1 /* Virtio ring implementation.
3 * Copyright 2007 Rusty Russell IBM Corporation
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.
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.
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
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>
28 /* For development, we want to crash whenever the ring is screwed. */
29 #define BAD_RING(_vq, fmt, args...) \
31 dev_err(&(_vq)->vq.vdev->dev, \
32 "%s:"fmt, (_vq)->vq.name, ##args); \
35 /* Caller is supposed to guarantee no reentry. */
36 #define START_USE(_vq) \
39 panic("%s:in_use = %i\n", \
40 (_vq)->vq.name, (_vq)->in_use); \
41 (_vq)->in_use = __LINE__; \
43 #define END_USE(_vq) \
44 do { BUG_ON(!(_vq)->in_use); (_vq)->in_use = 0; } while(0)
46 #define BAD_RING(_vq, fmt, args...) \
48 dev_err(&_vq->vq.vdev->dev, \
49 "%s:"fmt, (_vq)->vq.name, ##args); \
50 (_vq)->broken = true; \
56 struct vring_virtqueue
60 /* Actual memory layout for this queue */
63 /* Can we use weak barriers? */
66 /* Other side has made a mess, don't try any more. */
69 /* Host supports indirect buffers */
72 /* Host publishes avail event idx */
75 /* Head of free buffer list. */
76 unsigned int free_head
;
77 /* Number we've added since last sync. */
78 unsigned int num_added
;
80 /* Last used index we've seen. */
83 /* How to notify other side. FIXME: commonalize hcalls! */
84 void (*notify
)(struct virtqueue
*vq
);
87 /* They're supposed to lock for us. */
90 /* Figure out if their kicks are too delayed. */
91 bool last_add_time_valid
;
92 ktime_t last_add_time
;
95 /* Tokens for callbacks. */
99 #define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)
101 static inline struct scatterlist
*sg_next_chained(struct scatterlist
*sg
,
107 static inline struct scatterlist
*sg_next_arr(struct scatterlist
*sg
,
115 /* Set up an indirect table of descriptors and add it to the queue. */
116 static inline int vring_add_indirect(struct vring_virtqueue
*vq
,
117 struct scatterlist
*sgs
[],
118 struct scatterlist
*(*next
)
119 (struct scatterlist
*, unsigned int *),
120 unsigned int total_sg
,
121 unsigned int total_out
,
122 unsigned int total_in
,
123 unsigned int out_sgs
,
127 struct vring_desc
*desc
;
129 struct scatterlist
*sg
;
133 * We require lowmem mappings for the descriptors because
134 * otherwise virt_to_phys will give us bogus addresses in the
137 gfp
&= ~(__GFP_HIGHMEM
| __GFP_HIGH
);
139 desc
= kmalloc(total_sg
* sizeof(struct vring_desc
), gfp
);
143 /* Transfer entries from the sg lists into the indirect page */
145 for (n
= 0; n
< out_sgs
; n
++) {
146 for (sg
= sgs
[n
]; sg
; sg
= next(sg
, &total_out
)) {
147 desc
[i
].flags
= VRING_DESC_F_NEXT
;
148 desc
[i
].addr
= sg_phys(sg
);
149 desc
[i
].len
= sg
->length
;
154 for (; n
< (out_sgs
+ in_sgs
); n
++) {
155 for (sg
= sgs
[n
]; sg
; sg
= next(sg
, &total_in
)) {
156 desc
[i
].flags
= VRING_DESC_F_NEXT
|VRING_DESC_F_WRITE
;
157 desc
[i
].addr
= sg_phys(sg
);
158 desc
[i
].len
= sg
->length
;
163 BUG_ON(i
!= total_sg
);
165 /* Last one doesn't continue. */
166 desc
[i
-1].flags
&= ~VRING_DESC_F_NEXT
;
169 /* We're about to use a buffer */
172 /* Use a single buffer which doesn't continue */
173 head
= vq
->free_head
;
174 vq
->vring
.desc
[head
].flags
= VRING_DESC_F_INDIRECT
;
175 vq
->vring
