net/netmap.c - third_party/qemu - Git at Google

 /*
  * netmap access for qemu
  *
  * Copyright (c) 2012-2013 Luigi Rizzo
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
  * in the Software without restriction, including without limitation the rights
  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  * copies of the Software, and to permit persons to whom the Software is
  * furnished to do so, subject to the following conditions:
  *
  * The above copyright notice and this permission notice shall be included in
  * all copies or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */


 #include "qemu/osdep.h"
 #include <sys/ioctl.h>
 #include <net/if.h>
 #define NETMAP_WITH_LIBS
 #include <net/netmap.h>
 #include <net/netmap_user.h>

 #include "net/net.h"
 #include "net/tap.h"
 #include "clients.h"
 #include "sysemu/sysemu.h"
 #include "qemu/error-report.h"
 #include "qapi/error.h"
 #include "qemu/iov.h"
 #include "qemu/cutils.h"
 #include "qemu/main-loop.h"

 typedef struct NetmapState {
     NetClientState      nc;
     struct nm_desc      *nmd;
     char                ifname[IFNAMSIZ];
     struct netmap_ring  *tx;
     struct netmap_ring  *rx;
     bool                read_poll;
     bool                write_poll;
     struct iovec        iov[IOV_MAX];
     int                 vnet_hdr_len;  /* Current virtio-net header length. */
 } NetmapState;

 #ifndef __FreeBSD__
 #define pkt_copy bcopy
 #else
 /* A fast copy routine only for multiples of 64 bytes, non overlapped. */
 static inline void
 pkt_copy(const void *_src, void *_dst, int l)
 {
     const uint64_t *src = _src;
     uint64_t *dst = _dst;
     if (unlikely(l >= 1024)) {
         bcopy(src, dst, l);
         return;
     }
     for (; l > 0; l -= 64) {
         *dst++ = *src++;
         *dst++ = *src++;
         *dst++ = *src++;
         *dst++ = *src++;
         *dst++ = *src++;
         *dst++ = *src++;
         *dst++ = *src++;
         *dst++ = *src++;
     }
 }
 #endif /* __FreeBSD__ */

 /*
  * Open a netmap device. We assume there is only one queue
  * (which is the case for the VALE bridge).
  */
 static struct nm_desc *netmap_open(const NetdevNetmapOptions *nm_opts,
                                    Error **errp)
 {
     struct nm_desc *nmd;
     struct nmreq req;

     memset(&req, 0, sizeof(req));

     nmd = nm_open(nm_opts->ifname, &req, NETMAP_NO_TX_POLL,
                   NULL);
     if (nmd == NULL) {
         error_setg_errno(errp, errno, "Failed to nm_open() %s",
                          nm_opts->ifname);
         return NULL;
     }

     return nmd;
 }

 static void netmap_send(void *opaque);
 static void netmap_writable(void *opaque);

 /* Set the event-loop handlers for the netmap backend. */
 static void netmap_update_fd_handler(NetmapState *s)
 {
     qemu_set_fd_handler(s->nmd->fd,
                         s->read_poll ? netmap_send : NULL,
                         s->write_poll ? netmap_writable : NULL,
                         s);
 }

 /* Update the read handler. */
 static void netmap_read_poll(NetmapState *s, bool enable)
 {
     if (s->read_poll != enable) { /* Do nothing if not changed. */
         s->read_poll = enable;
         netmap_update_fd_handler(s);
     }
 }

 /* Update the write handler. */
 static void netmap_write_poll(NetmapState *s, bool enable)
 {
     if (s->write_poll != enable) {
         s->write_poll = enable;
         netmap_update_fd_handler(s);
     }
 }

 static void netmap_poll(NetClientState *nc, bool enable)
 {
     NetmapState *s = DO_UPCAST(NetmapState, nc, nc);

     if (s->read_poll != enable || s->write_poll != enable) {
         s->write_poll = enable;
         s->read_poll  = enable;
         netmap_update_fd_handler(s);
     }
 }

