ed(1): simplify by using arc4random_buf().

[freebsd-src.git] / sys / net / netmap_user.h

/*
 * Copyright (C) 2011-2014 Universita` di Pisa. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   1. Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer.
 *   2. Redistributions in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in the
 *      documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * $FreeBSD$
 *
 * Functions and macros to manipulate netmap structures and packets
 * in userspace. See netmap(4) for more information.
 *
 * The address of the struct netmap_if, say nifp, is computed from the
 * value returned from ioctl(.., NIOCREG, ...) and the mmap region:
 *      ioctl(fd, NIOCREG, &req);
 *      mem = mmap(0, ... );
 *      nifp = NETMAP_IF(mem, req.nr_nifp);
 *              (so simple, we could just do it manually)
 *
 * From there:
 *      struct netmap_ring *NETMAP_TXRING(nifp, index)
 *      struct netmap_ring *NETMAP_RXRING(nifp, index)
 *              we can access ring->cur, ring->head, ring->tail, etc.
 *
 *      ring->slot[i] gives us the i-th slot (we can access
 *              directly len, flags, buf_idx)
 *
 *      char *buf = NETMAP_BUF(ring, x) returns a pointer to
 *              the buffer numbered x
 *
 * All ring indexes (head, cur, tail) should always move forward.
 * To compute the next index in a circular ring you can use
 *      i = nm_ring_next(ring, i);
 *
 * To ease porting apps from pcap to netmap we supply a few fuctions
 * that can be called to open, close, read and write on netmap in a way
 * similar to libpcap. Note that the read/write function depend on
 * an ioctl()/select()/poll() being issued to refill rings or push
 * packets out.
 *
 * In order to use these, include #define NETMAP_WITH_LIBS
 * in the source file that invokes these functions.
 */

#ifndef _NET_NETMAP_USER_H_
#define _NET_NETMAP_USER_H_

#include <stdint.h>
#include <sys/socket.h>         /* apple needs sockaddr */
#include <net/if.h>             /* IFNAMSIZ */

#ifndef likely
#define likely(x)       __builtin_expect(!!(x), 1)
#define unlikely(x)     __builtin_expect(!!(x), 0)
#endif /* likely and unlikely */

#include <net/netmap.h>

/* helper macro */
#define _NETMAP_OFFSET(type, ptr, offset) \
        ((type)(void *)((char *)(ptr) + (offset)))

#define NETMAP_IF(_base, _ofs)  _NETMAP_OFFSET(struct netmap_if *, _base, _ofs)

#define NETMAP_TXRING(nifp, index) _NETMAP_OFFSET(struct netmap_ring *, \
        nifp, (nifp)->ring_ofs[index] )

#define NETMAP_RXRING(nifp, index) _NETMAP_OFFSET(struct netmap_ring *, \
        nifp, (nifp)->ring_ofs[index + (nifp)->ni_tx_rings + 1] )

#define NETMAP_BUF(ring, index)                         \
        ((char *)(ring) + (ring)->buf_ofs + ((index)*(ring)->nr_buf_size))

#define NETMAP_BUF_IDX(ring, buf)                       \
        ( ((char *)(buf) - ((char *)(ring) + (ring)->buf_ofs) ) / \
                (ring)->nr_buf_size )


static inline uint32_t
nm_ring_next(struct netmap_ring *r, uint32_t i)
{
        return ( unlikely(i + 1 == r->num_slots) ? 0 : i + 1);
}


/*
 * Return 1 if we have pending transmissions in the tx ring.
 * When everything is complete ring->head = ring->tail + 1 (modulo ring size)
 */
static inline int
nm_tx_pending(struct netmap_ring *r)
{
        return nm_ring_next(r, r->tail) != r->head;
}


static inline uint32_t
nm_ring_space(struct netmap_ring *ring)
{
        int ret = ring->tail - ring->cur;
        if (ret < 0)
                ret += ring->num_slots;
        return ret;
}


