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 */
    
    #if defined(__LP64__)
    #define M_HDR_PAD    6
    #else
    #define M_HDR_PAD    2
    #endif
    
    /*
     * 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 */
            uint8_t          pad[M_HDR_PAD];/* word align                  */
    };
    
    /*
    * 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 */
           /* variables for ip and tcp reassembly */
           void            *header;        /* pointer to packet header */
           int              len;           /* total packet length */
           /* variables for hardware checksum */
           int              csum_flags;    /* flags regarding checksum */
           int              csum_data;     /* data field used by csum routines */
           u_int16_t        tso_segsz;     /* TSO segment size */
           u_int16_t        ether_vtag;    /* Ethernet 802.1p+q vlan tag */
           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           0x00000001 /* has associated external storage */
   #define M_PKTHDR        0x00000002 /* start of record */
   #define M_EOR           0x00000004 /* end of record */
   #define M_RDONLY        0x00000008 /* associated data is marked read-only */
   #define M_PROTO1        0x00000010 /* protocol-specific */
   #define M_PROTO2        0x00000020 /* protocol-specific */
   #define M_PROTO3        0x00000040 /* protocol-specific */
   #define M_PROTO4        0x00000080 /* protocol-specific */
   #define M_PROTO5        0x00000100 /* protocol-specific */
   #define M_BCAST         0x00000200 /* send/received as link-level broadcast */
   #define M_MCAST         0x00000400 /* send/received as link-level multicast */
   #define M_FRAG          0x00000800 /* packet is a fragment of a larger packet */
   #define M_FIRSTFRAG     0x00001000 /* packet is first fragment */
   #define M_LASTFRAG      0x00002000 /* packet is last fragment */
   #define M_SKIP_FIREWALL 0x00004000 /* skip firewall processing */
   #define M_FREELIST      0x00008000 /* mbuf is on the free list */
   #define M_VLANTAG       0x00010000 /* ether_vtag is valid */
   #define M_PROMISC       0x00020000 /* packet was not for us */
   #define M_NOFREE        0x00040000 /* do not free mbuf, embedded in cluster */
   #define M_PROTO6        0x00080000 /* protocol-specific */
   #define M_PROTO7        0x00100000 /* protocol-specific */
   #define M_PROTO8        0x00200000 /* protocol-specific */
   /*
    * For RELENG_{6,7} steal these flags for limited multiple routing table
    * support. In RELENG_8 and beyond, use just one flag and a tag.
    */
   #define M_FIB           0xF0000000 /* steal some bits to store fib number. */
   
   #define M_NOTIFICATION  M_PROTO5    /* SCTP notification */
   
   /*
    * Flags to purge when crossing layers.
    */
   #define M_PROTOFLAGS \
       (M_PROTO1|M_PROTO2|M_PROTO3|M_PROTO4|M_PROTO5|M_PROTO6|M_PROTO7|M_PROTO8)
   
   /*
    * Flags preserved when copying m_pkthdr.
    */
   #define M_COPYFLAGS \
       (M_PKTHDR|M_EOR|M_RDONLY|M_PROTOFLAGS|M_SKIP_FIREWALL|M_BCAST|M_MCAST|\
        M_FRAG|M_FIRSTFRAG|M_LASTFRAG|M_VLANTAG|M_PROMISC|M_FIB)
   
   /*
    * External buffer types: identify ext_buf type.
    */
   #define EXT_CLUSTER     1       /* mbuf cluster */
   #define EXT_SFBUF       2       /* sendfile(2)'s sf_bufs */
   #define EXT_JUMBOP      3       /* jumbo cluster 4096 bytes */
   #define EXT_JUMBO9      4       /* jumbo cluster 9216 bytes */
   #define EXT_JUMBO16     5       /* jumbo cluster 16184 bytes */
   #define EXT_PACKET      6       /* mbuf+cluster from packet zone */
   #define EXT_MBUF        7       /* external mbuf reference (M_IOVEC) */
   #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 indicating hw checksum support and sw checksum requirements.  This
    * field can be directly tested against if_data.ifi_hwassist.
    */
   #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_TSO                0x0020          /* will do TSO */
   
