net/vhost-user.c - qemu - Git at Google

 /*
  * vhost-user.c
  *
  * Copyright (c) 2013 Virtual Open Systems Sarl.
  *
  * This work is licensed under the terms of the GNU GPL, version 2 or later.
  * See the COPYING file in the top-level directory.
  *
  */

 #include "qemu/osdep.h"
 #include "clients.h"
 #include "net/vhost_net.h"
 #include "net/vhost-user.h"
 #include "hw/virtio/vhost-user.h"
 #include "chardev/char-fe.h"
 #include "qapi/error.h"
 #include "qapi/qapi-commands-net.h"
 #include "qemu/config-file.h"
 #include "qemu/error-report.h"
 #include "qemu/option.h"
 #include "trace.h"

 typedef struct NetVhostUserState {
     NetClientState nc;
     CharBackend chr; /* only queue index 0 */
     VhostUserState *vhost_user;
     VHostNetState *vhost_net;
     guint watch;
     uint64_t acked_features;
     bool started;
 } NetVhostUserState;

 VHostNetState *vhost_user_get_vhost_net(NetClientState *nc)
 {
     NetVhostUserState *s = DO_UPCAST(NetVhostUserState, nc, nc);
     assert(nc->info->type == NET_CLIENT_DRIVER_VHOST_USER);
     return s->vhost_net;
 }

 uint64_t vhost_user_get_acked_features(NetClientState *nc)
 {
     NetVhostUserState *s = DO_UPCAST(NetVhostUserState, nc, nc);
     assert(nc->info->type == NET_CLIENT_DRIVER_VHOST_USER);
     return s->acked_features;
 }

 static void vhost_user_stop(int queues, NetClientState *ncs[])
 {
     NetVhostUserState *s;
     int i;

     for (i = 0; i < queues; i++) {
         assert(ncs[i]->info->type == NET_CLIENT_DRIVER_VHOST_USER);

         s = DO_UPCAST(NetVhostUserState, nc, ncs[i]);

         if (s->vhost_net) {
             /* save acked features */
             uint64_t features = vhost_net_get_acked_features(s->vhost_net);
             if (features) {
                 s->acked_features = features;
             }
             vhost_net_cleanup(s->vhost_net);
         }
     }
 }

 static int vhost_user_start(int queues, NetClientState *ncs[],
                             VhostUserState *be)
 {
     VhostNetOptions options;
     struct vhost_net *net = NULL;
     NetVhostUserState *s;
     int max_queues;
     int i;

     options.backend_type = VHOST_BACKEND_TYPE_USER;

     for (i = 0; i < queues; i++) {
         assert(ncs[i]->info->type == NET_CLIENT_DRIVER_VHOST_USER);

         s = DO_UPCAST(NetVhostUserState, nc, ncs[i]);

         options.net_backend = ncs[i];
         options.opaque      = be;
         options.busyloop_timeout = 0;
         net = vhost_net_init(&options);
         if (!net) {
             error_report("failed to init vhost_net for queue %d", i);
             goto err;
         }

         if (i == 0) {
             max_queues = vhost_net_get_max_queues(net);
             if (queues > max_queues) {
                 error_report("you are asking more queues than supported: %d",
                              max_queues);
                 goto err;
             }
         }

         if (s->vhost_net) {
             vhost_net_cleanup(s->vhost_net);
             g_free(s->vhost_net);
         }
         s->vhost_net = net;
     }

     return 0;

 err:
     if (net) {
         vhost_net_cleanup(net);
         g_free(net);
     }
     vhost_user_stop(i, ncs);
     return -1;
 }

 static ssize_t vhost_user_receive(NetClientState *nc, const uint8_t *buf,
                                   size_t size)
 {
     /* In case of RARP (message size is 60) notify backup to send a fake RARP.
        This fake RARP will be sent by backend only for guest
        without GUEST_ANNOUNCE capability.
      */
     if (size == 60) {
         NetVhostUserState *s = DO_UPCAST(NetVhostUserState, nc, nc);
         int r;
         static int display_rarp_failure = 1;
         char mac_addr[6];

