mbuf: add functions to dump offload flags

[dpdk.git] / lib / librte_mbuf / rte_mbuf.h

/*-
 *   BSD LICENSE
 *
 *   Copyright(c) 2010-2014 Intel Corporation. All rights reserved.
 *   Copyright 2014 6WIND S.A.
 *   All rights reserved.
 *
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 *
 *     * Redistributions of source code must retain the above copyright
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 *       distribution.
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 *       from this software without specific prior written permission.
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#ifndef _RTE_MBUF_H_
#define _RTE_MBUF_H_

/**
 * @file
 * RTE Mbuf
 *
 * The mbuf library provides the ability to create and destroy buffers
 * that may be used by the RTE application to store message
 * buffers. The message buffers are stored in a mempool, using the
 * RTE mempool library.
 *
 * This library provide an API to allocate/free packet mbufs, which are
 * used to carry network packets.
 *
 * To understand the concepts of packet buffers or mbufs, you
 * should read "TCP/IP Illustrated, Volume 2: The Implementation,
 * Addison-Wesley, 1995, ISBN 0-201-63354-X from Richard Stevens"
 * http://www.kohala.com/start/tcpipiv2.html
 */

#include <stdint.h>
#include <rte_common.h>
#include <rte_mempool.h>
#include <rte_memory.h>
#include <rte_atomic.h>
#include <rte_prefetch.h>
#include <rte_branch_prediction.h>
#include <rte_mbuf_ptype.h>

#ifdef __cplusplus
extern "C" {
#endif

/*
 * Packet Offload Features Flags. It also carry packet type information.
 * Critical resources. Both rx/tx shared these bits. Be cautious on any change
 *
 * - RX flags start at bit position zero, and get added to the left of previous
 *   flags.
 * - The most-significant 3 bits are reserved for generic mbuf flags
 * - TX flags therefore start at bit position 60 (i.e. 63-3), and new flags get
 *   added to the right of the previously defined flags i.e. they should count
 *   downwards, not upwards.
 *
 * Keep these flags synchronized with rte_get_rx_ol_flag_name() and
 * rte_get_tx_ol_flag_name().
 */

/**
 * RX packet is a 802.1q VLAN packet. This flag was set by PMDs when
 * the packet is recognized as a VLAN, but the behavior between PMDs
 * was not the same. This flag is kept for some time to avoid breaking
 * applications and should be replaced by PKT_RX_VLAN_STRIPPED.
 */
#define PKT_RX_VLAN_PKT      (1ULL << 0)

#define PKT_RX_RSS_HASH      (1ULL << 1)  /**< RX packet with RSS hash result. */
#define PKT_RX_FDIR          (1ULL << 2)  /**< RX packet with FDIR match indicate. */
#define PKT_RX_L4_CKSUM_BAD  (1ULL << 3)  /**< L4 cksum of RX pkt. is not OK. */
#define PKT_RX_IP_CKSUM_BAD  (1ULL << 4)  /**< IP cksum of RX pkt. is not OK. */
#define PKT_RX_EIP_CKSUM_BAD (1ULL << 5)  /**< External IP header checksum error. */

/**
 * A vlan has been stripped by the hardware and its tci is saved in
 * mbuf->vlan_tci. This can only happen if vlan stripping is enabled
 * in the RX configuration of the PMD.
 */
#define PKT_RX_VLAN_STRIPPED (1ULL << 6)

/* hole, some bits can be reused here  */

#define PKT_RX_IEEE1588_PTP  (1ULL << 9)  /**< RX IEEE1588 L2 Ethernet PT Packet. */
#define PKT_RX_IEEE1588_TMST (1ULL << 10) /**< RX IEEE1588 L2/L4 timestamped packet.*/
#define PKT_RX_FDIR_ID       (1ULL << 13) /**< FD id reported if FDIR match. */
#define PKT_RX_FDIR_FLX      (1ULL << 14) /**< Flexible bytes reported if FDIR match. */

/**
 * The 2 vlans have been stripped by the hardware and their tci are
 * saved in mbuf->vlan_tci (inner) and mbuf->vlan_tci_outer (outer).
 * This can only happen if vlan stripping is enabled in the RX
 * configuration of the PMD. If this flag is set, PKT_RX_VLAN_STRIPPED
 * must also be set.
 */
#define PKT_RX_QINQ_STRIPPED (1ULL << 15)

/**
 * Deprecated.
 * RX packet with double VLAN stripped.
 * This flag is replaced by PKT_RX_QINQ_STRIPPED.
 */
#define PKT_RX_QINQ_PKT      PKT_RX_QINQ_STRIPPED

/* add new RX flags here */

/* add new TX flags here */

/**
 * Bits 45:48 used for the tunnel type.
 * When doing Tx offload like TSO or checksum, the HW needs to configure the
 * tunnel type into the HW descriptors.
 */
#define PKT_TX_TUNNEL_VXLAN   (0x1ULL << 45)
#define PKT_TX_TUNNEL_GRE     (0x2ULL << 45)
#define PKT_TX_TUNNEL_IPIP    (0x3ULL << 45)
#define PKT_TX_TUNNEL_GENEVE  (0x4ULL << 45)
/* add new TX TUNNEL type here */
#define PKT_TX_TUNNEL_MASK    (0xFULL << 45)

/**
 * Second VLAN insertion (QinQ) flag.
 */
#define PKT_TX_QINQ_PKT    (1ULL << 49)   /**< TX packet with double VLAN inserted. */

/**
 * TCP segmentation offload. To enable this offload feature for a
 * packet to be transmitted on hardware supporting TSO:
 *  - set the PKT_TX_TCP_SEG flag in mbuf->ol_flags (this flag implies
 *    PKT_TX_TCP_CKSUM)
 *  - set the flag PKT_TX_IPV4 or PKT_TX_IPV6
 *  - if it's IPv4, set the PKT_TX_IP_CKSUM flag and write the IP checksum
 *    to 0 in the packet
 *  - fill the mbuf offload information: l2_len, l3_len, l4_len, tso_segsz
 *  - calculate the pseudo header checksum without taking ip_len in account,
 *    and set it in the TCP header. Refer to rte_ipv4_phdr_cksum() and
 *    rte_ipv6_phdr_cksum() that can be used as helpers.
 */
#define PKT_TX_TCP_SEG       (1ULL << 50)

#define PKT_TX_IEEE1588_TMST (1ULL << 51) /**< TX IEEE1588 packet to timestamp. */

