![Rusty Russell](/assets/img/avatar_default.png)
We force notification when the ring is full, even if the host has indicated it doesn't want to know. This seemed like a good idea at the time: if we fill the transmit ring, we should tell the host immediately. Unfortunately this logic also applies to the receiving ring, which is refilled constantly. We should introduce real notification thesholds to replace this logic. Meanwhile, removing the logic altogether breaks the heuristics which KVM uses, so we use a hack: only notify if there are outgoing parts of the new buffer. Here are the number of exits with lguest's crappy network implementation: Before: network xmit 7859051 recv 236420 After: network xmit 7858610 recv 118136 Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
327 lines
7.9 KiB
C
327 lines
7.9 KiB
C
/* Virtio ring implementation.
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*
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* Copyright 2007 Rusty Russell IBM Corporation
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#include <linux/virtio.h>
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#include <linux/virtio_ring.h>
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#include <linux/device.h>
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#ifdef DEBUG
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/* For development, we want to crash whenever the ring is screwed. */
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#define BAD_RING(vq, fmt...) \
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do { dev_err(&vq->vq.vdev->dev, fmt); BUG(); } while(0)
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#define START_USE(vq) \
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do { if ((vq)->in_use) panic("in_use = %i\n", (vq)->in_use); (vq)->in_use = __LINE__; mb(); } while(0)
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#define END_USE(vq) \
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do { BUG_ON(!(vq)->in_use); (vq)->in_use = 0; mb(); } while(0)
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#else
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#define BAD_RING(vq, fmt...) \
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do { dev_err(&vq->vq.vdev->dev, fmt); (vq)->broken = true; } while(0)
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#define START_USE(vq)
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#define END_USE(vq)
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#endif
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struct vring_virtqueue
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{
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struct virtqueue vq;
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/* Actual memory layout for this queue */
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struct vring vring;
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/* Other side has made a mess, don't try any more. */
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bool broken;
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/* Number of free buffers */
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unsigned int num_free;
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/* Head of free buffer list. */
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unsigned int free_head;
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/* Number we've added since last sync. */
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unsigned int num_added;
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/* Last used index we've seen. */
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u16 last_used_idx;
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/* How to notify other side. FIXME: commonalize hcalls! */
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void (*notify)(struct virtqueue *vq);
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#ifdef DEBUG
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/* They're supposed to lock for us. */
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unsigned int in_use;
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#endif
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/* Tokens for callbacks. */
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void *data[];
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};
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#define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)
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static int vring_add_buf(struct virtqueue *_vq,
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struct scatterlist sg[],
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unsigned int out,
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unsigned int in,
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void *data)
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{
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struct vring_virtqueue *vq = to_vvq(_vq);
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unsigned int i, avail, head, uninitialized_var(prev);
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BUG_ON(data == NULL);
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BUG_ON(out + in > vq->vring.num);
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BUG_ON(out + in == 0);
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START_USE(vq);
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if (vq->num_free < out + in) {
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pr_debug("Can't add buf len %i - avail = %i\n",
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out + in, vq->num_free);
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/* FIXME: for historical reasons, we force a notify here if
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* there are outgoing parts to the buffer. Presumably the
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* host should service the ring ASAP. */
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if (out)
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vq->notify(&vq->vq);
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END_USE(vq);
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return -ENOSPC;
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}
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/* We're about to use some buffers from the free list. */
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vq->num_free -= out + in;
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head = vq->free_head;
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for (i = vq->free_head; out; i = vq->vring.desc[i].next, out--) {
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vq->vring.desc[i].flags = VRING_DESC_F_NEXT;
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vq->vring.desc[i].addr = sg_phys(sg);
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vq->vring.desc[i].len = sg->length;
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prev = i;
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sg++;
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}
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for (; in; i = vq->vring.desc[i].next, in--) {
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vq->vring.desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
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vq->vring.desc[i].addr = sg_phys(sg);
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vq->vring.desc[i].len = sg->length;
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prev = i;
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sg++;
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}
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/* Last one doesn't continue. */
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vq->vring.desc[prev].flags &= ~VRING_DESC_F_NEXT;
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/* Update free pointer */
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vq->free_head = i;
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/* Set token. */
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vq->data[head] = data;
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/* Put entry in available array (but don't update avail->idx until they
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* do sync). FIXME: avoid modulus here? */
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avail = (vq->vring.avail->idx + vq->num_added++) % vq->vring.num;
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vq->vring.avail->ring[avail] = head;
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pr_debug("Added buffer head %i to %p\n", head, vq);
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END_USE(vq);
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return 0;
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}
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static void vring_kick(struct virtqueue *_vq)
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{
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struct vring_virtqueue *vq = to_vvq(_vq);
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START_USE(vq);
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/* Descriptors and available array need to be set before we expose the
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* new available array entries. */
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wmb();
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vq->vring.avail->idx += vq->num_added;
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vq->num_added = 0;
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/* Need to update avail index before checking if we should notify */
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mb();
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if (!(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY))
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/* Prod other side to tell it about changes. */
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vq->notify(&vq->vq);
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END_USE(vq);
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}
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static void detach_buf(struct vring_virtqueue *vq, unsigned int head)
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{
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unsigned int i;
