xnu-1228.12.14.tar.gz

[apple/xnu.git] / bsd / sys / kpi_mbuf.h

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/*!
        @header kpi_mbuf.h
        This header defines an API for interacting with mbufs. mbufs are the
        primary method of storing packets in the networking stack.
        
        mbufs are used to store various items in the networking stack. The
        most common usage of an mbuf is to store a packet or data on a
        socket waiting to be sent or received. The mbuf is a contiguous
        structure with some header followed by some data. To store more data
        than would fit in an mbuf, external data is used. Most mbufs with
        external data use clusters to store the external data.
        
        mbufs can be chained, contiguous data in a packet can be found by
        following the m_next chain. Packets may be bundled together using
        m_nextpacket. Many parts of the stack do not properly handle chains
        of packets. When in doubt, don't chain packets.
 */

#ifndef __KPI_MBUF__
#define __KPI_MBUF__
#include <sys/kernel_types.h>
#include <mach/vm_types.h>

/*!
        @enum mbuf_flags_t
        @abstract Constants defining mbuf flags. Only the flags listed below
                can be set or retrieved.
        @constant MBUF_EXT Indicates this mbuf has external data.
        @constant MBUF_PKTHDR Indicates this mbuf has a packet header.
        @constant MBUF_EOR Indicates this mbuf is the end of a record.
        @constant MBUF_BCAST Indicates this packet will be sent or was
                received as a brodcast.
        @constant MBUF_MCAST Indicates this packet will be sent or was
                received as a multicast.
        @constant MBUF_FRAG Indicates this packet is a fragment of a larger
                packet.
        @constant MBUF_FIRSTFRAG Indicates this packet is the first fragment.
        @constant MBUF_LASTFRAG Indicates this packet is the last fragment.
        @constant MBUF_PROMISC Indicates this packet was only received
                because the interface is in promiscuous mode. This should be set
                by the demux function. These packets will be discarded after
                being passed to any interface filters.
*/
enum {
        MBUF_EXT                = 0x0001,       /* has associated external storage */
        MBUF_PKTHDR             = 0x0002,       /* start of record */
        MBUF_EOR                = 0x0004,       /* end of record */
        
        MBUF_BCAST              = 0x0100,       /* send/received as link-level broadcast */
        MBUF_MCAST              = 0x0200,       /* send/received as link-level multicast */
        MBUF_FRAG               = 0x0400,       /* packet is a fragment of a larger packet */
        MBUF_FIRSTFRAG  = 0x0800,       /* packet is first fragment */
        MBUF_LASTFRAG   = 0x1000,       /* packet is last fragment */
        MBUF_PROMISC    = 0x2000        /* packet is promiscuous */
};
typedef u_int32_t mbuf_flags_t;

/*!
        @enum mbuf_type_t
        @abstract Types of mbufs.
        @discussion Some mbufs represent packets, some represnt data waiting
                on sockets. Other mbufs store control data or other various
                structures. The mbuf type is used to store what sort of data the
                mbuf contains.
        @constant MBUF_MT_FREE Indicates the mbuf is free and is
                sitting on the queue of free mbufs. If you find that an mbuf you
                have a reference to has this type, something has gone terribly
                wrong.
        @constant MBUF_MT_DATA Indicates this mbuf is being used to store
                data.
        @constant MBUF_MT_HEADER Indicates this mbuf has a packet header,
                this is probably a packet.
        @constant MBUF_MT_SOCKET Socket structure.
        @constant MBUF_MT_PCB Protocol control block.
        @constant MBUF_MT_RTABLE Routing table entry.
        @constant MBUF_MT_HTABLE IMP host tables???.
        @constant MBUF_MT_ATABLE Address resolution table data.
        @constant MBUF_MT_SONAME Socket name, usually a sockaddr of some
                sort.
        @constant MBUF_MT_FTABLE Fragment reassembly header.
        @constant MBUF_MT_RIGHTS Access rights.
        @constant MBUF_MT_IFADDR Interface address.
        @constant MBUF_MT_CONTROL Extra-data protocol message (control
                message).
        @constant MBUF_MT_OOBDATA Out of band data.
*/
enum {
        MBUF_TYPE_FREE          = 0,    /* should be on free list */
        MBUF_TYPE_DATA          = 1,    /* dynamic (data) allocation */
        MBUF_TYPE_HEADER        = 2,    /* packet header */
        MBUF_TYPE_SOCKET        = 3,    /* socket structure */
        MBUF_TYPE_PCB           = 4,    /* protocol control block */
        MBUF_TYPE_RTABLE        = 5,    /* routing tables */
        MBUF_TYPE_HTABLE        = 6,    /* IMP host tables */
        MBUF_TYPE_ATABLE        = 7,    /* address resolution tables */ 
        MBUF_TYPE_SONAME        = 8,    /* socket name */
        MBUF_TYPE_SOOPTS        = 10,   /* socket options */
        MBUF_TYPE_FTABLE        = 11,   /* fragment reassembly header */
        MBUF_TYPE_RIGHTS        = 12,   /* access rights */
        MBUF_TYPE_IFADDR        = 13,   /* interface address */
        MBUF_TYPE_CONTROL       = 14,   /* extra-data protocol message */
        MBUF_TYPE_OOBDATA       = 15    /* expedited data  */
};
typedef u_int32_t mbuf_type_t;

/*!
        @enum mbuf_csum_request_flags_t
        @abstract Checksum performed/requested flags.
        @discussion Mbufs often contain packets. Some hardware supports
                performing checksums in hardware. The stack uses these flags to
                indicate to the driver what sort of checksumming should be
                handled in by the driver/hardware. These flags will only be set
                if the driver indicates that it supports the corresponding
                checksums using ifnet_set_offload.
        @constant MBUF_CSUM_REQ_IP Indicates the IP checksum has not been
                calculated yet.
        @constant MBUF_CSUM_REQ_TCP Indicates the TCP checksum has not been
                calculated yet.
        @constant MBUF_CSUM_REQ_UDP Indicates the UDP checksum has not been
                calculated yet.
*/
enum {
#ifdef KERNEL_PRIVATE
        MBUF_CSUM_REQ_SUM16     = 0x1000, /* Weird apple hardware checksum */
#endif KERNEL_PRIVATE
        MBUF_CSUM_REQ_IP        = 0x0001,
        MBUF_CSUM_REQ_TCP       = 0x0002,
        MBUF_CSUM_REQ_UDP       = 0x0004
};
typedef u_int32_t mbuf_csum_request_flags_t;

