Re: [PATCH vhost v10 06/10] virtio_ring: packed-detach: support return dma info to driver
On Fri, Jun 02, 2023 at 05:22:02PM +0800, Xuan Zhuo wrote:
> Under the premapped mode, the driver needs to unmap the DMA address
> after receiving the buffer. The virtio core records the DMA address,
> so the driver needs a way to get the dma info from the virtio core.
>
> A straightforward approach is to pass an array to the virtio core when
> calling virtqueue_get_buf(). However, it is not feasible when there are
> multiple DMA addresses in the descriptor chain, and the array size is
> unknown.
>
> To solve this problem, a helper be introduced. After calling
> virtqueue_get_buf(), the driver can call the helper to
> retrieve a dma info. If the helper function returns -EAGAIN, it means
> that there are more DMA addresses to be processed, and the driver should
> call the helper function again.
Please, keep error codes for when an actual error occurs.
A common pattern would be:
<0 - error
0 - success, done
>0 - success, more to do
> To keep track of the current position in
> the chain, a cursor must be passed to the helper function, which is
> initialized by virtqueue_get_buf().
>
> Some processes are done inside this helper, so this helper MUST be
> called under the premapped mode.
>
> Signed-off-by: Xuan Zhuo
> ---
> drivers/virtio/virtio_ring.c | 105 ---
> include/linux/virtio.h | 9 ++-
> 2 files changed, 103 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index cdc4349f6066..cbc22daae7e1 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -1695,8 +1695,85 @@ static bool virtqueue_kick_prepare_packed(struct
> virtqueue *_vq)
> return needs_kick;
> }
>
> +static void detach_cursor_init_packed(struct vring_virtqueue *vq,
> + struct virtqueue_detach_cursor *cursor,
> u16 id)
> +{
> + struct vring_desc_state_packed *state = NULL;
> + u32 len;
> +
> + state = >packed.desc_state[id];
> +
> + /* Clear data ptr. */
> + state->data = NULL;
> +
> + vq->packed.desc_extra[state->last].next = vq->free_head;
> + vq->free_head = id;
> + vq->vq.num_free += state->num;
> +
> + /* init cursor */
> + cursor->curr = id;
> + cursor->done = 0;
> + cursor->pos = 0;
> +
> + if (vq->packed.desc_extra[id].flags & VRING_DESC_F_INDIRECT) {
> + len = vq->split.desc_extra[id].len;
> +
> + cursor->num = len / sizeof(struct vring_packed_desc);
> + cursor->indirect = true;
> +
> + vring_unmap_extra_packed(vq, >packed.desc_extra[id]);
> + } else {
> + cursor->num = state->num;
> + cursor->indirect = false;
> + }
> +}
> +
> +static int virtqueue_detach_packed(struct virtqueue *_vq, struct
> virtqueue_detach_cursor *cursor,
> +dma_addr_t *addr, u32 *len, enum
> dma_data_direction *dir)
> +{
> + struct vring_virtqueue *vq = to_vvq(_vq);
> +
> + if (unlikely(cursor->done))
> + return -EINVAL;
> +
> + if (!cursor->indirect) {
> + struct vring_desc_extra *extra;
> +
> + extra = >packed.desc_extra[cursor->curr];
> + cursor->curr = extra->next;
> +
> + *addr = extra->addr;
> + *len = extra->len;
> + *dir = (extra->flags & VRING_DESC_F_WRITE) ? DMA_FROM_DEVICE :
> DMA_TO_DEVICE;
> +
> + if (++cursor->pos == cursor->num) {
> + cursor->done = true;
> + return 0;
> + }
> + } else {
> + struct vring_packed_desc *indir_desc, *desc;
> + u16 flags;
> +
> + indir_desc = vq->packed.desc_state[cursor->curr].indir_desc;
> + desc = _desc[cursor->pos];
> +
> + flags = le16_to_cpu(desc->flags);
> + *addr = le64_to_cpu(desc->addr);
> + *len = le32_to_cpu(desc->len);
> + *dir = (flags & VRING_DESC_F_WRITE) ? DMA_FROM_DEVICE :
> DMA_TO_DEVICE;
> +
> + if (++cursor->pos == cursor->num) {
> + kfree(indir_desc);
> + cursor->done = true;
> + return 0;
> + }
> + }
> +
> + return -EAGAIN;
> +}
> +
> static void detach_buf_packed(struct vring_virtqueue *vq,
> - unsigned int id, void **ctx)
> + unsigned int id)
> {
> struct vring_desc_state_packed *state = NULL;
> struct vring_packed_desc *desc;
> @@ -1736,8 +1813,6 @@ static void detach_buf_packed(struct vring_virtqueue
> *vq,
> }
> kfree(desc);
> state->indir_desc = NULL;
> - } else if (ctx) {
> - *ctx = state->indir_desc;
> }
> }
>
> @@ -1768,7 +1843,8 @@ static bool more_used_packed(const struct
> vring_virtqueue *vq)
>
> static void
[PATCH vhost v10 06/10] virtio_ring: packed-detach: support return dma info to driver
Under the premapped mode, the driver needs to unmap the DMA address
after receiving the buffer. The virtio core records the DMA address,
so the driver needs a way to get the dma info from the virtio core.
