drivers/net/virtio/virtio_user/virtio_user_dev.c

   1 /* SPDX-License-Identifier: BSD-3-Clause
   2  * Copyright(c) 2010-2016 Intel Corporation
   3  */
   4
   5 #include <stdint.h>
   6 #include <stdio.h>
   7 #include <fcntl.h>
   8 #include <string.h>
   9 #include <errno.h>
  10 #include <sys/mman.h>
  11 #include <unistd.h>
  12 #include <sys/eventfd.h>
  13 #include <sys/types.h>
  14 #include <sys/stat.h>
  15
  16 #include <rte_eal_memconfig.h>
  17
  18 #include "vhost.h"
  19 #include "virtio_user_dev.h"
  20 #include "../virtio_ethdev.h"
  21
  22 #define VIRTIO_USER_MEM_EVENT_CLB_NAME "virtio_user_mem_event_clb"
  23
  24 static int
  25 virtio_user_create_queue(struct virtio_user_dev *dev, uint32_t queue_sel)
  26 {
  27         /* Of all per virtqueue MSGs, make sure VHOST_SET_VRING_CALL come
  28          * firstly because vhost depends on this msg to allocate virtqueue
  29          * pair.
  30          */
  31         struct vhost_vring_file file;
  32
  33         file.index = queue_sel;
  34         file.fd = dev->callfds[queue_sel];
  35         dev->ops->send_request(dev, VHOST_USER_SET_VRING_CALL, &file);
  36
  37         return 0;
  38 }
  39
  40 static int
  41 virtio_user_kick_queue(struct virtio_user_dev *dev, uint32_t queue_sel)
  42 {
  43         struct vhost_vring_file file;
  44         struct vhost_vring_state state;
  45         struct vring *vring = &dev->vrings[queue_sel];
  46         struct vhost_vring_addr addr = {
  47                 .index = queue_sel,
  48                 .desc_user_addr = (uint64_t)(uintptr_t)vring->desc,
  49                 .avail_user_addr = (uint64_t)(uintptr_t)vring->avail,
  50                 .used_user_addr = (uint64_t)(uintptr_t)vring->used,
  51                 .log_guest_addr = 0,
  52                 .flags = 0, /* disable log */
  53         };
  54
  55         state.index = queue_sel;
  56         state.num = vring->num;
  57         dev->ops->send_request(dev, VHOST_USER_SET_VRING_NUM, &state);
  58
  59         state.index = queue_sel;
  60         state.num = 0; /* no reservation */
  61         dev->ops->send_request(dev, VHOST_USER_SET_VRING_BASE, &state);
  62
  63         dev->ops->send_request(dev, VHOST_USER_SET_VRING_ADDR, &addr);
  64
  65         /* Of all per virtqueue MSGs, make sure VHOST_USER_SET_VRING_KICK comes
  66          * lastly because vhost depends on this msg to judge if
  67          * virtio is ready.
  68          */
  69         file.index = queue_sel;
  70         file.fd = dev->kickfds[queue_sel];
  71         dev->ops->send_request(dev, VHOST_USER_SET_VRING_KICK, &file);
  72
  73         return 0;
  74 }
  75
  76 static int
  77 virtio_user_queue_setup(struct virtio_user_dev *dev,
  78                         int (*fn)(struct virtio_user_dev *, uint32_t))
  79 {
  80         uint32_t i, queue_sel;
  81
  82         for (i = 0; i < dev->max_queue_pairs; ++i) {
  83                 queue_sel = 2 * i + VTNET_SQ_RQ_QUEUE_IDX;
  84                 if (fn(dev, queue_sel) < 0) {
  85                         PMD_DRV_LOG(INFO, "setup rx vq fails: %u", i);
  86                         return -1;
  87                 }
  88         }
  89         for (i = 0; i < dev->max_queue_pairs; ++i) {
  90                 queue_sel = 2 * i + VTNET_SQ_TQ_QUEUE_IDX;
  91                 if (fn(dev, queue_sel) < 0) {
  92                         PMD_DRV_LOG(INFO, "setup tx vq fails: %u", i);
  93                         return -1;
  94                 }
  95         }
  96
  97         return 0;
  98 }
  99
 100 int
 101 is_vhost_user_by_type(const char *path)
 102 {
 103         struct stat sb;
 104
 105         if (stat(path, &sb) == -1)
 106                 return 0;
 107
 108         return S_ISSOCK(sb.st_mode);
 109 }
 110
 111 int
 112 virtio_user_start_device(struct virtio_user_dev *dev)
 113 {
 114         struct rte_mem_config *mcfg = rte_eal_get_configuration()->mem_config;
 115         uint64_t features;
 116         int ret;
 117
 118         /*
 119          * XXX workaround!
