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Subject: Re: [PATCH v12 5/8] virtio-balloon: VIRTIO_BALLOON_F_SG
On 07/12/2017 09:06 PM, Michael S. Tsirkin wrote:
On Wed, Jul 12, 2017 at 08:40:18PM +0800, Wei Wang wrote:diff --git a/include/linux/virtio.h b/include/linux/virtio.h index 28b0e96..9f27101 100644 --- a/include/linux/virtio.h +++ b/include/linux/virtio.h @@ -57,8 +57,28 @@ int virtqueue_add_sgs(struct virtqueue *vq, void *data, gfp_t gfp);+/* A desc with this init id is treated as an invalid desc */+#define VIRTQUEUE_DESC_ID_INIT UINT_MAX +int virtqueue_add_chain_desc(struct virtqueue *_vq, + uint64_t addr, + uint32_t len, + unsigned int *head_id, + unsigned int *prev_id, + bool in); + +int virtqueue_add_chain(struct virtqueue *_vq, + unsigned int head, + bool indirect, + struct vring_desc *indirect_desc, + void *data, + void *ctx); + bool virtqueue_kick(struct virtqueue *vq);+bool virtqueue_kick_sync(struct virtqueue *vq);+ +bool virtqueue_kick_async(struct virtqueue *vq, wait_queue_head_t wq); + bool virtqueue_kick_prepare(struct virtqueue *vq);bool virtqueue_notify(struct virtqueue *vq);I don't much care for this API. It does exactly what balloon needs, but at cost of e.g. transparently busy-waiting. Unlikely to be a good fit for anything else.
If you were referring to this API - virtqueue_add_chain_desc(): Busy waiting only happens when the vq is full (i.e. no desc left). If necessary, I think we can add an input parameter like "bool busywaiting", then the caller can decide to simply get a -ENOSPC or busy wait to add when no desc is available.
If you don't like my original _first/_next/_last, you will need to come up with something else.
I thought the above virtqueue_add_chain_des() performs the same functionality as _first/next/last, which are used to grab descs from the vq and chain them together. If not, could you please elaborate the usage of the original proposal? Best, Wei
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