[PATCH v2 qemu-server 5/5] vma restore: skip page cache on block devices backed by zfspool

[Christian Ebner <c.ebner@proxmox.com>]

Skip the host page cache for restores on zvols, as page writeback
after filling the buffers can cause I/O delay on other ZFS-backed VMs
on certain setups, as reported in enterprise support and reproduced
internally. The restored data is not to be read back from cache
during restore anyways.

Keep for other storage types for now to reduce regression potential.

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
changes:
- fix formatting by invoking `make tidy`
- added comment to extend this to other storage types in the future
- hinted further that page writeback only kicks in after buffers are
  filled

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

diff --git a/src/PVE/QemuServer.pm b/src/PVE/QemuServer.pm
index b0edbbe6..01af9447 100644
--- a/src/PVE/QemuServer.pm
+++ b/src/PVE/QemuServer.pm
@@ -7681,8 +7681,17 @@ sub restore_vma_archive {
             }
 
             my $path = PVE::Storage::path($cfg, $volid);
+            my $scfg = PVE::Storage::storage_config($cfg, $storeid);
 
-            print $fifofh "${map_opts}format=$d->{format}:${write_zeros}:$d->{devname}=$path\n";
+            my $cache_none = '';
+            if ($scfg->{type} eq 'zfspool') {
+                #TODO: potentially extend to other storage types
+                $cache_none = ':cache=none';
+                print "skipping page cache for '$d->{devname}'\n";
+            }
+
+            print $fifofh
+                "${map_opts}format=$d->{format}${cache_none}:${write_zeros}:$d->{devname}=$path\n";
 
             print "map '$d->{devname}' to '$path' (write zeros = ${write_zeros})\n";
         }
-- 
2.47.3