/**
 * Bits 52+53 used for L4 packet type with checksum enabled: 00: Reserved,
 * 01: TCP checksum, 10: SCTP checksum, 11: UDP checksum. To use hardware
 * L4 checksum offload, the user needs to:
 *  - fill l2_len and l3_len in mbuf
 *  - set the flags PKT_TX_TCP_CKSUM, PKT_TX_SCTP_CKSUM or PKT_TX_UDP_CKSUM
 *  - set the flag PKT_TX_IPV4 or PKT_TX_IPV6
 *  - calculate the pseudo header checksum and set it in the L4 header (only
 *    for TCP or UDP). See rte_ipv4_phdr_cksum() and rte_ipv6_phdr_cksum().
 *    For SCTP, set the crc field to 0.
 */
#define PKT_TX_L4_NO_CKSUM   (0ULL << 52) /**< Disable L4 cksum of TX pkt. */
#define PKT_TX_TCP_CKSUM     (1ULL << 52) /**< TCP cksum of TX pkt. computed by NIC. */
#define PKT_TX_SCTP_CKSUM    (2ULL << 52) /**< SCTP cksum of TX pkt. computed by NIC. */
#define PKT_TX_UDP_CKSUM     (3ULL << 52) /**< UDP cksum of TX pkt. computed by NIC. */
#define PKT_TX_L4_MASK       (3ULL << 52) /**< Mask for L4 cksum offload request. */

/**
 * Offload the IP checksum in the hardware. The flag PKT_TX_IPV4 should
 * also be set by the application, although a PMD will only check
 * PKT_TX_IP_CKSUM.
 *  - set the IP checksum field in the packet to 0
 *  - fill the mbuf offload information: l2_len, l3_len
 */
#define PKT_TX_IP_CKSUM      (1ULL << 54)

/**
 * Packet is IPv4. This flag must be set when using any offload feature
 * (TSO, L3 or L4 checksum) to tell the NIC that the packet is an IPv4
 * packet. If the packet is a tunneled packet, this flag is related to
 * the inner headers.
 */
#define PKT_TX_IPV4          (1ULL << 55)

/**
 * Packet is IPv6. This flag must be set when using an offload feature
 * (TSO or L4 checksum) to tell the NIC that the packet is an IPv6
 * packet. If the packet is a tunneled packet, this flag is related to
 * the inner headers.
 */
#define PKT_TX_IPV6          (1ULL << 56)

#define PKT_TX_VLAN_PKT      (1ULL << 57) /**< TX packet is a 802.1q VLAN packet. */

/**
 * Offload the IP checksum of an external header in the hardware. The
 * flag PKT_TX_OUTER_IPV4 should also be set by the application, alto ugh
 * a PMD will only check PKT_TX_IP_CKSUM.  The IP checksum field in the
 * packet must be set to 0.
 *  - set the outer IP checksum field in the packet to 0
 *  - fill the mbuf offload information: outer_l2_len, outer_l3_len
 */
#define PKT_TX_OUTER_IP_CKSUM   (1ULL << 58)

/**
 * Packet outer header is IPv4. This flag must be set when using any
 * outer offload feature (L3 or L4 checksum) to tell the NIC that the
 * outer header of the tunneled packet is an IPv4 packet.
 */
#define PKT_TX_OUTER_IPV4   (1ULL << 59)

/**
 * Packet outer header is IPv6. This flag must be set when using any
 * outer offload feature (L4 checksum) to tell the NIC that the outer
 * header of the tunneled packet is an IPv6 packet.
 */
#define PKT_TX_OUTER_IPV6    (1ULL << 60)

#define __RESERVED           (1ULL << 61) /**< reserved for future mbuf use */

#define IND_ATTACHED_MBUF    (1ULL << 62) /**< Indirect attached mbuf */

/* Use final bit of flags to indicate a control mbuf */
#define CTRL_MBUF_FLAG       (1ULL << 63) /**< Mbuf contains control data */

/** Alignment constraint of mbuf private area. */
#define RTE_MBUF_PRIV_ALIGN 8

/**
 * Get the name of a RX offload flag
 *
 * @param mask
 *   The mask describing the flag.
 * @return
 *   The name of this flag, or NULL if it's not a valid RX flag.
 */
const char *rte_get_rx_ol_flag_name(uint64_t mask);

/**
 * Dump the list of RX offload flags in a buffer
 *
 * @param mask
 *   The mask describing the RX flags.
 * @param buf
 *   The output buffer.
 * @param buflen
 *   The length of the buffer.
 * @return
 *   0 on success, (-1) on error.
 */
int rte_get_rx_ol_flag_list(uint64_t mask, char *buf, size_t buflen);

/**
 * Get the name of a TX offload flag
 *
 * @param mask
 *   The mask describing the flag. Usually only one bit must be set.
 *   Several bits can be given if they belong to the same mask.
 *   Ex: PKT_TX_L4_MASK.
 * @return
 *   The name of this flag, or NULL if it's not a valid TX flag.
 */
const char *rte_get_tx_ol_flag_name(uint64_t mask);

/**
 * Dump the list of TX offload flags in a buffer
 *
 * @param mask
 *   The mask describing the TX flags.
 * @param buf
 *   The output buffer.
 * @param buflen
 *   The length of the buffer.
 * @return
 *   0 on success, (-1) on error.
 */
int rte_get_tx_ol_flag_list(uint64_t mask, char *buf, size_t buflen);

/**
 * Some NICs need at least 2KB buffer to RX standard Ethernet frame without
 * splitting it into multiple segments.
 * So, for mbufs that planned to be involved into RX/TX, the recommended
 * minimal buffer length is 2KB + RTE_PKTMBUF_HEADROOM.
 */
#define RTE_MBUF_DEFAULT_DATAROOM       2048
#define RTE_MBUF_DEFAULT_BUF_SIZE       \
        (RTE_MBUF_DEFAULT_DATAROOM + RTE_PKTMBUF_HEADROOM)

/* define a set of marker types that can be used to refer to set points in the
 * mbuf */
__extension__
typedef void    *MARKER[0];   /**< generic marker for a point in a structure */
__extension__
typedef uint8_t  MARKER8[0];  /**< generic marker with 1B alignment */
__extension__
typedef uint64_t MARKER64[0]; /**< marker that allows us to overwrite 8 bytes
                               * with a single assignment */

/**
 * The generic rte_mbuf, containing a packet mbuf.
 */
struct rte_mbuf {
        MARKER cacheline0;

        void *buf_addr;           /**< Virtual address of segment buffer. */
        phys_addr_t buf_physaddr; /**< Physical address of segment buffer. */

        uint16_t buf_len;         /**< Length of segment buffer. */

        /* next 6 bytes are initialised on RX descriptor rearm */
        MARKER8 rearm_data;
        uint16_t data_off;