 120          *
 121          * We need to make sure that the locks will be
 122          * taken in the correct order to avoid deadlocks.
 123          *
 124          * Before releasing this lock, this thread should
 125          * not trigger any memory hotplug events.
 126          *
 127          * This is a temporary workaround, and should be
 128          * replaced when we get proper supports from the
 129          * memory subsystem in the future.
 130          */
 131         rte_rwlock_read_lock(&mcfg->memory_hotplug_lock);
 132         pthread_mutex_lock(&dev->mutex);
 133
 134         if (is_vhost_user_by_type(dev->path) && dev->vhostfd < 0)
 135                 goto error;
 136
 137         /* Step 0: tell vhost to create queues */
 138         if (virtio_user_queue_setup(dev, virtio_user_create_queue) < 0)
 139                 goto error;
 140
 141         /* Step 1: set features */
 142         features = dev->features;
 143         /* Strip VIRTIO_NET_F_MAC, as MAC address is handled in vdev init */
 144         features &= ~(1ull << VIRTIO_NET_F_MAC);
 145         /* Strip VIRTIO_NET_F_CTRL_VQ, as devices do not really need to know */
 146         features &= ~(1ull << VIRTIO_NET_F_CTRL_VQ);
 147         features &= ~(1ull << VIRTIO_NET_F_STATUS);
 148         ret = dev->ops->send_request(dev, VHOST_USER_SET_FEATURES, &features);
 149         if (ret < 0)
 150                 goto error;
 151         PMD_DRV_LOG(INFO, "set features: %" PRIx64, features);
 152
 153         /* Step 2: share memory regions */
 154         ret = dev->ops->send_request(dev, VHOST_USER_SET_MEM_TABLE, NULL);
 155         if (ret < 0)
 156                 goto error;
 157
 158         /* Step 3: kick queues */
 159         if (virtio_user_queue_setup(dev, virtio_user_kick_queue) < 0)
 160                 goto error;
 161
 162         /* Step 4: enable queues
 163          * we enable the 1st queue pair by default.
 164          */
 165         dev->ops->enable_qp(dev, 0, 1);
 166
 167         dev->started = true;
 168         pthread_mutex_unlock(&dev->mutex);
 169         rte_rwlock_read_unlock(&mcfg->memory_hotplug_lock);
 170
 171         return 0;
 172 error:
 173         pthread_mutex_unlock(&dev->mutex);
 174         rte_rwlock_read_unlock(&mcfg->memory_hotplug_lock);
 175         /* TODO: free resource here or caller to check */
 176         return -1;
 177 }
 178
 179 int virtio_user_stop_device(struct virtio_user_dev *dev)
 180 {
 181         struct vhost_vring_state state;
 182         uint32_t i;
 183         int error = 0;
 184
 185         pthread_mutex_lock(&dev->mutex);
 186         if (!dev->started)
 187                 goto out;
 188
 189         for (i = 0; i < dev->max_queue_pairs; ++i)
 190                 dev->ops->enable_qp(dev, i, 0);
 191
 192         /* Stop the backend. */
 193         for (i = 0; i < dev->max_queue_pairs * 2; ++i) {
 194                 state.index = i;
 195                 if (dev->ops->send_request(dev, VHOST_USER_GET_VRING_BASE,
 196                                            &state) < 0) {
 197                         PMD_DRV_LOG(ERR, "get_vring_base failed, index=%u\n",
 198                                     i);
 199                         error = -1;
 200                         goto out;
 201                 }
 202         }
 203
 204         dev->started = false;
 205 out:
 206         pthread_mutex_unlock(&dev->mutex);
 207
 208         return error;
 209 }
 210
 211 static inline void
 212 parse_mac(struct virtio_user_dev *dev, const char *mac)
 213 {
 214         int i, r;
 215         uint32_t tmp[ETHER_ADDR_LEN];
 216
 217         if (!mac)
 218                 return;
 219
 220         r = sscanf(mac, "%x:%x:%x:%x:%x:%x", &tmp[0],
 221                         &tmp[1], &tmp[2], &tmp[3], &tmp[4], &tmp[5]);
 222         if (r == ETHER_ADDR_LEN) {
 223                 for (i = 0; i < ETHER_ADDR_LEN; ++i)
 224                         dev->mac_addr[i] = (uint8_t)tmp[i];
 225                 dev->mac_specified = 1;
 226         } else {
 227                 /* ignore the wrong mac, use random mac */
 228                 PMD_DRV_LOG(ERR, "wrong format of mac: %s", mac);
 229         }
 230 }
 231
 232 static int
 233 virtio_user_dev_init_notify(struct virtio_user_dev *dev)
 234 {
 235         uint32_t i, j;
 236         int callfd;
 237         int kickfd;
 238
 239         for (i = 0; i < VIRTIO_MAX_VIRTQUEUES; ++i) {
 240                 if (i >= dev->max_queue_pairs * 2) {
 241                         dev->kickfds[i] = -1;
 242                         dev->callfds[i] = -1;
 243                         continue;
 244                 }
 245
 246                 /* May use invalid flag, but some backend uses kickfd and
 247                  * callfd as criteria to judge if dev is alive. so finally we
 248                  * use real event_fd.