.desc
[head
].addr
= virt_to_phys(desc
);
176 vq
->vring
.desc
[head
].len
= i
* sizeof(struct vring_desc
);
178 /* Update free pointer */
179 vq
->free_head
= vq
->vring
.desc
[head
].next
;
184 static inline int virtqueue_add(struct virtqueue
*_vq
,
185 struct scatterlist
*sgs
[],
186 struct scatterlist
*(*next
)
187 (struct scatterlist
*, unsigned int *),
188 unsigned int total_out
,
189 unsigned int total_in
,
190 unsigned int out_sgs
,
195 struct vring_virtqueue
*vq
= to_vvq(_vq
);
196 struct scatterlist
*sg
;
197 unsigned int i
, n
, avail
, uninitialized_var(prev
), total_sg
;
202 BUG_ON(data
== NULL
);
206 ktime_t now
= ktime_get();
208 /* No kick or get, with .1 second between? Warn. */
209 if (vq
->last_add_time_valid
)
210 WARN_ON(ktime_to_ms(ktime_sub(now
, vq
->last_add_time
))
212 vq
->last_add_time
= now
;
213 vq
->last_add_time_valid
= true;
217 total_sg
= total_in
+ total_out
;
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
&& total_sg
> 1 && vq
->vq
.num_free
) {
222 head
= vring_add_indirect(vq
, sgs
, next
, total_sg
, total_out
,
224 out_sgs
, in_sgs
, gfp
);
225 if (likely(head
>= 0))
229 BUG_ON(total_sg
> vq
->vring
.num
);
230 BUG_ON(total_sg
== 0);
232 if (vq
->vq
.num_free
< total_sg
) {
233 pr_debug("Can't add buf len %i - avail = %i\n",
234 total_sg
, vq
->vq
.num_free
);
235 /* FIXME: for historical reasons, we force a notify here if
236 * there are outgoing parts to the buffer. Presumably the
237 * host should service the ring ASAP. */
244 /* We're about to use some buffers from the free list. */
245 vq
->vq
.num_free
-= total_sg
;
247 head
= i
= vq
->free_head
;
248 for (n
= 0; n
< out_sgs
; n
++) {
249 for (sg
= sgs
[n
]; sg
; sg
= next(sg
, &total_out
)) {
250 vq
->vring
.desc
[i
].flags
= VRING_DESC_F_NEXT
;
251 vq
->vring
.desc
[i
].addr
= sg_phys(sg
);
252 vq
->vring
.desc
[i
].len
= sg
->length
;
254 i
= vq
->vring
.desc
[i
].next
;
257 for (; n
< (out_sgs
+ in_sgs
); n
++) {
258 for (sg
= sgs
[n
]; sg
; sg
= next(sg
, &total_in
)) {
259 vq
->vring
.desc
[i
].flags
= VRING_DESC_F_NEXT
|VRING_DESC_F_WRITE
;
260 vq
->vring
.desc
[i
].addr
= sg_phys(sg
);
261 vq
->vring
.desc
[i
].len
= sg
->length
;
263 i
= vq
->vring
.desc
[i
].next
;
266 /* Last one doesn't continue. */
267 vq
->vring
.desc
[prev
].flags
&= ~VRING_DESC_F_NEXT
;
269 /* Update free pointer */
274 vq
->data
[head
] = data
;
276 /* Put entry in available array (but don't update avail->idx until they
278 avail
= (vq
->vring
.avail
->idx
& (vq
->vring
.num
-1));
279 vq
->vring
.avail
->ring
[avail
] = head
;
281 /* Descriptors and available array need to be set before we expose the
282 * new available array entries. */
283 virtio_wmb(vq
->weak_barriers
);
284 vq
->vring
.avail
->idx
++;
287 /* This is very unlikely, but theoretically possible. Kick
289 if (unlikely(vq
->num_added
== (1 << 16) - 1))
292 pr_debug("Added buffer head %i to %p\n", head
, vq
);
299 * virtqueue_add_buf - expose buffer to other end
300 * @vq: the struct virtqueue we're talking about.
301 * @sg: the description of the buffer(s).
302 * @out_num: the number of sg readable by other side
303 * @in_num: the number of sg which are writable (after readable ones)
304 * @data: the token identifying the buffer.
305 * @gfp: how to do memory allocations (if necessary).