         /* extract guest mac address from the RARP message */
         memcpy(mac_addr, &buf[6], 6);

         r = vhost_net_notify_migration_done(s->vhost_net, mac_addr);

         if ((r != 0) && (display_rarp_failure)) {
             fprintf(stderr,
                     "Vhost user backend fails to broadcast fake RARP\n");
             fflush(stderr);
             display_rarp_failure = 0;
         }
     }

     return size;
 }

 static void net_vhost_user_cleanup(NetClientState *nc)
 {
     NetVhostUserState *s = DO_UPCAST(NetVhostUserState, nc, nc);

     if (s->vhost_net) {
         vhost_net_cleanup(s->vhost_net);
         g_free(s->vhost_net);
         s->vhost_net = NULL;
     }
     if (nc->queue_index == 0) {
         if (s->watch) {
             g_source_remove(s->watch);
             s->watch = 0;
         }
         qemu_chr_fe_deinit(&s->chr, true);
         if (s->vhost_user) {
             vhost_user_cleanup(s->vhost_user);
             g_free(s->vhost_user);
             s->vhost_user = NULL;
         }
     }

     qemu_purge_queued_packets(nc);
 }

 static int vhost_user_set_vnet_endianness(NetClientState *nc,
                                           bool enable)
 {
     /* Nothing to do.  If the server supports
      * VHOST_USER_PROTOCOL_F_CROSS_ENDIAN, it will get the
      * vnet header endianness from there.  If it doesn't, negotiation
      * fails.
      */
     return 0;
 }

 static bool vhost_user_has_vnet_hdr(NetClientState *nc)
 {
     assert(nc->info->type == NET_CLIENT_DRIVER_VHOST_USER);

     return true;
 }

 static bool vhost_user_has_ufo(NetClientState *nc)
 {
     assert(nc->info->type == NET_CLIENT_DRIVER_VHOST_USER);

     return true;
 }

 static NetClientInfo net_vhost_user_info = {
         .type = NET_CLIENT_DRIVER_VHOST_USER,
         .size = sizeof(NetVhostUserState),
         .receive = vhost_user_receive,
         .cleanup = net_vhost_user_cleanup,
         .has_vnet_hdr = vhost_user_has_vnet_hdr,
         .has_ufo = vhost_user_has_ufo,
         .set_vnet_be = vhost_user_set_vnet_endianness,
         .set_vnet_le = vhost_user_set_vnet_endianness,
 };

 static gboolean net_vhost_user_watch(void *do_not_use, GIOCondition cond,
                                      void *opaque)
 {
     NetVhostUserState *s = opaque;

     qemu_chr_fe_disconnect(&s->chr);

     return TRUE;
 }

 static void net_vhost_user_event(void *opaque, QEMUChrEvent event);

 static void chr_closed_bh(void *opaque)
 {
     const char *name = opaque;
     NetClientState *ncs[MAX_QUEUE_NUM];
     NetVhostUserState *s;
     Error *err = NULL;
     int queues, i;

     queues = qemu_find_net_clients_except(name, ncs,
                                           NET_CLIENT_DRIVER_NIC,
                                           MAX_QUEUE_NUM);
     assert(queues < MAX_QUEUE_NUM);

     s = DO_UPCAST(NetVhostUserState, nc, ncs[0]);

     for (i = queues -1; i >= 0; i--) {
         s = DO_UPCAST(NetVhostUserState, nc, ncs[i]);

         if (s->vhost_net) {
             s->acked_features = vhost_net_get_acked_features(s->vhost_net);
         }
     }

     qmp_set_link(name, false, &err);

     qemu_chr_fe_set_handlers(&s->chr, NULL, NULL, net_vhost_user_event,
                              NULL, opaque, NULL, true);

     if (err) {
         error_report_err(err);
     }
 }

 static void net_vhost_user_event(void *opaque, QEMUChrEvent event)
 {
     const char *name = opaque;
     NetClientState *ncs[MAX_QUEUE_NUM];
     NetVhostUserState *s;
     Chardev *chr;
     Error *err = NULL;
     int queues;

