[PATCH storage 3/4] zfspool: export: skip hardcoded warning about no-preserve-encryption flag

[Stoiko Ivanov <s.ivanov@proxmox.com>]

currently `zfs send --no-preserve-encryption` prints:
`WARNING: no-preserve-encryption flag set, sending dataset $dataset without encryption`
if the dataset is encrypted.

This patch skips the warning to not clutter the output, as the choice
is made deliberately.

[0] https://github.com/openzfs/zfs/blob/d8c08a1cea6428fa37b3a6585150b10dedfd79b8/lib/libzfs/libzfs_sendrecv.c#L616

Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>
---
 src/PVE/Storage/ZFSPoolPlugin.pm | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/PVE/Storage/ZFSPoolPlugin.pm b/src/PVE/Storage/ZFSPoolPlugin.pm
index eaeeb9d..fcd7804 100644
--- a/src/PVE/Storage/ZFSPoolPlugin.pm
+++ b/src/PVE/Storage/ZFSPoolPlugin.pm
@@ -824,7 +824,17 @@ sub volume_export {
     }
     push @$cmd, '--', "$scfg->{pool}/$dataset\@$snapshot";
 
-    run_command($cmd, output => $fd);
+    run_command(
+        $cmd,
+        output => $fd,
+        errfunc => sub {
+            my $line = shift;
+            if ($line !~ /^WARNING: no-preserve-encryption flag set, sending dataset/) {
+                print STDERR $line;
+                *STDERR->flush();
+            }
+        },
+    );
 
     return;
 }
-- 
2.47.3