/*!
        @enum mbuf_csum_performed_flags_t
        @abstract Checksum performed/requested flags.
        @discussion Mbufs often contain packets. Some hardware supports
                performing checksums in hardware. The driver uses these flags to
                communicate to the stack the checksums that were calculated in
                hardware.
        @constant MBUF_CSUM_DID_IP Indicates that the driver/hardware verified
                the IP checksum in hardware.
        @constant MBUF_CSUM_IP_GOOD Indicates whether or not the IP checksum
                was good or bad. Only valid when MBUF_CSUM_DID_IP is set.
        @constant MBUF_CSUM_DID_DATA Indicates that the TCP or UDP checksum
                was calculated. The value for the checksum calculated in
                hardware should be passed as the second parameter of
                mbuf_set_csum_performed. The hardware calculated checksum value
                can be retrieved using the second parameter passed to
                mbuf_get_csum_performed.
        @constant MBUF_CSUM_PSEUDO_HDR If set, this indicates that the
                checksum value for MBUF_CSUM_DID_DATA includes the pseudo header
                value. If this is not set, the stack will calculate the pseudo
                header value and add that to the checksum. The value of this bit
                is only valid when MBUF_CSUM_DID_DATA is set.
*/
enum {
#ifdef KERNEL_PRIVATE
        MBUF_CSUM_TCP_SUM16             = MBUF_CSUM_REQ_SUM16,  /* Weird apple hardware checksum */
#endif
        MBUF_CSUM_DID_IP                = 0x0100,
        MBUF_CSUM_IP_GOOD               = 0x0200,
        MBUF_CSUM_DID_DATA              = 0x0400,
        MBUF_CSUM_PSEUDO_HDR    = 0x0800
};
typedef u_int32_t mbuf_csum_performed_flags_t;

/*!
        @enum mbuf_how_t
        @abstract Method of allocating an mbuf.
        @discussion Blocking will cause the funnel to be dropped. If the
                funnel is dropped, other threads may make changes to networking
                data structures. This can lead to very bad things happening.
                Blocking on the input our output path can also impact
                performance. There are some cases where making a blocking call
                is acceptable. When in doubt, use MBUF_DONTWAIT.
        @constant MBUF_WAITOK Allow a call to allocate an mbuf to block.
        @constant MBUF_DONTWAIT Don't allow the mbuf allocation call to
                block, if blocking is necessary fail and return immediately.
*/
enum {
        MBUF_WAITOK             = 0,    /* Ok to block to get memory */
        MBUF_DONTWAIT   = 1             /* Don't block, fail if blocking would be required */
};
typedef u_int32_t mbuf_how_t;

typedef u_int32_t mbuf_tag_id_t;
typedef u_int16_t mbuf_tag_type_t;

/*!
        @struct mbuf_stat
        @discussion The mbuf_stat contains mbuf statistics.
        @field mbufs Number of mbufs (free or otherwise).
        @field clusters Number of clusters (free or otherwise).
        @field clfree Number of free clusters.
        @field drops Number of times allocation failed.
        @field wait Number of times allocation blocked.
        @field drain Number of times protocol drain functions were called.
        @field mtypes An array of counts of each type of mbuf allocated.
        @field mcfail Number of times m_copym failed.
        @field mpfail Number of times m_pullup failed.
        @field msize Length of an mbuf.
        @field mclbytes Length of an mbuf cluster.
        @field minclsize Minimum length of data to allocate a cluster.
                Anything smaller than this should be placed in chained mbufs.
        @field mlen Length of data in an mbuf.
        @field mhlen Length of data in an mbuf with a packet header.
        @field bigclusters Number of big clusters.
        @field bigclfree Number of unused big clusters.
        @field bigmclbytes Length of a big mbuf cluster.
*/
struct mbuf_stat {
        u_long  mbufs;                  /* mbufs obtained from page pool */
        u_long  clusters;               /* clusters obtained from page pool */
        u_long  clfree;                 /* free clusters */
        u_long  drops;                  /* times failed to find space */
        u_long  wait;                   /* times waited for space */
        u_long  drain;                  /* times drained protocols for space */
        u_short mtypes[256];    /* type specific mbuf allocations */
        u_long  mcfail;                 /* times m_copym failed */
        u_long  mpfail;                 /* times m_pullup failed */
        u_long  msize;                  /* length of an mbuf */
        u_long  mclbytes;               /* length of an mbuf cluster */
        u_long  minclsize;              /* min length of data to allocate a cluster */
        u_long  mlen;                   /* length of data in an mbuf */
        u_long  mhlen;                  /* length of data in a header mbuf */
        u_long  bigclusters;    /* number of big clusters */
        u_long  bigclfree;              /* number of big clustser free */
        u_long  bigmclbytes;    /* length of data in a big cluster */
};

/* Parameter for m_copym to copy all bytes */
#define MBUF_COPYALL    1000000000

__BEGIN_DECLS
/* Data access */
/*!
        @function mbuf_data
        @discussion Returns a pointer to the start of data in this mbuf.
                There may be additional data on chained mbufs. The data you're
                looking for may not be virtually contiguous if it spans more
                than one mbuf.  In addition, data that is virtually contiguous
                might not be represented by physically contiguous pages; see
                further comments in mbuf_data_to_physical.  Use mbuf_len to
                determine the lenght of data available in this mbuf. If a data
                structure you want to access stradles two mbufs in a chain,
                either use mbuf_pullup to get the data contiguous in one mbuf
                or copy the pieces of data from each mbuf in to a contiguous
                buffer. Using mbuf_pullup has the advantage of not having to
                copy the data. On the other hand, if you don't make sure there
                is space in the mbuf, mbuf_pullup may fail and free the mbuf.
        @param mbuf The mbuf.
        @result A pointer to the data in the mbuf.
 */
void*           mbuf_data(mbuf_t mbuf);

/*!
        @function mbuf_datastart
        @discussion Returns the start of the space set aside for storing
                data in an mbuf. An mbuf's data may come from a cluster or be
                embedded in the mbuf structure itself. The data pointer
                retrieved by mbuf_data may not be at the start of the data
                (mbuf_leadingspace will be non-zero). This function will return to
                you a pointer that matches mbuf_data() - mbuf_leadingspace().
        @param mbuf The mbuf.
        @result A pointer to smallest possible value for data.
 */
void*           mbuf_datastart(mbuf_t mbuf);

