1 /* Virtio ring implementation. 2 * 3 * Copyright 2007 Rusty Russell IBM Corporation 4 * 5 * This program is free software; you can redistribute it and/or modify 6 * it under the terms of the GNU General Public License as published by 7 * the Free Software Foundation; either version 2 of the License, or 8 * (at your option) any later version. 9 * 10 * This program is distributed in the hope that it will be useful, 11 * but WITHOUT ANY WARRANTY; without even the implied warranty of 12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 13 * GNU General Public License for more details. 14 * 15 * You should have received a copy of the GNU General Public License 16 * along with this program; if not, write to the Free Software 17 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA 18 */ 19 #include <linux/virtio.h> 20 #include <linux/virtio_ring.h> 21 #include <linux/virtio_config.h> 22 #include <linux/device.h> 23 #include <linux/slab.h> 24 #include <linux/module.h> 25 #include <linux/hrtimer.h> 26 27 /* virtio guest is communicating with a virtual "device" that actually runs on 28 * a host processor. Memory barriers are used to control SMP effects. */ 29 #ifdef CONFIG_SMP 30 /* Where possible, use SMP barriers which are more lightweight than mandatory 31 * barriers, because mandatory barriers control MMIO effects on accesses 32 * through relaxed memory I/O windows (which virtio-pci does not use). */ 33 #define virtio_mb(vq) \ 34 do { if ((vq)->weak_barriers) smp_mb(); else mb(); } while(0) 35 #define virtio_rmb(vq) \ 36 do { if ((vq)->weak_barriers) smp_rmb(); else rmb(); } while(0) 37 #define virtio_wmb(vq) \ 38 do { if ((vq)->weak_barriers) smp_wmb(); else wmb(); } while(0) 39 #else 40 /* We must force memory ordering even if guest is UP since host could be 41 * running on another CPU, but SMP barriers are defined to barrier() in that 42 * configuration. So fall back to mandatory barriers instead. */ 43 #define virtio_mb(vq) mb() 44 #define virtio_rmb(vq) rmb() 45 #define virtio_wmb(vq) wmb() 46 #endif 47 48 #ifdef DEBUG 49 /* For development, we want to crash whenever the ring is screwed. */ 50 #define BAD_RING(_vq, fmt, args...) \ 51 do { \ 52 dev_err(&(_vq)->vq.vdev->dev, \ 53 "%s:"fmt, (_vq)->vq.name, ##args); \ 54 BUG(); \ 55 } while (0) 56 /* Caller is supposed to guarantee no reentry. */ 57 #define START_USE(_vq) \ 58 do { \ 59 if ((_vq)->in_use) \ 60 panic("%s:in_use = %i\n", \ 61 (_vq)->vq.name, (_vq)->in_use); \ 62 (_vq)->in_use = __LINE__; \ 63 } while (0) 64 #define END_USE(_vq) \ 65 do { BUG_ON(!(_vq)->in_use); (_vq)->in_use = 0; } while(0) 66 #else 67 #define BAD_RING(_vq, fmt, args...) \ 68 do { \ 69 dev_err(&_vq->vq.vdev->dev, \ 70 "%s:"fmt, (_vq)->vq.name, ##args); \ 71 (_vq)->broken = true; \ 72 } while (0) 73 #define START_USE(vq) 74 #define END_USE(vq) 75 #endif 76 77 struct vring_virtqueue 78 { 79 struct virtqueue vq; 80 81 /* Actual memory layout for this queue */ 82 struct vring vring; 83 84 /* Can we use weak barriers? */ 85 bool weak_barriers; 86 87 /* Other side has made a mess, don't try any more. */ 88 bool broken; 89 90 /* Host supports indirect buffers */ 91 bool indirect; 92 93 /* Host publishes avail event idx */ 94 bool event; 95 96 /* Number of free buffers */ 97 unsigned int num_free; 98 /* Head of free buffer list. */ 99 unsigned int free_head; 100 /* Number we've added since last sync. */ 101 unsigned int num_added; 102 103 /* Last used index we've seen. */ 104 u16 last_used_idx; 105 106 /* How to notify other side. FIXME: commonalize hcalls! */ 