On Mon, Jul 24, 2023 at 05:46:10PM +0200, Stefano Garzarella wrote: > libblkio 1.3.0 added support of "fd" property for virtio-blk-vhost-vdpa > driver. In QEMU, starting from commit cad2ccc395 ("block/blkio: use > qemu_open() to support fd passing for virtio-blk") we are using > `blkio_get_int(..., "fd")` to check if the "fd" property is supported > for all the virtio-blk-* driver. > > Unfortunately that property is also available for those driver that do > not support it, such as virtio-blk-vhost-user. Indeed now QEMU is > failing if used with virtio-blk-vhost-user in this way: > > -blockdev > node-name=drive0,driver=virtio-blk-vhost-user,path=vhost-user-blk.sock,cache.direct=on: > Could not open 'vhost-user-blk.sock': No such device or address > > So, `blkio_get_int()` is not enough to check whether the driver supports > the `fd` property or not. This is because the virito-blk common libblkio > driver only checks whether or not `fd` is set during `blkio_connect()` > and fails for those transports that do not support it (all except > vhost-vdpa for now). > > So for now let's also check that the driver is virtio-blk-vhost-vdpa, > since that's the only one that supports it.
What happens when more virtio-blk-* libblkio drivers gain support for `fd`? I think we'll be back to the same problem because QEMU will be unable to distinguish between old and new libraries. How about retrying with `path` if opening with `fd` fails? > > Fixes: cad2ccc395 ("block/blkio: use qemu_open() to support fd passing for > virtio-blk") > Reported-by: Qing Wang <qinw...@redhat.com> > Signed-off-by: Stefano Garzarella <sgarz...@redhat.com> > --- > block/blkio.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/block/blkio.c b/block/blkio.c > index 1798648134..ca1149042a 100644 > --- a/block/blkio.c > +++ b/block/blkio.c > @@ -662,6 +662,7 @@ static int blkio_virtio_blk_common_open(BlockDriverState > *bs, > QDict *options, int flags, Error **errp) > { > const char *path = qdict_get_try_str(options, "path"); > + const char *blkio_driver = bs->drv->protocol_name; > BDRVBlkioState *s = bs->opaque; > bool fd_supported = false; > int fd, ret; > @@ -676,7 +677,8 @@ static int blkio_virtio_blk_common_open(BlockDriverState > *bs, > return -EINVAL; > } > > - if (blkio_get_int(s->blkio, "fd", &fd) == 0) { > + if (strcmp(blkio_driver, "virtio-blk-vhost-vdpa") == 0 && > + blkio_get_int(s->blkio, "fd", &fd) == 0) { > fd_supported = true; > } > > -- > 2.41.0 >
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