/*!
        @function mbuf_setdata
        @discussion Sets the data and length values for an mbuf. The data
        value must be in a valid range. In the case of an mbuf with a cluster,
        the data value must point to a location in the cluster and the data
        value plus the length, must be less than the end of the cluster. For
        data embedded directly in an mbuf (no cluster), the data value must
        fall somewhere between the start and end of the data area in the
        mbuf and the data + length must also be in the same range.
        @param mbuf The mbuf.
        @param data The new pointer value for data.
        @param len The new length of data in the mbuf.
        @result 0 on success, errno error on failure.
 */
errno_t         mbuf_setdata(mbuf_t mbuf, void *data, size_t len);

/*!
        @function mbuf_align_32
        @discussion mbuf_align_32 is a replacement for M_ALIGN and MH_ALIGN.
                mbuf_align_32 will set the data pointer to a location aligned on
                a four byte boundry with at least 'len' bytes between the data
                pointer and the end of the data block.
        @param mbuf The mbuf.
        @param len The minimum length of space that should follow the new
                data location.
        @result 0 on success, errno error on failure.
 */
errno_t         mbuf_align_32(mbuf_t mbuf, size_t len);

/*!
        @function mbuf_data_to_physical
        @discussion mbuf_data_to_physical is a replacement for mcl_to_paddr.
                Given a pointer returned from mbuf_data of mbuf_datastart,
                mbuf_data_to_physical will return the phyical address for that
                block of data.  Note that even though the data is in virtually
                contiguous span, the underlying physical pages might not be
                physically contiguous.  Because of this, callers must ensure
                to call this routine for each page boundary.  Device drivers
                that deal with DMA are strongly encouraged to utilize the
                IOMbufNaturalMemoryCursor and walk down the list of vectors
                instead of using this interface to obtain the physical address.
                Use of this routine is therefore discouraged.
        @param ptr A pointer to data stored in an mbuf.
        @result The 64 bit physical address of the mbuf data or NULL if ptr
                does not point to data stored in an mbuf.
 */
addr64_t        mbuf_data_to_physical(void* ptr);


/* Allocation */

/*!
        @function mbuf_get
        @discussion Allocates an mbuf without a cluster for external data.
        @param how Blocking or non-blocking.
        @param type The type of the mbuf.
        @param mbuf The mbuf.
        @result 0 on success, errno error on failure.
 */
errno_t         mbuf_get(mbuf_how_t how, mbuf_type_t type, mbuf_t* mbuf);

/*!
        @function mbuf_gethdr
        @discussion Allocates an mbuf without a cluster for external data.
                Sets a flag to indicate there is a packet header and initializes
                the packet header.
        @param how Blocking or non-blocking.
        @param type The type of the mbuf.
        @param mbuf The mbuf.
        @result 0 on success, errno error on failure.
 */
errno_t         mbuf_gethdr(mbuf_how_t how, mbuf_type_t type, mbuf_t* mbuf);

/*!
        @function mbuf_attachcluster
        @discussion Attach an external buffer as a cluster for an mbuf.  If mbuf
                points to a NULL mbuf_t, an mbuf will be allocated for you.  If
                mbuf points to a non-NULL mbuf_t, the user-supplied mbuf will
                be used instead.  The caller is responsible for allocating the
                external buffer by calling mbuf_alloccluster().
        @param how Blocking or non-blocking.
        @param type The type of the mbuf if mbuf is non-NULL; otherwise ignored.
        @param mbuf Pointer to the address of the mbuf; if NULL, an mbuf will
                be allocated, otherwise, it must point to a valid mbuf address.
                If the user-supplied mbuf is already attached to a cluster, the
                current cluster will be freed before the mbuf gets attached to
                the supplied external buffer.  Note that this routine may return
                a different mbuf_t than the one you passed in.
        @param extbuf Address of the external buffer.
        @param extfree Free routine for the external buffer; the caller is
                required to defined a routine that will be invoked when the
                mbuf is freed.
        @param extsize Size of the external buffer.
        @param extarg Private value that will be passed to the free routine
                when it is called at the time the mbuf is freed.
        @result 0 on success
                EINVAL - Invalid parameter
                ENOMEM - Not enough memory available
 */
errno_t
mbuf_attachcluster(mbuf_how_t how, mbuf_type_t type, mbuf_t *mbuf,
    caddr_t extbuf, void (*extfree)(caddr_t , u_int, caddr_t),
    size_t extsize, caddr_t extarg);

/*!
        @function mbuf_alloccluster
        @discussion Allocate a cluster that can be later attached to an
                mbuf by calling mbuf_attachcluster().  The allocated cluster
                can also be freed (without being attached to an mbuf) by
                calling mbuf_freecluster().  At the moment this routine
                will either return a cluster of 2048, 4096 or 16384 bytes
                depending on the requested size.  Note that clusters greater
                than 4096 bytes might not be available in all configurations;
                the caller must additionally check for ENOTSUP (see below).
        @param how Blocking or non-blocking.
        @param size Pointer to size of requested cluster.  Sizes up to 2048
                will be rounded up to 2048; sizes greater than 2048 and up
                to 4096 will be rounded up to 4096.  Sizes greater than 4096
                will be rounded up to 16384.
        @param addr Pointer to the address of the requested cluster.
        @result 0 on success or ENOMEM if failure.  If the caller requests
                greater than 4096 bytes and the system is unable to fulfill
                the request due to the lack of jumbo clusters support based
                on the configuration, this routine will return ENOTSUP.
                In this case, the caller is advised to use 4096 bytes or
                smaller during subseqent requests.
 */
errno_t mbuf_alloccluster(mbuf_how_t how, size_t *size, caddr_t *addr);

/*!
        @function mbuf_freecluster
        @discussion Free a cluster that was previously allocated by a call
                to mbuf_alloccluster().  The caller must pass the actual
                size of the cluster as returned by mbuf_alloccluster(),
                which at this point must be either 2048, 4096 or 16384 bytes.
        @param addr The address of the cluster.
        @param size The actual size of the cluster.
 */
void mbuf_freecluster(caddr_t addr, size_t size);

