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7ab358c23c
Add an API that tells the other side that callbacks should be delayed until a lot of work has been done. Implement using the new event_idx feature. Note: it might seem advantageous to let the drivers ask for a callback after a specific capacity has been reached. However, as a single head can free many entries in the descriptor table, we don't really have a clue about capacity until get_buf is called. The API is the simplest to implement at the moment, we'll see what kind of hints drivers can pass when there's more than one user of the feature. Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
532 lines
14 KiB
C
532 lines
14 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/virtio_config.h>
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#include <linux/device.h>
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#include <linux/slab.h>
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/* virtio guest is communicating with a virtual "device" that actually runs on
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* a host processor. Memory barriers are used to control SMP effects. */
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#ifdef CONFIG_SMP
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/* Where possible, use SMP barriers which are more lightweight than mandatory
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* barriers, because mandatory barriers control MMIO effects on accesses
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* through relaxed memory I/O windows (which virtio does not use). */
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#define virtio_mb() smp_mb()
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#define virtio_rmb() smp_rmb()
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#define virtio_wmb() smp_wmb()
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#else
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/* We must force memory ordering even if guest is UP since host could be
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* running on another CPU, but SMP barriers are defined to barrier() in that
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* configuration. So fall back to mandatory barriers instead. */
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#define virtio_mb() mb()
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#define virtio_rmb() rmb()
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#define virtio_wmb() wmb()
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#endif
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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, args...) \
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do { \
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dev_err(&(_vq)->vq.vdev->dev, \
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"%s:"fmt, (_vq)->vq.name, ##args); \
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BUG(); \
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} while (0)
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/* Caller is supposed to guarantee no reentry. */
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#define START_USE(_vq) \
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do { \
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if ((_vq)->in_use) \
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panic("%s:in_use = %i\n", \
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(_vq)->vq.name, (_vq)->in_use); \
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(_vq)->in_use = __LINE__; \
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} while (0)
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#define END_USE(_vq) \
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do { BUG_ON(!(_vq)->in_use); (_vq)->in_use = 0; } while(0)
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#else
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#define BAD_RING(_vq, fmt, args...) \
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do { \
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dev_err(&_vq->vq.vdev->dev, \
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"%s:"fmt, (_vq)->vq.name, ##args); \
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(_vq)->broken = true; \
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} 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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/* Host supports indirect buffers */
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bool indirect;
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/* Host publishes avail event idx */
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bool event;
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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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/* Set up an indirect table of descriptors and add it to the queue. */
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static int vring_add_indirect(struct vring_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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gfp_t gfp)
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{
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struct vring_desc *desc;
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unsigned head;
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int i;
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desc = kmalloc((out + in) * sizeof(struct vring_desc), gfp);
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if (!desc)
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return -ENOMEM;
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/* Transfer entries from the sg list into the indirect page */
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for (i = 0; i < out; i++) {
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desc[i].flags = VRING_DESC_F_NEXT;
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desc[i].addr = sg_phys(sg);
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desc[i].len = sg->length;
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desc[i].next = i+1;
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sg++;
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}
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for (; i < (out + in); i++) {
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desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
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desc[i].addr = sg_phys(sg);
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desc[i].len = sg->length;
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desc[i].next = i+1;
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sg++;
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}
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/* Last one doesn't continue. */
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desc[i-1].flags &= ~VRING_DESC_F_NEXT;
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desc[i-1].next = 0;
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/* We're about to use a buffer */
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vq->num_free--;
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/* Use a single buffer which doesn't continue */
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head = vq->free_head;
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vq->vring.desc[head].flags = VRING_DESC_F_INDIRECT;
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vq->vring.desc[head].addr = virt_to_phys(desc);
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vq->vring.desc[head].len = i * sizeof(struct vring_desc);
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/* Update free pointer */
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vq->free_head = vq->vring.desc[head].next;
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return head;
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}
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int virtqueue_add_buf_gfp(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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gfp_t gfp)
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{
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struct vring_virtqueue *vq = to_vvq(_vq);
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unsigned int i, avail, uninitialized_var(prev);
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int head;
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START_USE(vq);
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BUG_ON(data == NULL);
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/* If the host supports indirect descriptor tables, and we have multiple
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* buffers, then go indirect. FIXME: tune this threshold */
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if (vq->indirect && (out + in) > 1 && vq->num_free) {
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head = vring_add_indirect(vq, sg, out, in, gfp);
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if (likely(head >= 0))
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goto add_head;
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}
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BUG_ON(out + in > vq->vring.num);
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BUG_ON(out + in == 0);
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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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add_head:
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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 vq->num_free;
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}
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EXPORT_SYMBOL_GPL(virtqueue_add_buf_gfp);
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void virtqueue_kick(struct virtqueue *_vq)
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{
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struct vring_virtqueue *vq = to_vvq(_vq);
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u16 new, old;
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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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virtio_wmb();
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old = vq->vring.avail->idx;
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new = vq->vring.avail->idx = old + 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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virtio_mb();
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if (vq->event ?
