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virtio_ring: determine descriptor flags at one time

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Let's determine the last descriptor by counting the number of sg. This
would be consistent with packed virtqueue implementation and ease the
future in-order implementation.

Acked-by: Eugenio Pérez <eperezma@redhat.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20251230064649.55597-15-jasowang@redhat.com>
This commit is contained in:
Jason Wang
2025-12-30 14:46:44 +08:00
committed by Michael S. Tsirkin
parent 1208473f9b
commit 03f05c4eeb
1 changed files with 13 additions and 15 deletions
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28
drivers/virtio/virtio_ring.c
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@@ -574,7 +574,7 @@ static inline int virtqueue_add_split(struct vring_virtqueue *vq,
struct vring_desc_extra *extra;
struct scatterlist *sg;
struct vring_desc *desc;
unsigned int i, n, avail, descs_used, prev, err_idx;
unsigned int i, n, avail, descs_used, err_idx, sg_count = 0;
int head;
bool indirect;
@@ -634,42 +634,40 @@ static inline int virtqueue_add_split(struct vring_virtqueue *vq,
for (sg = sgs[n]; sg; sg = sg_next(sg)) {
dma_addr_t addr;
u32 len;
u16 flags = 0;
if (++sg_count != total_sg)
flags |= VRING_DESC_F_NEXT;
if (vring_map_one_sg(vq, sg, DMA_TO_DEVICE, &addr, &len, premapped))
goto unmap_release;
prev = i;
/* Note that we trust indirect descriptor
* table since it use stream DMA mapping.
*/
i = virtqueue_add_desc_split(vq, desc, extra, i, addr, len,
VRING_DESC_F_NEXT,
premapped);
i = virtqueue_add_desc_split(vq, desc, extra, i, addr,
len, flags, premapped);
}
}
for (; n < (out_sgs + in_sgs); n++) {
for (sg = sgs[n]; sg; sg = sg_next(sg)) {
dma_addr_t addr;
u32 len;
u16 flags = VRING_DESC_F_WRITE;
if (++sg_count != total_sg)
flags |= VRING_DESC_F_NEXT;
if (vring_map_one_sg(vq, sg, DMA_FROM_DEVICE, &addr, &len, premapped))
goto unmap_release;
prev = i;
/* Note that we trust indirect descriptor
* table since it use stream DMA mapping.
*/
i = virtqueue_add_desc_split(vq, desc, extra, i, addr, len,
VRING_DESC_F_NEXT |
VRING_DESC_F_WRITE,
premapped);
i = virtqueue_add_desc_split(vq, desc, extra, i, addr,
len, flags, premapped);
}
}
/* Last one doesn't continue. */
desc[prev].flags &= cpu_to_virtio16(vq->vq.vdev, ~VRING_DESC_F_NEXT);
if (!indirect && vring_need_unmap_buffer(vq, &extra[prev]))
vq->split.desc_extra[prev & (vq->split.vring.num - 1)].flags &=
~VRING_DESC_F_NEXT;
if (indirect) {
/* Now that the indirect table is filled in, map it. */