/*!
        @function mbuf_getcluster
        @discussion Allocate a cluster of the requested size and attach it to
                an mbuf for use as external data. If mbuf points to a NULL
                mbuf_t, an mbuf will be allocated for you. If mbuf points to
                a non-NULL mbuf_t, mbuf_getcluster may return a different
                mbuf_t than the one you passed in.
        @param how Blocking or non-blocking.
        @param type The type of the mbuf.
        @param size The size of the cluster to be allocated. Supported sizes
                for a cluster are be 2048, 4096, or 16384. Any other value
                with return EINVAL.  Note that clusters greater than 4096
                bytes might not be available in all configurations; the
                caller must additionally check for ENOTSUP (see below).
        @param mbuf The mbuf the cluster will be attached to.
        @result 0 on success, errno error on failure. If you specified NULL
                for the mbuf, any intermediate mbuf that may have been allocated
                will be freed. If you specify an mbuf value in *mbuf,
                mbuf_mclget will not free it.
                EINVAL - Invalid parameter
                ENOMEM - Not enough memory available
                ENOTSUP - The caller had requested greater than 4096 bytes
                    cluster and the system is unable to fulfill it due to the
                    lack of jumbo clusters support based on the configuration.
                    In this case, the caller is advised to use 4096 bytes or
                    smaller during subsequent requests.
 */
errno_t         mbuf_getcluster(mbuf_how_t how, mbuf_type_t type, size_t size, mbuf_t* mbuf);

/*!
        @function mbuf_mclget
        @discussion Allocate a cluster and attach it to an mbuf for use as
                external data. If mbuf points to a NULL mbuf_t, an mbuf will be
                allocated for you. If mbuf points to a non-NULL mbuf_t,
                mbuf_mclget may return a different mbuf_t than the one you
                passed in.
        @param how Blocking or non-blocking.
        @param type The type of the mbuf.
        @param mbuf The mbuf the cluster will be attached to.
        @result 0 on success, errno error on failure. If you specified NULL
                for the mbuf, any intermediate mbuf that may have been allocated
                will be freed. If you specify an mbuf value in *mbuf,
                mbuf_mclget will not free it.
 */
errno_t         mbuf_mclget(mbuf_how_t how, mbuf_type_t type, mbuf_t* mbuf);

/*!
        @function mbuf_allocpacket
        @discussion Allocate an mbuf chain to store a single packet of the
                requested length.  According to the requested length, a chain
                of mbufs will be created. The mbuf type will be set to
                MBUF_TYPE_DATA. The caller may specify the maximum number of
                buffer.
        @param how Blocking or non-blocking
        @param packetlen The total length of the packet mbuf to be allocated.
                The length must be greater than zero.
        @param maxchunks An input/output pointer to the maximum number of mbufs
                segments making up the chain.  On input, if maxchunks is NULL,
                or the value pointed to by maxchunks is zero, the packet will
                be made up of as few or as many buffer segments as necessary
                to fit the length.  The allocation will fail with ENOBUFS if
                the number of segments requested is too small and the sum of
                the maximum size of each individual segment is less than the
                packet length.  On output, if the allocation succeed and
                maxchunks is non-NULL, it will point to the actual number
                of segments allocated.
                Additional notes for packetlen greater than 4096 bytes:
                the caller may pass a non-NULL maxchunks and initialize it
                with zero such that upon success, it can find out whether
                or not the system configuration allows for larger than
                4096 bytes cluster allocations, by checking on the value
                pointed to by maxchunks.  E.g. a request for 9018 bytes may
                result in 1 chunk when jumbo clusters are available, or
                3 chunks otherwise.
        @param Upon success, *mbuf will be a reference to the new mbuf.
        @result Returns 0 upon success or the following error code:
                EINVAL - Invalid parameter
                ENOMEM - Not enough memory available
                ENOBUFS - Buffers not big enough for the maximum number of
                    chunks requested
*/
errno_t mbuf_allocpacket(mbuf_how_t how, size_t packetlen, unsigned int * maxchunks, mbuf_t *mbuf);

/*!
        @function mbuf_allocpacket_list
        @discussion Allocate a linked list of packets.  According to the
                requested length, each packet will made of a chain of one
                or more mbufs.  The mbuf type will be set to MBUF_TYPE_DATA.
                The caller may specify the maximum number of element for
                each mbuf chain making up a packet.
        @param numpkts Number of packets to allocate
        @param how Blocking or non-blocking
        @param packetlen The total length of the packet mbuf to be allocated.
                The length must be greater than zero.
        @param maxchunks An input/output pointer to the maximum number of
                mbufs segments making up the chain.  On input, if maxchunks is
                zero, or the value pointed to by maxchunks is zero, the packet
                will be made of as few or as many buffer segments as necessary
                to fit the length.  The allocation will fail with ENOBUFS if
                the number of segments requested is too small and the sum of
                the maximum size of each individual segment is less than the
                packet length.  On output, if the allocation succeed and
                maxchunks is non zero, it will point to the actual number
                of segments allocated.
                Additional notes for packetlen greater than 4096 bytes:
                the caller may pass a non-NULL maxchunks and initialize it
                with zero such that upon success, it can find out whether
                or not the system configuration allows for larger than
                4096 bytes cluster allocations, by checking on the value
                pointed to by maxchunks.  E.g. a request for 9018 bytes may
                result in 1 chunk when jumbo clusters are available, or
                3 chunks otherwise.
        @param Upon success, *mbuf will be a reference to the new mbuf.
        @result Returns 0 upon success or the following error code:
                EINVAL - Invalid parameter
                ENOMEM - Not enough memory available
                ENOBUFS - Buffers not big enough for the maximum number of
                    chunks requested
*/
errno_t mbuf_allocpacket_list(unsigned int numpkts, mbuf_how_t how, size_t packetlen, unsigned int * maxchunks, mbuf_t *mbuf);


/*!
        @function mbuf_getpacket
        @discussion Allocate an mbuf, allocate and attach a cluster, and set
                the packet header flag.
        @param how Blocking or non-blocking.
        @param mbuf Upon success, *mbuf will be a reference to the new mbuf.
        @result 0 on success, errno error on failure.
 */
errno_t         mbuf_getpacket(mbuf_how_t how, mbuf_t* mbuf);

/*!
        @function mbuf_free
        @discussion Frees a single mbuf. Not commonly used because it
                doesn't touch the rest of the mbufs on the chain.
        @param mbuf The mbuf to free.
        @result The next mbuf in the chain.
 */
mbuf_t          mbuf_free(mbuf_t mbuf);

/*!
        @function mbuf_freem
        @discussion Frees a chain of mbufs link through mnext.
        @param mbuf The first mbuf in the chain to free.
 */
void            mbuf_freem(mbuf_t mbuf);