307 * Caller must ensure we don't call this with other virtqueue operations
308 * at the same time (except where noted).
310 * Returns zero or a negative error (ie. ENOSPC, ENOMEM).
312 int virtqueue_add_buf(struct virtqueue
*_vq
,
313 struct scatterlist sg
[],
319 struct scatterlist
*sgs
[2];
324 return virtqueue_add(_vq
, sgs
, sg_next_arr
,
325 out
, in
, out
? 1 : 0, in
? 1 : 0, data
, gfp
);
327 EXPORT_SYMBOL_GPL(virtqueue_add_buf
);
330 * virtqueue_add_sgs - expose buffers to other end
331 * @vq: the struct virtqueue we're talking about.
332 * @sgs: array of terminated scatterlists.
333 * @out_num: the number of scatterlists readable by other side
334 * @in_num: the number of scatterlists which are writable (after readable ones)
335 * @data: the token identifying the buffer.
336 * @gfp: how to do memory allocations (if necessary).
338 * Caller must ensure we don't call this with other virtqueue operations
339 * at the same time (except where noted).
341 * Returns zero or a negative error (ie. ENOSPC, ENOMEM).
343 int virtqueue_add_sgs(struct virtqueue
*_vq
,
344 struct scatterlist
*sgs
[],
345 unsigned int out_sgs
,
350 unsigned int i
, total_out
, total_in
;
352 /* Count them first. */
353 for (i
= total_out
= total_in
= 0; i
< out_sgs
; i
++) {
354 struct scatterlist
*sg
;
355 for (sg
= sgs
[i
]; sg
; sg
= sg_next(sg
))
358 for (; i
< out_sgs
+ in_sgs
; i
++) {
359 struct scatterlist
*sg
;
360 for (sg
= sgs
[i
]; sg
; sg
= sg_next(sg
))
363 return virtqueue_add(_vq
, sgs
, sg_next_chained
,
364 total_out
, total_in
, out_sgs
, in_sgs
, data
, gfp
);
366 EXPORT_SYMBOL_GPL(virtqueue_add_sgs
);
369 * virtqueue_add_outbuf - expose output buffers to other end
370 * @vq: the struct virtqueue we're talking about.
371 * @sgs: array of scatterlists (need not be terminated!)
372 * @num: the number of scatterlists readable by other side
373 * @data: the token identifying the buffer.
374 * @gfp: how to do memory allocations (if necessary).
376 * Caller must ensure we don't call this with other virtqueue operations
377 * at the same time (except where noted).
379 * Returns zero or a negative error (ie. ENOSPC, ENOMEM).
381 int virtqueue_add_outbuf(struct virtqueue
*vq
,
382 struct scatterlist sg
[], unsigned int num
,
386 return virtqueue_add(vq
, &sg
, sg_next_arr
, num
, 0, 1, 0, data
, gfp
);
388 EXPORT_SYMBOL_GPL(virtqueue_add_outbuf
);
391 * virtqueue_add_inbuf - expose input buffers to other end
392 * @vq: the struct virtqueue we're talking about.
393 * @sgs: array of scatterlists (need not be terminated!)
394 * @num: the number of scatterlists writable by other side
395 * @data: the token identifying the buffer.
396 * @gfp: how to do memory allocations (if necessary).
398 * Caller must ensure we don't call this with other virtqueue operations
399 * at the same time (except where noted).
401 * Returns zero or a negative error (ie. ENOSPC, ENOMEM).
403 int virtqueue_add_inbuf(struct virtqueue
*vq
,
404 struct scatterlist sg
[], unsigned int num
,
408 return virtqueue_add(vq
, &sg
, sg_next_arr
, 0, num
, 0, 1, data
, gfp
);
410 EXPORT_SYMBOL_GPL(virtqueue_add_inbuf
);
413 * virtqueue_kick_prepare - first half of split virtqueue_kick call.
414 * @vq: the struct virtqueue
416 * Instead of virtqueue_kick(), you can do:
417 * if (virtqueue_kick_prepare(vq))
418 * virtqueue_notify(vq);
420 * This is sometimes useful because the virtqueue_kick_prepare() needs
421 * to be serialized, but the actual virtqueue_notify() call does not.