107 void (*notify)(struct virtqueue *vq); 108 109 #ifdef DEBUG 110 /* They're supposed to lock for us. */ 111 unsigned int in_use; 112 113 /* Figure out if their kicks are too delayed. */ 114 bool last_add_time_valid; 115 ktime_t last_add_time; 116 #endif 117 118 /* Tokens for callbacks. */ 119 void *data[]; 120 }; 121 122 #define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq) 123 124 /* Set up an indirect table of descriptors and add it to the queue. */ 125 static int vring_add_indirect(struct vring_virtqueue *vq, 126 struct scatterlist sg[], 127 unsigned int out, 128 unsigned int in, 129 gfp_t gfp) 130 { 131 struct vring_desc *desc; 132 unsigned head; 133 int i; 134 135 desc = kmalloc((out + in) * sizeof(struct vring_desc), gfp); 136 if (!desc) 137 return -ENOMEM; 138 139 /* Transfer entries from the sg list into the indirect page */ 140 for (i = 0; i < out; i++) { 141 desc[i].flags = VRING_DESC_F_NEXT; 142 desc[i].addr = sg_phys(sg); 143 desc[i].len = sg->length; 144 desc[i].next = i+1; 145 sg++; 146 } 147 for (; i < (out + in); i++) { 148 desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE; 149 desc[i].addr = sg_phys(sg); 150 desc[i].len = sg->length; 151 desc[i].next = i+1; 152 sg++; 153 } 154 155 /* Last one doesn't continue. */ 156 desc[i-1].flags &= ~VRING_DESC_F_NEXT; 157 desc[i-1].next = 0; 158 159 /* We're about to use a buffer */ 160 vq->num_free--; 161 162 /* Use a single buffer which doesn't continue */ 163 head = vq->free_head; 164 vq->vring.desc[head].flags = VRING_DESC_F_INDIRECT; 165 vq->vring.desc[head].addr = virt_to_phys(desc); 166 vq->vring.desc[head].len = i * sizeof(struct vring_desc); 167 168 /* Update free pointer */ 169 vq->free_head = vq->vring.desc[head].next; 170 171 return head; 172 } 173 174 /** 175 * virtqueue_add_buf - expose buffer to other end 176 * @vq: the struct virtqueue we're talking about. 177 * @sg: the description of the buffer(s). 178 * @out_num: the number of sg readable by other side 179 * @in_num: the number of sg which are writable (after readable ones) 180 * @data: the token identifying the buffer. 181 * @gfp: how to do memory allocations (if necessary). 182 * 183 * Caller must ensure we don't call this with other virtqueue operations 184 * at the same time (except where noted). 185 * 186 * Returns remaining capacity of queue or a negative error 187 * (ie. ENOSPC). Note that it only really makes sense to treat all 188 * positive return values as "available": indirect buffers mean that 189 * we can put an entire sg[] array inside a single queue entry. 190 */ 191 int virtqueue_add_buf(struct virtqueue *_vq, 192 struct scatterlist sg[], 193 unsigned int out, 194 unsigned int in, 195 void *data, 196 gfp_t gfp) 197 { 198 struct vring_virtqueue *vq = to_vvq(_vq); 199 unsigned int i, avail, uninitialized_var(prev); 200 int head; 201 202 START_USE(vq); 203 204 BUG_ON(data == NULL); 205 206 #ifdef DEBUG 207 { 208 ktime_t now = ktime_get(); 209 210 /* No kick or get, with .1 second between? Warn. */ 211 if (vq->last_add_time_valid) 212 WARN_ON(ktime_to_ms(ktime_sub(now, vq->last_add_time)) 213 > 100); 214 vq->last_add_time = now; 215 vq->last_add_time_valid = true; 216 } 217 #endif 218 219 /* If the host supports indirect descriptor tables, and we have multiple 220 * buffers, then go indirect. FIXME: tune this threshold */ 221 if (vq->indirect && (out + in) > 1 && vq->num_free) { 222 head = vring_add_indirect(vq, sg, out, in, gfp); 223 if (likely(head >= 0)) 224 goto add_head; 225 } 226 227 BUG_ON(out + in > vq->vring.num); 228 