/*!
        @function mbuf_freem_list
        @discussion Frees linked list of mbuf chains. Walks through
                mnextpackt and does the equivalent of mbuf_freem to each.
        @param mbuf The first mbuf in the linked list to free.
        @result The number of mbufs freed.
 */
int                     mbuf_freem_list(mbuf_t mbuf);

/*!
        @function mbuf_leadingspace
        @discussion Determines the space available in the mbuf proceeding
                the current data.
        @param mbuf The mbuf.
        @result The number of unused bytes at the start of the mbuf.
 */
size_t          mbuf_leadingspace(const mbuf_t mbuf);

/*!
        @function mbuf_trailingspace
        @discussion Determines the space available in the mbuf following
                the current data.
        @param mbuf The mbuf.
        @result The number of unused bytes following the current data.
 */
size_t          mbuf_trailingspace(const mbuf_t mbuf);

/* Manipulation */

/*!
        @function mbuf_copym
        @discussion Copies len bytes from offset from src to a new mbuf.  If
            the original mbuf contains a packet header, the new mbuf will
            contain similar packet header except for any tags which may be
            associated with the original mbuf.  mbuf_dup() should be used
            instead if tags are to be copied to the new mbuf.
        @param src The source mbuf.
        @param offset The offset in the mbuf to start copying from.
        @param len The the number of bytes to copy.
        @param how To block or not to block, that is a question.
        @param new_mbuf Upon success, the newly allocated mbuf.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_copym(const mbuf_t src, size_t offset, size_t len,
                                                mbuf_how_t how, mbuf_t* new_mbuf);

/*!
        @function mbuf_dup
        @discussion Exactly duplicates an mbuf chain.  If the original mbuf
            contains a packet header (including tags), the new mbuf will have
            the same packet header contents and a copy of each tag associated
            with the original mbuf.
        @param src The source mbuf.
        @param how Blocking or non-blocking.
        @param new_mbuf Upon success, the newly allocated mbuf.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_dup(const mbuf_t src, mbuf_how_t how, mbuf_t* new_mbuf);

/*!
        @function mbuf_prepend
        @discussion Prepend len bytes to an mbuf. If there is space
                (mbuf_leadingspace >= len), the mbuf's data ptr is changed and
                the same mbuf is returned. If there is no space, a new mbuf may
                be allocated and prepended to the mbuf chain. If the operation
                fails, the mbuf may be freed (*mbuf will be NULL).
        @param mbuf The mbuf to prepend data to. This may change if a new
                mbuf must be allocated or may be NULL if the operation fails.
        @param len The length, in bytes, to be prepended to the mbuf.
        @param how Blocking or non-blocking.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_prepend(mbuf_t* mbuf, size_t len, mbuf_how_t how);

/*!
        @function mbuf_split
        @discussion Split an mbuf chain at a specific offset.
        @param src The mbuf to be split.
        @param offset The offset in the buffer where the mbuf should be
                split.
        @param how Blocking or non-blocking.
        @param new_mbuf Upon success, the second half of the split mbuf
                chain.
        @result 0 upon success otherwise the errno error. In the case of
                failure, the original mbuf chain passed in to src will be
                preserved.
 */
errno_t         mbuf_split(mbuf_t src, size_t offset,
                                                mbuf_how_t how, mbuf_t* new_mbuf);

/*!
        @function mbuf_pullup
        @discussion Move the next len bytes in to mbuf from other mbufs in
                the chain. This is commonly used to get the IP and TCP or UDP
                header contiguous in the first mbuf. If mbuf_pullup fails, the
                entire mbuf chain will be freed.
        @param mbuf The mbuf in the chain the data should be contiguous in.
        @param len The number of bytes to pull from the next mbuf(s).
        @result 0 upon success otherwise the errno error. In the case of an
                error, the mbuf chain has been freed.
 */
errno_t         mbuf_pullup(mbuf_t* mbuf, size_t len);

/*!
        @function mbuf_pulldown
        @discussion Make length bytes at offset in the mbuf chain
                contiguous. Nothing before offset bytes in the chain will be
                modified. Upon return, location will be the mbuf the data is
                contiguous in and offset will be the offset in that mbuf at
                which the data is located.  In the case of a failure, the mbuf
                chain will be freed.
        @param src The start of the mbuf chain.
        @param offset Pass in a pointer to a value with the offset of the
                data you're interested in making contiguous. Upon success, this
                will be overwritten with the offset from the mbuf returned in
                location.
        @param length The length of data that should be made contiguous.
        @param location Upon success, *location will be the mbuf the data is
                in.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_pulldown(mbuf_t src, size_t *offset, size_t length, mbuf_t *location);

/*!
        @function mbuf_adj
        @discussion Trims len bytes from the mbuf. If the length is greater
                than zero, the bytes are trimmed from the front of the mbuf. If
                the length is less than zero, the bytes are trimmed from the end
                of the mbuf chain.
        @param mbuf The mbuf chain to trim.
        @param len The number of bytes to trim from the mbuf chain.
 */
void            mbuf_adj(mbuf_t mbuf, int len);

/*!
        @function mbuf_adjustlen
        @discussion Adds amount to the mbuf len. Verifies that the new
                length is valid (greater than or equal to zero and less than
                maximum amount of data that may be stored in the mbuf). This
                function will not adjust the packet header length field or
                affect any other mbufs in a chain.
        @param mbuf The mbuf to adjust.
        @param amount The number of bytes increment the length by.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_adjustlen(mbuf_t mbuf, int amount);

/*!
        @function mbuf_copydata
        @discussion Copies data out of an mbuf in to a specified buffer. If
                the data is stored in a chain of mbufs, the data will be copied
                from each mbuf in the chain until length bytes have been copied.
        @param mbuf The mbuf chain to copy data out of.
        @param offset The offset in to the mbuf to start copying.
        @param length The number of bytes to copy.
        @param out_data A pointer to the location where the data will be
                copied.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_copydata(const mbuf_t mbuf, size_t offset, size_t length, void* out_data);

/*!
        @function mbuf_copyback
        @discussion Copies data from a buffer to an mbuf chain.
                mbuf_copyback will grow the chain to fit the specified buffer.
                
                If mbuf_copydata is unable to allocate enough mbufs to grow the
                chain, ENOBUFS will be returned. The mbuf chain will be shorter
                than expected but all of the data up to the end of the mbuf
                chain will be valid.
                