 /*
  * The fd_write() callback, invoked if the fd is marked as
  * writable after a poll. Unregister the handler and flush any
  * buffered packets.
  */
 static void netmap_writable(void *opaque)
 {
     NetmapState *s = opaque;

     netmap_write_poll(s, false);
     qemu_flush_queued_packets(&s->nc);
 }

 static ssize_t netmap_receive_iov(NetClientState *nc,
                     const struct iovec *iov, int iovcnt)
 {
     NetmapState *s = DO_UPCAST(NetmapState, nc, nc);
     struct netmap_ring *ring = s->tx;
     unsigned int tail = ring->tail;
     ssize_t totlen = 0;
     uint32_t last;
     uint32_t idx;
     uint8_t *dst;
     int j;
     uint32_t i;

     last = i = ring->head;

     if (nm_ring_space(ring) < iovcnt) {
         /* Not enough netmap slots. Tell the kernel that we have seen the new
          * available slots (so that it notifies us again when it has more
          * ones), but without publishing any new slots to be processed
          * (e.g., we don't advance ring->head). */
         ring->cur = tail;
         netmap_write_poll(s, true);
         return 0;
     }

     for (j = 0; j < iovcnt; j++) {
         int iov_frag_size = iov[j].iov_len;
         int offset = 0;
         int nm_frag_size;

         totlen += iov_frag_size;

         /* Split each iovec fragment over more netmap slots, if
            necessary. */
         while (iov_frag_size) {
             nm_frag_size = MIN(iov_frag_size, ring->nr_buf_size);

             if (unlikely(i == tail)) {
                 /* We ran out of netmap slots while splitting the
                    iovec fragments. */
                 ring->cur = tail;
                 netmap_write_poll(s, true);
                 return 0;
             }

             idx = ring->slot[i].buf_idx;
             dst = (uint8_t *)NETMAP_BUF(ring, idx);

             ring->slot[i].len = nm_frag_size;
             ring->slot[i].flags = NS_MOREFRAG;
             pkt_copy(iov[j].iov_base + offset, dst, nm_frag_size);

             last = i;
             i = nm_ring_next(ring, i);

             offset += nm_frag_size;
             iov_frag_size -= nm_frag_size;
         }
     }
     /* The last slot must not have NS_MOREFRAG set. */
     ring->slot[last].flags &= ~NS_MOREFRAG;

     /* Now update ring->head and ring->cur to publish the new slots and
      * the new wakeup point. */
     ring->head = ring->cur = i;

     ioctl(s->nmd->fd, NIOCTXSYNC, NULL);

     return totlen;
 }

 static ssize_t netmap_receive(NetClientState *nc,
       const uint8_t *buf, size_t size)
 {
     struct iovec iov;

     iov.iov_base = (void *)buf;
     iov.iov_len = size;

     return netmap_receive_iov(nc, &iov, 1);
 }

 /* Complete a previous send (backend --> guest) and enable the
    fd_read callback. */
 static void netmap_send_completed(NetClientState *nc, ssize_t len)
 {
     NetmapState *s = DO_UPCAST(NetmapState, nc, nc);

     netmap_read_poll(s, true);
 }

 static void netmap_send(void *opaque)
 {
     NetmapState *s = opaque;
     struct netmap_ring *ring = s->rx;
     unsigned int tail = ring->tail;

     /* Keep sending while there are available slots in the netmap
        RX ring and the forwarding path towards the peer is open. */
     while (ring->head != tail) {
         uint32_t i = ring->head;
         uint32_t idx;
         bool morefrag;
         int iovcnt = 0;
         int iovsize;