        /**
         * 16-bit Reference counter.
         * It should only be accessed using the following functions:
         * rte_mbuf_refcnt_update(), rte_mbuf_refcnt_read(), and
         * rte_mbuf_refcnt_set(). The functionality of these functions (atomic,
         * or non-atomic) is controlled by the CONFIG_RTE_MBUF_REFCNT_ATOMIC
         * config option.
         */
        RTE_STD_C11
        union {
                rte_atomic16_t refcnt_atomic; /**< Atomically accessed refcnt */
                uint16_t refcnt;              /**< Non-atomically accessed refcnt */
        };
        uint8_t nb_segs;          /**< Number of segments. */
        uint8_t port;             /**< Input port. */

        uint64_t ol_flags;        /**< Offload features. */

        /* remaining bytes are set on RX when pulling packet from descriptor */
        MARKER rx_descriptor_fields1;

        /*
         * The packet type, which is the combination of outer/inner L2, L3, L4
         * and tunnel types. The packet_type is about data really present in the
         * mbuf. Example: if vlan stripping is enabled, a received vlan packet
         * would have RTE_PTYPE_L2_ETHER and not RTE_PTYPE_L2_VLAN because the
         * vlan is stripped from the data.
         */
        RTE_STD_C11
        union {
                uint32_t packet_type; /**< L2/L3/L4 and tunnel information. */
                struct {
                        uint32_t l2_type:4; /**< (Outer) L2 type. */
                        uint32_t l3_type:4; /**< (Outer) L3 type. */
                        uint32_t l4_type:4; /**< (Outer) L4 type. */
                        uint32_t tun_type:4; /**< Tunnel type. */
                        uint32_t inner_l2_type:4; /**< Inner L2 type. */
                        uint32_t inner_l3_type:4; /**< Inner L3 type. */
                        uint32_t inner_l4_type:4; /**< Inner L4 type. */
                };
        };

        uint32_t pkt_len;         /**< Total pkt len: sum of all segments. */
        uint16_t data_len;        /**< Amount of data in segment buffer. */
        /** VLAN TCI (CPU order), valid if PKT_RX_VLAN_STRIPPED is set. */
        uint16_t vlan_tci;

        union {
                uint32_t rss;     /**< RSS hash result if RSS enabled */
                struct {
                        RTE_STD_C11
                        union {
                                struct {
                                        uint16_t hash;
                                        uint16_t id;
                                };
                                uint32_t lo;
                                /**< Second 4 flexible bytes */
                        };
                        uint32_t hi;
                        /**< First 4 flexible bytes or FD ID, dependent on
                             PKT_RX_FDIR_* flag in ol_flags. */
                } fdir;           /**< Filter identifier if FDIR enabled */
                struct {
                        uint32_t lo;
                        uint32_t hi;
                } sched;          /**< Hierarchical scheduler */
                uint32_t usr;     /**< User defined tags. See rte_distributor_process() */
        } hash;                   /**< hash information */

        uint32_t seqn; /**< Sequence number. See also rte_reorder_insert() */

        /** Outer VLAN TCI (CPU order), valid if PKT_RX_QINQ_STRIPPED is set. */
        uint16_t vlan_tci_outer;

        /* second cache line - fields only used in slow path or on TX */
        MARKER cacheline1 __rte_cache_min_aligned;

        RTE_STD_C11
        union {
                void *userdata;   /**< Can be used for external metadata */
                uint64_t udata64; /**< Allow 8-byte userdata on 32-bit */
        };

        struct rte_mempool *pool; /**< Pool from which mbuf was allocated. */
        struct rte_mbuf *next;    /**< Next segment of scattered packet. */

        /* fields to support TX offloads */
        RTE_STD_C11
        union {
                uint64_t tx_offload;       /**< combined for easy fetch */
                __extension__
                struct {
                        uint64_t l2_len:7;
                        /**< L2 (MAC) Header Length for non-tunneling pkt.
                         * Outer_L4_len + ... + Inner_L2_len for tunneling pkt.
                         */
                        uint64_t l3_len:9; /**< L3 (IP) Header Length. */
                        uint64_t l4_len:8; /**< L4 (TCP/UDP) Header Length. */
                        uint64_t tso_segsz:16; /**< TCP TSO segment size */

                        /* fields for TX offloading of tunnels */
                        uint64_t outer_l3_len:9; /**< Outer L3 (IP) Hdr Length. */
                        uint64_t outer_l2_len:7; /**< Outer L2 (MAC) Hdr Length. */

                        /* uint64_t unused:8; */
                };
        };

        /** Size of the application private data. In case of an indirect
         * mbuf, it stores the direct mbuf private data size. */
        uint16_t priv_size;

        /** Timesync flags for use with IEEE1588. */
        uint16_t timesync;
} __rte_cache_aligned;

/**
 * Prefetch the first part of the mbuf
 *
 * The first 64 bytes of the mbuf corresponds to fields that are used early
 * in the receive path. If the cache line of the architecture is higher than
 * 64B, the second part will also be prefetched.
 *
 * @param m
 *   The pointer to the mbuf.
 */
static inline void
rte_mbuf_prefetch_part1(struct rte_mbuf *m)
{
        rte_prefetch0(&m->cacheline0);
}

/**
 * Prefetch the second part of the mbuf
 *
 * The next 64 bytes of the mbuf corresponds to fields that are used in the
 * transmit path. If the cache line of the architecture is higher than 64B,
 * this function does nothing as it is expected that the full mbuf is
 * already in cache.
 *
 * @param m
 *   The pointer to the mbuf.
 */
static inline void
rte_mbuf_prefetch_part2(struct rte_mbuf *m)
{
#if RTE_CACHE_LINE_SIZE == 64
        rte_prefetch0(&m->cacheline1);
#else
        RTE_SET_USED(m);
#endif
}


static inline uint16_t rte_pktmbuf_priv_size(struct rte_mempool *mp);

/**
 * Return the DMA address of the beginning of the mbuf data
 *
 * @param mb
 *   The pointer to the mbuf.
 * @return
 *   The physical address of the beginning of the mbuf data
 */
static inline phys_addr_t
rte_mbuf_data_dma_addr(const struct rte_mbuf *mb)
{
        return mb->buf_physaddr + mb->data_off;
}

/**
 * Return the default DMA address of the beginning of the mbuf data
 *
 * This function is used by drivers in their receive function, as it
 * returns the location where data should be written by the NIC, taking
 * the default headroom in account.
 *
 * @param mb
 *   The pointer to the mbuf.
 * @return
 *   The physical address of the beginning of the mbuf data
 */
static inline phys_addr_t
rte_mbuf_data_dma_addr_default(const struct rte_mbuf *mb)
{
        return mb->buf_physaddr + RTE_PKTMBUF_HEADROOM;
}

/**
 * Return the mbuf owning the data buffer address of an indirect mbuf.
 *
 * @param mi
 *   The pointer to the indirect mbuf.
 * @return
 *   The address of the direct mbuf corresponding to buffer_addr.
 */
static inline struct rte_mbuf *
rte_mbuf_from_indirect(struct rte_mbuf *mi)
{
        return (struct rte_mbuf *)RTE_PTR_SUB(mi->buf_addr, sizeof(*mi) + mi->priv_size);
}