     queues = qemu_find_net_clients_except(name, ncs,
                                           NET_CLIENT_DRIVER_NIC,
                                           MAX_QUEUE_NUM);
     assert(queues < MAX_QUEUE_NUM);

     s = DO_UPCAST(NetVhostUserState, nc, ncs[0]);
     chr = qemu_chr_fe_get_driver(&s->chr);
     trace_vhost_user_event(chr->label, event);
     switch (event) {
     case CHR_EVENT_OPENED:
         if (vhost_user_start(queues, ncs, s->vhost_user) < 0) {
             qemu_chr_fe_disconnect(&s->chr);
             return;
         }
         s->watch = qemu_chr_fe_add_watch(&s->chr, G_IO_HUP,
                                          net_vhost_user_watch, s);
         qmp_set_link(name, true, &err);
         s->started = true;
         break;
     case CHR_EVENT_CLOSED:
         /* a close event may happen during a read/write, but vhost
          * code assumes the vhost_dev remains setup, so delay the
          * stop & clear to idle.
          * FIXME: better handle failure in vhost code, remove bh
          */
         if (s->watch) {
             AioContext *ctx = qemu_get_current_aio_context();

             g_source_remove(s->watch);
             s->watch = 0;
             qemu_chr_fe_set_handlers(&s->chr, NULL, NULL, NULL, NULL,
                                      NULL, NULL, false);

             aio_bh_schedule_oneshot(ctx, chr_closed_bh, opaque);
         }
         break;
     case CHR_EVENT_BREAK:
     case CHR_EVENT_MUX_IN:
     case CHR_EVENT_MUX_OUT:
         /* Ignore */
         break;
     }

     if (err) {
         error_report_err(err);
     }
 }

 static int net_vhost_user_init(NetClientState *peer, const char *device,
                                const char *name, Chardev *chr,
                                int queues)
 {
     Error *err = NULL;
     NetClientState *nc, *nc0 = NULL;
     NetVhostUserState *s = NULL;
     VhostUserState *user;
     int i;

     assert(name);
     assert(queues > 0);

     user = g_new0(struct VhostUserState, 1);
     for (i = 0; i < queues; i++) {
         nc = qemu_new_net_client(&net_vhost_user_info, peer, device, name);
         snprintf(nc->info_str, sizeof(nc->info_str), "vhost-user%d to %s",
                  i, chr->label);
         nc->queue_index = i;
         if (!nc0) {
             nc0 = nc;
             s = DO_UPCAST(NetVhostUserState, nc, nc);
             if (!qemu_chr_fe_init(&s->chr, chr, &err) ||
                 !vhost_user_init(user, &s->chr, &err)) {
                 error_report_err(err);
                 goto err;
             }
         }
         s = DO_UPCAST(NetVhostUserState, nc, nc);
         s->vhost_user = user;
     }

     s = DO_UPCAST(NetVhostUserState, nc, nc0);
     do {
         if (qemu_chr_fe_wait_connected(&s->chr, &err) < 0) {
             error_report_err(err);
             goto err;
         }
         qemu_chr_fe_set_handlers(&s->chr, NULL, NULL,
                                  net_vhost_user_event, NULL, nc0->name, NULL,
                                  true);
     } while (!s->started);

     assert(s->vhost_net);

     return 0;

 err:
     if (user) {
         vhost_user_cleanup(user);
         g_free(user);
         if (s) {
             s->vhost_user = NULL;
         }
     }
     if (nc0) {
         qemu_del_net_client(nc0);
     }

     return -1;
 }

 static Chardev *net_vhost_claim_chardev(
     const NetdevVhostUserOptions *opts, Error **errp)
 {
     Chardev *chr = qemu_chr_find(opts->chardev);

     if (chr == NULL) {
         error_setg(errp, "chardev \"%s\" not found", opts->chardev);
         return NULL;
     }