A straightforward approach is to pass an array to the virtio core when
calling virtqueue_get_buf(). However, it is not feasible when there are
multiple DMA addresses in the descriptor chain, and the array size is
unknown.
To solve this problem, a helper be introduced. After calling
virtqueue_get_buf(), the driver can call the helper to
retrieve a dma info. If the helper function returns -EAGAIN, it means
that there are more DMA addresses to be processed, and the driver should
call the helper function again. To keep track of the current position in
the chain, a cursor must be passed to the helper function, which is
initialized by virtqueue_get_buf().
Some processes are done inside this helper, so this helper MUST be
called under the premapped mode.
Signed-off-by: Xuan Zhuo
---
drivers/virtio/virtio_ring.c | 105 ---
include/linux/virtio.h | 9 ++-
2 files changed, 103 insertions(+), 11 deletions(-)
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index cdc4349f6066..cbc22daae7e1 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1695,8 +1695,85 @@ static bool virtqueue_kick_prepare_packed(struct
virtqueue *_vq)
return needs_kick;
}
+static void detach_cursor_init_packed(struct vring_virtqueue *vq,
+ struct virtqueue_detach_cursor *cursor,
u16 id)
+{
+ struct vring_desc_state_packed *state = NULL;
+ u32 len;
+
+ state = >packed.desc_state[id];
+
+ /* Clear data ptr. */
+ state->data = NULL;
+
+ vq->packed.desc_extra[state->last].next = vq->free_head;
+ vq->free_head = id;
+ vq->vq.num_free += state->num;
+
+ /* init cursor */
+ cursor->curr = id;
+ cursor->done = 0;
+ cursor->pos = 0;
+
+ if (vq->packed.desc_extra[id].flags & VRING_DESC_F_INDIRECT) {
+ len = vq->split.desc_extra[id].len;
+
+ cursor->num = len / sizeof(struct vring_packed_desc);
+ cursor->indirect = true;
+
+ vring_unmap_extra_packed(vq, >packed.desc_extra[id]);
+ } else {
+ cursor->num = state->num;
+ cursor->indirect = false;
+ }
+}
+
+static int virtqueue_detach_packed(struct virtqueue *_vq, struct
virtqueue_detach_cursor *cursor,
+ dma_addr_t *addr, u32 *len, enum
dma_data_direction *dir)
+{
+ struct vring_virtqueue *vq = to_vvq(_vq);
+
+ if (unlikely(cursor->done))
+ return -EINVAL;
+
+ if (!cursor->indirect) {
+ struct vring_desc_extra *extra;
+
+ extra = >packed.desc_extra[cursor->curr];
+ cursor->curr = extra->next;
+
+ *addr = extra->addr;
+ *len = extra->len;
+ *dir = (extra->flags & VRING_DESC_F_WRITE) ? DMA_FROM_DEVICE :
DMA_TO_DEVICE;
+
+ if (++cursor->pos == cursor->num) {
+ cursor->done = true;
+ return 0;
+ }
+ } else {
+ struct vring_packed_desc *indir_desc, *desc;
+ u16 flags;
+
+ indir_desc = vq->packed.desc_state[cursor->curr].indir_desc;
+ desc = _desc[cursor->pos];
+
+ flags = le16_to_cpu(desc->flags);
+ *addr = le64_to_cpu(desc->addr);
+ *len = le32_to_cpu(desc->len);
+ *dir = (flags & VRING_DESC_F_WRITE) ? DMA_FROM_DEVICE :
DMA_TO_DEVICE;
+
+ if (++cursor->pos == cursor->num) {
+ kfree(indir_desc);
+ cursor->done = true;
+ return 0;
+ }
+ }
+
+ return -EAGAIN;
+}
+
static void detach_buf_packed(struct vring_virtqueue *vq,
- unsigned int id, void **ctx)
+ unsigned int id)
{
struct vring_desc_state_packed *state = NULL;
struct vring_packed_desc *desc;
@@ -1736,8 +1813,6 @@ static void detach_buf_packed(struct vring_virtqueue *vq,
}
kfree(desc);
state->indir_desc = NULL;
- } else if (ctx) {
- *ctx = state->indir_desc;
}
}
@@ -1768,7 +1843,8 @@ static bool more_used_packed(const struct vring_virtqueue
*vq)
static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq,
unsigned int *len,
- void **ctx)
+ void **ctx,
+ struct virtqueue_detach_cursor
*cursor)
{
struct vring_virtqueue *vq = to_vvq(_vq);
u16 last_used, id,