         /* Get a (possibly multi-slot) packet. */
         do {
             idx = ring->slot[i].buf_idx;
             morefrag = (ring->slot[i].flags & NS_MOREFRAG);
             s->iov[iovcnt].iov_base = (void *)NETMAP_BUF(ring, idx);
             s->iov[iovcnt].iov_len = ring->slot[i].len;
             iovcnt++;
             i = nm_ring_next(ring, i);
         } while (i != tail && morefrag);

         /* Advance ring->cur to tell the kernel that we have seen the slots. */
         ring->cur = i;

         if (unlikely(morefrag)) {
             /* This is a truncated packet, so we can stop without releasing the
              * incomplete slots by updating ring->head. We will hopefully
              * re-read the complete packet the next time we are called. */
             break;
         }

         iovsize = qemu_sendv_packet_async(&s->nc, s->iov, iovcnt,
                                             netmap_send_completed);

         /* Release the slots to the kernel. */
         ring->head = i;

         if (iovsize == 0) {
             /* The peer does not receive anymore. Packet is queued, stop
              * reading from the backend until netmap_send_completed(). */
             netmap_read_poll(s, false);
             break;
         }
     }
 }

 /* Flush and close. */
 static void netmap_cleanup(NetClientState *nc)
 {
     NetmapState *s = DO_UPCAST(NetmapState, nc, nc);

     qemu_purge_queued_packets(nc);

     netmap_poll(nc, false);
     nm_close(s->nmd);
     s->nmd = NULL;
 }

 /* Offloading manipulation support callbacks. */
 static int netmap_fd_set_vnet_hdr_len(NetmapState *s, int len)
 {
     struct nmreq req;

     /* Issue a NETMAP_BDG_VNET_HDR command to change the virtio-net header
      * length for the netmap adapter associated to 's->ifname'.
      */
     memset(&req, 0, sizeof(req));
     pstrcpy(req.nr_name, sizeof(req.nr_name), s->ifname);
     req.nr_version = NETMAP_API;
     req.nr_cmd = NETMAP_BDG_VNET_HDR;
     req.nr_arg1 = len;

     return ioctl(s->nmd->fd, NIOCREGIF, &req);
 }

 static bool netmap_has_vnet_hdr_len(NetClientState *nc, int len)
 {
     NetmapState *s = DO_UPCAST(NetmapState, nc, nc);
     int prev_len = s->vnet_hdr_len;

     /* Check that we can set the new length. */
     if (netmap_fd_set_vnet_hdr_len(s, len)) {
         return false;
     }

     /* Restore the previous length. */
     if (netmap_fd_set_vnet_hdr_len(s, prev_len)) {
         error_report("Failed to restore vnet-hdr length %d on %s: %s",
                      prev_len, s->ifname, strerror(errno));
         abort();
     }

     return true;
 }

 /* A netmap interface that supports virtio-net headers always
  * supports UFO, so we use this callback also for the has_ufo hook. */
 static bool netmap_has_vnet_hdr(NetClientState *nc)
 {
     return netmap_has_vnet_hdr_len(nc, sizeof(struct virtio_net_hdr));
 }

 static void netmap_using_vnet_hdr(NetClientState *nc, bool enable)
 {
 }

 static void netmap_set_vnet_hdr_len(NetClientState *nc, int len)
 {
     NetmapState *s = DO_UPCAST(NetmapState, nc, nc);
     int err;

     err = netmap_fd_set_vnet_hdr_len(s, len);
     if (err) {
         error_report("Unable to set vnet-hdr length %d on %s: %s",
                      len, s->ifname, strerror(errno));
     } else {
         /* Keep track of the current length. */
         s->vnet_hdr_len = len;
     }
 }

 static void netmap_set_offload(NetClientState *nc, int csum, int tso4, int tso6,
                                int ecn, int ufo)
 {
     NetmapState *s = DO_UPCAST(NetmapState, nc, nc);

     /* Setting a virtio-net header length greater than zero automatically
      * enables the offloadings. */
     if (!s->vnet_hdr_len) {
         netmap_set_vnet_hdr_len(nc, sizeof(struct virtio_net_hdr));
     }
 }