     if (!qemu_chr_has_feature(chr, QEMU_CHAR_FEATURE_RECONNECTABLE)) {
         error_setg(errp, "chardev \"%s\" is not reconnectable",
                    opts->chardev);
         return NULL;
     }
     if (!qemu_chr_has_feature(chr, QEMU_CHAR_FEATURE_FD_PASS)) {
         error_setg(errp, "chardev \"%s\" does not support FD passing",
                    opts->chardev);
         return NULL;
     }

     return chr;
 }

 static int net_vhost_check_net(void *opaque, QemuOpts *opts, Error **errp)
 {
     const char *name = opaque;
     const char *driver, *netdev;

     driver = qemu_opt_get(opts, "driver");
     netdev = qemu_opt_get(opts, "netdev");

     if (!driver || !netdev) {
         return 0;
     }

     if (strcmp(netdev, name) == 0 &&
         !g_str_has_prefix(driver, "virtio-net-")) {
         error_setg(errp, "vhost-user requires frontend driver virtio-net-*");
         return -1;
     }

     return 0;
 }

 int net_init_vhost_user(const Netdev *netdev, const char *name,
                         NetClientState *peer, Error **errp)
 {
     int queues;
     const NetdevVhostUserOptions *vhost_user_opts;
     Chardev *chr;

     assert(netdev->type == NET_CLIENT_DRIVER_VHOST_USER);
     vhost_user_opts = &netdev->u.vhost_user;

     chr = net_vhost_claim_chardev(vhost_user_opts, errp);
     if (!chr) {
         return -1;
     }

     /* verify net frontend */
     if (qemu_opts_foreach(qemu_find_opts("device"), net_vhost_check_net,
                           (char *)name, errp)) {
         return -1;
     }

     queues = vhost_user_opts->has_queues ? vhost_user_opts->queues : 1;
     if (queues < 1 || queues > MAX_QUEUE_NUM) {
         error_setg(errp,
                    "vhost-user number of queues must be in range [1, %d]",
                    MAX_QUEUE_NUM);
         return -1;
     }

     return net_vhost_user_init(peer, "vhost_user", name, chr, queues);
 }
	/*
	* vhost-user.c
	*
	* Copyright (c) 2013 Virtual Open Systems Sarl.
	*
	* This work is licensed under the terms of the GNU GPL, version 2 or later.
	* See the COPYING file in the top-level directory.
	*
	*/

	#include "qemu/osdep.h"
	#include "clients.h"
	#include "net/vhost_net.h"
	#include "net/vhost-user.h"
	#include "hw/virtio/vhost-user.h"
	#include "chardev/char-fe.h"
	#include "qapi/error.h"
	#include "qapi/qapi-commands-net.h"
	#include "qemu/config-file.h"
	#include "qemu/error-report.h"
	#include "qemu/option.h"
	#include "trace.h"

	typedef struct NetVhostUserState {
	NetClientState nc;
	CharBackend chr; /* only queue index 0 */
	VhostUserState *vhost_user;
	VHostNetState *vhost_net;
	guint watch;
	uint64_t acked_features;
	bool started;
	} NetVhostUserState;

	VHostNetState vhost_user_get_vhost_net(NetClientState nc)
	{
	NetVhostUserState *s = DO_UPCAST(NetVhostUserState, nc, nc);
	assert(nc->info->type == NET_CLIENT_DRIVER_VHOST_USER);
	return s->vhost_net;
	}

	uint64_t vhost_user_get_acked_features(NetClientState *nc)
	{
	NetVhostUserState *s = DO_UPCAST(NetVhostUserState, nc, nc);
	assert(nc->info->type == NET_CLIENT_DRIVER_VHOST_USER);
	return s->acked_features;
	}

	static void vhost_user_stop(int queues, NetClientState *ncs[])
	{
	NetVhostUserState *s;
	int i;

	for (i = 0; i < queues; i++) {
	assert(ncs[i]->info->type == NET_CLIENT_DRIVER_VHOST_USER);

	s = DO_UPCAST(NetVhostUserState, nc, ncs[i]);

