Just spotted this in my git-pull...
Alexander Yarygin <yary...@linux.vnet.ibm.com> writes:
> Each call of the virtio_blk_reset() function calls blk_drain_all(),
> which works for all existing BlockDriverStates, while draining only
> one is needed.
>
> This patch replaces blk_drain_all() by blk_drain() in
> virtio_blk_reset(). virtio_blk_data_plane_stop() should be called
> after draining because it restores vblk->complete_request.
>
> Cc: "Michael S. Tsirkin" <m...@redhat.com>
> Cc: Christian Borntraeger <borntrae...@de.ibm.com>
> Cc: Cornelia Huck <cornelia.h...@de.ibm.com>
> Cc: Kevin Wolf <kw...@redhat.com>
> Cc: Paolo Bonzini <pbonz...@redhat.com>
> Cc: Stefan Hajnoczi <stefa...@redhat.com>
> Signed-off-by: Alexander Yarygin <yary...@linux.vnet.ibm.com>
> ---
> hw/block/virtio-blk.c | 15 ++++++++++-----
> 1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index e6afe97..d8a906f 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -651,16 +651,21 @@ static void virtio_blk_dma_restart_cb(void *opaque, int
> running,
> static void virtio_blk_reset(VirtIODevice *vdev)
> {
> VirtIOBlock *s = VIRTIO_BLK(vdev);
> -
> - if (s->dataplane) {
> - virtio_blk_data_plane_stop(s->dataplane);
> - }
> + AioContext *ctx;
>
> /*
> * This should cancel pending requests, but can't do nicely until there
> * are per-device request lists.
> */
> - blk_drain_all();
> + ctx = blk_get_aio_context(s->blk);
> + aio_context_acquire(ctx);
> + blk_drain(s->blk);
> +
> + if (s->dataplane) {
> + virtio_blk_data_plane_stop(s->dataplane);
> + }
> + aio_context_release(ctx);
> +
> blk_set_enable_write_cache(s->blk, s->original_wce);
> }
>From bdrv_drain_all()'s comment:
* Note that completion of an asynchronous I/O operation can trigger any
* number of other I/O operations on other devices---for example a coroutine
* can be arbitrarily complex and a constant flow of I/O can come until the
* coroutine is complete. Because of this, it is not possible to have a
* function to drain a single device's I/O queue.
>From bdrv_drain()'s comment:
* See the warning in bdrv_drain_all(). This function can only be called if
* you are sure nothing can generate I/O because you have op blockers
* installed.
blk_drain() and blk_drain_all() are trivial wrappers.
Ignorant questions:
* Why does blk_drain() suffice here?
* Is blk_drain() (created in PATCH 1) even a safe interface?