   #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       MT_DATA /* packet header, use M_PKTHDR instead */
   #define MT_SONAME       8       /* socket name */
   #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 */
   
   #define MB_NOTAGS       0x1UL   /* no tags attached to mbuf */
   
   /*
    * General mbuf allocator statistics structure.
    *
    * Many of these statistics are no longer used; we instead track many
    * allocator statistics through UMA's built in statistics mechanism.
    */
   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_PACKET_MEM_NAME    "mbuf_packet"
   #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_TAG_MEM_NAME       "mbuf_tag"
   #define MBUF_EXTREFCNT_MEM_NAME "mbuf_ext_refcnt"
   
   #ifdef _KERNEL
   
   #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;
   extern uma_zone_t       zone_ext_refcnt;
   
   static __inline struct mbuf     *m_getcl(int how, short type, int flags);
   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_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_last(struct mbuf *m);
   
   static __inline int
   m_gettype(int size)
   {
           int type;
           
           switch (size) {
           case MSIZE:
                   type = EXT_MBUF;
                   break;
           case MCLBYTES:
                   type = EXT_CLUSTER;
                   break;
   #if MJUMPAGESIZE != MCLBYTES
           case MJUMPAGESIZE:
                   type = EXT_JUMBOP;
                   break;
   #endif
           case MJUM9BYTES:
                   type = EXT_JUMBO9;
                   break;
           case MJUM16BYTES:
                   type = EXT_JUMBO16;
                   break;
           default:
                   panic("%s: m_getjcl: invalid cluster size", __func__);
           }
   
           return (type);
   }
   
   static __inline uma_zone_t
   m_getzone(int size)
   {
           uma_zone_t zone;
           
           switch (size) {
           case MSIZE:
                   zone = zone_mbuf;
                   break;
           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 (zone);
   }
   
   static __inline struct mbuf *
   m_get(int how, short type)
   {
           struct mb_args args;
   
           args.flags = 0;
           args.type = type;
           return ((struct mbuf *)(uma_zalloc_arg(zone_mbuf, &args, how)));
   }
   
   /*
    * XXX This should be deprecated, 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 ((struct mbuf *)(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 ((struct mbuf *)(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.
    *
    * XXX: This is rather large, should be real function maybe.
    */
   static __inline 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);
   
           zone = m_getzone(size);
           n = uma_zalloc_arg(zone, m, how);
           if (n == NULL) {
                   uma_zfree(zone_mbuf, m);
                   return (NULL);
           }
           return (m);
   }
   
   static __inline void
   m_free_fast(struct mbuf *m)
   {
           KASSERT(SLIST_EMPTY(&m->m_pkthdr.tags), ("doing fast free of mbuf with tags"));
   
           uma_zfree_arg(zone_mbuf, m, (void *)MB_NOTAGS);
   }
   
   static __inline struct mbuf *
   m_free(struct mbuf *m)
   {
           struct mbuf *n = m->m_next;
   
           if (m->m_flags & M_EXT)
                   mb_free_ext(m);
           else if ((m->m_flags & M_NOFREE) == 0)
                   uma_zfree(zone_mbuf, m);
           return (n);
   }
   
   static __inline void
   m_clget(struct mbuf *m, int how)
   {
   
           if (m->m_flags & M_EXT)
                   printf("%s: %p mbuf already has cluster\n", __func__, m);
           m->m_ext.ext_buf = (char *)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;
   
           zone = m_getzone(size);
           return (uma_zalloc_arg(zone, m, how));
   }
   
   static __inline void
   m_cljset(struct mbuf *m, void *cl, int type)
   {
           uma_zone_t zone;
           int size;
           