#ifdef NETMAP_WITH_LIBS
/*
 * Support for simple I/O libraries.
 * Include other system headers required for compiling this.
 */

#ifndef HAVE_NETMAP_WITH_LIBS
#define HAVE_NETMAP_WITH_LIBS

#include <stdio.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <string.h>     /* memset */
#include <sys/ioctl.h>
#include <sys/errno.h>  /* EINVAL */
#include <fcntl.h>      /* O_RDWR */
#include <unistd.h>     /* close() */
#include <signal.h>
#include <stdlib.h>

#ifndef ND /* debug macros */
/* debug support */
#define ND(_fmt, ...) do {} while(0)
#define D(_fmt, ...)                                            \
        do {                                                    \
                struct timeval _t0;                             \
                gettimeofday(&_t0, NULL);                       \
                fprintf(stderr, "%03d.%06d %s [%d] " _fmt "\n", \
                    (int)(_t0.tv_sec % 1000), (int)_t0.tv_usec, \
                    __FUNCTION__, __LINE__, ##__VA_ARGS__);     \
        } while (0)

/* Rate limited version of "D", lps indicates how many per second */
#define RD(lps, format, ...)                                    \
    do {                                                        \
        static int __t0, __cnt;                                 \
        struct timeval __xxts;                                  \
        gettimeofday(&__xxts, NULL);                            \
        if (__t0 != __xxts.tv_sec) {                            \
            __t0 = __xxts.tv_sec;                               \
            __cnt = 0;                                          \
        }                                                       \
        if (__cnt++ < lps) {                                    \
            D(format, ##__VA_ARGS__);                           \
        }                                                       \
    } while (0)
#endif

struct nm_pkthdr {      /* same as pcap_pkthdr */
        struct timeval  ts;
        uint32_t        caplen;
        uint32_t        len;
};

struct nm_stat {        /* same as pcap_stat    */
        u_int   ps_recv;
        u_int   ps_drop;
        u_int   ps_ifdrop;
#ifdef WIN32
        u_int   bs_capt;
#endif /* WIN32 */
};

#define NM_ERRBUF_SIZE  512

struct nm_desc {
        struct nm_desc *self; /* point to self if netmap. */
        int fd;
        void *mem;
        uint32_t memsize;
        int done_mmap;  /* set if mem is the result of mmap */
        struct netmap_if * const nifp;
        uint16_t first_tx_ring, last_tx_ring, cur_tx_ring;
        uint16_t first_rx_ring, last_rx_ring, cur_rx_ring;
        struct nmreq req;       /* also contains the nr_name = ifname */
        struct nm_pkthdr hdr;

        /*
         * The memory contains netmap_if, rings and then buffers.
         * Given a pointer (e.g. to nm_inject) we can compare with
         * mem/buf_start/buf_end to tell if it is a buffer or
         * some other descriptor in our region.
         * We also store a pointer to some ring as it helps in the
         * translation from buffer indexes to addresses.
         */
        struct netmap_ring * const some_ring;
        void * const buf_start;
        void * const buf_end;
        /* parameters from pcap_open_live */
        int snaplen;
        int promisc;
        int to_ms;
        char *errbuf;

        /* save flags so we can restore them on close */
        uint32_t if_flags;
        uint32_t if_reqcap;
        uint32_t if_curcap;

        struct nm_stat st;
        char msg[NM_ERRBUF_SIZE];
};

/*
 * when the descriptor is open correctly, d->self == d
 * Eventually we should also use some magic number.
 */
#define P2NMD(p)                ((struct nm_desc *)(p))
#define IS_NETMAP_DESC(d)       ((d) && P2NMD(d)->self == P2NMD(d))
#define NETMAP_FD(d)            (P2NMD(d)->fd)