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vring_need_event(vring_avail_event(&vq->vring), new, old) :
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!(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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EXPORT_SYMBOL_GPL(virtqueue_kick);
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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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/* Free the indirect table */
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if (vq->vring.desc[i].flags & VRING_DESC_F_INDIRECT)
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kfree(phys_to_virt(vq->vring.desc[i].addr));
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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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void *virtqueue_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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/* Only get used array entries after they have been exposed by host. */
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virtio_rmb();
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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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/* If we expect an interrupt for the next entry, tell host
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* by writing event index and flush out the write before
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* the read in the next get_buf call. */
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if (!(vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT)) {
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vring_used_event(&vq->vring) = vq->last_used_idx;
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virtio_mb();
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}
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END_USE(vq);
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return ret;
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}
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EXPORT_SYMBOL_GPL(virtqueue_get_buf);
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void virtqueue_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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EXPORT_SYMBOL_GPL(virtqueue_disable_cb);
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bool virtqueue_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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/* Depending on the VIRTIO_RING_F_EVENT_IDX feature, we need to
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* either clear the flags bit or point the event index at the next
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* entry. Always do both to keep code simple. */
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vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
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vring_used_event(&vq->vring) = vq->last_used_idx;
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virtio_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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EXPORT_SYMBOL_GPL(virtqueue_enable_cb);
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bool virtqueue_enable_cb_delayed(struct virtqueue *_vq)
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{
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struct vring_virtqueue *vq = to_vvq(_vq);
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u16 bufs;
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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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/* Depending on the VIRTIO_RING_F_USED_EVENT_IDX feature, we need to
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* either clear the flags bit or point the event index at the next
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* entry. Always do both to keep code simple. */
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vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
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/* TODO: tune this threshold */
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bufs = (u16)(vq->vring.avail->idx - vq->last_used_idx) * 3 / 4;
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vring_used_event(&vq->vring) = vq->last_used_idx + bufs;
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virtio_mb();
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if (unlikely((u16)(vq->vring.used->idx - vq->last_used_idx) > bufs)) {
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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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EXPORT_SYMBOL_GPL(virtqueue_enable_cb_delayed);
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void *virtqueue_detach_unused_buf(struct virtqueue *_vq)
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{
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struct vring_virtqueue *vq = to_vvq(_vq);
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unsigned int i;
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void *buf;
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START_USE(vq);
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for (i = 0; i < vq->vring.num; i++) {
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if (!vq->data[i])
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continue;
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/* detach_buf clears data, so grab it now. */
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buf = vq->data[i];
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detach_buf(vq, i);
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vq->vring.avail->idx--;
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END_USE(vq);
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return buf;
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}
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/* That should have freed everything. */
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BUG_ON(vq->num_free != vq->vring.num);
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END_USE(vq);
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return NULL;
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}
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EXPORT_SYMBOL_GPL(virtqueue_detach_unused_buf);
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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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struct virtqueue *vring_new_virtqueue(unsigned int num,
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unsigned int vring_align,
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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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const char *name)
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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, vring_align);
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vq->vq.callback = callback;
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vq->vq.vdev = vdev;
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vq->vq.name = name;
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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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list_add_tail(&vq->vq.list, &vdev->vqs);
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#ifdef DEBUG
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vq->in_use = false;
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#endif
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vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC);
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vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);
|
|
|
|
/* No callback? Tell other side not to bother us. */
|
|
if (!callback)
|
|
vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
|
|
|
|
/* Put everything in free lists. */
|
|
vq->num_free = num;
|
|
vq->free_head = 0;
|
|
for (i = 0; i < num-1; i++) {
|
|
vq->vring.desc[i].next = i+1;
|
|
vq->data[i] = NULL;
|
|
}
|
|
vq->data[i] = NULL;
|
|
|
|
return &vq->vq;
|
|
}
|
|
EXPORT_SYMBOL_GPL(vring_new_virtqueue);
|
|
|
|
void vring_del_virtqueue(struct virtqueue *vq)
|
|
{
|
|
list_del(&vq->list);
|
|
kfree(to_vvq(vq));
|
|
}
|
|
EXPORT_SYMBOL_GPL(vring_del_virtqueue);
|
|
|
|
/* Manipulates transport-specific feature bits. */
|
|
void vring_transport_features(struct virtio_device *vdev)
|
|
{
|
|
unsigned int i;
|
|
|
|
for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++) {
|
|
switch (i) {
|
|
case VIRTIO_RING_F_INDIRECT_DESC:
|
|
break;
|
|
case VIRTIO_RING_F_EVENT_IDX:
|
|
break;
|
|
default:
|
|
/* We don't understand this bit. */
|
|
clear_bit(i, vdev->features);
|
|
}
|
|
}
|
|
}
|
|
EXPORT_SYMBOL_GPL(vring_transport_features);
|
|
|
|
MODULE_LICENSE("GPL");
|