BUG_ON(out + in == 0); 229 230 if (vq->num_free < out + in) { 231 pr_debug("Can't add buf len %i - avail = %i\n", 232 out + in, vq->num_free); 233 /* FIXME: for historical reasons, we force a notify here if 234 * there are outgoing parts to the buffer. Presumably the 235 * host should service the ring ASAP. */ 236 if (out) 237 vq->notify(&vq->vq); 238 END_USE(vq); 239 return -ENOSPC; 240 } 241 242 /* We're about to use some buffers from the free list. */ 243 vq->num_free -= out + in; 244 245 head = vq->free_head; 246 for (i = vq->free_head; out; i = vq->vring.desc[i].next, out--) { 247 vq->vring.desc[i].flags = VRING_DESC_F_NEXT; 248 vq->vring.desc[i].addr = sg_phys(sg); 249 vq->vring.desc[i].len = sg->length; 250 prev = i; 251 sg++; 252 } 253 for (; in; i = vq->vring.desc[i].next, in--) { 254 vq->vring.desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE; 255 vq->vring.desc[i].addr = sg_phys(sg); 256 vq->vring.desc[i].len = sg->length; 257 prev = i; 258 sg++; 259 } 260 /* Last one doesn't continue. */ 261 vq->vring.desc[prev].flags &= ~VRING_DESC_F_NEXT; 262 263 /* Update free pointer */ 264 vq->free_head = i; 265 266 add_head: 267 /* Set token. */ 268 vq->data[head] = data; 269 270 /* Put entry in available array (but don't update avail->idx until they 271 * do sync). */ 272 avail = (vq->vring.avail->idx & (vq->vring.num-1)); 273 vq->vring.avail->ring[avail] = head; 274 275 /* Descriptors and available array need to be set before we expose the 276 * new available array entries. */ 277 virtio_wmb(vq); 278 vq->vring.avail->idx++; 279 vq->num_added++; 280 281 /* This is very unlikely, but theoretically possible. Kick 282 * just in case. */ 283 if (unlikely(vq->num_added == (1 << 16) - 1)) 284 virtqueue_kick(_vq); 285 286 pr_debug("Added buffer head %i to %p\n", head, vq); 287 END_USE(vq); 288 289 return vq->num_free; 290 } 291 EXPORT_SYMBOL_GPL(virtqueue_add_buf); 292 293 /** 294 * virtqueue_kick_prepare - first half of split virtqueue_kick call. 295 * @vq: the struct virtqueue 296 * 297 * Instead of virtqueue_kick(), you can do: 298 * if (virtqueue_kick_prepare(vq)) 299 * virtqueue_notify(vq); 300 * 301 * This is sometimes useful because the virtqueue_kick_prepare() needs 302 * to be serialized, but the actual virtqueue_notify() call does not. 303 */ 304 bool virtqueue_kick_prepare(struct virtqueue *_vq) 305 { 306 struct vring_virtqueue *vq = to_vvq(_vq); 307 u16 new, old; 308 bool needs_kick; 309 310 START_USE(vq); 311 /* We need to expose available array entries before checking avail 312 * event. */ 313 virtio_mb(vq); 314 315 old = vq->vring.avail->idx - vq->num_added; 316 new = vq->vring.avail->idx; 317 vq->num_added = 0; 318 319 #ifdef DEBUG 320 if (vq->last_add_time_valid) { 321 WARN_ON(ktime_to_ms(ktime_sub(ktime_get(), 322 vq->last_add_time)) > 100); 323 } 324 vq->last_add_time_valid = false; 325 #endif 326 327 if (vq->event) { 328 needs_kick = vring_need_event(vring_avail_event(&vq->vring), 329 new, old); 330 } else { 331 needs_kick = !(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY); 332 } 333 END_USE(vq); 334 return needs_kick; 335 } 336 EXPORT_SYMBOL_GPL(virtqueue_kick_prepare); 337 338 /** 339 * virtqueue_notify - second half of split virtqueue_kick call. 340 * @vq: the struct virtqueue 341 * 342 * This does not need to be serialized. 