[pve-devel] [PATCH container] backup: warn that tar does not honor exclusion pattern with a trailing slash

[Fiona Ebner]

As reported in the community forum [0], for tar, an exclusion pattern
with a trailing slash will not match a folder with that name. For
rsync and proxmox-backup-client however, such a pattern will exclude
a directory with that name, but not a file.

rsync is used for 'suspend' mode backup and tar is used for all
non-PBS backups to create the archive. So currently, in the presence
of an exclusion pattern with a trailing slash, there is inconsistency
between different backup modes (because for 'suspend' mode, rsync will
already do the exclusion too) as well as between PBS and non-PBS
backups.

There doesn't seem to be a straight-forward way to align the behavior
for tar with command-line options exactly. The trailing slash can't be
removed from the pattern, because that would also match files.
Matching with
> some/pattern/*
> some/pattern/.*
rather than
> some/pattern/
gets pretty close, which was suggested by Dominik. Just the empty
directory is still included.

In any case, modifying current behavior would be a breaking change, so
actually aligning the exclusion (more closely) is better done in the
next major release.

Signed-off-by: Fiona Ebner <f.ebner at proxmox.com>
---

One could argue such a change is a bug-fix and so does not need to
wait until the next major release. I opted for the safer variant for
now, but happy to go with the aligning already if that is preferred.

 src/PVE/VZDump/LXC.pm | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/PVE/VZDump/LXC.pm b/src/PVE/VZDump/LXC.pm
index 8c28a5e..914ede2 100644
--- a/src/PVE/VZDump/LXC.pm
+++ b/src/PVE/VZDump/LXC.pm
@@ -442,7 +442,16 @@ sub archive {
 	    } else {
 		push @findexcl_anchored, $pattern;
 	    }
-	}
+
+	    # NOTE rsync and proxmox-backup-client will match directories, but not files when there
+	    # is a trailing slash, tar won't match either. For suspend mode, rsync already did the
+	    # exclusion, so no need to warn.
+	    # TODO PVE 9 - consider matching "$pattern*" and "$pattern.*" in this case, which will
+	    # only include the empty directory to more closely align the behavior between different
+	    # modes. Don't forget to update the docs!
+	    $self->log("warn", "tar does not match exclusion with a trailing slash '$pattern'")
+		if $pattern =~ m|/$| && $task->{mode} ne 'suspend';
+        }
 
 	push @$tar, '--no-anchored';
 	push @$tar, '--exclude=lost+found' if $userns_cmd;
-- 
2.39.2