 /* NetClientInfo methods */
 static NetClientInfo net_netmap_info = {
     .type = NET_CLIENT_DRIVER_NETMAP,
     .size = sizeof(NetmapState),
     .receive = netmap_receive,
     .receive_iov = netmap_receive_iov,
     .poll = netmap_poll,
     .cleanup = netmap_cleanup,
     .has_ufo = netmap_has_vnet_hdr,
     .has_vnet_hdr = netmap_has_vnet_hdr,
     .has_vnet_hdr_len = netmap_has_vnet_hdr_len,
     .using_vnet_hdr = netmap_using_vnet_hdr,
     .set_offload = netmap_set_offload,
     .set_vnet_hdr_len = netmap_set_vnet_hdr_len,
 };

 /* The exported init function
  *
  * ... -net netmap,ifname="..."
  */
 int net_init_netmap(const Netdev *netdev,
                     const char *name, NetClientState *peer, Error **errp)
 {
     const NetdevNetmapOptions *netmap_opts = &netdev->u.netmap;
     struct nm_desc *nmd;
     NetClientState *nc;
     Error *err = NULL;
     NetmapState *s;

     nmd = netmap_open(netmap_opts, &err);
     if (err) {
         error_propagate(errp, err);
         return -1;
     }
     /* Create the object. */
     nc = qemu_new_net_client(&net_netmap_info, peer, "netmap", name);
     s = DO_UPCAST(NetmapState, nc, nc);
     s->nmd = nmd;
     s->tx = NETMAP_TXRING(nmd->nifp, 0);
     s->rx = NETMAP_RXRING(nmd->nifp, 0);
     s->vnet_hdr_len = 0;
     pstrcpy(s->ifname, sizeof(s->ifname), netmap_opts->ifname);
     netmap_read_poll(s, true); /* Initially only poll for reads. */

     return 0;
 }
	/*
	* netmap access for qemu
	*
	* Copyright (c) 2012-2013 Luigi Rizzo
	*
	* Permission is hereby granted, free of charge, to any person obtaining a copy
	* of this software and associated documentation files (the "Software"), to deal
	* in the Software without restriction, including without limitation the rights
	* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	* copies of the Software, and to permit persons to whom the Software is
	* furnished to do so, subject to the following conditions:
	*
	* The above copyright notice and this permission notice shall be included in
	* all copies or substantial portions of the Software.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
	* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
	* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
	* THE SOFTWARE.
	*/


	#include "qemu/osdep.h"
	#include <sys/ioctl.h>
	#include <net/if.h>
	#define NETMAP_WITH_LIBS
	#include <net/netmap.h>
	#include <net/netmap_user.h>

	#include "net/net.h"
	#include "net/tap.h"
	#include "clients.h"
	#include "sysemu/sysemu.h"
	#include "qemu/error-report.h"
	#include "qapi/error.h"
	#include "qemu/iov.h"
	#include "qemu/cutils.h"
	#include "qemu/main-loop.h"

	typedef struct NetmapState {
	NetClientState nc;
	struct nm_desc *nmd;
	char ifname[IFNAMSIZ];
	struct netmap_ring *tx;
	struct netmap_ring *rx;
	bool read_poll;
	bool write_poll;
	struct iovec iov[IOV_MAX];
	int vnet_hdr_len; /* Current virtio-net header length. */
	} NetmapState;

	#ifndef __FreeBSD__
	#define pkt_copy bcopy
	#else
	/* A fast copy routine only for multiples of 64 bytes, non overlapped. */
	static inline void
	pkt_copy(const void _src, void _dst, int l)
	{
	const uint64_t *src = _src;
	uint64_t *dst = _dst;
	if (unlikely(l >= 1024)) {
	bcopy(src, dst, l);
	return;
	}
	for (; l > 0; l -= 64) {
	dst++ = src++;
	dst++ = src++;
	dst++ = src++;
	dst++ = src++;
	dst++ = src++;
	dst++ = src++;
	dst++ = src++;
	dst++ = src++;
	}
	}
	#endif /* __FreeBSD__ */

