Root/drivers/virtio/virtio_ring.c

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
77struct 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. */
125static 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 */
191int 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
266add_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}
291EXPORT_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 */
304bool 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}
336EXPORT_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 */
344void 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}
351EXPORT_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 */
363void virtqueue_kick(struct virtqueue *vq)
364{
365    if (virtqueue_kick_prepare(vq))
366        virtqueue_notify(vq);
367}
368EXPORT_SYMBOL_GPL(virtqueue_kick);
369
370static 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
395static 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 */
416void *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}
471EXPORT_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 */
482void 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}
488EXPORT_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 */
501bool 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}
523EXPORT_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 */
538bool 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}
563EXPORT_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 */
573void *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}
597EXPORT_SYMBOL_GPL(virtqueue_detach_unused_buf);
598
599irqreturn_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}
617EXPORT_SYMBOL_GPL(vring_interrupt);
618
619struct 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}
674EXPORT_SYMBOL_GPL(vring_new_virtqueue);
675
676void vring_del_virtqueue(struct virtqueue *vq)
677{
678    list_del(&vq->list);
679    kfree(to_vvq(vq));
680}
681EXPORT_SYMBOL_GPL(vring_del_virtqueue);
682
683/* Manipulates transport-specific feature bits. */
684void 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}
700EXPORT_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 */
709unsigned 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}
716EXPORT_SYMBOL_GPL(virtqueue_get_vring_size);
717
718MODULE_LICENSE("GPL");
719

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