 249                  */
 250                 callfd = eventfd(0, EFD_CLOEXEC | EFD_NONBLOCK);
 251                 if (callfd < 0) {
 252                         PMD_DRV_LOG(ERR, "callfd error, %s", strerror(errno));
 253                         break;
 254                 }
 255                 kickfd = eventfd(0, EFD_CLOEXEC | EFD_NONBLOCK);
 256                 if (kickfd < 0) {
 257                         PMD_DRV_LOG(ERR, "kickfd error, %s", strerror(errno));
 258                         break;
 259                 }
 260                 dev->callfds[i] = callfd;
 261                 dev->kickfds[i] = kickfd;
 262         }
 263
 264         if (i < VIRTIO_MAX_VIRTQUEUES) {
 265                 for (j = 0; j <= i; ++j) {
 266                         close(dev->callfds[j]);
 267                         close(dev->kickfds[j]);
 268                 }
 269
 270                 return -1;
 271         }
 272
 273         return 0;
 274 }
 275
 276 static int
 277 virtio_user_fill_intr_handle(struct virtio_user_dev *dev)
 278 {
 279         uint32_t i;
 280         struct rte_eth_dev *eth_dev = &rte_eth_devices[dev->port_id];
 281
 282         if (!eth_dev->intr_handle) {
 283                 eth_dev->intr_handle = malloc(sizeof(*eth_dev->intr_handle));
 284                 if (!eth_dev->intr_handle) {
 285                         PMD_DRV_LOG(ERR, "fail to allocate intr_handle");
 286                         return -1;
 287                 }
 288                 memset(eth_dev->intr_handle, 0, sizeof(*eth_dev->intr_handle));
 289         }
 290
 291         for (i = 0; i < dev->max_queue_pairs; ++i)
 292                 eth_dev->intr_handle->efds[i] = dev->callfds[i];
 293         eth_dev->intr_handle->nb_efd = dev->max_queue_pairs;
 294         eth_dev->intr_handle->max_intr = dev->max_queue_pairs + 1;
 295         eth_dev->intr_handle->type = RTE_INTR_HANDLE_VDEV;
 296         /* For virtio vdev, no need to read counter for clean */
 297         eth_dev->intr_handle->efd_counter_size = 0;
 298         eth_dev->intr_handle->fd = -1;
 299         if (dev->vhostfd >= 0)
 300                 eth_dev->intr_handle->fd = dev->vhostfd;
 301         else if (dev->is_server)
 302                 eth_dev->intr_handle->fd = dev->listenfd;
 303
 304         return 0;
 305 }
 306
 307 static void
 308 virtio_user_mem_event_cb(enum rte_mem_event type __rte_unused,
 309                                                  const void *addr __rte_unused,
 310                                                  size_t len __rte_unused,
 311                                                  void *arg)
 312 {
 313         struct virtio_user_dev *dev = arg;
 314         struct rte_memseg_list *msl;
 315         uint16_t i;
 316
 317         /* ignore externally allocated memory */
 318         msl = rte_mem_virt2memseg_list(addr);
 319         if (msl->external)
 320                 return;
 321
 322         pthread_mutex_lock(&dev->mutex);
 323
 324         if (dev->started == false)
 325                 goto exit;
 326
 327         /* Step 1: pause the active queues */
 328         for (i = 0; i < dev->queue_pairs; i++)
 329                 dev->ops->enable_qp(dev, i, 0);
 330
 331         /* Step 2: update memory regions */
 332         dev->ops->send_request(dev, VHOST_USER_SET_MEM_TABLE, NULL);
 333
 334         /* Step 3: resume the active queues */
 335         for (i = 0; i < dev->queue_pairs; i++)
 336                 dev->ops->enable_qp(dev, i, 1);
 337
 338 exit:
 339         pthread_mutex_unlock(&dev->mutex);
 340 }
 341
 342 static int
 343 virtio_user_dev_setup(struct virtio_user_dev *dev)
 344 {
 345         uint32_t q;
 346
 347         dev->vhostfd = -1;
 348         dev->vhostfds = NULL;
 349         dev->tapfds = NULL;
 350
 351         if (dev->is_server) {
