct mbuf *, int, int, caddr_t);
   struct  mbuf    *m_copym(struct mbuf *, int, int, int);
   struct  mbuf    *m_copypacket(struct mbuf *, int);
   void             m_copy_pkthdr(struct mbuf *, struct mbuf *);
   struct  mbuf    *m_copyup(struct mbuf *n, int len, int dstoff);
   struct  mbuf    *m_defrag(struct mbuf *, int);
   struct  mbuf    *m_devget(char *, int, int, struct ifnet *,
                       void (*)(char *, caddr_t, u_int));
   struct  mbuf    *m_dup(struct mbuf *, int);
   int              m_dup_pkthdr(struct mbuf *, struct mbuf *, int);
   u_int            m_fixhdr(struct mbuf *);
   struct  mbuf    *m_fragment(struct mbuf *, int, int);
   void             m_freem(struct mbuf *);
   struct  mbuf    *m_getm(struct mbuf *, int, int, short);
   struct  mbuf    *m_getptr(struct mbuf *, int, int *);
   u_int            m_length(struct mbuf *, struct mbuf **);
   void             m_move_pkthdr(struct mbuf *, struct mbuf *);
   struct  mbuf    *m_prepend(struct mbuf *, int, int);
   void             m_print(const struct mbuf *, int);
   struct  mbuf    *m_pulldown(struct mbuf *, int, int, int *);
   struct  mbuf    *m_pullup(struct mbuf *, int);
   struct  mbuf    *m_split(struct mbuf *, int, int);
   struct  mbuf    *m_uiotombuf(struct uio *, int, int, int);
   struct  mbuf    *m_unshare(struct mbuf *, int how);
   
   /*-
    * Network packets may have annotations attached by affixing a list
    * of "packet tags" to the pkthdr structure.  Packet tags are
    * dynamically allocated semi-opaque data structures that have
    * a fixed header (struct m_tag) that specifies the size of the
    * memory block and a <cookie,type> pair that identifies it.
    * The cookie is a 32-bit unique unsigned value used to identify
    * a module or ABI.  By convention this value is chose as the
    * date+time that the module is created, expressed as the number of
    * seconds since the epoch (e.g., using date -u +'%s').  The type value
    * is an ABI/module-specific value that identifies a particular annotation
    * and is private to the module.  For compatibility with systems
    * like OpenBSD that define packet tags w/o an ABI/module cookie,
    * the value PACKET_ABI_COMPAT is used to implement m_tag_get and
    * m_tag_find compatibility shim functions and several tag types are
    * defined below.  Users that do not require compatibility should use
    * a private cookie value so that packet tag-related definitions
    * can be maintained privately.
    *
    * Note that the packet tag returned by m_tag_alloc has the default
    * memory alignment implemented by malloc.  To reference private data
    * one can use a construct like:
    *
    *      struct m_tag *mtag = m_tag_alloc(...);
    *      struct foo *p = (struct foo *)(mtag+1);
    *
    * if the alignment of struct m_tag is sufficient for referencing members
    * of struct foo.  Otherwise it is necessary to embed struct m_tag within
    * the private data structure to insure proper alignment; e.g.,
    *
    *      struct foo {
    *              struct m_tag    tag;
    *              ...
    *      };
    *      struct foo *p = (struct foo *) m_tag_alloc(...);
    *      struct m_tag *mtag = &p->tag;
    */
   
   /*
    * Persistent tags stay with an mbuf until the mbuf is reclaimed.
    * Otherwise tags are expected to ``vanish'' when they pass through
    * a network interface.  For most interfaces this happens normally
    * as the tags are reclaimed when the mbuf is free'd.  However in
    * some special cases reclaiming must be done manually.  An example
    * is packets that pass through the loopback interface.  Also, one
    * must be careful to do this when ``turning around'' packets (e.g.,
    * icmp_reflect).
    *
    * To mark a tag persistent bit-or this flag in when defining the
    * tag id.  The tag will then be treated as described above.
    */
   #define MTAG_PERSISTENT                         0x800
   