/*
 * this is a slightly optimized copy routine which rounds
 * to multiple of 64 bytes and is often faster than dealing
 * with other odd sizes. We assume there is enough room
 * in the source and destination buffers.
 *
 * XXX only for multiples of 64 bytes, non overlapped.
 */
static inline void
nm_pkt_copy(const void *_src, void *_dst, int l)
{
        const uint64_t *src = (const uint64_t *)_src;
        uint64_t *dst = (uint64_t *)_dst;

        if (unlikely(l >= 1024)) {
                memcpy(dst, src, l);
                return;
        }
        for (; likely(l > 0); l-=64) {
                *dst++ = *src++;
                *dst++ = *src++;
                *dst++ = *src++;
                *dst++ = *src++;
                *dst++ = *src++;
                *dst++ = *src++;
                *dst++ = *src++;
                *dst++ = *src++;
        }
}


/*
 * The callback, invoked on each received packet. Same as libpcap
 */
typedef void (*nm_cb_t)(u_char *, const struct nm_pkthdr *, const u_char *d);

/*
 *--- the pcap-like API ---
 *
 * nm_open() opens a file descriptor, binds to a port and maps memory.
 *
 * ifname       (netmap:foo or vale:foo) is the port name
 *              a suffix can indicate the follwing:
 *              ^               bind the host (sw) ring pair
 *              *               bind host and NIC ring pairs (transparent)
 *              -NN             bind individual NIC ring pair
 *              {NN             bind master side of pipe NN
 *              }NN             bind slave side of pipe NN
 *              a suffix starting with + and the following flags,
 *              in any order:
 *              x               exclusive access
 *              z               zero copy monitor
 *              t               monitor tx side
 *              r               monitor rx side
 *
 * req          provides the initial values of nmreq before parsing ifname.
 *              Remember that the ifname parsing will override the ring
 *              number in nm_ringid, and part of nm_flags;
 * flags        special functions, normally 0
 *              indicates which fields of *arg are significant
 * arg          special functions, normally NULL
 *              if passed a netmap_desc with mem != NULL,
 *              use that memory instead of mmap.
 */

static struct nm_desc *nm_open(const char *ifname, const struct nmreq *req,
        uint64_t flags, const struct nm_desc *arg);

/*
 * nm_open can import some fields from the parent descriptor.
 * These flags control which ones.
 * Also in flags you can specify NETMAP_NO_TX_POLL and NETMAP_DO_RX_POLL,
 * which set the initial value for these flags.
 * Note that the 16 low bits of the flags are reserved for data
 * that may go into the nmreq.
 */
enum {
        NM_OPEN_NO_MMAP =       0x040000, /* reuse mmap from parent */
        NM_OPEN_IFNAME =        0x080000, /* nr_name, nr_ringid, nr_flags */
        NM_OPEN_ARG1 =          0x100000,
        NM_OPEN_ARG2 =          0x200000,
        NM_OPEN_ARG3 =          0x400000,
        NM_OPEN_RING_CFG =      0x800000, /* tx|rx rings|slots */
};


/*
 * nm_close()   closes and restores the port to its previous state
 */

static int nm_close(struct nm_desc *);

/*
 * nm_inject() is the same as pcap_inject()
 * nm_dispatch() is the same as pcap_dispatch()
 * nm_nextpkt() is the same as pcap_next()
 */

static int nm_inject(struct nm_desc *, const void *, size_t);
static int nm_dispatch(struct nm_desc *, int, nm_cb_t, u_char *);
static u_char *nm_nextpkt(struct nm_desc *, struct nm_pkthdr *);