 352                 if (access(dev->path, F_OK) == 0 &&
 353                     !is_vhost_user_by_type(dev->path)) {
 354                         PMD_DRV_LOG(ERR, "Server mode doesn't support vhost-kernel!");
 355                         return -1;
 356                 }
 357                 dev->ops = &virtio_ops_user;
 358         } else {
 359                 if (is_vhost_user_by_type(dev->path)) {
 360                         dev->ops = &virtio_ops_user;
 361                 } else {
 362                         dev->ops = &virtio_ops_kernel;
 363
 364                         dev->vhostfds = malloc(dev->max_queue_pairs *
 365                                                sizeof(int));
 366                         dev->tapfds = malloc(dev->max_queue_pairs *
 367                                              sizeof(int));
 368                         if (!dev->vhostfds || !dev->tapfds) {
 369                                 PMD_INIT_LOG(ERR, "Failed to malloc");
 370                                 return -1;
 371                         }
 372
 373                         for (q = 0; q < dev->max_queue_pairs; ++q) {
 374                                 dev->vhostfds[q] = -1;
 375                                 dev->tapfds[q] = -1;
 376                         }
 377                 }
 378         }
 379
 380         if (dev->ops->setup(dev) < 0)
 381                 return -1;
 382
 383         if (virtio_user_dev_init_notify(dev) < 0)
 384                 return -1;
 385
 386         if (virtio_user_fill_intr_handle(dev) < 0)
 387                 return -1;
 388
 389         return 0;
 390 }
 391
 392 /* Use below macro to filter features from vhost backend */
 393 #define VIRTIO_USER_SUPPORTED_FEATURES                  \
 394         (1ULL << VIRTIO_NET_F_MAC               |       \
 395          1ULL << VIRTIO_NET_F_STATUS            |       \
 396          1ULL << VIRTIO_NET_F_MQ                |       \
 397          1ULL << VIRTIO_NET_F_CTRL_MAC_ADDR     |       \
 398          1ULL << VIRTIO_NET_F_CTRL_VQ           |       \
 399          1ULL << VIRTIO_NET_F_CTRL_RX           |       \
 400          1ULL << VIRTIO_NET_F_CTRL_VLAN         |       \
 401          1ULL << VIRTIO_NET_F_CSUM              |       \
 402          1ULL << VIRTIO_NET_F_HOST_TSO4         |       \
 403          1ULL << VIRTIO_NET_F_HOST_TSO6         |       \
 404          1ULL << VIRTIO_NET_F_MRG_RXBUF         |       \
 405          1ULL << VIRTIO_RING_F_INDIRECT_DESC    |       \
 406          1ULL << VIRTIO_NET_F_GUEST_CSUM        |       \
 407          1ULL << VIRTIO_NET_F_GUEST_TSO4        |       \
 408          1ULL << VIRTIO_NET_F_GUEST_TSO6        |       \
 409          1ULL << VIRTIO_F_IN_ORDER              |       \
 410          1ULL << VIRTIO_F_VERSION_1)
 411
 412 int
 413 virtio_user_dev_init(struct virtio_user_dev *dev, char *path, int queues,
 414                      int cq, int queue_size, const char *mac, char **ifname,
 415                      int mrg_rxbuf, int in_order)
 416 {
 417         pthread_mutex_init(&dev->mutex, NULL);
 418         snprintf(dev->path, PATH_MAX, "%s", path);
 419         dev->started = 0;
 420         dev->max_queue_pairs = queues;
 421         dev->queue_pairs = 1; /* mq disabled by default */
 422         dev->queue_size = queue_size;
 423         dev->mac_specified = 0;
 424         dev->frontend_features = 0;
 425         dev->unsupported_features = ~VIRTIO_USER_SUPPORTED_FEATURES;
 426         parse_mac(dev, mac);
 427
 428         if (*ifname) {
 429                 dev->ifname = *ifname;
 430                 *ifname = NULL;
 431         }
 432
 433         if (virtio_user_dev_setup(dev) < 0) {
 434                 PMD_INIT_LOG(ERR, "backend set up fails");
 435                 return -1;
 436         }
 437