                If an offset is specified, mbuf_copyback will skip that many
                bytes in the mbuf chain before starting to write the buffer in
                to the chain. If the mbuf chain does not contain this many
                bytes, mbufs will be allocated to create the space.
        @param mbuf The first mbuf in the chain to copy the data in to.
        @param offset Offset in bytes to skip before copying data.
        @param length The length, in bytes, of the data to copy in to the mbuf
                chain.
        @param data A pointer to data in the kernel's address space.
        @param how Blocking or non-blocking.
        @result 0 upon success, EINVAL or ENOBUFS upon failure.
 */
errno_t         mbuf_copyback(mbuf_t mbuf, size_t offset, size_t length,
                                                  const void *data, mbuf_how_t how);

/*!
        @function mbuf_mclhasreference
        @discussion Check if a cluster of an mbuf is referenced by another mbuf.
                References may be taken, for example, as a result of a call to 
                mbuf_split or mbuf_copym
        @param mbuf The mbuf with the cluster to test.
        @result 0 if there is no reference by another mbuf, 1 otherwise.
 */
int                     mbuf_mclhasreference(mbuf_t mbuf);


/* mbuf header */

/*!
        @function mbuf_next
        @discussion Returns the next mbuf in the chain.
        @param mbuf The mbuf.
        @result The next mbuf in the chain.
 */
mbuf_t          mbuf_next(const mbuf_t mbuf);

/*!
        @function mbuf_setnext
        @discussion Sets the next mbuf in the chain.
        @param mbuf The mbuf.
        @param next The new next mbuf.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_setnext(mbuf_t mbuf, mbuf_t next);

/*!
        @function mbuf_nextpkt
        @discussion Gets the next packet from the mbuf.
        @param mbuf The mbuf.
        @result The nextpkt.
 */
mbuf_t          mbuf_nextpkt(const mbuf_t mbuf);

/*!
        @function mbuf_setnextpkt
        @discussion Sets the next packet attached to this mbuf.
        @param mbuf The mbuf.
        @param nextpkt The new next packet.
 */
void            mbuf_setnextpkt(mbuf_t mbuf, mbuf_t nextpkt);

/*!
        @function mbuf_len
        @discussion Gets the length of data in this mbuf.
        @param mbuf The mbuf.
        @result The length.
 */
size_t          mbuf_len(const mbuf_t mbuf);

/*!
        @function mbuf_setlen
        @discussion Sets the length of data in this packet. Be careful to
                not set the length over the space available in the mbuf.
        @param mbuf The mbuf.
        @param len The new length.
        @result 0 upon success otherwise the errno error.
 */
void            mbuf_setlen(mbuf_t mbuf, size_t len);

/*!
        @function mbuf_maxlen
        @discussion Retrieves the maximum length of data that may be stored
                in this mbuf. This value assumes that the data pointer was set
                to the start of the possible range for that pointer
                (mbuf_data_start).
        @param mbuf The mbuf.
        @result The maximum lenght of data for this mbuf.
 */
size_t          mbuf_maxlen(const mbuf_t mbuf);

/*!
        @function mbuf_type
        @discussion Gets the type of mbuf.
        @param mbuf The mbuf.
        @result The type.
 */
mbuf_type_t     mbuf_type(const mbuf_t mbuf);

/*!
        @function mbuf_settype
        @discussion Sets the type of mbuf.
        @param mbuf The mbuf.
        @param new_type The new type.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_settype(mbuf_t mbuf, mbuf_type_t new_type);

/*!
        @function mbuf_flags
        @discussion Returns the set flags.
        @param mbuf The mbuf.
        @result The flags.
 */
mbuf_flags_t    mbuf_flags(const mbuf_t mbuf);

/*!
        @function mbuf_setflags
        @discussion Sets the set of set flags.
        @param mbuf The mbuf.
        @param flags The flags that should be set, all other flags will be cleared.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_setflags(mbuf_t mbuf, mbuf_flags_t flags);

/*!
        @function mbuf_setflags_mask
        @discussion Useful for setting or clearing individual flags. Easier
                than calling mbuf_setflags(m, mbuf_flags(m) | M_FLAG).
        @param mbuf The mbuf.
        @param flags The flags that should be set or cleared.
        @param mask The mask controlling which flags will be modified.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_setflags_mask(mbuf_t mbuf, mbuf_flags_t flags,
                                                           mbuf_flags_t mask);

/*!
        @function mbuf_copy_pkthdr
        @discussion Copies the packet header from src to dest.
        @param src The mbuf from which the packet header will be copied.
        @param mbuf The mbuf to which the packet header will be copied.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_copy_pkthdr(mbuf_t dest, const mbuf_t src);

/*!
        @function mbuf_pkthdr_len
        @discussion Returns the length as reported by the packet header.
        @param mbuf The mbuf containing the packet header with the length to
                be changed.
        @result The length, in bytes, of the packet.
 */
size_t          mbuf_pkthdr_len(const mbuf_t mbuf);

/*!
        @function mbuf_pkthdr_setlen
        @discussion Sets the length of the packet in the packet header.
        @param mbuf The mbuf containing the packet header.
        @param len The new length of the packet.
 */
void            mbuf_pkthdr_setlen(mbuf_t mbuf, size_t len);

/*!
        @function mbuf_pkthdr_adjustlen
        @discussion Adjusts the length of the packet in the packet header.
        @param mbuf The mbuf containing the packet header.
        @param amount The number of bytes to adjust the packet header length
                field by.
 */
void            mbuf_pkthdr_adjustlen(mbuf_t mbuf, int amount);

/*!
        @function mbuf_pkthdr_rcvif
        @discussion Returns the interface the packet was received on. This
                funciton does not modify the reference count of the interface.
                The interface is only valid for as long as the mbuf is not freed
                and the rcvif for the mbuf is not changed. Take a reference on
                the interface that you will release later before doing any of
                the following: free the mbuf, change the rcvif, pass the mbuf to
                any function that may free the mbuf or change the rcvif.
        @param mbuf The mbuf containing the packet header.
        @result A reference to the interface.
 */
ifnet_t         mbuf_pkthdr_rcvif(const mbuf_t mbuf);

/*!
        @function mbuf_pkthdr_setrcvif
        @discussion Sets the interface the packet was received on.
        @param mbuf The mbuf containing the packet header.
        @param ifnet A reference to an interface.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_pkthdr_setrcvif(mbuf_t mbuf, ifnet_t ifp);

/*!
        @function mbuf_pkthdr_header
        @discussion Returns a pointer to the packet header.
        @param mbuf The mbuf containing the packet header.
        @result A pointer to the packet header.
 */
void*           mbuf_pkthdr_header(const mbuf_t mbuf);