	if (s->vhost_net) {
	/* save acked features */
	uint64_t features = vhost_net_get_acked_features(s->vhost_net);
	if (features) {
	s->acked_features = features;
	}
	vhost_net_cleanup(s->vhost_net);
	}
	}
	}

	static int vhost_user_start(int queues, NetClientState *ncs[],
	VhostUserState *be)
	{
	VhostNetOptions options;
	struct vhost_net *net = NULL;
	NetVhostUserState *s;
	int max_queues;
	int i;

	options.backend_type = VHOST_BACKEND_TYPE_USER;

	for (i = 0; i < queues; i++) {
	assert(ncs[i]->info->type == NET_CLIENT_DRIVER_VHOST_USER);

	s = DO_UPCAST(NetVhostUserState, nc, ncs[i]);

	options.net_backend = ncs[i];
	options.opaque = be;
	options.busyloop_timeout = 0;
	net = vhost_net_init(&options);
	if (!net) {
	error_report("failed to init vhost_net for queue %d", i);
	goto err;
	}

	if (i == 0) {
	max_queues = vhost_net_get_max_queues(net);
	if (queues > max_queues) {
	error_report("you are asking more queues than supported: %d",
	max_queues);
	goto err;
	}
	}

	if (s->vhost_net) {
	vhost_net_cleanup(s->vhost_net);
	g_free(s->vhost_net);
	}
	s->vhost_net = net;
	}

	return 0;

	err:
	if (net) {
	vhost_net_cleanup(net);
	g_free(net);
	}
	vhost_user_stop(i, ncs);
	return -1;
	}

	static ssize_t vhost_user_receive(NetClientState nc, const uint8_t buf,
	size_t size)
	{
	/* In case of RARP (message size is 60) notify backup to send a fake RARP.
	This fake RARP will be sent by backend only for guest
	without GUEST_ANNOUNCE capability.
	*/
	if (size == 60) {
	NetVhostUserState *s = DO_UPCAST(NetVhostUserState, nc, nc);
	int r;
	static int display_rarp_failure = 1;
	char mac_addr[6];

	/* extract guest mac address from the RARP message */
	memcpy(mac_addr, &buf[6], 6);

	r = vhost_net_notify_migration_done(s->vhost_net, mac_addr);

	if ((r != 0) && (display_rarp_failure)) {
	fprintf(stderr,
	"Vhost user backend fails to broadcast fake RARP\n");
	fflush(stderr);
	display_rarp_failure = 0;
	}
	}

	return size;
	}

	static void net_vhost_user_cleanup(NetClientState *nc)
	{
	NetVhostUserState *s = DO_UPCAST(NetVhostUserState, nc, nc);

	if (s->vhost_net) {
	vhost_net_cleanup(s->vhost_net);
	g_free(s->vhost_net);
	s->vhost_net = NULL;
	}
	if (nc->queue_index == 0) {
	if (s->watch) {
	g_source_remove(s->watch);
	s->watch = 0;
	}
	qemu_chr_fe_deinit(&s->chr, true);
	if (s->vhost_user) {
	vhost_user_cleanup(s->vhost_user);
	g_free(s->vhost_user);
	s->vhost_user = NULL;
	}
	}

	qemu_purge_queued_packets(nc);
	}

	static int vhost_user_set_vnet_endianness(NetClientState *nc,
	bool enable)
	{
	/* Nothing to do. If the server supports
	* VHOST_USER_PROTOCOL_F_CROSS_ENDIAN, it will get the
	* vnet header endianness from there. If it doesn't, negotiation
	* fails.
	*/
	return 0;
	}

	static bool vhost_user_has_vnet_hdr(NetClientState *nc)
	{
	assert(nc->info->type == NET_CLIENT_DRIVER_VHOST_USER);

	return true;
	}

	static bool vhost_user_has_ufo(NetClientState *nc)
	{
	assert(nc->info->type == NET_CLIENT_DRIVER_VHOST_USER);