423 bool virtqueue_kick_prepare(struct virtqueue
*_vq
)
425 struct vring_virtqueue
*vq
= to_vvq(_vq
);
430 /* We need to expose available array entries before checking avail
432 virtio_mb(vq
->weak_barriers
);
434 old
= vq
->vring
.avail
->idx
- vq
->num_added
;
435 new = vq
->vring
.avail
->idx
;
439 if (vq
->last_add_time_valid
) {
440 WARN_ON(ktime_to_ms(ktime_sub(ktime_get(),
441 vq
->last_add_time
)) > 100);
443 vq
->last_add_time_valid
= false;
447 needs_kick
= vring_need_event(vring_avail_event(&vq
->vring
),
450 needs_kick
= !(vq
->vring
.used
->flags
& VRING_USED_F_NO_NOTIFY
);
455 EXPORT_SYMBOL_GPL(virtqueue_kick_prepare
);
458 * virtqueue_notify - second half of split virtqueue_kick call.
459 * @vq: the struct virtqueue
461 * This does not need to be serialized.
463 void virtqueue_notify(struct virtqueue
*_vq
)
465 struct vring_virtqueue
*vq
= to_vvq(_vq
);
467 /* Prod other side to tell it about changes. */
470 EXPORT_SYMBOL_GPL(virtqueue_notify
);
473 * virtqueue_kick - update after add_buf
474 * @vq: the struct virtqueue
476 * After one or more virtqueue_add_buf calls, invoke this to kick
479 * Caller must ensure we don't call this with other virtqueue
480 * operations at the same time (except where noted).
482 void virtqueue_kick(struct virtqueue
*vq
)
484 if (virtqueue_kick_prepare(vq
))
485 virtqueue_notify(vq
);
487 EXPORT_SYMBOL_GPL(virtqueue_kick
);
489 static void detach_buf(struct vring_virtqueue
*vq
, unsigned int head
)
493 /* Clear data ptr. */
494 vq
->data
[head
] = NULL
;
496 /* Put back on free list: find end */
499 /* Free the indirect table */
500 if (vq
->vring
.desc
[i
].flags
& VRING_DESC_F_INDIRECT
)
501 kfree(phys_to_virt(vq
->vring
.desc
[i
].addr
));
503 while (vq
->vring
.desc
[i
].flags
& VRING_DESC_F_NEXT
) {
504 i
= vq
->vring
.desc
[i
].next
;
508 vq
->vring
.desc
[i
].next
= vq
->free_head
;
509 vq
->free_head
= head
;
510 /* Plus final descriptor */
514 static inline bool more_used(const struct vring_virtqueue
*vq
)
516 return vq
->last_used_idx
!= vq
->vring
.used
->idx
;
520 * virtqueue_get_buf - get the next used buffer
521 * @vq: the struct virtqueue we're talking about.
522 * @len: the length written into the buffer
524 * If the driver wrote data into the buffer, @len will be set to the
525 * amount written. This means you don't need to clear the buffer
526 * beforehand to ensure there's no data leakage in the case of short
529 * Caller must ensure we don't call this with other virtqueue
530 * operations at the same time (except where noted).
532 * Returns NULL if there are no used buffers, or the "data" token
533 * handed to virtqueue_add_buf().
535 void *virtqueue_get_buf(struct virtqueue
*_vq
, unsigned int *len
)
537 struct vring_virtqueue
*vq
= to_vvq(_vq
);
544 if (unlikely(vq
->broken
)) {
549 if (!more_used(vq
)) {
550 pr_debug("No more buffers in queue\n");
555 /* Only get used array entries after they have been exposed by host. */
556 virtio_rmb(vq
->weak_barriers
);
558 last_used
= (vq
->last_used_idx
& (vq
->vring
.num
- 1));
559 i
= vq
->vring
.used
->ring
[last_used
].id
;
560 *len
= vq
->vring
.used
->ring
[last_used
].len
;
562 if (unlikely(i
>= vq
->vring
.num
)) {
563 BAD_RING(vq
, "id %u out of range\n", i
);
566 if (unlikely(!vq
->data
[i
])) {
567 BAD_RING(vq
, "id %u is not a head!\n", i
);
571 /* detach_buf clears data, so grab it now. */
575 /* If we expect an interrupt for the next entry, tell host
576 * by writing event index and flush out the write before
577 * the read in the next get_buf call. */
578 if (!(vq
->vring
.avail
->flags
& VRING_AVAIL_F_NO_INTERRUPT
)) {
579 vring_used_event(&vq
->vring
) = vq
->last_used_idx
;
580 virtio_mb(vq
->weak_barriers
);
584 vq
->last_add_time_valid
= false;
590 EXPORT_SYMBOL_GPL(virtqueue_get_buf
);
593 * virtqueue_disable_cb - disable callbacks
594 * @vq: the struct virtqueue we're talking about.
