[PATCH 1/2] block/blkio: fix opening virtio-blk drivers

[Stefano Garzarella]

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.

Fixes: cad2ccc395 ("block/blkio: use qemu_open() to support fd passing for 
virtio-blk")
Reported-by: Qing Wang <qinwang@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@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