           switch (type) {
           case EXT_CLUSTER:
                   size = MCLBYTES;
                   zone = zone_clust;
                   break;
   #if MJUMPAGESIZE != MCLBYTES
           case EXT_JUMBOP:
                   size = MJUMPAGESIZE;
                   zone = zone_jumbop;
                   break;
   #endif
           case EXT_JUMBO9:
                   size = MJUM9BYTES;
                   zone = zone_jumbo9;
                   break;
           case EXT_JUMBO16:
                   size = MJUM16BYTES;
                   zone = zone_jumbo16;
                   break;
           default:
                   panic("unknown cluster type");
                   break;
           }
   
           m->m_data = m->m_ext.ext_buf = cl;
           m->m_ext.ext_free = m->m_ext.ext_args = NULL;
           m->m_ext.ext_size = size;
           m->m_ext.ext_type = type;
           m->m_ext.ref_cnt = uma_find_refcnt(zone, cl);
           m->m_flags |= M_EXT;
   
   }
   
   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).
    */
   #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))
   #define m_getm(m, len, how, type)                                       \
       m_getm2((m), (len), (how), (type), M_PKTHDR)
   
   /*
    * 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)) ||                  \
                            (*((m)->m_ext.ref_cnt) == 1)) )                \
   
   /* 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.
    *
    * XXX: Broken at the moment.  Need some UMA magic to make it work again.
    */
   #define M_ASSERTVALID(m)                                                \
           KASSERT((((struct mbuf *)m)->m_flags & 0) == 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 {                                            \
           KASSERT(!((m)->m_flags & (M_PKTHDR|M_EXT)),                     \
                   ("%s: M_ALIGN not normal mbuf", __func__));             \
           KASSERT((m)->m_data == (m)->m_dat,                              \
                   ("%s: M_ALIGN not a virgin mbuf", __func__));           \
           (m)->m_data += (MLEN - (len)) & ~(sizeof(long) - 1);            \
   } while (0)
   
   /*
    * As above, for mbufs allocated with m_gethdr/MGETHDR or initialized by
    * M_DUP/MOVE_PKTHDR.
    */
   #define MH_ALIGN(m, len) do {                                           \
           KASSERT((m)->m_flags & M_PKTHDR && !((m)->m_flags & M_EXT),     \
                   ("%s: MH_ALIGN not PKTHDR mbuf", __func__));            \
           KASSERT((m)->m_data == (m)->m_pktdat,                           \
                   ("%s: MH_ALIGN not a virgin mbuf", __func__));          \
           (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);
   struct mbuf     *m_collapse(struct mbuf *, 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_copymdata(struct mbuf *, struct mbuf *,
                       int, 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);
   void             m_demote(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_getm2(struct mbuf *, int, int, short, int);
   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);
   int             m_sanity(struct mbuf *, int);
   struct mbuf     *m_split(struct mbuf *, int, int);
   struct mbuf     *m_uiotombuf(struct uio *, int, 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 chosen 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                           21 /* PF + ALTQ information */
   #define PACKET_TAG_RTSOCKFAM                    25 /* rtsock sa family */
   #define PACKET_TAG_IPOPTIONS                    27 /* Saved IP options */
   #define PACKET_TAG_CARP                         28 /* CARP info */
   
   /* Specific cookies and tags. */
   
   /* 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) ? (struct m_tag *)NULL :
               m_tag_locate(m, MTAG_ABI_COMPAT, type, start));
   }
   
   /* XXX temporary FIB methods probably eventually use tags.*/
   #define M_FIBSHIFT    28
   #define M_FIBMASK       0x0F
   
   /* get the fib from an mbuf and if it is not set, return the default */
   #define M_GETFIB(_m) \
       ((((_m)->m_flags & M_FIB) >> M_FIBSHIFT) & M_FIBMASK)
   
   #define M_SETFIB(_m, _fib) do {                                         \
           _m->m_flags &= ~M_FIB;                                          \
           _m->m_flags |= (((_fib) << M_FIBSHIFT) & M_FIB);  \
   } while (0) 
   
   #endif /* _KERNEL */
   
   #endif /* !_SYS_MBUF_H_ */

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