/*
 * Try to open, return descriptor if successful, NULL otherwise.
 * An invalid netmap name will return errno = 0;
 * You can pass a pointer to a pre-filled nm_desc to add special
 * parameters. Flags is used as follows
 * NM_OPEN_NO_MMAP      use the memory from arg, only
 *                      if the nr_arg2 (memory block) matches.
 * NM_OPEN_ARG1         use req.nr_arg1 from arg
 * NM_OPEN_ARG2         use req.nr_arg2 from arg
 * NM_OPEN_RING_CFG     user ring config from arg
 */
static struct nm_desc *
nm_open(const char *ifname, const struct nmreq *req,
        uint64_t new_flags, const struct nm_desc *arg)
{
        struct nm_desc *d = NULL;
        const struct nm_desc *parent = arg;
        u_int namelen;
        uint32_t nr_ringid = 0, nr_flags, nr_reg;
        const char *port = NULL;
#define MAXERRMSG 80
        char errmsg[MAXERRMSG] = "";
        enum { P_START, P_RNGSFXOK, P_GETNUM, P_FLAGS, P_FLAGSOK } p_state;
        long num;

        if (strncmp(ifname, "netmap:", 7) && strncmp(ifname, "vale", 4)) {
                errno = 0; /* name not recognised, not an error */
                return NULL;
        }
        if (ifname[0] == 'n')
                ifname += 7;
        /* scan for a separator */
        for (port = ifname; *port && !index("-*^{}/", *port); port++)
                ;
        namelen = port - ifname;
        if (namelen >= sizeof(d->req.nr_name)) {
                snprintf(errmsg, MAXERRMSG, "name too long");
                goto fail;
        }
        p_state = P_START;
        nr_flags = NR_REG_ALL_NIC; /* default for no suffix */
        while (*port) {
                switch (p_state) {
                case P_START:
                        switch (*port) {
                        case '^': /* only SW ring */
                                nr_flags = NR_REG_SW;
                                p_state = P_RNGSFXOK;
                                break;
                        case '*': /* NIC and SW */
                                nr_flags = NR_REG_NIC_SW;
                                p_state = P_RNGSFXOK;
                                break;
                        case '-': /* one NIC ring pair */
                                nr_flags = NR_REG_ONE_NIC;
                                p_state = P_GETNUM;
                                break;
                        case '{': /* pipe (master endpoint) */
                                nr_flags = NR_REG_PIPE_MASTER;
                                p_state = P_GETNUM;
                                break;
                        case '}': /* pipe (slave endoint) */
                                nr_flags = NR_REG_PIPE_SLAVE;
                                p_state = P_GETNUM;
                                break;
                        case '/': /* start of flags */
                                p_state = P_FLAGS;
                                break;
                        default:
                                snprintf(errmsg, MAXERRMSG, "unknown modifier: '%c'", *port);
                                goto fail;
                        }
                        port++;
                        break;
                case P_RNGSFXOK:
                        switch (*port) {
                        case '/':
                                p_state = P_FLAGS;
                                break;
                        default:
                                snprintf(errmsg, MAXERRMSG, "unexpected character: '%c'", *port);
                                goto fail;
                        }
                        port++;
                        break;
                case P_GETNUM:
                        num = strtol(port, (char **)&port, 10);
                        if (num < 0 || num >= NETMAP_RING_MASK) {
                                snprintf(errmsg, MAXERRMSG, "'%ld' out of range [0, %d)",
                                                num, NETMAP_RING_MASK);
                                goto fail;
                        }
                        nr_ringid = num & NETMAP_RING_MASK;
                        p_state = P_RNGSFXOK;
                        break;
                case P_FLAGS:
                case P_FLAGSOK:
                        switch (*port) {
                        case 'x':
                                nr_flags |= NR_EXCLUSIVE;
                                break;
                        case 'z':
                                nr_flags |= NR_ZCOPY_MON;
                                break;
                        case 't':
                                nr_flags |= NR_MONITOR_TX;
                                break;
                        case 'r':
                                nr_flags |= NR_MONITOR_RX;
                                break;
                        default:
                                snprintf(errmsg, MAXERRMSG, "unrecognized flag: '%c'", *port);
                                goto fail;
                        }
                        port++;
                        p_state = P_FLAGSOK;
                        break;
                }
        }
        if (p_state != P_START && p_state != P_RNGSFXOK && p_state != P_FLAGSOK) {
                snprintf(errmsg, MAXERRMSG, "unexpected end of port name");
                goto fail;
        }
        ND("flags: %s %s %s %s",
                        (nr_flags & NR_EXCLUSIVE) ? "EXCLUSIVE" : "",
                        (nr_flags & NR_ZCOPY_MON) ? "ZCOPY_MON" : "",
                        (nr_flags & NR_MONITOR_TX) ? "MONITOR_TX" : "",
                        (nr_flags & NR_MONITOR_RX) ? "MONITOR_RX" : "");
        d = (struct nm_desc *)calloc(1, sizeof(*d));
        if (d == NULL) {
                snprintf(errmsg, MAXERRMSG, "nm_desc alloc failure");
                errno = ENOMEM;
                return NULL;
        }
        d->self = d;    /* set this early so nm_close() works */
        d->fd = open("/dev/netmap", O_RDWR);
        if (d->fd < 0) {
                snprintf(errmsg, MAXERRMSG, "cannot open /dev/netmap: %s", strerror(errno));
                goto fail;
        }