343 */ 344 void virtqueue_notify(struct virtqueue *_vq) 345 { 346 struct vring_virtqueue *vq = to_vvq(_vq); 347 348 /* Prod other side to tell it about changes. */ 349 vq->notify(_vq); 350 } 351 EXPORT_SYMBOL_GPL(virtqueue_notify); 352 353 /** 354 * virtqueue_kick - update after add_buf 355 * @vq: the struct virtqueue 356 * 357 * After one or more virtqueue_add_buf calls, invoke this to kick 358 * the other side. 359 * 360 * Caller must ensure we don't call this with other virtqueue 361 * operations at the same time (except where noted). 362 */ 363 void virtqueue_kick(struct virtqueue *vq) 364 { 365 if (virtqueue_kick_prepare(vq)) 366 virtqueue_notify(vq); 367 } 368 EXPORT_SYMBOL_GPL(virtqueue_kick); 369 370 static void detach_buf(struct vring_virtqueue *vq, unsigned int head) 371 { 372 unsigned int i; 373 374 /* Clear data ptr. */ 375 vq->data[head] = NULL; 376 377 /* Put back on free list: find end */ 378 i = head; 379 380 /* Free the indirect table */ 381 if (vq->vring.desc[i].flags & VRING_DESC_F_INDIRECT) 382 kfree(phys_to_virt(vq->vring.desc[i].addr)); 383 384 while (vq->vring.desc[i].flags & VRING_DESC_F_NEXT) { 385 i = vq->vring.desc[i].next; 386 vq->num_free++; 387 } 388 389 vq->vring.desc[i].next = vq->free_head; 390 vq->free_head = head; 391 /* Plus final descriptor */ 392 vq->num_free++; 393 } 394 395 static inline bool more_used(const struct vring_virtqueue *vq) 396 { 397 return vq->last_used_idx != vq->vring.used->idx; 398 } 399 400 /** 401 * virtqueue_get_buf - get the next used buffer 402 * @vq: the struct virtqueue we're talking about. 403 * @len: the length written into the buffer 404 * 405 * If the driver wrote data into the buffer, @len will be set to the 406 * amount written. This means you don't need to clear the buffer 407 * beforehand to ensure there's no data leakage in the case of short 408 * writes. 409 * 410 * Caller must ensure we don't call this with other virtqueue 411 * operations at the same time (except where noted). 412 * 413 * Returns NULL if there are no used buffers, or the "data" token 414 * handed to virtqueue_add_buf(). 415 */ 416 void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len) 417 { 418 struct vring_virtqueue *vq = to_vvq(_vq); 419 void *ret; 420 unsigned int i; 421 u16 last_used; 422 423 START_USE(vq); 424 425 if (unlikely(vq->broken)) { 426 END_USE(vq); 427 return NULL; 428 } 429 430 if (!more_used(vq)) { 431 pr_debug("No more buffers in queue\n"); 432 END_USE(vq); 433 return NULL; 434 } 435 436 /* Only get used array entries after they have been exposed by host. */ 437 virtio_rmb(vq); 438 439 last_used = (vq->last_used_idx & (vq->vring.num - 1)); 440 i = vq->vring.used->ring[last_used].id; 441 *len = vq->vring.used->ring[last_used].len; 442 443 if (unlikely(i >= vq->vring.num)) { 444 BAD_RING(vq, "id %u out of range\n", i); 445 return NULL; 446 } 447 if (unlikely(!vq->data[i])) { 448 BAD_RING(vq, "id %u is not a head!\n", i); 449 return NULL; 450 } 451 452 /* detach_buf clears data, so grab it now. */ 453 ret = vq->data[i]; 454 detach_buf(vq, i); 455 vq->last_used_idx++; 456 /* If we expect an interrupt for the next entry, tell host 457 * by writing event index and flush out the write before 458 * the read in the next get_buf call. */ 459 if (!(vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT)) { 460 vring_used_event(&vq->vring) = vq->last_used_idx; 461 virtio_mb(vq); 462 } 463 464 #ifdef DEBUG 465 vq->last_add_time_valid = false; 466 #endif 467 468 END_USE(vq); 469 return ret; 470 } 471 EXPORT_SYMBOL_GPL(virtqueue_get_buf); 472 473 /** 474 * virtqueue_disable_cb - disable callbacks 475 * @vq: the struct virtqueue we're talking about. 476 * 477 * Note that this is not necessarily synchronous, hence unreliable and only 478 * useful as an optimization. 