[Qemu-block] [PATCH 1/3] block: Allow x-blockdev-del on a BB with a monitor-owned BDS

[Alberto Garcia]

When x-blockdev-del is performed on a BlockBackend that has inserted
media it will only succeed if the BDS doesn't have any additional
references.

The only problem with this is that if the BDS was created separately
using blockdev-add then the backend won't be able to be destroyed
unless the BDS is ejected first. This is an unnecessary restriction.

Now that we have a list of monitor-owned BDSs we can allow
x-blockdev-del to work in this scenario if the BDS has exactly one
extra reference and that reference is from the monitor.

Signed-off-by: Alberto Garcia <address@hidden>
---
 blockdev.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index e1b6b0f..847058d 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -3966,9 +3966,16 @@ void qmp_x_blockdev_del(bool has_id, const char *id,
         }
 
         if (bs->refcnt > 1) {
-            error_setg(errp, "Block device %s is in use",
-                       bdrv_get_device_or_node_name(bs));
-            goto out;
+            /* We allow deleting a BlockBackend that has a BDS with an
+             * extra reference if that extra reference is from the
+             * monitor. */
+            bool bs_has_only_monitor_ref =
+                blk && bs->monitor_list.tqe_prev && bs->refcnt == 2;
+            if (!bs_has_only_monitor_ref) {
+                error_setg(errp, "Block device %s is in use",
+                           bdrv_get_device_or_node_name(bs));
+                goto out;
+            }
         }
     }
 
-- 
2.7.0