 438         if (!dev->is_server) {
 439                 if (dev->ops->send_request(dev, VHOST_USER_SET_OWNER,
 440                                            NULL) < 0) {
 441                         PMD_INIT_LOG(ERR, "set_owner fails: %s",
 442                                      strerror(errno));
 443                         return -1;
 444                 }
 445
 446                 if (dev->ops->send_request(dev, VHOST_USER_GET_FEATURES,
 447                                            &dev->device_features) < 0) {
 448                         PMD_INIT_LOG(ERR, "get_features failed: %s",
 449                                      strerror(errno));
 450                         return -1;
 451                 }
 452         } else {
 453                 /* We just pretend vhost-user can support all these features.
 454                  * Note that this could be problematic that if some feature is
 455                  * negotiated but not supported by the vhost-user which comes
 456                  * later.
 457                  */
 458                 dev->device_features = VIRTIO_USER_SUPPORTED_FEATURES;
 459         }
 460
 461         if (!mrg_rxbuf)
 462                 dev->unsupported_features |= (1ull << VIRTIO_NET_F_MRG_RXBUF);
 463
 464         if (!in_order)
 465                 dev->unsupported_features |= (1ull << VIRTIO_F_IN_ORDER);
 466
 467         if (dev->mac_specified)
 468                 dev->frontend_features |= (1ull << VIRTIO_NET_F_MAC);
 469         else
 470                 dev->unsupported_features |= (1ull << VIRTIO_NET_F_MAC);
 471
 472         if (cq) {
 473                 /* device does not really need to know anything about CQ,
 474                  * so if necessary, we just claim to support CQ
 475                  */
 476                 dev->frontend_features |= (1ull << VIRTIO_NET_F_CTRL_VQ);
 477         } else {
 478                 dev->unsupported_features |= (1ull << VIRTIO_NET_F_CTRL_VQ);
 479                 /* Also disable features that depend on VIRTIO_NET_F_CTRL_VQ */
 480                 dev->unsupported_features |= (1ull << VIRTIO_NET_F_CTRL_RX);
 481                 dev->unsupported_features |= (1ull << VIRTIO_NET_F_CTRL_VLAN);
 482                 dev->unsupported_features |=
 483                         (1ull << VIRTIO_NET_F_GUEST_ANNOUNCE);
 484                 dev->unsupported_features |= (1ull << VIRTIO_NET_F_MQ);
 485                 dev->unsupported_features |=
 486                         (1ull << VIRTIO_NET_F_CTRL_MAC_ADDR);
 487         }
 488
 489         /* The backend will not report this feature, we add it explicitly */
 490         if (is_vhost_user_by_type(dev->path))
 491                 dev->frontend_features |= (1ull << VIRTIO_NET_F_STATUS);
 492
 493         /*
 494          * Device features =
 495          *     (frontend_features | backend_features) & ~unsupported_features;
 496          */
 497         dev->device_features |= dev->frontend_features;
 498         dev->device_features &= ~dev->unsupported_features;
 499
 500         if (rte_mem_event_callback_register(VIRTIO_USER_MEM_EVENT_CLB_NAME,
 501                                 virtio_user_mem_event_cb, dev)) {
 502                 if (rte_errno != ENOTSUP) {
 503                         PMD_INIT_LOG(ERR, "Failed to register mem event"
 504                                         " callback\n");
 505                         return -1;
 506                 }
 507         }
 508
 509         return 0;
 510 }
 511
 512 void
 513 virtio_user_dev_uninit(struct virtio_user_dev *dev)
 514 {
 515         uint32_t i;
 516
 517         virtio_user_stop_device(dev);
 518
 519         rte_mem_event_callback_unregister(VIRTIO_USER_MEM_EVENT_CLB_NAME, dev);
 520
 521         for (i = 0; i < dev->max_queue_pairs * 2; ++i) {
 522                 close(dev->callfds[i]);