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/* Clear data ptr. */
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vq->data[head] = NULL;
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/* Put back on free list: find end */
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i = head;
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while (vq->vring.desc[i].flags & VRING_DESC_F_NEXT) {
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i = vq->vring.desc[i].next;
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vq->num_free++;
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}
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vq->vring.desc[i].next = vq->free_head;
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vq->free_head = head;
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/* Plus final descriptor */
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vq->num_free++;
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}
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static inline bool more_used(const struct vring_virtqueue *vq)
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{
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return vq->last_used_idx != vq->vring.used->idx;
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}
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static void *vring_get_buf(struct virtqueue *_vq, unsigned int *len)
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{
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struct vring_virtqueue *vq = to_vvq(_vq);
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void *ret;
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unsigned int i;
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START_USE(vq);
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if (unlikely(vq->broken)) {
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END_USE(vq);
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return NULL;
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}
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if (!more_used(vq)) {
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pr_debug("No more buffers in queue\n");
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END_USE(vq);
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return NULL;
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}
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i = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].id;
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*len = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].len;
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if (unlikely(i >= vq->vring.num)) {
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BAD_RING(vq, "id %u out of range\n", i);
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return NULL;
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}
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if (unlikely(!vq->data[i])) {
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BAD_RING(vq, "id %u is not a head!\n", i);
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return NULL;
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}
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/* detach_buf clears data, so grab it now. */
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ret = vq->data[i];
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detach_buf(vq, i);
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vq->last_used_idx++;
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END_USE(vq);
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return ret;
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}
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static void vring_disable_cb(struct virtqueue *_vq)
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{
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struct vring_virtqueue *vq = to_vvq(_vq);
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vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
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}
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static bool vring_enable_cb(struct virtqueue *_vq)
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{
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struct vring_virtqueue *vq = to_vvq(_vq);
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START_USE(vq);
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/* We optimistically turn back on interrupts, then check if there was
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* more to do. */
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vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
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mb();
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if (unlikely(more_used(vq))) {
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END_USE(vq);
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return false;
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}
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END_USE(vq);
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return true;
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}
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irqreturn_t vring_interrupt(int irq, void *_vq)
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{
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struct vring_virtqueue *vq = to_vvq(_vq);
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if (!more_used(vq)) {
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pr_debug("virtqueue interrupt with no work for %p\n", vq);
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return IRQ_NONE;
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}
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if (unlikely(vq->broken))
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return IRQ_HANDLED;
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pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback);
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if (vq->vq.callback)
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vq->vq.callback(&vq->vq);
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return IRQ_HANDLED;
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}
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EXPORT_SYMBOL_GPL(vring_interrupt);
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static struct virtqueue_ops vring_vq_ops = {
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.add_buf = vring_add_buf,
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.get_buf = vring_get_buf,
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.kick = vring_kick,
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.disable_cb = vring_disable_cb,
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.enable_cb = vring_enable_cb,
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};
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struct virtqueue *vring_new_virtqueue(unsigned int num,
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struct virtio_device *vdev,
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void *pages,
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void (*notify)(struct virtqueue *),
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void (*callback)(struct virtqueue *))
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{
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struct vring_virtqueue *vq;
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unsigned int i;
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/* We assume num is a power of 2. */
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if (num & (num - 1)) {
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dev_warn(&vdev->dev, "Bad virtqueue length %u\n", num);
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return NULL;
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}
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vq = kmalloc(sizeof(*vq) + sizeof(void *)*num, GFP_KERNEL);
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if (!vq)
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return NULL;
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vring_init(&vq->vring, num, pages, PAGE_SIZE);
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vq->vq.callback = callback;
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vq->vq.vdev = vdev;
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vq->vq.vq_ops = &vring_vq_ops;
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vq->notify = notify;
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vq->broken = false;
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vq->last_used_idx = 0;
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vq->num_added = 0;
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#ifdef DEBUG
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vq->in_use = false;
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#endif
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/* No callback? Tell other side not to bother us. */
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if (!callback)
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vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
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/* Put everything in free lists. */
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vq->num_free = num;
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vq->free_head = 0;
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for (i = 0; i < num-1; i++)
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vq->vring.desc[i].next = i+1;
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return &vq->vq;
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}
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EXPORT_SYMBOL_GPL(vring_new_virtqueue);
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void vring_del_virtqueue(struct virtqueue *vq)
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{
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kfree(to_vvq(vq));
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}
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EXPORT_SYMBOL_GPL(vring_del_virtqueue);
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MODULE_LICENSE("GPL");
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