[pve-devel] [PATCH container] fix #3424: vzdump: cleanup: wait for active replication

[Fabian Ebner <f.ebner@proxmox.com>]

As replication and backup can happen at the same time, the vzdump
snapshot might be actively used by replication when backup tries
to cleanup, resulting in a not (or only partially) removed snapshot
and locked (snapshot-delete) container.

Wait up to 10 minutes for any ongoing replication. If replication
doesn't finish in time, the fact that there is no attempt to remove
the snapshot means that there's no risk for the container to end up in
a locked state. And the beginning of the next backup will force remove
the left-over snapshot, which will very likely succeed even at the
storage layer, because the replication really should be done by then
(subsequent replications shouldn't matter as they don't need to
re-transfer the vzdump snapshot).

Suggested-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>
---

VM backups are not affected by this, because they don't use
storage/config snapshots, but use pve-qemu's block layer.

Decided to go for this approach rather than replication waiting on
backup, because "full backup can take much longer than replication
usually does", and even if we time out, we can just skip the removal
for now and have the next backup do it.

 src/PVE/VZDump/LXC.pm | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/PVE/VZDump/LXC.pm b/src/PVE/VZDump/LXC.pm
index b7f7463..10edae9 100644
--- a/src/PVE/VZDump/LXC.pm
+++ b/src/PVE/VZDump/LXC.pm
@@ -8,6 +8,7 @@ use File::Path;
 use POSIX qw(strftime);
 
 use PVE::Cluster qw(cfs_read_file);
+use PVE::GuestHelpers;
 use PVE::INotify;
 use PVE::LXC::Config;
 use PVE::LXC;
@@ -476,8 +477,14 @@ sub cleanup {
     }
 
     if ($task->{cleanup}->{remove_snapshot}) {
-	$self->loginfo("cleanup temporary 'vzdump' snapshot");
-	PVE::LXC::Config->snapshot_delete($vmid, 'vzdump', 0);
+	$self->loginfo("checking/waiting for replication..");
+	eval {
+	    PVE::GuestHelpers::guest_migration_lock($vmid, 600, sub {
+		$self->loginfo("cleanup temporary 'vzdump' snapshot");
+		PVE::LXC::Config->snapshot_delete($vmid, 'vzdump', 0);
+	    });
+	};
+	die "snapshot 'vzdump' was not (fully) removed - $@" if $@;
     }
 }
 
-- 
2.30.2