        if (req)
                d->req = *req;
        d->req.nr_version = NETMAP_API;
        d->req.nr_ringid &= ~NETMAP_RING_MASK;

        /* these fields are overridden by ifname and flags processing */
        d->req.nr_ringid |= nr_ringid;
        d->req.nr_flags = nr_flags;
        memcpy(d->req.nr_name, ifname, namelen);
        d->req.nr_name[namelen] = '\0';
        /* optionally import info from parent */
        if (IS_NETMAP_DESC(parent) && new_flags) {
                if (new_flags & NM_OPEN_ARG1)
                        D("overriding ARG1 %d", parent->req.nr_arg1);
                d->req.nr_arg1 = new_flags & NM_OPEN_ARG1 ?
                        parent->req.nr_arg1 : 4;
                if (new_flags & NM_OPEN_ARG2)
                        D("overriding ARG2 %d", parent->req.nr_arg2);
                d->req.nr_arg2 = new_flags & NM_OPEN_ARG2 ?
                        parent->req.nr_arg2 : 0;
                if (new_flags & NM_OPEN_ARG3)
                        D("overriding ARG3 %d", parent->req.nr_arg3);
                d->req.nr_arg3 = new_flags & NM_OPEN_ARG3 ?
                        parent->req.nr_arg3 : 0;
                if (new_flags & NM_OPEN_RING_CFG) {
                        D("overriding RING_CFG");
                        d->req.nr_tx_slots = parent->req.nr_tx_slots;
                        d->req.nr_rx_slots = parent->req.nr_rx_slots;
                        d->req.nr_tx_rings = parent->req.nr_tx_rings;
                        d->req.nr_rx_rings = parent->req.nr_rx_rings;
                }
                if (new_flags & NM_OPEN_IFNAME) {
                        D("overriding ifname %s ringid 0x%x flags 0x%x",
                                parent->req.nr_name, parent->req.nr_ringid,
                                parent->req.nr_flags);
                        memcpy(d->req.nr_name, parent->req.nr_name,
                                sizeof(d->req.nr_name));
                        d->req.nr_ringid = parent->req.nr_ringid;
                        d->req.nr_flags = parent->req.nr_flags;
                }
        }
        /* add the *XPOLL flags */
        d->req.nr_ringid |= new_flags & (NETMAP_NO_TX_POLL | NETMAP_DO_RX_POLL);

        if (ioctl(d->fd, NIOCREGIF, &d->req)) {
                snprintf(errmsg, MAXERRMSG, "NIOCREGIF failed: %s", strerror(errno));
                goto fail;
        }