596 * Note that this is not necessarily synchronous, hence unreliable and only
597 * useful as an optimization.
599 * Unlike other operations, this need not be serialized.
601 void virtqueue_disable_cb(struct virtqueue
*_vq
)
603 struct vring_virtqueue
*vq
= to_vvq(_vq
);
605 vq
->vring
.avail
->flags
|= VRING_AVAIL_F_NO_INTERRUPT
;
607 EXPORT_SYMBOL_GPL(virtqueue_disable_cb
);
610 * virtqueue_enable_cb - restart callbacks after disable_cb.
611 * @vq: the struct virtqueue we're talking about.
613 * This re-enables callbacks; it returns "false" if there are pending
614 * buffers in the queue, to detect a possible race between the driver
615 * checking for more work, and enabling callbacks.
617 * Caller must ensure we don't call this with other virtqueue
618 * operations at the same time (except where noted).
620 bool virtqueue_enable_cb(struct virtqueue
*_vq
)
622 struct vring_virtqueue
*vq
= to_vvq(_vq
);
626 /* We optimistically turn back on interrupts, then check if there was
628 /* Depending on the VIRTIO_RING_F_EVENT_IDX feature, we need to
629 * either clear the flags bit or point the event index at the next
630 * entry. Always do both to keep code simple. */
631 vq
->vring
.avail
->flags
&= ~VRING_AVAIL_F_NO_INTERRUPT
;
632 vring_used_event(&vq
->vring
) = vq
->last_used_idx
;
633 virtio_mb(vq
->weak_barriers
);
634 if (unlikely(more_used(vq
))) {
642 EXPORT_SYMBOL_GPL(virtqueue_enable_cb
);
645 * virtqueue_enable_cb_delayed - restart callbacks after disable_cb.
646 * @vq: the struct virtqueue we're talking about.
648 * This re-enables callbacks but hints to the other side to delay
649 * interrupts until most of the available buffers have been processed;
650 * it returns "false" if there are many pending buffers in the queue,
651 * to detect a possible race between the driver checking for more work,
652 * and enabling callbacks.
654 * Caller must ensure we don't call this with other virtqueue
655 * operations at the same time (except where noted).
657 bool virtqueue_enable_cb_delayed(struct virtqueue
*_vq
)
659 struct vring_virtqueue
*vq
= to_vvq(_vq
);
664 /* We optimistically turn back on interrupts, then check if there was
666 /* Depending on the VIRTIO_RING_F_USED_EVENT_IDX feature, we need to
667 * either clear the flags bit or point the event index at the next
668 * entry. Always do both to keep code simple. */
669 vq
->vring
.avail
->flags
&= ~VRING_AVAIL_F_NO_INTERRUPT
;
670 /* TODO: tune this threshold */
671 bufs
= (u16
)(vq
->vring
.avail
->idx
- vq
->last_used_idx
) * 3 / 4;
672 vring_used_event(&vq
->vring
) = vq
->last_used_idx
+ bufs
;
673 virtio_mb(vq
->weak_barriers
);
674 if (unlikely((u16
)(vq
->vring
.used
->idx
- vq
->last_used_idx
) > bufs
)) {
682 EXPORT_SYMBOL_GPL(virtqueue_enable_cb_delayed
);
685 * virtqueue_detach_unused_buf - detach first unused buffer
686 * @vq: the struct virtqueue we're talking about.
688 * Returns NULL or the "data" token handed to virtqueue_add_buf().
