Re: [PATCH v11 08/40] virtio_ring: split: extract the logic of alloc queue

Xuan Zhuo
2022-07-05T02:23:11Z

On Mon, 4 Jul 2022 11:59:03 +0800, Jason Wang <jasowang@redhat.com> wrote:
>
> 在 2022/7/1 16:45, Xuan Zhuo 写道:
> > On Fri, 1 Jul 2022 16:26:25 +0800, Jason Wang <jasowang@redhat.com> wrote:
> >> 在 2022/6/29 14:56, Xuan Zhuo 写道:
> >>> Separate the logic of split to create vring queue.
> >>>
> >>> This feature is required for subsequent virtuqueue reset vring.
> >>>
> >>> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> >>> ---
> >>> drivers/virtio/virtio_ring.c | 68 ++++++++++++++++++++++--------------
> >>> 1 file changed, 42 insertions(+), 26 deletions(-)
> >>>
> >>> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> >>> index 49d61e412dc6..a9ceb9c16c54 100644
> >>> --- a/drivers/virtio/virtio_ring.c
> >>> +++ b/drivers/virtio/virtio_ring.c
> >>> @@ -949,28 +949,19 @@ static void vring_free_split(struct vring_virtqueue_split *vring,
> >>> kfree(vring->desc_extra);
> >>> }
> >>>
> >>> -static struct virtqueue *vring_create_virtqueue_split(
> >>> - unsigned int index,
> >>> - unsigned int num,
> >>> - unsigned int vring_align,
> >>> - struct virtio_device *vdev,
> >>> - bool weak_barriers,
> >>> - bool may_reduce_num,
> >>> - bool context,
> >>> - bool (*notify)(struct virtqueue *),
> >>> - void (*callback)(struct virtqueue *),
> >>> - const char *name)
> >>> +static int vring_alloc_queue_split(struct vring_virtqueue_split *vring,
> >>> + struct virtio_device *vdev,
> >>> + u32 num,
> >>> + unsigned int vring_align,
> >>> + bool may_reduce_num)
> >>> {
> >>> - struct virtqueue *vq;
> >>> void *queue = NULL;
> >>> dma_addr_t dma_addr;
> >>> - size_t queue_size_in_bytes;
> >>> - struct vring vring;
> >>>
> >>> /* We assume num is a power of 2. */
> >>> if (num & (num - 1)) {
> >>> dev_warn(&vdev->dev, "Bad virtqueue length %u\n", num);
> >>> - return NULL;
> >>> + return -EINVAL;
> >>> }
> >>>
> >>> /* TODO: allocate each queue chunk individually */
> >>> @@ -981,11 +972,11 @@ static struct virtqueue *vring_create_virtqueue_split(
> >>> if (queue)
> >>> break;
> >>> if (!may_reduce_num)
> >>> - return NULL;
> >>> + return -ENOMEM;
> >>> }
> >>>
> >>> if (!num)
> >>> - return NULL;
> >>> + return -ENOMEM;
> >>>
> >>> if (!queue) {
> >>> /* Try to get a single page. You are my only hope! */
> >>> @@ -993,21 +984,46 @@ static struct virtqueue *vring_create_virtqueue_split(
> >>> &dma_addr, GFP_KERNEL|__GFP_ZERO);
> >>> }
> >>> if (!queue)
> >>> - return NULL;
> >>> + return -ENOMEM;
> >>> +
> >>> + vring_init(&vring->vring, num, queue, vring_align);
> >>>
> >>> - queue_size_in_bytes = vring_size(num, vring_align);
> >>> - vring_init(&vring, num, queue, vring_align);
> >>> + vring->queue_dma_addr = dma_addr;
> >>> + vring->queue_size_in_bytes = vring_size(num, vring_align);
> >>> +
> >>> + return 0;
> >>> +}
> >>> +
> >>> +static struct virtqueue *vring_create_virtqueue_split(
> >>> + unsigned int index,
> >>> + unsigned int num,
> >>> + unsigned int vring_align,
> >>> + struct virtio_device *vdev,
> >>> + bool weak_barriers,
> >>> + bool may_reduce_num,
> >>> + bool context,
> >>> + bool (*notify)(struct virtqueue *),
> >>> + void (*callback)(struct virtqueue *),
> >>> + const char *name)
> >>> +{
> >>> + struct vring_virtqueue_split vring = {};
> >>> + struct virtqueue *vq;
> >>> + int err;
> >>> +
> >>> + err = vring_alloc_queue_split(&vring, vdev, num, vring_align,
> >>> + may_reduce_num);
> >>> + if (err)
> >>> + return NULL;
> >>>
> >>> - vq = __vring_new_virtqueue(index, vring, vdev, weak_barriers, context,
> >>> - notify, callback, name);
> >>> + vq = __vring_new_virtqueue(index, vring.vring, vdev, weak_barriers,
> >>> + context, notify, callback, name);
> >>> if (!vq) {
> >>> - vring_free_queue(vdev, queue_size_in_bytes, queue,
> >>> - dma_addr);
> >>> + vring_free_split(&vring, vdev);
> >>> return NULL;
> >>> }
> >>>
> >>> - to_vvq(vq)->split.queue_dma_addr = dma_addr;
> >>> - to_vvq(vq)->split.queue_size_in_bytes = queue_size_in_bytes;
> >>> + to_vvq(vq)->split.queue_dma_addr = vring.queue_dma_addr;
> >>
> >> Nit: having two queue_dma_addr seems redundant (so did queue_size_in_bytes).
> > two?
> >
> > Where is the problem I don't understand?
> >
> > Thanks.
>
>
> I meant we had:
>
>         vring.vring = _vring;
>
> in __vring_new_virtqueue().
>
> This means we'd better initialize vring fully before that?
>
> E.g
>
> vring.queue_dma_addr = dma_addr;
>
> ...
>
> __vring_new_virtqueue()

oh, my bad, maybe the repeated use of the name "vring" led to a
misunderstanding.

What is passed to __vring_new_virtqueue is the structure struct vring

struct vring {
unsigned int num;

vring_desc_t *desc;

vring_avail_t *avail;

vring_used_t *used;
};

And what contains queue_dma_addr is our newly split structure struct
vring_virtqueue_split

struct vring_virtqueue_split {
/* Actual memory layout for this queue. */
struct vring vring;

/* Last written value to avail->flags */
u16 avail_flags_shadow;

/*
* Last written value to avail->idx in
* guest byte order.
*/
u16 avail_idx_shadow;

/* Per-descriptor state. */
struct vring_desc_state_split *desc_state;
struct vring_desc_extra *desc_extra;

/* DMA address and size information */
dma_addr_t queue_dma_addr;
size_t queue_size_in_bytes;

/*
* The parameters for creating vrings are reserved for creating new
* vring.
*/
u32 vring_align;
bool may_reduce_num;
};

We have no way to pass queue_dma_addr into __vring_new_virtqueue. But for the
uniformity of the interface, I create a temporary struct vring_virtqueue_split
vring_split(your suggestion) in __vring_new_virtqueue. Then assign the passed
in struct vring to it

vring.vring = _vring.

So here vring is an empty temporary variable.

As you have replied in other patches, my re-use of the name vring is a mistake,
I will change some places to vring_split and vring_packed.

Thanks.

>
> Thanks
>
>
> >
> >> Thanks
> >>
> >>
> >>> + to_vvq(vq)->split.queue_size_in_bytes = vring.queue_size_in_bytes;
> >>> to_vvq(vq)->we_own_ring = true;
> >>>
> >>> return vq;
>