/**
 * Return the buffer address embedded in the given mbuf.
 *
 * @param md
 *   The pointer to the mbuf.
 * @return
 *   The address of the data buffer owned by the mbuf.
 */
static inline char *
rte_mbuf_to_baddr(struct rte_mbuf *md)
{
        char *buffer_addr;
        buffer_addr = (char *)md + sizeof(*md) + rte_pktmbuf_priv_size(md->pool);
        return buffer_addr;
}

/**
 * Returns TRUE if given mbuf is indirect, or FALSE otherwise.
 */
#define RTE_MBUF_INDIRECT(mb)   ((mb)->ol_flags & IND_ATTACHED_MBUF)

/**
 * Returns TRUE if given mbuf is direct, or FALSE otherwise.
 */
#define RTE_MBUF_DIRECT(mb)     (!RTE_MBUF_INDIRECT(mb))

/**
 * Private data in case of pktmbuf pool.
 *
 * A structure that contains some pktmbuf_pool-specific data that are
 * appended after the mempool structure (in private data).
 */
struct rte_pktmbuf_pool_private {
        uint16_t mbuf_data_room_size; /**< Size of data space in each mbuf. */
        uint16_t mbuf_priv_size;      /**< Size of private area in each mbuf. */
};

#ifdef RTE_LIBRTE_MBUF_DEBUG

/**  check mbuf type in debug mode */
#define __rte_mbuf_sanity_check(m, is_h) rte_mbuf_sanity_check(m, is_h)

#else /*  RTE_LIBRTE_MBUF_DEBUG */

/**  check mbuf type in debug mode */
#define __rte_mbuf_sanity_check(m, is_h) do { } while (0)

#endif /*  RTE_LIBRTE_MBUF_DEBUG */

#ifdef RTE_MBUF_REFCNT_ATOMIC

/**
 * Reads the value of an mbuf's refcnt.
 * @param m
 *   Mbuf to read
 * @return
 *   Reference count number.
 */
static inline uint16_t
rte_mbuf_refcnt_read(const struct rte_mbuf *m)
{
        return (uint16_t)(rte_atomic16_read(&m->refcnt_atomic));
}

/**
 * Sets an mbuf's refcnt to a defined value.
 * @param m
 *   Mbuf to update
 * @param new_value
 *   Value set
 */
static inline void
rte_mbuf_refcnt_set(struct rte_mbuf *m, uint16_t new_value)
{
        rte_atomic16_set(&m->refcnt_atomic, new_value);
}

/**
 * Adds given value to an mbuf's refcnt and returns its new value.
 * @param m
 *   Mbuf to update
 * @param value
 *   Value to add/subtract
 * @return
 *   Updated value
 */
static inline uint16_t
rte_mbuf_refcnt_update(struct rte_mbuf *m, int16_t value)
{
        /*
         * The atomic_add is an expensive operation, so we don't want to
         * call it in the case where we know we are the uniq holder of
         * this mbuf (i.e. ref_cnt == 1). Otherwise, an atomic
         * operation has to be used because concurrent accesses on the
         * reference counter can occur.
         */
        if (likely(rte_mbuf_refcnt_read(m) == 1)) {
                rte_mbuf_refcnt_set(m, 1 + value);
                return 1 + value;
        }

        return (uint16_t)(rte_atomic16_add_return(&m->refcnt_atomic, value));
}

#else /* ! RTE_MBUF_REFCNT_ATOMIC */

/**
 * Adds given value to an mbuf's refcnt and returns its new value.
 */
static inline uint16_t
rte_mbuf_refcnt_update(struct rte_mbuf *m, int16_t value)
{
        m->refcnt = (uint16_t)(m->refcnt + value);
        return m->refcnt;
}

/**
 * Reads the value of an mbuf's refcnt.
 */
static inline uint16_t
rte_mbuf_refcnt_read(const struct rte_mbuf *m)
{
        return m->refcnt;
}

/**
 * Sets an mbuf's refcnt to the defined value.
 */
static inline void
rte_mbuf_refcnt_set(struct rte_mbuf *m, uint16_t new_value)
{
        m->refcnt = new_value;
}

#endif /* RTE_MBUF_REFCNT_ATOMIC */

/** Mbuf prefetch */
#define RTE_MBUF_PREFETCH_TO_FREE(m) do {       \
        if ((m) != NULL)                        \
                rte_prefetch0(m);               \
} while (0)


/**
 * Sanity checks on an mbuf.
 *
 * Check the consistency of the given mbuf. The function will cause a
 * panic if corruption is detected.
 *
 * @param m
 *   The mbuf to be checked.
 * @param is_header
 *   True if the mbuf is a packet header, false if it is a sub-segment
 *   of a packet (in this case, some fields like nb_segs are not checked)
 */
void
rte_mbuf_sanity_check(const struct rte_mbuf *m, int is_header);

/**
 * Allocate an unitialized mbuf from mempool *mp*.
 *
 * This function can be used by PMDs (especially in RX functions) to
 * allocate an unitialized mbuf. The driver is responsible of
 * initializing all the required fields. See rte_pktmbuf_reset().
 * For standard needs, prefer rte_pktmbuf_alloc().
 *
 * @param mp
 *   The mempool from which mbuf is allocated.
 * @return
 *   - The pointer to the new mbuf on success.
 *   - NULL if allocation failed.
 */
static inline struct rte_mbuf *rte_mbuf_raw_alloc(struct rte_mempool *mp)
{
        struct rte_mbuf *m;
        void *mb = NULL;

        if (rte_mempool_get(mp, &mb) < 0)
                return NULL;
        m = (struct rte_mbuf *)mb;
        RTE_ASSERT(rte_mbuf_refcnt_read(m) == 0);
        rte_mbuf_refcnt_set(m, 1);
        __rte_mbuf_sanity_check(m, 0);

        return m;
}

/**
 * @internal Put mbuf back into its original mempool.
 * The use of that function is reserved for RTE internal needs.
 * Please use rte_pktmbuf_free().
 *
 * @param m
 *   The mbuf to be freed.
 */
static inline void __attribute__((always_inline))
__rte_mbuf_raw_free(struct rte_mbuf *m)
{
        RTE_ASSERT(rte_mbuf_refcnt_read(m) == 0);
        rte_mempool_put(m->pool, m);
}

/* Operations on ctrl mbuf */

/**
 * The control mbuf constructor.
 *
 * This function initializes some fields in an mbuf structure that are
 * not modified by the user once created (mbuf type, origin pool, buffer
 * start address, and so on). This function is given as a callback function
 * to rte_mempool_create() at pool creation time.
 *
 * @param mp
 *   The mempool from which the mbuf is allocated.
 * @param opaque_arg
 *   A pointer that can be used by the user to retrieve useful information
 *   for mbuf initialization. This pointer comes from the ``init_arg``
 *   parameter of rte_mempool_create().
 * @param m
 *   The mbuf to initialize.
 * @param i
 *   The index of the mbuf in the pool table.
 */
void rte_ctrlmbuf_init(struct rte_mempool *mp, void *opaque_arg,
                void *m, unsigned i);