/*!
        @function mbuf_pkthdr_setheader
        @discussion Sets the pointer to the packet header.
        @param mbuf The mbuf containing the packet header.
        @param ifnet A pointer to the header.
        @result 0 upon success otherwise the errno error.
 */
void            mbuf_pkthdr_setheader(mbuf_t mbuf, void* header);

/* Checksums */

/*!
        @function mbuf_inbound_modified
        @discussion This function will clear the checksum flags to indicate
                that a hardware checksum should not be used. Any filter
                modifying data should call this function on an mbuf before
                passing the packet up the stack. If a filter modifies a packet
                in a way that affects any checksum, the filter is responsible
                for either modifying the checksum to compensate for the changes
                or verifying the checksum before making the changes and then
                modifying the data and calculating a new checksum only if the
                original checksum was valid.
        @param mbuf The mbuf that has been modified.
 */
void            mbuf_inbound_modified(mbuf_t mbuf);

/*!
        @function mbuf_outbound_finalize
        @discussion This function will "finalize" the packet allowing your
                code to inspect the final packet.
                
                There are a number of operations that are performed in hardware,
                such as calculating checksums. This function will perform in
                software the various opterations that were scheduled to be done
                in hardware. Future operations may include IPSec processing or
                vlan support. If you are redirecting a packet to a new interface
                which may not have the same hardware support or encapsulating
                the packet, you should call this function to force the stack to
                calculate and fill out the checksums. This will bypass hardware
                checksums but give you a complete packet to work with. If you
                need to inspect aspects of the packet which may be generated by
                hardware, you must call this function to get an aproximate final
                packet. If you plan to modify the packet in any way, you should
                call this function.
                
                This function should be called before modifying any outbound
                packets.
                
                This function may be called at various levels, in some cases
                additional headers may have already been prepended, such as the
                case of a packet seen by an interface filter. To handle this,
                the caller must pass the protocol family of the packet as well
                as the offset from the start of the packet to the protocol
                header.
        @param mbuf The mbuf that should be finalized.
        @param protocol_family The protocol family of the packet in the
                mbuf.
        @param protocol_offset The offset from the start of the mbuf to the
                protocol header. For an IP packet with an ethernet header, this
                would be the length of an ethernet header.
 */
void            mbuf_outbound_finalize(mbuf_t mbuf, u_long protocol_family,
                                size_t protocol_offset);

/*!
        @function mbuf_set_vlan_tag
        @discussion This function is used by interfaces that support vlan
                tagging in hardware. This function will set properties in the
                mbuf to indicate which vlan the packet was received for.
        @param mbuf The mbuf containing the packet.
        @param vlan The protocol family of the aux data to add.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_set_vlan_tag(mbuf_t mbuf, u_int16_t vlan);

/*!
        @function mbuf_get_vlan_tag
        @discussion This function is used by drivers that support hardware
                vlan tagging to determine which vlan this packet belongs to. To
                differentiate between the case where the vlan tag is zero and
                the case where there is no vlan tag, this function will return
                ENXIO when there is no vlan.
        @param mbuf The mbuf containing the packet.
        @param vlan The protocol family of the aux data to add.
        @result 0 upon success otherwise the errno error. ENXIO indicates
                that the vlan tag is not set.
 */
errno_t         mbuf_get_vlan_tag(mbuf_t mbuf, u_int16_t *vlan);

/*!
        @function mbuf_clear_vlan_tag
        @discussion This function will clear any vlan tag associated with
                the mbuf.
        @param mbuf The mbuf containing the packet.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_clear_vlan_tag(mbuf_t mbuf);

#ifdef KERNEL_PRIVATE
/*
        @function mbuf_set_csum_requested
        @discussion This function is used by the stack to indicate which
                checksums should be calculated in hardware. The stack normally
                sets these flags as the packet is processed in the outbound
                direction. Just before send the packe to the interface, the
                stack will look at these flags and perform any checksums in
                software that are not supported by the interface.
        @param mbuf The mbuf containing the packet.
        @param request Flags indicating which checksums are being requested
                for this packet.
        @param value This parameter is currently unsupported.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_set_csum_requested(mbuf_t mbuf,
                                mbuf_csum_request_flags_t request, u_int32_t value);
#endif

/*!
        @function mbuf_get_csum_requested
        @discussion This function is used by the driver to determine which
                checksum operations should be performed in hardware.
        @param mbuf The mbuf containing the packet.
        @param request Flags indicating which checksums are being requested
                for this packet.
        @param value This parameter is currently unsupported.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_get_csum_requested(mbuf_t mbuf,
                                mbuf_csum_request_flags_t *request, u_int32_t *value);

/*!
        @function mbuf_clear_csum_requested
        @discussion This function clears the checksum request flags.
        @param mbuf The mbuf containing the packet.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_clear_csum_requested(mbuf_t mbuf);

/*!
        @function mbuf_set_csum_performed
        @discussion This is used by the driver to indicate to the stack which
                checksum operations were performed in hardware.
        @param mbuf The mbuf containing the packet.
        @param flags Flags indicating which hardware checksum operations
                were performed.
        @param value If the MBUF_CSUM_DID_DATA flag is set, value should be
                set to the value of the TCP or UDP header as calculated by the
                hardware.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_set_csum_performed(mbuf_t mbuf,
                                mbuf_csum_performed_flags_t flags, u_int32_t value);

#ifdef KERNEL_PRIVATE
/*
        @function mbuf_get_csum_performed
        @discussion This is used by the stack to determine which checksums
                were calculated in hardware on the inbound path.
        @param mbuf The mbuf containing the packet.
        @param flags Flags indicating which hardware checksum operations
                were performed.
        @param value If the MBUF_CSUM_DID_DATA flag is set, value will be
                set to the value of the TCP or UDP header as calculated by the
                hardware.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_get_csum_performed(mbuf_t mbuf,
                                mbuf_csum_performed_flags_t *flags, u_int32_t *value);
#endif

/*!
        @function mbuf_clear_csum_performed
        @discussion Clears the hardware checksum flags and values.
        @param mbuf The mbuf containing the packet.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_clear_csum_performed(mbuf_t mbuf);

/*!
        @function mbuf_inet_cksum
        @discussions Calculates 16-bit 1's complement Internet checksum of the
                transport segment with or without the pseudo header checksum
                of a given IPv4 packet.  If the caller specifies a non-zero
                transport protocol, the checksum returned will also include
                the pseudo header checksum for the corresponding transport
                header.  Otherwise, no header parsing will be done and the
                caller may use this to calculate the Internet checksum of
                an arbitrary span of data.

