[PATCH 1/2] qemu-img: rebase: stop when reaching EOF of old backing file

[Andrey Drobyshev via <qemu-devel@nongnu.org>]

In case when we're rebasing within one backing chain, and when target image
is larger than old backing file, bdrv_is_allocated_above() ends up setting
*pnum = 0.  As a result, target offset isn't getting incremented, and we
get stuck in an infinite for loop.  Let's detect this case and break the
loop, as there's no more data to be read and merged from the old backing.

Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
---
 qemu-img.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/qemu-img.c b/qemu-img.c
index 27f48051b0..55b6ce407c 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -3813,6 +3813,13 @@ static int img_rebase(int argc, char **argv)
                                  strerror(-ret));
                     goto out;
                 }
+                if (!n) {
+                    /*
+                     * We've reached EOF of the old backing, therefore there's
+                     * no more mergeable data.
+                     */
+                    break;
+                }
                 if (!ret) {
                     continue;
                 }
-- 
2.31.1