/**
 * Allocate a new mbuf (type is ctrl) from mempool *mp*.
 *
 * This new mbuf is initialized with data pointing to the beginning of
 * buffer, and with a length of zero.
 *
 * @param mp
 *   The mempool from which the mbuf is allocated.
 * @return
 *   - The pointer to the new mbuf on success.
 *   - NULL if allocation failed.
 */
#define rte_ctrlmbuf_alloc(mp) rte_pktmbuf_alloc(mp)

/**
 * Free a control mbuf back into its original mempool.
 *
 * @param m
 *   The control mbuf to be freed.
 */
#define rte_ctrlmbuf_free(m) rte_pktmbuf_free(m)

/**
 * A macro that returns the pointer to the carried data.
 *
 * The value that can be read or assigned.
 *
 * @param m
 *   The control mbuf.
 */
#define rte_ctrlmbuf_data(m) ((char *)((m)->buf_addr) + (m)->data_off)

/**
 * A macro that returns the length of the carried data.
 *
 * The value that can be read or assigned.
 *
 * @param m
 *   The control mbuf.
 */
#define rte_ctrlmbuf_len(m) rte_pktmbuf_data_len(m)

/**
 * Tests if an mbuf is a control mbuf
 *
 * @param m
 *   The mbuf to be tested
 * @return
 *   - True (1) if the mbuf is a control mbuf
 *   - False(0) otherwise
 */
static inline int
rte_is_ctrlmbuf(struct rte_mbuf *m)
{
        return !!(m->ol_flags & CTRL_MBUF_FLAG);
}

/* Operations on pkt mbuf */

/**
 * The packet mbuf constructor.
 *
 * This function initializes some fields in the mbuf structure that are
 * not modified by the user once created (origin pool, buffer start
 * address, and so on). This function is given as a callback function to
 * rte_mempool_create() at pool creation time.
 *
 * @param mp
 *   The mempool from which mbufs originate.
 * @param opaque_arg
 *   A pointer that can be used by the user to retrieve useful information
 *   for mbuf initialization. This pointer comes from the ``init_arg``
 *   parameter of rte_mempool_create().
 * @param m
 *   The mbuf to initialize.
 * @param i
 *   The index of the mbuf in the pool table.
 */
void rte_pktmbuf_init(struct rte_mempool *mp, void *opaque_arg,
                      void *m, unsigned i);


/**
 * A  packet mbuf pool constructor.
 *
 * This function initializes the mempool private data in the case of a
 * pktmbuf pool. This private data is needed by the driver. The
 * function is given as a callback function to rte_mempool_create() at
 * pool creation. It can be extended by the user, for example, to
 * provide another packet size.
 *
 * @param mp
 *   The mempool from which mbufs originate.
 * @param opaque_arg
 *   A pointer that can be used by the user to retrieve useful information
 *   for mbuf initialization. This pointer comes from the ``init_arg``
 *   parameter of rte_mempool_create().
 */
void rte_pktmbuf_pool_init(struct rte_mempool *mp, void *opaque_arg);

/**
 * Create a mbuf pool.
 *
 * This function creates and initializes a packet mbuf pool. It is
 * a wrapper to rte_mempool_create() with the proper packet constructor
 * and mempool constructor.
 *
 * @param name
 *   The name of the mbuf pool.
 * @param n
 *   The number of elements in the mbuf pool. The optimum size (in terms
 *   of memory usage) for a mempool is when n is a power of two minus one:
 *   n = (2^q - 1).
 * @param cache_size
 *   Size of the per-core object cache. See rte_mempool_create() for
 *   details.
 * @param priv_size
 *   Size of application private are between the rte_mbuf structure
 *   and the data buffer. This value must be aligned to RTE_MBUF_PRIV_ALIGN.
 * @param data_room_size
 *   Size of data buffer in each mbuf, including RTE_PKTMBUF_HEADROOM.
 * @param socket_id
 *   The socket identifier where the memory should be allocated. The
 *   value can be *SOCKET_ID_ANY* if there is no NUMA constraint for the
 *   reserved zone.
 * @return
 *   The pointer to the new allocated mempool, on success. NULL on error
 *   with rte_errno set appropriately. Possible rte_errno values include:
 *    - E_RTE_NO_CONFIG - function could not get pointer to rte_config structure
 *    - E_RTE_SECONDARY - function was called from a secondary process instance
 *    - EINVAL - cache size provided is too large, or priv_size is not aligned.
 *    - ENOSPC - the maximum number of memzones has already been allocated
 *    - EEXIST - a memzone with the same name already exists
 *    - ENOMEM - no appropriate memory area found in which to create memzone
 */
struct rte_mempool *
rte_pktmbuf_pool_create(const char *name, unsigned n,
        unsigned cache_size, uint16_t priv_size, uint16_t data_room_size,
        int socket_id);

/**
 * Get the data room size of mbufs stored in a pktmbuf_pool
 *
 * The data room size is the amount of data that can be stored in a
 * mbuf including the headroom (RTE_PKTMBUF_HEADROOM).
 *
 * @param mp
 *   The packet mbuf pool.
 * @return
 *   The data room size of mbufs stored in this mempool.
 */
static inline uint16_t
rte_pktmbuf_data_room_size(struct rte_mempool *mp)
{
        struct rte_pktmbuf_pool_private *mbp_priv;

        mbp_priv = (struct rte_pktmbuf_pool_private *)rte_mempool_get_priv(mp);
        return mbp_priv->mbuf_data_room_size;
}

/**
 * Get the application private size of mbufs stored in a pktmbuf_pool
 *
 * The private size of mbuf is a zone located between the rte_mbuf
 * structure and the data buffer where an application can store data
 * associated to a packet.
 *
 * @param mp
 *   The packet mbuf pool.
 * @return
 *   The private size of mbufs stored in this mempool.
 */
static inline uint16_t
rte_pktmbuf_priv_size(struct rte_mempool *mp)
{
        struct rte_pktmbuf_pool_private *mbp_priv;

        mbp_priv = (struct rte_pktmbuf_pool_private *)rte_mempool_get_priv(mp);
        return mbp_priv->mbuf_priv_size;
}

/**
 * Reset the data_off field of a packet mbuf to its default value.
 *
 * The given mbuf must have only one segment, which should be empty.
 *
 * @param m
 *   The packet mbuf's data_off field has to be reset.
 */
static inline void rte_pktmbuf_reset_headroom(struct rte_mbuf *m)
{
        m->data_off = RTE_MIN(RTE_PKTMBUF_HEADROOM, (uint16_t)m->buf_len);
}

