diff mbox series

[PULL,01/27] qemu-img: rebase: stop when reaching EOF of old backing file

Message ID 20231031185918.346940-2-kwolf@redhat.com
State New
Headers show
Series [PULL,01/27] qemu-img: rebase: stop when reaching EOF of old backing file | expand

Commit Message

Kevin Wolf Oct. 31, 2023, 6:58 p.m. UTC 
From: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>

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 proceed
further down the loop body, as the offsets beyond the old backing size need
to be explicitly zeroed.

Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
Reviewed-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Hanna Czenczek <hreitz@redhat.com>
Message-ID: <20230919165804.439110-2-andrey.drobyshev@virtuozzo.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 qemu-img.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/qemu-img.c b/qemu-img.c
index 585b65640f..2b2a3a86ca 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -3814,6 +3814,8 @@  static int img_rebase(int argc, char **argv)
             }
 
             if (prefix_chain_bs) {
+                uint64_t bytes = n;
+
                 /*
                  * If cluster wasn't changed since prefix_chain, we don't need
                  * to take action
@@ -3826,9 +3828,18 @@  static int img_rebase(int argc, char **argv)
                                  strerror(-ret));
                     goto out;
                 }
-                if (!ret) {
+                if (!ret && n) {
                     continue;
                 }
+                if (!n) {
+                    /*
+                     * If we've reached EOF of the old backing, it means that
+                     * offsets beyond the old backing size were read as zeroes.
+                     * Now we will need to explicitly zero the cluster in
+                     * order to preserve that state after the rebase.
+                     */
+                    n = bytes;
+                }
             }
 
             /*