block/block: add BDRV flag for io_uring

Signed-off-by: NAarushi Mehta <mehta.aaru20@gmail.com>
Reviewed-by: NMaxim Levitsky <maximlevitsky@gmail.com>
Acked-by: NStefano Garzarella <sgarzare@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>
Message-id: 20200120141858.587874-4-stefanha@redhat.com
Message-Id: <20200120141858.587874-4-stefanha@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

include/block/block.h

@@ -114,6 +114,7 @@ typedef struct HDGeometry {
                                       ignoring the format layer */
 #define BDRV_O_NO_IO       0x10000 /* don't initialize for I/O */
 #define BDRV_O_AUTO_RDONLY 0x20000 /* degrade to read-only if opening read-write fails */
+#define BDRV_O_IO_URING    0x40000 /* use io_uring instead of the thread pool */
 
 #define BDRV_O_CACHE_MASK  (BDRV_O_NOCACHE | BDRV_O_NO_FLUSH)