479 * 480 * Unlike other operations, this need not be serialized. 481 */ 482 void virtqueue_disable_cb(struct virtqueue *_vq) 483 { 484 struct vring_virtqueue *vq = to_vvq(_vq); 485 486 vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT; 487 } 488 EXPORT_SYMBOL_GPL(virtqueue_disable_cb); 489 490 /** 491 * virtqueue_enable_cb - restart callbacks after disable_cb. 492 * @vq: the struct virtqueue we're talking about. 493 * 494 * This re-enables callbacks; it returns "false" if there are pending 495 * buffers in the queue, to detect a possible race between the driver 496 * checking for more work, and enabling callbacks. 497 * 498 * Caller must ensure we don't call this with other virtqueue 499 * operations at the same time (except where noted). 500 */ 501 bool virtqueue_enable_cb(struct virtqueue *_vq) 502 { 503 struct vring_virtqueue *vq = to_vvq(_vq); 504 505 START_USE(vq); 506 507 /* We optimistically turn back on interrupts, then check if there was 508 * more to do. */ 509 /* Depending on the VIRTIO_RING_F_EVENT_IDX feature, we need to 510 * either clear the flags bit or point the event index at the next 511 * entry. Always do both to keep code simple. */ 512 vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT; 513 vring_used_event(&vq->vring) = vq->last_used_idx; 514 virtio_mb(vq); 515 if (unlikely(more_used(vq))) { 516 END_USE(vq); 517 return false; 518 } 519 520 END_USE(vq); 521 return true; 522 } 523 EXPORT_SYMBOL_GPL(virtqueue_enable_cb); 524 525 /** 526 * virtqueue_enable_cb_delayed - restart callbacks after disable_cb. 527 * @vq: the struct virtqueue we're talking about. 528 * 529 * This re-enables callbacks but hints to the other side to delay 530 * interrupts until most of the available buffers have been processed; 531 * it returns "false" if there are many pending buffers in the queue, 532 * to detect a possible race between the driver checking for more work, 533 * and enabling callbacks. 534 * 535 * Caller must ensure we don't call this with other virtqueue 536 * operations at the same time (except where noted). 537 */ 538 bool virtqueue_enable_cb_delayed(struct virtqueue *_vq) 539 { 540 struct vring_virtqueue *vq = to_vvq(_vq); 541 u16 bufs; 542 543 START_USE(vq); 544 545 /* We optimistically turn back on interrupts, then check if there was 546 * more to do. */ 547 /* Depending on the VIRTIO_RING_F_USED_EVENT_IDX feature, we need to 548 * either clear the flags bit or point the event index at the next 549 * entry. Always do both to keep code simple. */ 550 vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT; 551 /* TODO: tune this threshold */ 552 bufs = (u16)(vq->vring.avail->idx - vq->last_used_idx) * 3 / 4; 553 vring_used_event(&vq->vring) = vq->last_used_idx + bufs; 554 virtio_mb(vq); 555 if (unlikely((u16)(vq->vring.used->idx - vq->last_used_idx) > bufs)) { 556 END_USE(vq); 557 return false; 558 } 559 560 END_USE(vq); 561 return true; 562 } 563 EXPORT_SYMBOL_GPL(virtqueue_enable_cb_delayed); 564 565 /** 566 * virtqueue_detach_unused_buf - detach first unused buffer 567 * @vq: the struct virtqueue we're talking about. 568 * 569 * Returns NULL or the "data" token handed to virtqueue_add_buf(). 570 * This is not valid on an active queue; it is useful only for device 571 * shutdown. 