add check for fsfreeze before snapshot

In order to take a snapshot of a container volume, which can be mounted
read-only with RBD, the volume needs to be frozen (fsfreeze (8)) before taking
the snapshot.

This commit adds helpers to determine if the FIFREEZE ioctl needs to be called
for the volume.

Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>

PVE/Storage.pm

@@ -41,11 +41,11 @@ use PVE::Storage::DRBDPlugin;
 use PVE::Storage::PBSPlugin;
 
 # Storage API version. Increment it on changes in storage API interface.
-use constant APIVER => 6;
+use constant APIVER => 7;
 # Age is the number of versions we're backward compatible with.
 # This is like having 'current=APIVER' and age='APIAGE' in libtool,
 # see https://www.gnu.org/software/libtool/manual/html_node/Libtool-versioning.html
-use constant APIAGE => 5;
+use constant APIAGE => 6;
 
 # load standard plugins
 PVE::Storage::DirPlugin->register();
@@ -287,6 +287,18 @@ sub volume_snapshot_delete {
     }
 }
 
+# check if a filesystem on top of a volume needs to flush its journal for
+# consistency (see fsfreeze(8)) before a snapshot is taken - needed for
+# container mountpoints
+sub volume_snapshot_needs_fsfreeze {
+    my ($cfg, $volid) = @_;
+
+    my ($storeid, $volname) = parse_volume_id($volid);
+    my $scfg = storage_config($cfg, $storeid);
+    my $plugin = PVE::Storage::Plugin->lookup($scfg->{type});
+    return $plugin->volume_snapshot_needs_fsfreeze();
+}
+
 # check if a volume or snapshot supports a given feature
 # $feature - one of:
 #            clone - linked clone is possible

PVE/Storage/Plugin.pm

@@ -888,6 +888,10 @@ sub volume_snapshot_delete {
     return undef;
 }
 
+sub volume_snapshot_needs_fsfreeze {
+
+    return 0;
+}
 sub storage_can_replicate {
     my ($class, $scfg, $storeid, $format) = @_;
 

PVE/Storage/RBDPlugin.pm

@@ -694,6 +694,11 @@ sub volume_snapshot_delete {
     return undef;
 }
 
+sub volume_snapshot_needs_fsfreeze {
+
+    return 1;
+}
+
 sub volume_has_feature {
     my ($class, $scfg, $feature, $storeid, $volname, $snapname, $running) = @_;