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    Subject[PATCH RFC v6 05/11] vhost: format-independent API for used buffers
    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 334529ebecab..f4a6ff9ef77a 100644
    --- a/drivers/vhost/vhost.c
    +++ b/drivers/vhost/vhost.c
    @@ -2339,13 +2339,12 @@ static void unfetch_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;
    @@ -2358,6 +2357,8 @@ 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;
    @@ -2387,6 +2388,7 @@ 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;
    @@ -2402,9 +2404,11 @@ 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;
    @@ -2412,14 +2416,22 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,

    vq->first_desc = i + 1;

    - return ret;
    + return 1;

    err:
    unfetch_descs(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);

    /* Reverse the effect of vhost_get_vq_desc. Useful for error handling. */
    void vhost_discard_vq_desc(struct vhost_virtqueue *vq, int n)
    @@ -2511,6 +2523,26 @@ 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 fed36af5c444..28eea0155efb 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;
    +};
    +
    /* The virtqueue structure describes a queue attached to a device. */
    struct vhost_virtqueue {
    struct vhost_dev *dev;
    @@ -195,7 +202,12 @@ 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,
    @@ -204,6 +216,9 @@ 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 *);
    --
    MST
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