	/*
	* Open a netmap device. We assume there is only one queue
	* (which is the case for the VALE bridge).
	*/
	static struct nm_desc netmap_open(const NetdevNetmapOptions nm_opts,
	Error **errp)
	{
	struct nm_desc *nmd;
	struct nmreq req;

	memset(&req, 0, sizeof(req));

	nmd = nm_open(nm_opts->ifname, &req, NETMAP_NO_TX_POLL,
	NULL);
	if (nmd == NULL) {
	error_setg_errno(errp, errno, "Failed to nm_open() %s",
	nm_opts->ifname);
	return NULL;
	}

	return nmd;
	}

	static void netmap_send(void *opaque);
	static void netmap_writable(void *opaque);

	/* Set the event-loop handlers for the netmap backend. */
	static void netmap_update_fd_handler(NetmapState *s)
	{
	qemu_set_fd_handler(s->nmd->fd,
	s->read_poll ? netmap_send : NULL,
	s->write_poll ? netmap_writable : NULL,
	s);
	}

	/* Update the read handler. */
	static void netmap_read_poll(NetmapState *s, bool enable)
	{
	if (s->read_poll != enable) { /* Do nothing if not changed. */
	s->read_poll = enable;
	netmap_update_fd_handler(s);
	}
	}

	/* Update the write handler. */
	static void netmap_write_poll(NetmapState *s, bool enable)
	{
	if (s->write_poll != enable) {
	s->write_poll = enable;
	netmap_update_fd_handler(s);
	}
	}

	static void netmap_poll(NetClientState *nc, bool enable)
	{
	NetmapState *s = DO_UPCAST(NetmapState, nc, nc);

	if (s->read_poll != enable \|\| s->write_poll != enable) {
	s->write_poll = enable;
	s->read_poll = enable;
	netmap_update_fd_handler(s);
	}
	}

	/*
	* The fd_write() callback, invoked if the fd is marked as
	* writable after a poll. Unregister the handler and flush any
	* buffered packets.
	*/
	static void netmap_writable(void *opaque)
	{
	NetmapState *s = opaque;

	netmap_write_poll(s, false);
	qemu_flush_queued_packets(&s->nc);
	}

	static ssize_t netmap_receive_iov(NetClientState *nc,
	const struct iovec *iov, int iovcnt)
	{
	NetmapState *s = DO_UPCAST(NetmapState, nc, nc);
	struct netmap_ring *ring = s->tx;
	unsigned int tail = ring->tail;
	ssize_t totlen = 0;
	uint32_t last;
	uint32_t idx;
	uint8_t *dst;
	int j;
	uint32_t i;

	last = i = ring->head;

	if (nm_ring_space(ring) < iovcnt) {
	/* Not enough netmap slots. Tell the kernel that we have seen the new
	* available slots (so that it notifies us again when it has more
	* ones), but without publishing any new slots to be processed
	* (e.g., we don't advance ring->head). */
	ring->cur = tail;
	netmap_write_poll(s, true);
	return 0;
	}

	for (j = 0; j < iovcnt; j++) {
	int iov_frag_size = iov[j].iov_len;
	int offset = 0;
	int nm_frag_size;

	totlen += iov_frag_size;