689 * This is not valid on an active queue; it is useful only for device
692 void *virtqueue_detach_unused_buf(struct virtqueue
*_vq
)
694 struct vring_virtqueue
*vq
= to_vvq(_vq
);
700 for (i
= 0; i
< vq
->vring
.num
; i
++) {
703 /* detach_buf clears data, so grab it now. */
706 vq
->vring
.avail
->idx
--;
710 /* That should have freed everything. */
711 BUG_ON(vq
->vq
.num_free
!= vq
->vring
.num
);
716 EXPORT_SYMBOL_GPL(virtqueue_detach_unused_buf
);
718 irqreturn_t
vring_interrupt(int irq
, void *_vq
)
720 struct vring_virtqueue
*vq
= to_vvq(_vq
);
722 if (!more_used(vq
)) {
723 pr_debug("virtqueue interrupt with no work for %p\n", vq
);
727 if (unlikely(vq
->broken
))
730 pr_debug("virtqueue callback for %p (%p)\n", vq
, vq
->vq
.callback
);
732 vq
->vq
.callback(&vq
->vq
);
736 EXPORT_SYMBOL_GPL(vring_interrupt
);
738 struct virtqueue
*vring_new_virtqueue(unsigned int index
,
740 unsigned int vring_align
,
741 struct virtio_device
*vdev
,
744 void (*notify
)(struct virtqueue
*),
745 void (*callback
)(struct virtqueue
*),
748 struct vring_virtqueue
*vq
;
751 /* We assume num is a power of 2. */
752 if (num
& (num
- 1)) {
753 dev_warn(&vdev
->dev
, "Bad virtqueue length %u\n", num
);
757 vq
= kmalloc(sizeof(*vq
) + sizeof(void *)*num
, GFP_KERNEL
);
761 vring_init(&vq
->vring
, num
, pages
, vring_align
);
762 vq
->vq
.callback
= callback
;
765 vq
->vq
.num_free
= num
;
766 vq
->vq
.index
= index
;
768 vq
->weak_barriers
= weak_barriers
;
770 vq
->last_used_idx
= 0;
772 list_add_tail(&vq
->vq
.list
, &vdev
->vqs
);
775 vq
->last_add_time_valid
= false;
778 vq
->indirect
= virtio_has_feature(vdev
, VIRTIO_RING_F_INDIRECT_DESC
);
779 vq
->event
= virtio_has_feature(vdev
, VIRTIO_RING_F_EVENT_IDX
);
781 /* No callback? Tell other side not to bother us. */
783 vq
->vring
.avail
->flags
|= VRING_AVAIL_F_NO_INTERRUPT
;
785 /* Put everything in free lists. */
787 for (i
= 0; i
< num
-1; i
++) {
788 vq
->vring
.desc
[i
].next
= i
+1;
795 EXPORT_SYMBOL_GPL(vring_new_virtqueue
);
797 void vring_del_virtqueue(struct virtqueue
*vq
)
802 EXPORT_SYMBOL_GPL(vring_del_virtqueue
);
804 /* Manipulates transport-specific feature bits. */
805 void vring_transport_features(struct virtio_device
*vdev
)
809 for (i
= VIRTIO_TRANSPORT_F_START
; i
< VIRTIO_TRANSPORT_F_END
; i
++) {
811 case VIRTIO_RING_F_INDIRECT_DESC
:
813 case VIRTIO_RING_F_EVENT_IDX
:
816 /* We don't understand this bit. */
817 clear_bit(i
, vdev
->features
);
821 EXPORT_SYMBOL_GPL(vring_transport_features
);
824 * virtqueue_get_vring_size - return the size of the virtqueue's vring
825 * @vq: the struct virtqueue containing the vring of interest.
827 * Returns the size of the vring. This is mainly used for boasting to
828 * userspace. Unlike other operations, this need not be serialized.
830 unsigned int virtqueue_get_vring_size(struct virtqueue
*_vq
)
833 struct vring_virtqueue
*vq
= to_vvq(_vq
);
835 return vq
->vring
.num
;
837 EXPORT_SYMBOL_GPL(virtqueue_get_vring_size
);
839 MODULE_LICENSE("GPL");