block/blkio: enable the completion eventfd

[PATCH] block/blkio: enable the completion eventfd

Posted by Stefano Garzarella 9 months, 1 week ago

Until libblkio 1.3.0, virtio-blk drivers had completion eventfd
notifications enabled from the start, but from the next releases
this is no longer the case, so we have to explicitly enable them.

In fact, the libblkio documentation says they could be disabled,
so we should always enable them at the start if we want to be
sure to get completion eventfd notifications:

    By default, the driver might not generate completion events for
    requests so it is necessary to explicitly enable the completion
    file descriptor before use:

    void blkioq_set_completion_fd_enabled(struct blkioq *q, bool enable);

I discovered this while trying a development version of libblkio:
the guest kernel hangs during boot, while probing the device.

Fixes: fd66dbd424f5 ("blkio: add libblkio block driver")
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
 block/blkio.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/block/blkio.c b/block/blkio.c
index 1798648134..bc1fac48b7 100644
--- a/block/blkio.c
+++ b/block/blkio.c
@@ -845,6 +845,7 @@ static int blkio_file_open(BlockDriverState *bs, QDict *options, int flags,
     QLIST_INIT(&s->bounce_bufs);
     s->blkioq = blkio_get_queue(s->blkio, 0);
     s->completion_fd = blkioq_get_completion_fd(s->blkioq);
+    blkioq_set_completion_fd_enabled(s->blkioq, true);
 
     blkio_attach_aio_context(bs, bdrv_get_aio_context(bs));
     return 0;
-- 
2.41.0

Re: [PATCH] block/blkio: enable the completion eventfd

Posted by Stefan Hajnoczi 9 months, 1 week ago

On Tue, Jul 25, 2023 at 12:37:44PM +0200, Stefano Garzarella wrote:
> Until libblkio 1.3.0, virtio-blk drivers had completion eventfd
> notifications enabled from the start, but from the next releases
> this is no longer the case, so we have to explicitly enable them.
> 
> In fact, the libblkio documentation says they could be disabled,
> so we should always enable them at the start if we want to be
> sure to get completion eventfd notifications:
> 
>     By default, the driver might not generate completion events for
>     requests so it is necessary to explicitly enable the completion
>     file descriptor before use:
> 
>     void blkioq_set_completion_fd_enabled(struct blkioq *q, bool enable);
> 
> I discovered this while trying a development version of libblkio:
> the guest kernel hangs during boot, while probing the device.
> 
> Fixes: fd66dbd424f5 ("blkio: add libblkio block driver")
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
>  block/blkio.c | 1 +
>  1 file changed, 1 insertion(+)

Thanks, applied to my block tree:
https://gitlab.com/stefanha/qemu/commits/block

Stefan