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    SubjectRe: [PATCH RFC 07/13] vhost: format-independent API for used buffers
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    On 2020/6/2 下午9:06, Michael S. Tsirkin wrote:
    > Add a new API that doesn't assume used ring, heads, etc.
    > For now, we keep the old APIs around to make it easier
    > to convert drivers.
    >
    > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
    > ---
    > drivers/vhost/vhost.c | 52 ++++++++++++++++++++++++++++++++++---------
    > drivers/vhost/vhost.h | 17 +++++++++++++-
    > 2 files changed, 58 insertions(+), 11 deletions(-)
    >
    > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
    > index b4a6e44d56a8..be822f0c9428 100644
    > --- a/drivers/vhost/vhost.c
    > +++ b/drivers/vhost/vhost.c
    > @@ -2292,13 +2292,12 @@ static int fetch_descs(struct vhost_virtqueue *vq)
    > * number of output then some number of input descriptors, it's actually two
    > * iovecs, but we pack them into one and note how many of each there were.
    > *
    > - * This function returns the descriptor number found, or vq->num (which is
    > - * never a valid descriptor number) if none was found. A negative code is
    > - * returned on error. */
    > -int vhost_get_vq_desc(struct vhost_virtqueue *vq,
    > - struct iovec iov[], unsigned int iov_size,
    > - unsigned int *out_num, unsigned int *in_num,
    > - struct vhost_log *log, unsigned int *log_num)
    > + * This function returns a value > 0 if a descriptor was found, or 0 if none were found.
    > + * A negative code is returned on error. */
    > +int vhost_get_avail_buf(struct vhost_virtqueue *vq, struct vhost_buf *buf,
    > + struct iovec iov[], unsigned int iov_size,
    > + unsigned int *out_num, unsigned int *in_num,
    > + struct vhost_log *log, unsigned int *log_num)
    > {
    > int ret = fetch_descs(vq);
    > int i;
    > @@ -2311,6 +2310,8 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
    > *out_num = *in_num = 0;
    > if (unlikely(log))
    > *log_num = 0;
    > + buf->in_len = buf->out_len = 0;
    > + buf->descs = 0;
    >
    > for (i = vq->first_desc; i < vq->ndescs; ++i) {
    > unsigned iov_count = *in_num + *out_num;
    > @@ -2340,6 +2341,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
    > /* If this is an input descriptor,
    > * increment that count. */
    > *in_num += ret;
    > + buf->in_len += desc->len;
    > if (unlikely(log && ret)) {
    > log[*log_num].addr = desc->addr;
    > log[*log_num].len = desc->len;
    > @@ -2355,9 +2357,11 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
    > goto err;
    > }
    > *out_num += ret;
    > + buf->out_len += desc->len;
    > }
    >
    > - ret = desc->id;
    > + buf->id = desc->id;
    > + ++buf->descs;
    >
    > if (!(desc->flags & VRING_DESC_F_NEXT))
    > break;
    > @@ -2365,7 +2369,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
    >
    > vq->first_desc = i + 1;
    >
    > - return ret;
    > + return 1;
    >
    > err:
    > for (i = vq->first_desc; i < vq->ndescs; ++i)
    > @@ -2375,7 +2379,15 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
    >
    > return ret;
    > }
    > -EXPORT_SYMBOL_GPL(vhost_get_vq_desc);
    > +EXPORT_SYMBOL_GPL(vhost_get_avail_buf);
    > +
    > +/* Reverse the effect of vhost_get_avail_buf. Useful for error handling. */
    > +void vhost_discard_avail_bufs(struct vhost_virtqueue *vq,
    > + struct vhost_buf *buf, unsigned count)
    > +{
    > + vhost_discard_vq_desc(vq, count);
    > +}
    > +EXPORT_SYMBOL_GPL(vhost_discard_avail_bufs);
    >
    > static int __vhost_add_used_n(struct vhost_virtqueue *vq,
    > struct vring_used_elem *heads,
    > @@ -2459,6 +2471,26 @@ int vhost_add_used(struct vhost_virtqueue *vq, unsigned int head, int len)
    > }
    > EXPORT_SYMBOL_GPL(vhost_add_used);
    >
    > +int vhost_put_used_buf(struct vhost_virtqueue *vq, struct vhost_buf *buf)
    > +{
    > + return vhost_add_used(vq, buf->id, buf->in_len);
    > +}
    > +EXPORT_SYMBOL_GPL(vhost_put_used_buf);
    > +
    > +int vhost_put_used_n_bufs(struct vhost_virtqueue *vq,
    > + struct vhost_buf *bufs, unsigned count)
    > +{
    > + unsigned i;
    > +
    > + for (i = 0; i < count; ++i) {
    > + vq->heads[i].id = cpu_to_vhost32(vq, bufs[i].id);
    > + vq->heads[i].len = cpu_to_vhost32(vq, bufs[i].in_len);
    > + }
    > +
    > + return vhost_add_used_n(vq, vq->heads, count);
    > +}
    > +EXPORT_SYMBOL_GPL(vhost_put_used_n_bufs);
    > +
    > static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
    > {
    > __u16 old, new;
    > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
    > index a67bda9792ec..6c10e99ff334 100644
    > --- a/drivers/vhost/vhost.h
    > +++ b/drivers/vhost/vhost.h
    > @@ -67,6 +67,13 @@ struct vhost_desc {
    > u16 id;
    > };
    >
    > +struct vhost_buf {
    > + u32 out_len;
    > + u32 in_len;
    > + u16 descs;
    > + u16 id;
    > +};