                This routine does not modify the contents of the packet.  If
                the caller specifies a non-zero protocol and/or offset, the
                routine expects the complete protocol header to be present
                at the beginning of the first mbuf.
        @param mbuf The mbuf (or chain of mbufs) containing the packet.
        @param protocol A zero or non-zero value.  A non-zero value specifies
                the transport protocol used for pseudo header checksum.
        @param offset A zero or non-zero value; if the latter, it specifies
                the offset of the transport header from the beginning of mbuf.
        @param length The total (non-zero) length of the transport segment.
        @param csum Pointer to the checksum variable; upon success, this
                routine will return the calculated Internet checksum through
                this variable.  The caller must set it to a non-NULL value.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_inet_cksum(mbuf_t mbuf, int protocol, u_int32_t offset,
                    u_int32_t length, u_int16_t *csum);

/*!
        @function mbuf_inet6_cksum
        @discussions Calculates 16-bit 1's complement Internet checksum of the
                transport segment with or without the pseudo header checksum
                of a given IPv6 packet.  If the caller specifies a non-zero
                transport protocol, the checksum returned will also include
                the pseudo header checksum for the corresponding transport
                header.  Otherwise, no header parsing will be done and the
                caller may use this to calculate the Internet checksum of
                an arbitrary span of data.

                This routine does not modify the contents of the packet.  If
                the caller specifies a non-zero protocol and/or offset, the
                routine expects the complete protocol header(s) to be present
                at the beginning of the first mbuf.
        @param mbuf The mbuf (or chain of mbufs) containing the packet.
        @param protocol A zero or non-zero value.  A non-zero value specifies
                the transport protocol used for pseudo header checksum.
        @param offset A zero or non-zero value; if the latter, it specifies
                the offset of the transport header from the beginning of mbuf.
        @param length The total (non-zero) length of the transport segment.
        @param csum Pointer to the checksum variable; upon success, this
                routine will return the calculated Internet checksum through
                this variable.  The caller must set it to a non-NULL value.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_inet6_cksum(mbuf_t mbuf, int protocol, u_int32_t offset,
                    u_int32_t length, u_int16_t *csum);

/* mbuf tags */

/*!
        @function mbuf_tag_id_find
        @discussion Lookup the module id for a string. If there is no module
                id assigned to this string, a new module id will be assigned.
                The string should be the bundle id of the kext. In the case of a
                tag that will be shared across multiple kexts, a common bundle id
                style string should be used.
                
                The lookup operation is not optimized. A module should call this
                function once during startup and chache the module id. The module id
                will not be resassigned until the machine reboots.
        @param module_string A unique string identifying your module.
                Example: com.apple.nke.SharedIP.
        @param module_id Upon return, a unique identifier for use with
                mbuf_tag_* functions. This identifier is valid until the machine
                is rebooted.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_tag_id_find(const char *module_string,
                                                         mbuf_tag_id_t *module_id);

/*!
        @function mbuf_tag_allocate
        @discussion Allocate an mbuf tag. Mbuf tags allow various portions
                of the stack to tag mbufs with data that will travel with the
                mbuf through the stack.
                
                Tags may only be added to mbufs with packet headers 
                (MBUF_PKTHDR flag is set). Mbuf tags are freed when the mbuf is
                freed or when mbuf_tag_free is called.
        @param mbuf The mbuf to attach this tag to.
        @param module_id A module identifier returned by mbuf_tag_id_find.
        @param type A 16 bit type value. For a given module_id, you can use
                a number of different tag types.
        @param length The length, in bytes, to allocate for storage that
                will be associated with this tag on this mbuf.
        @param how Indicate whether you want to block and wait for memory if
                memory is not immediately available.
        @param data_p Upon successful return, *data_p will point to the
                buffer allocated for the mtag.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_tag_allocate(mbuf_t mbuf, mbuf_tag_id_t module_id,
                                                          mbuf_tag_type_t type, size_t length,
                                                          mbuf_how_t how, void** data_p);

/*!
        @function mbuf_tag_find
        @discussion Find the data associated with an mbuf tag.
        @param mbuf The mbuf the tag is attached to.
        @param module_id A module identifier returned by mbuf_tag_id_find.
        @param type The 16 bit type of the tag to find.
        @param length Upon success, the length of data will be store in
                *length.
        @param data_p Upon successful return, *data_p will point to the
                buffer allocated for the mtag.
        @result 0 upon success otherwise the errno error.
 */
errno_t         mbuf_tag_find(mbuf_t mbuf, mbuf_tag_id_t module_id,
                                                  mbuf_tag_type_t type, size_t *length, void** data_p);

/*!
        @function mbuf_tag_free
        @discussion Frees a previously allocated mbuf tag.
        @param mbuf The mbuf the tag was allocated on.
        @param module_id The ID of the tag to free.
        @param type The type of the tag to free.
 */
void            mbuf_tag_free(mbuf_t mbuf, mbuf_tag_id_t module_id,
                                                  mbuf_tag_type_t type);

/* mbuf stats */

/*!
        @function mbuf_stats
        @discussion Get the mbuf statistics.
        @param stats Storage to copy the stats in to.
 */
void            mbuf_stats(struct mbuf_stat* stats);



/* IF_QUEUE interaction */

#define IF_ENQUEUE_MBUF(ifq, m) { \
        mbuf_setnextpkt((m), 0); \
        if ((ifq)->ifq_tail == 0) \
                (ifq)->ifq_head = (m); \
        else \
                mbuf_setnextpkt((mbuf_t)(ifq)->ifq_tail, (m)); \
        (ifq)->ifq_tail = (m); \
        (ifq)->ifq_len++; \
}
#define IF_PREPEND_MBUF(ifq, m) { \
        mbuf_setnextpkt((m), (ifq)->ifq_head); \
        if ((ifq)->ifq_tail == 0) \
                (ifq)->ifq_tail = (m); \
        (ifq)->ifq_head = (m); \
        (ifq)->ifq_len++; \
}
#define IF_DEQUEUE_MBUF(ifq, m) { \
        (m) = (ifq)->ifq_head; \
        if (m) { \
                if (((ifq)->ifq_head = mbuf_nextpkt((m))) == 0) \
                        (ifq)->ifq_tail = 0; \
                mbuf_setnextpkt((m), 0); \
                (ifq)->ifq_len--; \
        } \
}

__END_DECLS
#endif