[PATCH for 9.0] migration: Skip only empty block devices

["Cédric Le Goater" <clg@redhat.com>]

The block .save_setup() handler calls a helper routine
init_blk_migration() which builds a list of block devices to take into
account for migration. When one device is found to be empty (sectors
== 0), the loop exits and all the remaining devices are ignored. This
is a regression introduced when bdrv_iterate() was removed.

Change that by skipping only empty devices.

Cc: Markus Armbruster <armbru@redhat.com>
Suggested: Kevin Wolf <kwolf@redhat.com>
Fixes: fea68bb6e9fa ("block: Eliminate bdrv_iterate(), use bdrv_next()")
Signed-off-by: Cédric Le Goater <clg@redhat.com>
---
 migration/block.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/migration/block.c b/migration/block.c
index 8c6ebafacc1ffe930d1d4f19d968817b14852c69..2b9054889ad2ba739828594c50cf047703757e96 100644
--- a/migration/block.c
+++ b/migration/block.c
@@ -402,7 +402,10 @@ static int init_blk_migration(QEMUFile *f)
         }
 
         sectors = bdrv_nb_sectors(bs);
-        if (sectors <= 0) {
+        if (sectors == 0) {
+            continue;
+        }
+        if (sectors < 0) {
             ret = sectors;
             bdrv_next_cleanup(&it);
             goto out;
-- 
2.44.0