block/blkio: enable the completion eventfd

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>
Message-id: 20230725103744.77343-1-sgarzare@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

diff --git a/block/blkio.c b/block/blkio.c
index 179864813434a1dd7df4e2a84895b51ed7ed2e18..bc1fac48b7e51916ab54872f9279c820726cad44 100644 (file)
--- 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;