        if (IS_NETMAP_DESC(parent) && parent->mem &&
            parent->req.nr_arg2 == d->req.nr_arg2) {
                /* do not mmap, inherit from parent */
                d->memsize = parent->memsize;
                d->mem = parent->mem;
        } else {
                /* XXX TODO: check if memsize is too large (or there is overflow) */
                d->memsize = d->req.nr_memsize;
                d->mem = mmap(0, d->memsize, PROT_WRITE | PROT_READ, MAP_SHARED,
                                d->fd, 0);
                if (d->mem == MAP_FAILED) {
                        snprintf(errmsg, MAXERRMSG, "mmap failed: %s", strerror(errno));
                        goto fail;
                }
                d->done_mmap = 1;
        }
        {
                struct netmap_if *nifp = NETMAP_IF(d->mem, d->req.nr_offset);
                struct netmap_ring *r = NETMAP_RXRING(nifp, );

                *(struct netmap_if **)(uintptr_t)&(d->nifp) = nifp;
                *(struct netmap_ring **)(uintptr_t)&d->some_ring = r;
                *(void **)(uintptr_t)&d->buf_start = NETMAP_BUF(r, 0);
                *(void **)(uintptr_t)&d->buf_end =
                        (char *)d->mem + d->memsize;
        }

        nr_reg = d->req.nr_flags & NR_REG_MASK;

        if (nr_reg ==  NR_REG_SW) { /* host stack */
                d->first_tx_ring = d->last_tx_ring = d->req.nr_tx_rings;
                d->first_rx_ring = d->last_rx_ring = d->req.nr_rx_rings;
        } else if (nr_reg ==  NR_REG_ALL_NIC) { /* only nic */
                d->first_tx_ring = 0;
                d->first_rx_ring = 0;
                d->last_tx_ring = d->req.nr_tx_rings - 1;
                d->last_rx_ring = d->req.nr_rx_rings - 1;
        } else if (nr_reg ==  NR_REG_NIC_SW) {
                d->first_tx_ring = 0;
                d->first_rx_ring = 0;
                d->last_tx_ring = d->req.nr_tx_rings;
                d->last_rx_ring = d->req.nr_rx_rings;
        } else if (nr_reg == NR_REG_ONE_NIC) {
                /* XXX check validity */
                d->first_tx_ring = d->last_tx_ring =
                d->first_rx_ring = d->last_rx_ring = d->req.nr_ringid & NETMAP_RING_MASK;
        } else { /* pipes */
                d->first_tx_ring = d->last_tx_ring = 0;
                d->first_rx_ring = d->last_rx_ring = 0;
        }

#ifdef DEBUG_NETMAP_USER
    { /* debugging code */
        int i;

        D("%s tx %d .. %d %d rx %d .. %d %d", ifname,
                d->first_tx_ring, d->last_tx_ring, d->req.nr_tx_rings,
                d->first_rx_ring, d->last_rx_ring, d->req.nr_rx_rings);
        for (i = 0; i <= d->req.nr_tx_rings; i++) {
                struct netmap_ring *r = NETMAP_TXRING(d->nifp, i);
                D("TX%d %p h %d c %d t %d", i, r, r->head, r->cur, r->tail);
        }
        for (i = 0; i <= d->req.nr_rx_rings; i++) {
                struct netmap_ring *r = NETMAP_RXRING(d->nifp, i);
                D("RX%d %p h %d c %d t %d", i, r, r->head, r->cur, r->tail);
        }
    }
#endif /* debugging */

        d->cur_tx_ring = d->first_tx_ring;
        d->cur_rx_ring = d->first_rx_ring;
        return d;

fail:
        nm_close(d);
        if (errmsg[0])
                D("%s %s", errmsg, ifname);
        if (errno == 0)
                errno = EINVAL;
        return NULL;
}


static int
nm_close(struct nm_desc *d)
{
        /*
         * ugly trick to avoid unused warnings
         */
        static void *__xxzt[] __attribute__ ((unused))  =
                { (void *)nm_open, (void *)nm_inject,
                  (void *)nm_dispatch, (void *)nm_nextpkt } ;

        if (d == NULL || d->self != d)
                return EINVAL;
        if (d->done_mmap && d->mem)
                munmap(d->mem, d->memsize);
        if (d->fd != -1)
                close(d->fd);
        bzero(d, sizeof(*d));
        free(d);
        return 0;
}