/**
 * Reset the fields of a packet mbuf to their default values.
 *
 * The given mbuf must have only one segment.
 *
 * @param m
 *   The packet mbuf to be resetted.
 */
static inline void rte_pktmbuf_reset(struct rte_mbuf *m)
{
        m->next = NULL;
        m->pkt_len = 0;
        m->tx_offload = 0;
        m->vlan_tci = 0;
        m->vlan_tci_outer = 0;
        m->nb_segs = 1;
        m->port = 0xff;

        m->ol_flags = 0;
        m->packet_type = 0;
        rte_pktmbuf_reset_headroom(m);

        m->data_len = 0;
        __rte_mbuf_sanity_check(m, 1);
}

/**
 * Allocate a new mbuf from a mempool.
 *
 * This new mbuf contains one segment, which has a length of 0. The pointer
 * to data is initialized to have some bytes of headroom in the buffer
 * (if buffer size allows).
 *
 * @param mp
 *   The mempool from which the mbuf is allocated.
 * @return
 *   - The pointer to the new mbuf on success.
 *   - NULL if allocation failed.
 */
static inline struct rte_mbuf *rte_pktmbuf_alloc(struct rte_mempool *mp)
{
        struct rte_mbuf *m;
        if ((m = rte_mbuf_raw_alloc(mp)) != NULL)
                rte_pktmbuf_reset(m);
        return m;
}

/**
 * Allocate a bulk of mbufs, initialize refcnt and reset the fields to default
 * values.
 *
 *  @param pool
 *    The mempool from which mbufs are allocated.
 *  @param mbufs
 *    Array of pointers to mbufs
 *  @param count
 *    Array size
 *  @return
 *   - 0: Success
 */
static inline int rte_pktmbuf_alloc_bulk(struct rte_mempool *pool,
         struct rte_mbuf **mbufs, unsigned count)
{
        unsigned idx = 0;
        int rc;

        rc = rte_mempool_get_bulk(pool, (void **)mbufs, count);
        if (unlikely(rc))
                return rc;

        /* To understand duff's device on loop unwinding optimization, see
         * https://en.wikipedia.org/wiki/Duff's_device.
         * Here while() loop is used rather than do() while{} to avoid extra
         * check if count is zero.
         */
        switch (count % 4) {
        case 0:
                while (idx != count) {
                        RTE_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 0);
                        rte_mbuf_refcnt_set(mbufs[idx], 1);
                        rte_pktmbuf_reset(mbufs[idx]);
                        idx++;
        case 3:
                        RTE_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 0);
                        rte_mbuf_refcnt_set(mbufs[idx], 1);
                        rte_pktmbuf_reset(mbufs[idx]);
                        idx++;
        case 2:
                        RTE_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 0);
                        rte_mbuf_refcnt_set(mbufs[idx], 1);
                        rte_pktmbuf_reset(mbufs[idx]);
                        idx++;
        case 1:
                        RTE_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 0);
                        rte_mbuf_refcnt_set(mbufs[idx], 1);
                        rte_pktmbuf_reset(mbufs[idx]);
                        idx++;
                }
        }
        return 0;
}

/**
 * Attach packet mbuf to another packet mbuf.
 *
 * After attachment we refer the mbuf we attached as 'indirect',
 * while mbuf we attached to as 'direct'.
 * The direct mbuf's reference counter is incremented.
 *
 * Right now, not supported:
 *  - attachment for already indirect mbuf (e.g. - mi has to be direct).
 *  - mbuf we trying to attach (mi) is used by someone else
 *    e.g. it's reference counter is greater then 1.
 *
 * @param mi
 *   The indirect packet mbuf.
 * @param m
 *   The packet mbuf we're attaching to.
 */
static inline void rte_pktmbuf_attach(struct rte_mbuf *mi, struct rte_mbuf *m)
{
        struct rte_mbuf *md;

        RTE_ASSERT(RTE_MBUF_DIRECT(mi) &&
            rte_mbuf_refcnt_read(mi) == 1);

        /* if m is not direct, get the mbuf that embeds the data */
        if (RTE_MBUF_DIRECT(m))
                md = m;
        else
                md = rte_mbuf_from_indirect(m);

        rte_mbuf_refcnt_update(md, 1);
        mi->priv_size = m->priv_size;
        mi->buf_physaddr = m->buf_physaddr;
        mi->buf_addr = m->buf_addr;
        mi->buf_len = m->buf_len;

        mi->next = m->next;
        mi->data_off = m->data_off;
        mi->data_len = m->data_len;
        mi->port = m->port;
        mi->vlan_tci = m->vlan_tci;
        mi->vlan_tci_outer = m->vlan_tci_outer;
        mi->tx_offload = m->tx_offload;
        mi->hash = m->hash;

        mi->next = NULL;
        mi->pkt_len = mi->data_len;
        mi->nb_segs = 1;
        mi->ol_flags = m->ol_flags | IND_ATTACHED_MBUF;
        mi->packet_type = m->packet_type;

        __rte_mbuf_sanity_check(mi, 1);
        __rte_mbuf_sanity_check(m, 0);
}

/**
 * Detach an indirect packet mbuf.
 *
 *  - restore original mbuf address and length values.
 *  - reset pktmbuf data and data_len to their default values.
 *  - decrement the direct mbuf's reference counter. When the
 *  reference counter becomes 0, the direct mbuf is freed.
 *
 * All other fields of the given packet mbuf will be left intact.
 *
 * @param m
 *   The indirect attached packet mbuf.
 */
static inline void rte_pktmbuf_detach(struct rte_mbuf *m)
{
        struct rte_mbuf *md = rte_mbuf_from_indirect(m);
        struct rte_mempool *mp = m->pool;
        uint32_t mbuf_size, buf_len, priv_size;

        priv_size = rte_pktmbuf_priv_size(mp);
        mbuf_size = sizeof(struct rte_mbuf) + priv_size;
        buf_len = rte_pktmbuf_data_room_size(mp);

        m->priv_size = priv_size;
        m->buf_addr = (char *)m + mbuf_size;
        m->buf_physaddr = rte_mempool_virt2phy(mp, m) + mbuf_size;
        m->buf_len = (uint16_t)buf_len;
        rte_pktmbuf_reset_headroom(m);
        m->data_len = 0;
        m->ol_flags = 0;

        if (rte_mbuf_refcnt_update(md, -1) == 0)
                __rte_mbuf_raw_free(md);
}

static inline struct rte_mbuf* __attribute__((always_inline))
__rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
{
        __rte_mbuf_sanity_check(m, 0);

        if (likely(rte_mbuf_refcnt_update(m, -1) == 0)) {
                /* if this is an indirect mbuf, it is detached. */
                if (RTE_MBUF_INDIRECT(m))
                        rte_pktmbuf_detach(m);
                return m;
        }
        return NULL;
}