	/* Split each iovec fragment over more netmap slots, if
	necessary. */
	while (iov_frag_size) {
	nm_frag_size = MIN(iov_frag_size, ring->nr_buf_size);

	if (unlikely(i == tail)) {
	/* We ran out of netmap slots while splitting the
	iovec fragments. */
	ring->cur = tail;
	netmap_write_poll(s, true);
	return 0;
	}

	idx = ring->slot[i].buf_idx;
	dst = (uint8_t *)NETMAP_BUF(ring, idx);

	ring->slot[i].len = nm_frag_size;
	ring->slot[i].flags = NS_MOREFRAG;
	pkt_copy(iov[j].iov_base + offset, dst, nm_frag_size);

	last = i;
	i = nm_ring_next(ring, i);

	offset += nm_frag_size;
	iov_frag_size -= nm_frag_size;
	}
	}
	/* The last slot must not have NS_MOREFRAG set. */
	ring->slot[last].flags &= ~NS_MOREFRAG;

	/* Now update ring->head and ring->cur to publish the new slots and
	* the new wakeup point. */
	ring->head = ring->cur = i;

	ioctl(s->nmd->fd, NIOCTXSYNC, NULL);

	return totlen;
	}

	static ssize_t netmap_receive(NetClientState *nc,
	const uint8_t *buf, size_t size)
	{
	struct iovec iov;

	iov.iov_base = (void *)buf;
	iov.iov_len = size;

	return netmap_receive_iov(nc, &iov, 1);
	}

	/* Complete a previous send (backend --> guest) and enable the
	fd_read callback. */
	static void netmap_send_completed(NetClientState *nc, ssize_t len)
	{
	NetmapState *s = DO_UPCAST(NetmapState, nc, nc);

	netmap_read_poll(s, true);
	}

	static void netmap_send(void *opaque)
	{
	NetmapState *s = opaque;
	struct netmap_ring *ring = s->rx;
	unsigned int tail = ring->tail;

	/* Keep sending while there are available slots in the netmap
	RX ring and the forwarding path towards the peer is open. */
	while (ring->head != tail) {
	uint32_t i = ring->head;
	uint32_t idx;
	bool morefrag;
	int iovcnt = 0;
	int iovsize;

	/* Get a (possibly multi-slot) packet. */
	do {
	idx = ring->slot[i].buf_idx;
	morefrag = (ring->slot[i].flags & NS_MOREFRAG);
	s->iov[iovcnt].iov_base = (void *)NETMAP_BUF(ring, idx);
	s->iov[iovcnt].iov_len = ring->slot[i].len;
	iovcnt++;
	i = nm_ring_next(ring, i);
	} while (i != tail && morefrag);

	/* Advance ring->cur to tell the kernel that we have seen the slots. */
	ring->cur = i;

	if (unlikely(morefrag)) {
	/* This is a truncated packet, so we can stop without releasing the
	* incomplete slots by updating ring->head. We will hopefully
	* re-read the complete packet the next time we are called. */
	break;
	}

	iovsize = qemu_sendv_packet_async(&s->nc, s->iov, iovcnt,
	netmap_send_completed);

	/* Release the slots to the kernel. */
	ring->head = i;

	if (iovsize == 0) {
	/* The peer does not receive anymore. Packet is queued, stop
	* reading from the backend until netmap_send_completed(). */
	netmap_read_poll(s, false);
	break;
	}
	}
	}

	/* Flush and close. */
	static void netmap_cleanup(NetClientState *nc)
	{
	NetmapState *s = DO_UPCAST(NetmapState, nc, nc);

	qemu_purge_queued_packets(nc);

	netmap_poll(nc, false);
	nm_close(s->nmd);
	s->nmd = NULL;
	}

	/* Offloading manipulation support callbacks. */
	static int netmap_fd_set_vnet_hdr_len(NetmapState *s, int len)
	{
	struct nmreq req;

	/* Issue a NETMAP_BDG_VNET_HDR command to change the virtio-net header
	* length for the netmap adapter associated to 's->ifname'.
	*/
	memset(&req, 0, sizeof(req));
	pstrcpy(req.nr_name, sizeof(req.nr_name), s->ifname);
	req.nr_version = NETMAP_API;
	req.nr_cmd = NETMAP_BDG_VNET_HDR;
	req.nr_arg1 = len;

	return ioctl(s->nmd->fd, NIOCREGIF, &req);
	}

	static bool netmap_has_vnet_hdr_len(NetClientState *nc, int len)
	{
	NetmapState *s = DO_UPCAST(NetmapState, nc, nc);
	int prev_len = s->vnet_hdr_len;

