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    Subject[RFC PATCH] Subject: virtio: Add unused buffers detach from vring
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    Date
    I submit one split patch for review to make sure that's the right format.
    I copied Rusty's comment for the commit message, and change destroy
    to detach since we destroy the buffers in caller. This patch is built
    against Dave's net-next tree.

    There's currently no way for a virtio driver to ask for unused
    buffers, so it has to keep a list itself to reclaim them at shutdown.
    This is redundant, since virtio_ring stores that information. So
    add a new hook to do this: virtio_net will be the first user.

    Signed-off-by: Shirley Ma <xma@us.ibm.com>
    ---
    drivers/virtio/virtio_ring.c | 24 ++++++++++++++++++++++++
    include/linux/virtio.h | 1 +
    2 files changed, 25 insertions(+), 0 deletions(-)

    diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
    index fbd2ecd..f847bc3 100644
    --- a/drivers/virtio/virtio_ring.c
    +++ b/drivers/virtio/virtio_ring.c
    @@ -334,6 +334,29 @@ static bool vring_enable_cb(struct virtqueue *_vq)
    return true;
    }

    +/* This function is used to return vring unused buffers to caller for free */
    +static void *vring_detach_bufs(struct virtqueue *_vq)
    +{
    + struct vring_virtqueue *vq = to_vvq(_vq);
    + unsigned int i;
    +
    + START_USE(vq);
    +
    + for (i = 0; i < vq->vring.num; ++i) {
    + if (vq->data[i]) {
    + /* detach_buf clears data, so grab it now. */
    + detach_buf(vq, i);
    + END_USE(vq);
    + return vq->data[i];
    + }
    + }
    + /* That should have freed everything. */
    + BUG_ON(vq->num_free != vq->vring.num);
    +
    + END_USE(vq);
    + return NULL;
    +}
    +
    irqreturn_t vring_interrupt(int irq, void *_vq)
    {
    struct vring_virtqueue *vq = to_vvq(_vq);
    @@ -360,6 +383,7 @@ static struct virtqueue_ops vring_vq_ops = {
    .kick = vring_kick,
    .disable_cb = vring_disable_cb,
    .enable_cb = vring_enable_cb,
    + .detach_bufs = vring_detach_bufs,
    };

    struct virtqueue *vring_new_virtqueue(unsigned int num,
    diff --git a/include/linux/virtio.h b/include/linux/virtio.h
    index 057a2e0..d7da456 100644
    --- a/include/linux/virtio.h
    +++ b/include/linux/virtio.h
    @@ -71,6 +71,7 @@ struct virtqueue_ops {

    void (*disable_cb)(struct virtqueue *vq);
    bool (*enable_cb)(struct virtqueue *vq);
    + void *(*detach_bufs)(struct virtqueue *vq);
    };

    /**
    Thanks
    Shirley



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