/**
 * Free a segment of a packet mbuf into its original mempool.
 *
 * Free an mbuf, without parsing other segments in case of chained
 * buffers.
 *
 * @param m
 *   The packet mbuf segment to be freed.
 */
static inline void __attribute__((always_inline))
rte_pktmbuf_free_seg(struct rte_mbuf *m)
{
        if (likely(NULL != (m = __rte_pktmbuf_prefree_seg(m)))) {
                m->next = NULL;
                __rte_mbuf_raw_free(m);
        }
}

/**
 * Free a packet mbuf back into its original mempool.
 *
 * Free an mbuf, and all its segments in case of chained buffers. Each
 * segment is added back into its original mempool.
 *
 * @param m
 *   The packet mbuf to be freed.
 */
static inline void rte_pktmbuf_free(struct rte_mbuf *m)
{
        struct rte_mbuf *m_next;

        __rte_mbuf_sanity_check(m, 1);

        while (m != NULL) {
                m_next = m->next;
                rte_pktmbuf_free_seg(m);
                m = m_next;
        }
}

/**
 * Creates a "clone" of the given packet mbuf.
 *
 * Walks through all segments of the given packet mbuf, and for each of them:
 *  - Creates a new packet mbuf from the given pool.
 *  - Attaches newly created mbuf to the segment.
 * Then updates pkt_len and nb_segs of the "clone" packet mbuf to match values
 * from the original packet mbuf.
 *
 * @param md
 *   The packet mbuf to be cloned.
 * @param mp
 *   The mempool from which the "clone" mbufs are allocated.
 * @return
 *   - The pointer to the new "clone" mbuf on success.
 *   - NULL if allocation fails.
 */
static inline struct rte_mbuf *rte_pktmbuf_clone(struct rte_mbuf *md,
                struct rte_mempool *mp)
{
        struct rte_mbuf *mc, *mi, **prev;
        uint32_t pktlen;
        uint8_t nseg;

        if (unlikely ((mc = rte_pktmbuf_alloc(mp)) == NULL))
                return NULL;

        mi = mc;
        prev = &mi->next;
        pktlen = md->pkt_len;
        nseg = 0;

        do {
                nseg++;
                rte_pktmbuf_attach(mi, md);
                *prev = mi;
                prev = &mi->next;
        } while ((md = md->next) != NULL &&
            (mi = rte_pktmbuf_alloc(mp)) != NULL);

        *prev = NULL;
        mc->nb_segs = nseg;
        mc->pkt_len = pktlen;

        /* Allocation of new indirect segment failed */
        if (unlikely (mi == NULL)) {
                rte_pktmbuf_free(mc);
                return NULL;
        }

        __rte_mbuf_sanity_check(mc, 1);
        return mc;
}

/**
 * Adds given value to the refcnt of all packet mbuf segments.
 *
 * Walks through all segments of given packet mbuf and for each of them
 * invokes rte_mbuf_refcnt_update().
 *
 * @param m
 *   The packet mbuf whose refcnt to be updated.
 * @param v
 *   The value to add to the mbuf's segments refcnt.
 */
static inline void rte_pktmbuf_refcnt_update(struct rte_mbuf *m, int16_t v)
{
        __rte_mbuf_sanity_check(m, 1);

        do {
                rte_mbuf_refcnt_update(m, v);
        } while ((m = m->next) != NULL);
}

/**
 * Get the headroom in a packet mbuf.
 *
 * @param m
 *   The packet mbuf.
 * @return
 *   The length of the headroom.
 */
static inline uint16_t rte_pktmbuf_headroom(const struct rte_mbuf *m)
{
        __rte_mbuf_sanity_check(m, 1);
        return m->data_off;
}

/**
 * Get the tailroom of a packet mbuf.
 *
 * @param m
 *   The packet mbuf.
 * @return
 *   The length of the tailroom.
 */
static inline uint16_t rte_pktmbuf_tailroom(const struct rte_mbuf *m)
{
        __rte_mbuf_sanity_check(m, 1);
        return (uint16_t)(m->buf_len - rte_pktmbuf_headroom(m) -
                          m->data_len);
}

/**
 * Get the last segment of the packet.
 *
 * @param m
 *   The packet mbuf.
 * @return
 *   The last segment of the given mbuf.
 */
static inline struct rte_mbuf *rte_pktmbuf_lastseg(struct rte_mbuf *m)
{
        struct rte_mbuf *m2 = (struct rte_mbuf *)m;

        __rte_mbuf_sanity_check(m, 1);
        while (m2->next != NULL)
                m2 = m2->next;
        return m2;
}

/**
 * A macro that points to an offset into the data in the mbuf.
 *
 * The returned pointer is cast to type t. Before using this
 * function, the user must ensure that the first segment is large
 * enough to accommodate its data.
 *
 * @param m
 *   The packet mbuf.
 * @param o
 *   The offset into the mbuf data.
 * @param t
 *   The type to cast the result into.
 */
#define rte_pktmbuf_mtod_offset(m, t, o)        \
        ((t)((char *)(m)->buf_addr + (m)->data_off + (o)))

/**
 * A macro that points to the start of the data in the mbuf.
 *
 * The returned pointer is cast to type t. Before using this
 * function, the user must ensure that the first segment is large
 * enough to accommodate its data.
 *
 * @param m
 *   The packet mbuf.
 * @param t
 *   The type to cast the result into.
 */
#define rte_pktmbuf_mtod(m, t) rte_pktmbuf_mtod_offset(m, t, 0)

/**
 * A macro that returns the physical address that points to an offset of the
 * start of the data in the mbuf
 *
 * @param m
 *   The packet mbuf.
 * @param o
 *   The offset into the data to calculate address from.
 */
#define rte_pktmbuf_mtophys_offset(m, o) \
        (phys_addr_t)((m)->buf_physaddr + (m)->data_off + (o))

/**
 * A macro that returns the physical address that points to the start of the
 * data in the mbuf
 *
 * @param m
 *   The packet mbuf.
 */
#define rte_pktmbuf_mtophys(m) rte_pktmbuf_mtophys_offset(m, 0)

/**
 * A macro that returns the length of the packet.
 *
 * The value can be read or assigned.
 *
 * @param m
 *   The packet mbuf.
 */
#define rte_pktmbuf_pkt_len(m) ((m)->pkt_len)

/**
 * A macro that returns the length of the segment.
 *
 * The value can be read or assigned.
 *
 * @param m
 *   The packet mbuf.
 */
#define rte_pktmbuf_data_len(m) ((m)->data_len)