   #define PACKET_TAG_NONE                         0  /* Nadda */
   
   /* Packet tags for use with PACKET_ABI_COMPAT. */
   #define PACKET_TAG_IPSEC_IN_DONE                1  /* IPsec applied, in */
   #define PACKET_TAG_IPSEC_OUT_DONE               2  /* IPsec applied, out */
   #define PACKET_TAG_IPSEC_IN_CRYPTO_DONE         3  /* NIC IPsec crypto done */
   #define PACKET_TAG_IPSEC_OUT_CRYPTO_NEEDED      4  /* NIC IPsec crypto req'ed */
   #define PACKET_TAG_IPSEC_IN_COULD_DO_CRYPTO     5  /* NIC notifies IPsec */
   #define PACKET_TAG_IPSEC_PENDING_TDB            6  /* Reminder to do IPsec */
   #define PACKET_TAG_BRIDGE                       7  /* Bridge processing done */
   #define PACKET_TAG_GIF                          8  /* GIF processing done */
   #define PACKET_TAG_GRE                          9  /* GRE processing done */
   #define PACKET_TAG_IN_PACKET_CHECKSUM           10 /* NIC checksumming done */
   #define PACKET_TAG_ENCAP                        11 /* Encap.  processing */
   #define PACKET_TAG_IPSEC_SOCKET                 12 /* IPSEC socket ref */
   #define PACKET_TAG_IPSEC_HISTORY                13 /* IPSEC history */
   #define PACKET_TAG_IPV6_INPUT                   14 /* IPV6 input processing */
   #define PACKET_TAG_DUMMYNET                     15 /* dummynet info */
   #define PACKET_TAG_DIVERT                       17 /* divert info */
   #define PACKET_TAG_IPFORWARD                    18 /* ipforward info */
   #define PACKET_TAG_MACLABEL     (19 | MTAG_PERSISTENT) /* MAC label */
   #define PACKET_TAG_PF_ROUTED                    21 /* PF routed, avoid loops */
   #define PACKET_TAG_PF_FRAGCACHE                 22 /* PF fragment cached */
   #define PACKET_TAG_PF_QID                       23 /* PF ALTQ queue id */
   #define PACKET_TAG_PF_TAG                       24 /* PF tagged */
   #define PACKET_TAG_RTSOCKFAM                    25 /* rtsock sa family */
   #define PACKET_TAG_PF_TRANSLATE_LOCALHOST       26 /* PF translate localhost */
   #define PACKET_TAG_IPOPTIONS                    27 /* Saved IP options */
   #define PACKET_TAG_CARP                         28 /* CARP info */
   
   /* Packet tag routines. */
   struct  m_tag   *m_tag_alloc(u_int32_t, int, int, int);
   void             m_tag_delete(struct mbuf *, struct m_tag *);
   void             m_tag_delete_chain(struct mbuf *, struct m_tag *);
   void             m_tag_free_default(struct m_tag *);
   struct  m_tag   *m_tag_locate(struct mbuf *, u_int32_t, int, struct m_tag *);
   struct  m_tag   *m_tag_copy(struct m_tag *, int);
   int              m_tag_copy_chain(struct mbuf *, struct mbuf *, int);
   void             m_tag_delete_nonpersistent(struct mbuf *);
   
   /*
    * Initialize the list of tags associated with an mbuf.
    */
   static __inline void
   m_tag_init(struct mbuf *m)
   {
           SLIST_INIT(&m->m_pkthdr.tags);
   }
   
   /*
    * Set up the contents of a tag.  Note that this does not
    * fill in the free method; the caller is expected to do that.
    *
    * XXX probably should be called m_tag_init, but that was
    * already taken.
    */
   static __inline void
   m_tag_setup(struct m_tag *t, u_int32_t cookie, int type, int len)
   {
           t->m_tag_id = type;
           t->m_tag_len = len;
           t->m_tag_cookie = cookie;
   }
   
   /*
    * Reclaim resources associated with a tag.
    */
   static __inline void
   m_tag_free(struct m_tag *t)
   {
           (*t->m_tag_free)(t);
   }
   
   /*
    * Return the first tag associated with an mbuf.
    */
   static __inline struct m_tag *
   m_tag_first(struct mbuf *m)
   {
           return (SLIST_FIRST(&m->m_pkthdr.tags));
   }
   
   /*
    * Return the next tag in the list of tags associated with an mbuf.
    */
   static __inline struct m_tag *
   m_tag_next(struct mbuf *m, struct m_tag *t)
   {
           return (SLIST_NEXT(t, m_tag_link));
   }
   
   /*
    * Prepend a tag to the list of tags associated with an mbuf.
    */
   static __inline void
   m_tag_prepend(struct mbuf *m, struct m_tag *t)
   {
           SLIST_INSERT_HEAD(&m->m_pkthdr.tags, t, m_tag_link);
   }
   
   /*
    * Unlink a tag from the list of tags associated with an mbuf.
    */
   static __inline void
   m_tag_unlink(struct mbuf *m, struct m_tag *t)
   {
           SLIST_REMOVE(&m->m_pkthdr.tags, t, m_tag, m_tag_link);
   }
   
   /* These are for OpenBSD compatibility. */
   #define MTAG_ABI_COMPAT         0               /* compatibility ABI */
   
   static __inline struct m_tag *
   m_tag_get(int type, int length, int wait)
   {
           return (m_tag_alloc(MTAG_ABI_COMPAT, type, length, wait));
   }
   
   static __inline struct m_tag *
   m_tag_find(struct mbuf *m, int type, struct m_tag *start)
   {
           return (SLIST_EMPTY(&m->m_pkthdr.tags) ?
               NULL : m_tag_locate(m, MTAG_ABI_COMPAT, type, start));
   }
   
   #endif /* _KERNEL */
   
   #endif /* !_SYS_MBUF_H_ */

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