	return true;
	}

	static NetClientInfo net_vhost_user_info = {
	.type = NET_CLIENT_DRIVER_VHOST_USER,
	.size = sizeof(NetVhostUserState),
	.receive = vhost_user_receive,
	.cleanup = net_vhost_user_cleanup,
	.has_vnet_hdr = vhost_user_has_vnet_hdr,
	.has_ufo = vhost_user_has_ufo,
	.set_vnet_be = vhost_user_set_vnet_endianness,
	.set_vnet_le = vhost_user_set_vnet_endianness,
	};

	static gboolean net_vhost_user_watch(void *do_not_use, GIOCondition cond,
	void *opaque)
	{
	NetVhostUserState *s = opaque;

	qemu_chr_fe_disconnect(&s->chr);

	return TRUE;
	}

	static void net_vhost_user_event(void *opaque, QEMUChrEvent event);

	static void chr_closed_bh(void *opaque)
	{
	const char *name = opaque;
	NetClientState *ncs[MAX_QUEUE_NUM];
	NetVhostUserState *s;
	Error *err = NULL;
	int queues, i;

	queues = qemu_find_net_clients_except(name, ncs,
	NET_CLIENT_DRIVER_NIC,
	MAX_QUEUE_NUM);
	assert(queues < MAX_QUEUE_NUM);

	s = DO_UPCAST(NetVhostUserState, nc, ncs[0]);

	for (i = queues -1; i >= 0; i--) {
	s = DO_UPCAST(NetVhostUserState, nc, ncs[i]);

	if (s->vhost_net) {
	s->acked_features = vhost_net_get_acked_features(s->vhost_net);
	}
	}

	qmp_set_link(name, false, &err);

	qemu_chr_fe_set_handlers(&s->chr, NULL, NULL, net_vhost_user_event,
	NULL, opaque, NULL, true);

	if (err) {
	error_report_err(err);
	}
	}

	static void net_vhost_user_event(void *opaque, QEMUChrEvent event)
	{
	const char *name = opaque;
	NetClientState *ncs[MAX_QUEUE_NUM];
	NetVhostUserState *s;
	Chardev *chr;
	Error *err = NULL;
	int queues;

	queues = qemu_find_net_clients_except(name, ncs,
	NET_CLIENT_DRIVER_NIC,
	MAX_QUEUE_NUM);
	assert(queues < MAX_QUEUE_NUM);

	s = DO_UPCAST(NetVhostUserState, nc, ncs[0]);
	chr = qemu_chr_fe_get_driver(&s->chr);
	trace_vhost_user_event(chr->label, event);
	switch (event) {
	case CHR_EVENT_OPENED:
	if (vhost_user_start(queues, ncs, s->vhost_user) < 0) {
	qemu_chr_fe_disconnect(&s->chr);
	return;
	}
	s->watch = qemu_chr_fe_add_watch(&s->chr, G_IO_HUP,
	net_vhost_user_watch, s);
	qmp_set_link(name, true, &err);
	s->started = true;
	break;
	case CHR_EVENT_CLOSED:
	/* a close event may happen during a read/write, but vhost
	* code assumes the vhost_dev remains setup, so delay the
	* stop & clear to idle.
	* FIXME: better handle failure in vhost code, remove bh
	*/
	if (s->watch) {
	AioContext *ctx = qemu_get_current_aio_context();

	g_source_remove(s->watch);
	s->watch = 0;
	qemu_chr_fe_set_handlers(&s->chr, NULL, NULL, NULL, NULL,
	NULL, NULL, false);

	aio_bh_schedule_oneshot(ctx, chr_closed_bh, opaque);
	}
	break;
	case CHR_EVENT_BREAK:
	case CHR_EVENT_MUX_IN:
	case CHR_EVENT_MUX_OUT:
	/* Ignore */
	break;
	}

	if (err) {
	error_report_err(err);
	}
	}

	static int net_vhost_user_init(NetClientState peer, const char device,
	const char name, Chardev chr,
	int queues)
	{
	Error *err = NULL;
	NetClientState nc, nc0 = NULL;
	NetVhostUserState *s = NULL;
	VhostUserState *user;
	int i;