/**
 * Prepend len bytes to an mbuf data area.
 *
 * Returns a pointer to the new
 * data start address. If there is not enough headroom in the first
 * segment, the function will return NULL, without modifying the mbuf.
 *
 * @param m
 *   The pkt mbuf.
 * @param len
 *   The amount of data to prepend (in bytes).
 * @return
 *   A pointer to the start of the newly prepended data, or
 *   NULL if there is not enough headroom space in the first segment
 */
static inline char *rte_pktmbuf_prepend(struct rte_mbuf *m,
                                        uint16_t len)
{
        __rte_mbuf_sanity_check(m, 1);

        if (unlikely(len > rte_pktmbuf_headroom(m)))
                return NULL;

        m->data_off -= len;
        m->data_len = (uint16_t)(m->data_len + len);
        m->pkt_len  = (m->pkt_len + len);

        return (char *)m->buf_addr + m->data_off;
}

/**
 * Append len bytes to an mbuf.
 *
 * Append len bytes to an mbuf and return a pointer to the start address
 * of the added data. If there is not enough tailroom in the last
 * segment, the function will return NULL, without modifying the mbuf.
 *
 * @param m
 *   The packet mbuf.
 * @param len
 *   The amount of data to append (in bytes).
 * @return
 *   A pointer to the start of the newly appended data, or
 *   NULL if there is not enough tailroom space in the last segment
 */
static inline char *rte_pktmbuf_append(struct rte_mbuf *m, uint16_t len)
{
        void *tail;
        struct rte_mbuf *m_last;

        __rte_mbuf_sanity_check(m, 1);

        m_last = rte_pktmbuf_lastseg(m);
        if (unlikely(len > rte_pktmbuf_tailroom(m_last)))
                return NULL;

        tail = (char *)m_last->buf_addr + m_last->data_off + m_last->data_len;
        m_last->data_len = (uint16_t)(m_last->data_len + len);
        m->pkt_len  = (m->pkt_len + len);
        return (char*) tail;
}

/**
 * Remove len bytes at the beginning of an mbuf.
 *
 * Returns a pointer to the start address of the new data area. If the
 * length is greater than the length of the first segment, then the
 * function will fail and return NULL, without modifying the mbuf.
 *
 * @param m
 *   The packet mbuf.
 * @param len
 *   The amount of data to remove (in bytes).
 * @return
 *   A pointer to the new start of the data.
 */
static inline char *rte_pktmbuf_adj(struct rte_mbuf *m, uint16_t len)
{
        __rte_mbuf_sanity_check(m, 1);

        if (unlikely(len > m->data_len))
                return NULL;

        m->data_len = (uint16_t)(m->data_len - len);
        m->data_off += len;
        m->pkt_len  = (m->pkt_len - len);
        return (char *)m->buf_addr + m->data_off;
}

/**
 * Remove len bytes of data at the end of the mbuf.
 *
 * If the length is greater than the length of the last segment, the
 * function will fail and return -1 without modifying the mbuf.
 *
 * @param m
 *   The packet mbuf.
 * @param len
 *   The amount of data to remove (in bytes).
 * @return
 *   - 0: On success.
 *   - -1: On error.
 */
static inline int rte_pktmbuf_trim(struct rte_mbuf *m, uint16_t len)
{
        struct rte_mbuf *m_last;

        __rte_mbuf_sanity_check(m, 1);

        m_last = rte_pktmbuf_lastseg(m);
        if (unlikely(len > m_last->data_len))
                return -1;

        m_last->data_len = (uint16_t)(m_last->data_len - len);
        m->pkt_len  = (m->pkt_len - len);
        return 0;
}

/**
 * Test if mbuf data is contiguous.
 *
 * @param m
 *   The packet mbuf.
 * @return
 *   - 1, if all data is contiguous (one segment).
 *   - 0, if there is several segments.
 */
static inline int rte_pktmbuf_is_contiguous(const struct rte_mbuf *m)
{
        __rte_mbuf_sanity_check(m, 1);
        return !!(m->nb_segs == 1);
}

/**
 * @internal used by rte_pktmbuf_read().
 */
const void *__rte_pktmbuf_read(const struct rte_mbuf *m, uint32_t off,
        uint32_t len, void *buf);

/**
 * Read len data bytes in a mbuf at specified offset.
 *
 * If the data is contiguous, return the pointer in the mbuf data, else
 * copy the data in the buffer provided by the user and return its
 * pointer.
 *
 * @param m
 *   The pointer to the mbuf.
 * @param off
 *   The offset of the data in the mbuf.
 * @param len
 *   The amount of bytes to read.
 * @param buf
 *   The buffer where data is copied if it is not contigous in mbuf
 *   data. Its length should be at least equal to the len parameter.
 * @return
 *   The pointer to the data, either in the mbuf if it is contiguous,
 *   or in the user buffer. If mbuf is too small, NULL is returned.
 */
static inline const void *rte_pktmbuf_read(const struct rte_mbuf *m,
        uint32_t off, uint32_t len, void *buf)
{
        if (likely(off + len <= rte_pktmbuf_data_len(m)))
                return rte_pktmbuf_mtod_offset(m, char *, off);
        else
                return __rte_pktmbuf_read(m, off, len, buf);
}

/**
 * Chain an mbuf to another, thereby creating a segmented packet.
 *
 * Note: The implementation will do a linear walk over the segments to find
 * the tail entry. For cases when there are many segments, it's better to
 * chain the entries manually.
 *
 * @param head
 *   The head of the mbuf chain (the first packet)
 * @param tail
 *   The mbuf to put last in the chain
 *
 * @return
 *   - 0, on success.
 *   - -EOVERFLOW, if the chain is full (256 entries)
 */
static inline int rte_pktmbuf_chain(struct rte_mbuf *head, struct rte_mbuf *tail)
{
        struct rte_mbuf *cur_tail;

        /* Check for number-of-segments-overflow */
        if (head->nb_segs + tail->nb_segs >= 1 << (sizeof(head->nb_segs) * 8))
                return -EOVERFLOW;

        /* Chain 'tail' onto the old tail */
        cur_tail = rte_pktmbuf_lastseg(head);
        cur_tail->next = tail;

        /* accumulate number of segments and total length. */
        head->nb_segs = (uint8_t)(head->nb_segs + tail->nb_segs);
        head->pkt_len += tail->pkt_len;

        /* pkt_len is only set in the head */
        tail->pkt_len = tail->data_len;

        return 0;
}

/**
 * Dump an mbuf structure to the console.
 *
 * Dump all fields for the given packet mbuf and all its associated
 * segments (in the case of a chained buffer).
 *
 * @param f
 *   A pointer to a file for output
 * @param m
 *   The packet mbuf.
 * @param dump_len
 *   If dump_len != 0, also dump the "dump_len" first data bytes of
 *   the packet.
 */
void rte_pktmbuf_dump(FILE *f, const struct rte_mbuf *m, unsigned dump_len);

#ifdef __cplusplus
}
#endif

#endif /* _RTE_MBUF_H_ */