From bd8d9c618a1921355c94adb6ab07de8540f02f6e Mon Sep 17 00:00:00 2001 From: Andrey Drobyshev Date: Tue, 19 Sep 2023 19:57:57 +0300 Subject: [PATCH] qemu-img: rebase: stop when reaching EOF of old backing file 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 Reviewed-by: Denis V. Lunev Reviewed-by: Hanna Czenczek Message-ID: <20230919165804.439110-2-andrey.drobyshev@virtuozzo.com> Reviewed-by: Kevin Wolf Signed-off-by: Kevin Wolf (cherry picked from commit 8b097fd6b06ec295faefd4f30f96f8709abc9605) Signed-off-by: Michael Tokarev --- qemu-img.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/qemu-img.c b/qemu-img.c index 27f48051b0..78433f3746 100644 --- a/qemu-img.c +++ b/qemu-img.c @@ -3801,6 +3801,8 @@ 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 @@ -3813,9 +3815,18 @@ 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; + } } /*