/*
 * Same prototype as pcap_inject(), only need to cast.
 */
static int
nm_inject(struct nm_desc *d, const void *buf, size_t size)
{
        u_int c, n = d->last_tx_ring - d->first_tx_ring + 1;

        for (c = 0; c < n ; c++) {
                /* compute current ring to use */
                struct netmap_ring *ring;
                uint32_t i, idx;
                uint32_t ri = d->cur_tx_ring + c;

                if (ri > d->last_tx_ring)
                        ri = d->first_tx_ring;
                ring = NETMAP_TXRING(d->nifp, ri);
                if (nm_ring_empty(ring)) {
                        continue;
                }
                i = ring->cur;
                idx = ring->slot[i].buf_idx;
                ring->slot[i].len = size;
                nm_pkt_copy(buf, NETMAP_BUF(ring, idx), size);
                d->cur_tx_ring = ri;
                ring->head = ring->cur = nm_ring_next(ring, i);
                return size;
        }
        return 0; /* fail */
}


/*
 * Same prototype as pcap_dispatch(), only need to cast.
 */
static int
nm_dispatch(struct nm_desc *d, int cnt, nm_cb_t cb, u_char *arg)
{
        int n = d->last_rx_ring - d->first_rx_ring + 1;
        int c, got = 0, ri = d->cur_rx_ring;

        if (cnt == 0)
                cnt = -1;
        /* cnt == -1 means infinite, but rings have a finite amount
         * of buffers and the int is large enough that we never wrap,
         * so we can omit checking for -1
         */
        for (c=0; c < n && cnt != got; c++) {
                /* compute current ring to use */
                struct netmap_ring *ring;

                ri = d->cur_rx_ring + c;
                if (ri > d->last_rx_ring)
                        ri = d->first_rx_ring;
                ring = NETMAP_RXRING(d->nifp, ri);
                for ( ; !nm_ring_empty(ring) && cnt != got; got++) {
                        u_int i = ring->cur;
                        u_int idx = ring->slot[i].buf_idx;
                        u_char *buf = (u_char *)NETMAP_BUF(ring, idx);

                        // __builtin_prefetch(buf);
                        d->hdr.len = d->hdr.caplen = ring->slot[i].len;
                        d->hdr.ts = ring->ts;
                        cb(arg, &d->hdr, buf);
                        ring->head = ring->cur = nm_ring_next(ring, i);
                }
        }
        d->cur_rx_ring = ri;
        return got;
}

static u_char *
nm_nextpkt(struct nm_desc *d, struct nm_pkthdr *hdr)
{
        int ri = d->cur_rx_ring;

        do {
                /* compute current ring to use */
                struct netmap_ring *ring = NETMAP_RXRING(d->nifp, ri);
                if (!nm_ring_empty(ring)) {
                        u_int i = ring->cur;
                        u_int idx = ring->slot[i].buf_idx;
                        u_char *buf = (u_char *)NETMAP_BUF(ring, idx);

                        // __builtin_prefetch(buf);
                        hdr->ts = ring->ts;
                        hdr->len = hdr->caplen = ring->slot[i].len;
                        ring->cur = nm_ring_next(ring, i);
                        /* we could postpone advancing head if we want
                         * to hold the buffer. This can be supported in
                         * the future.
                         */
                        ring->head = ring->cur;
                        d->cur_rx_ring = ri;
                        return buf;
                }
                ri++;
                if (ri > d->last_rx_ring)
                        ri = d->first_rx_ring;
        } while (ri != d->cur_rx_ring);
        return NULL; /* nothing found */
}

#endif /* !HAVE_NETMAP_WITH_LIBS */

#endif /* NETMAP_WITH_LIBS */

#endif /* _NET_NETMAP_USER_H_ */