    So it looks to me the struct vhost_buf can work for both split ring and
    packed ring.

    If this is true, we'd better make struct vhost_desc work for both.

    Thanks


    > +
    > /* The virtqueue structure describes a queue attached to a device. */
    > struct vhost_virtqueue {
    > struct vhost_dev *dev;
    > @@ -193,7 +200,12 @@ int vhost_get_vq_desc(struct vhost_virtqueue *,
    > unsigned int *out_num, unsigned int *in_num,
    > struct vhost_log *log, unsigned int *log_num);
    > void vhost_discard_vq_desc(struct vhost_virtqueue *, int n);
    > -
    > +int vhost_get_avail_buf(struct vhost_virtqueue *, struct vhost_buf *buf,
    > + struct iovec iov[], unsigned int iov_count,
    > + unsigned int *out_num, unsigned int *in_num,
    > + struct vhost_log *log, unsigned int *log_num);
    > +void vhost_discard_avail_bufs(struct vhost_virtqueue *,
    > + struct vhost_buf *, unsigned count);
    > int vhost_vq_init_access(struct vhost_virtqueue *);
    > int vhost_add_used(struct vhost_virtqueue *, unsigned int head, int len);
    > int vhost_add_used_n(struct vhost_virtqueue *, struct vring_used_elem *heads,
    > @@ -202,6 +214,9 @@ void vhost_add_used_and_signal(struct vhost_dev *, struct vhost_virtqueue *,
    > unsigned int id, int len);
    > void vhost_add_used_and_signal_n(struct vhost_dev *, struct vhost_virtqueue *,
    > struct vring_used_elem *heads, unsigned count);
    > +int vhost_put_used_buf(struct vhost_virtqueue *, struct vhost_buf *buf);
    > +int vhost_put_used_n_bufs(struct vhost_virtqueue *,
    > + struct vhost_buf *bufs, unsigned count);
    > void vhost_signal(struct vhost_dev *, struct vhost_virtqueue *);
    > void vhost_disable_notify(struct vhost_dev *, struct vhost_virtqueue *);
    > bool vhost_vq_avail_empty(struct vhost_dev *, struct vhost_virtqueue *);

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