	/* Check that we can set the new length. */
	if (netmap_fd_set_vnet_hdr_len(s, len)) {
	return false;
	}

	/* Restore the previous length. */
	if (netmap_fd_set_vnet_hdr_len(s, prev_len)) {
	error_report("Failed to restore vnet-hdr length %d on %s: %s",
	prev_len, s->ifname, strerror(errno));
	abort();
	}

	return true;
	}

	/* A netmap interface that supports virtio-net headers always
	* supports UFO, so we use this callback also for the has_ufo hook. */
	static bool netmap_has_vnet_hdr(NetClientState *nc)
	{
	return netmap_has_vnet_hdr_len(nc, sizeof(struct virtio_net_hdr));
	}

	static void netmap_using_vnet_hdr(NetClientState *nc, bool enable)
	{
	}

	static void netmap_set_vnet_hdr_len(NetClientState *nc, int len)
	{
	NetmapState *s = DO_UPCAST(NetmapState, nc, nc);
	int err;

	err = netmap_fd_set_vnet_hdr_len(s, len);
	if (err) {
	error_report("Unable to set vnet-hdr length %d on %s: %s",
	len, s->ifname, strerror(errno));
	} else {
	/* Keep track of the current length. */
	s->vnet_hdr_len = len;
	}
	}

	static void netmap_set_offload(NetClientState *nc, int csum, int tso4, int tso6,
	int ecn, int ufo)
	{
	NetmapState *s = DO_UPCAST(NetmapState, nc, nc);

	/* Setting a virtio-net header length greater than zero automatically
	* enables the offloadings. */
	if (!s->vnet_hdr_len) {
	netmap_set_vnet_hdr_len(nc, sizeof(struct virtio_net_hdr));
	}
	}

	/* NetClientInfo methods */
	static NetClientInfo net_netmap_info = {
	.type = NET_CLIENT_DRIVER_NETMAP,
	.size = sizeof(NetmapState),
	.receive = netmap_receive,
	.receive_iov = netmap_receive_iov,
	.poll = netmap_poll,
	.cleanup = netmap_cleanup,
	.has_ufo = netmap_has_vnet_hdr,
	.has_vnet_hdr = netmap_has_vnet_hdr,
	.has_vnet_hdr_len = netmap_has_vnet_hdr_len,
	.using_vnet_hdr = netmap_using_vnet_hdr,
	.set_offload = netmap_set_offload,
	.set_vnet_hdr_len = netmap_set_vnet_hdr_len,
	};

	/* The exported init function
	*
	* ... -net netmap,ifname="..."
	*/
	int net_init_netmap(const Netdev *netdev,
	const char name, NetClientState peer, Error **errp)
	{
	const NetdevNetmapOptions *netmap_opts = &netdev->u.netmap;
	struct nm_desc *nmd;
	NetClientState *nc;
	Error *err = NULL;
	NetmapState *s;

	nmd = netmap_open(netmap_opts, &err);
	if (err) {
	error_propagate(errp, err);
	return -1;
	}
	/* Create the object. */
	nc = qemu_new_net_client(&net_netmap_info, peer, "netmap", name);
	s = DO_UPCAST(NetmapState, nc, nc);
	s->nmd = nmd;
	s->tx = NETMAP_TXRING(nmd->nifp, 0);
	s->rx = NETMAP_RXRING(nmd->nifp, 0);
	s->vnet_hdr_len = 0;
	pstrcpy(s->ifname, sizeof(s->ifname), netmap_opts->ifname);
	netmap_read_poll(s, true); /* Initially only poll for reads. */

	return 0;
	}