572 */ 573 void *virtqueue_detach_unused_buf(struct virtqueue *_vq) 574 { 575 struct vring_virtqueue *vq = to_vvq(_vq); 576 unsigned int i; 577 void *buf; 578 579 START_USE(vq); 580 581 for (i = 0; i < vq->vring.num; i++) { 582 if (!vq->data[i]) 583 continue; 584 /* detach_buf clears data, so grab it now. */ 585 buf = vq->data[i]; 586 detach_buf(vq, i); 587 vq->vring.avail->idx--; 588 END_USE(vq); 589 return buf; 590 } 591 /* That should have freed everything. */ 592 BUG_ON(vq->num_free != vq->vring.num); 593 594 END_USE(vq); 595 return NULL; 596 } 597 EXPORT_SYMBOL_GPL(virtqueue_detach_unused_buf); 598 599 irqreturn_t vring_interrupt(int irq, void *_vq) 600 { 601 struct vring_virtqueue *vq = to_vvq(_vq); 602 603 if (!more_used(vq)) { 604 pr_debug("virtqueue interrupt with no work for %p\n", vq); 605 return IRQ_NONE; 606 } 607 608 if (unlikely(vq->broken)) 609 return IRQ_HANDLED; 610 611 pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback); 612 if (vq->vq.callback) 613 vq->vq.callback(&vq->vq); 614 615 return IRQ_HANDLED; 616 } 617 EXPORT_SYMBOL_GPL(vring_interrupt); 618 619 struct virtqueue *vring_new_virtqueue(unsigned int num, 620 unsigned int vring_align, 621 struct virtio_device *vdev, 622 bool weak_barriers, 623 void *pages, 624 void (*notify)(struct virtqueue *), 625 void (*callback)(struct virtqueue *), 626 const char *name) 627 { 628 struct vring_virtqueue *vq; 629 unsigned int i; 630 631 /* We assume num is a power of 2. */ 632 if (num & (num - 1)) { 633 dev_warn(&vdev->dev, "Bad virtqueue length %u\n", num); 634 return NULL; 635 } 636 637 vq = kmalloc(sizeof(*vq) + sizeof(void *)*num, GFP_KERNEL); 638 if (!vq) 639 return NULL; 640 641 vring_init(&vq->vring, num, pages, vring_align); 642 vq->vq.callback = callback; 643 vq->vq.vdev = vdev; 644 vq->vq.name = name; 645 vq->notify = notify; 646 vq->weak_barriers = weak_barriers; 647 vq->broken = false; 648 vq->last_used_idx = 0; 649 vq->num_added = 0; 650 list_add_tail(&vq->vq.list, &vdev->vqs); 651 #ifdef DEBUG 652 vq->in_use = false; 653 vq->last_add_time_valid = false; 654 #endif 655 656 vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC); 657 vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX); 658 659 /* No callback? Tell other side not to bother us. */ 660 if (!callback) 661 vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT; 662 663 /* Put everything in free lists. */ 664 vq->num_free = num; 665 vq->free_head = 0; 666 for (i = 0; i < num-1; i++) { 667 vq->vring.desc[i].next = i+1; 668 vq->data[i] = NULL; 669 } 670 vq->data[i] = NULL; 671 672 return &vq->vq; 673 } 674 EXPORT_SYMBOL_GPL(vring_new_virtqueue); 675 676 void vring_del_virtqueue(struct virtqueue *vq) 677 { 678 list_del(&vq->list); 679 kfree(to_vvq(vq)); 680 } 681 EXPORT_SYMBOL_GPL(vring_del_virtqueue); 682 683 /* Manipulates transport-specific feature bits. */ 684 void vring_transport_features(struct virtio_device *vdev) 685 { 686 unsigned int i; 687 688 for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++) { 689 switch (i) { 690 case VIRTIO_RING_F_INDIRECT_DESC: 691 break; 692 case VIRTIO_RING_F_EVENT_IDX: 693 break; 694 default: 695 /* We don't understand this bit. */ 696 clear_bit(i, vdev->features); 697 } 698 } 699 } 700 EXPORT_SYMBOL_GPL(vring_transport_features); 701 702 /** 703 * virtqueue_get_vring_size - return the size of the virtqueue's vring 704 * @vq: the struct virtqueue containing the vring of interest. 705 * 706 * Returns the size of the vring. This is mainly used for boasting to 707 * userspace. Unlike other operations, this need not be serialized. 708 */ 709 unsigned int virtqueue_get_vring_size(struct virtqueue *_vq) 710 { 711 712 struct vring_virtqueue *vq = to_vvq(_vq); 713 714 return vq->vring.num; 715 } 716 EXPORT_SYMBOL_GPL(virtqueue_get_vring_size); 717 718 MODULE_LICENSE("GPL"); 719