	assert(name);
	assert(queues > 0);

	user = g_new0(struct VhostUserState, 1);
	for (i = 0; i < queues; i++) {
	nc = qemu_new_net_client(&net_vhost_user_info, peer, device, name);
	snprintf(nc->info_str, sizeof(nc->info_str), "vhost-user%d to %s",
	i, chr->label);
	nc->queue_index = i;
	if (!nc0) {
	nc0 = nc;
	s = DO_UPCAST(NetVhostUserState, nc, nc);
	if (!qemu_chr_fe_init(&s->chr, chr, &err) \|\|
	!vhost_user_init(user, &s->chr, &err)) {
	error_report_err(err);
	goto err;
	}
	}
	s = DO_UPCAST(NetVhostUserState, nc, nc);
	s->vhost_user = user;
	}

	s = DO_UPCAST(NetVhostUserState, nc, nc0);
	do {
	if (qemu_chr_fe_wait_connected(&s->chr, &err) < 0) {
	error_report_err(err);
	goto err;
	}
	qemu_chr_fe_set_handlers(&s->chr, NULL, NULL,
	net_vhost_user_event, NULL, nc0->name, NULL,
	true);
	} while (!s->started);

	assert(s->vhost_net);

	return 0;

	err:
	if (user) {
	vhost_user_cleanup(user);
	g_free(user);
	if (s) {
	s->vhost_user = NULL;
	}
	}
	if (nc0) {
	qemu_del_net_client(nc0);
	}

	return -1;
	}

	static Chardev *net_vhost_claim_chardev(
	const NetdevVhostUserOptions opts, Error *errp)
	{
	Chardev *chr = qemu_chr_find(opts->chardev);

	if (chr == NULL) {
	error_setg(errp, "chardev \"%s\" not found", opts->chardev);
	return NULL;
	}

	if (!qemu_chr_has_feature(chr, QEMU_CHAR_FEATURE_RECONNECTABLE)) {
	error_setg(errp, "chardev \"%s\" is not reconnectable",
	opts->chardev);
	return NULL;
	}
	if (!qemu_chr_has_feature(chr, QEMU_CHAR_FEATURE_FD_PASS)) {
	error_setg(errp, "chardev \"%s\" does not support FD passing",
	opts->chardev);
	return NULL;
	}

	return chr;
	}

	static int net_vhost_check_net(void opaque, QemuOpts opts, Error **errp)
	{
	const char *name = opaque;
	const char driver, netdev;

	driver = qemu_opt_get(opts, "driver");
	netdev = qemu_opt_get(opts, "netdev");

	if (!driver \|\| !netdev) {
	return 0;
	}

	if (strcmp(netdev, name) == 0 &&
	!g_str_has_prefix(driver, "virtio-net-")) {
	error_setg(errp, "vhost-user requires frontend driver virtio-net-*");
	return -1;
	}

	return 0;
	}

	int net_init_vhost_user(const Netdev netdev, const char name,
	NetClientState peer, Error *errp)
	{
	int queues;
	const NetdevVhostUserOptions *vhost_user_opts;
	Chardev *chr;

	assert(netdev->type == NET_CLIENT_DRIVER_VHOST_USER);
	vhost_user_opts = &netdev->u.vhost_user;

	chr = net_vhost_claim_chardev(vhost_user_opts, errp);
	if (!chr) {
	return -1;
	}

	/* verify net frontend */
	if (qemu_opts_foreach(qemu_find_opts("device"), net_vhost_check_net,
	(char *)name, errp)) {
	return -1;
	}

	queues = vhost_user_opts->has_queues ? vhost_user_opts->queues : 1;
	if (queues < 1 \|\| queues > MAX_QUEUE_NUM) {
	error_setg(errp,
	"vhost-user number of queues must be in range [1, %d]",
	MAX_QUEUE_NUM);
	return -1;
	}

	return net_vhost_user_init(peer, "vhost_user", name, chr, queues);
	}