 523                 close(dev->kickfds[i]);
 524         }
 525
 526         close(dev->vhostfd);
 527
 528         if (dev->is_server && dev->listenfd >= 0) {
 529                 close(dev->listenfd);
 530                 dev->listenfd = -1;
 531         }
 532
 533         if (dev->vhostfds) {
 534                 for (i = 0; i < dev->max_queue_pairs; ++i)
 535                         close(dev->vhostfds[i]);
 536                 free(dev->vhostfds);
 537                 free(dev->tapfds);
 538         }
 539
 540         free(dev->ifname);
 541
 542         if (dev->is_server)
 543                 unlink(dev->path);
 544 }
 545
 546 uint8_t
 547 virtio_user_handle_mq(struct virtio_user_dev *dev, uint16_t q_pairs)
 548 {
 549         uint16_t i;
 550         uint8_t ret = 0;
 551
 552         if (q_pairs > dev->max_queue_pairs) {
 553                 PMD_INIT_LOG(ERR, "multi-q config %u, but only %u supported",
 554                              q_pairs, dev->max_queue_pairs);
 555                 return -1;
 556         }
 557
 558         /* Server mode can't enable queue pairs if vhostfd is invalid,
 559          * always return 0 in this case.
 560          */
 561         if (!dev->is_server || dev->vhostfd >= 0) {
 562                 for (i = 0; i < q_pairs; ++i)
 563                         ret |= dev->ops->enable_qp(dev, i, 1);
 564                 for (i = q_pairs; i < dev->max_queue_pairs; ++i)
 565                         ret |= dev->ops->enable_qp(dev, i, 0);
 566         }
 567         dev->queue_pairs = q_pairs;
 568
 569         return ret;
 570 }
 571
 572 static uint32_t
 573 virtio_user_handle_ctrl_msg(struct virtio_user_dev *dev, struct vring *vring,
 574                             uint16_t idx_hdr)
 575 {
 576         struct virtio_net_ctrl_hdr *hdr;
 577         virtio_net_ctrl_ack status = ~0;
 578         uint16_t i, idx_data, idx_status;
 579         uint32_t n_descs = 0;
 580
 581         /* locate desc for header, data, and status */
 582         idx_data = vring->desc[idx_hdr].next;
 583         n_descs++;
 584
 585         i = idx_data;
 586         while (vring->desc[i].flags == VRING_DESC_F_NEXT) {
 587                 i = vring->desc[i].next;
 588                 n_descs++;
 589         }
 590
 591         /* locate desc for status */
 592         idx_status = i;
 593         n_descs++;
 594
 595         hdr = (void *)(uintptr_t)vring->desc[idx_hdr].addr;
 596         if (hdr->class == VIRTIO_NET_CTRL_MQ &&
 597             hdr->cmd == VIRTIO_NET_CTRL_MQ_VQ_PAIRS_SET) {
 598                 uint16_t queues;
 599
 600                 queues = *(uint16_t *)(uintptr_t)vring->desc[idx_data].addr;
 601                 status = virtio_user_handle_mq(dev, queues);
 602         }
 603
 604         /* Update status */
 605         *(virtio_net_ctrl_ack *)(uintptr_t)vring->desc[idx_status].addr = status;
 606
 607         return n_descs;
 608 }
 609
 610 void
 611 virtio_user_handle_cq(struct virtio_user_dev *dev, uint16_t queue_idx)
 612 {
 613         uint16_t avail_idx, desc_idx;
 614         struct vring_used_elem *uep;
 615         uint32_t n_descs;
 616         struct vring *vring = &dev->vrings[queue_idx];
 617
 618         /* Consume avail ring, using used ring idx as first one */
 619         while (vring->used->idx != vring->avail->idx) {
 620                 avail_idx = (vring->used->idx) & (vring->num - 1);
 621                 desc_idx = vring->avail->ring[avail_idx];
 622
 623                 n_descs = virtio_user_handle_ctrl_msg(dev, vring, desc_idx);
 624
 625                 /* Update used ring */
 626                 uep = &vring->used->ring[avail_idx];
 627                 uep->id = avail_idx;
 628                 uep->len = n_descs;
 629
 630                 vring->used->idx++;
 631         }
 632 }