[RFC storage 3/3] close #7204: lvm thin plugin: die if thin pool does not have zeroing configured

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

Thin pools with zeroing during allocation turned off are currently not
supported for VM images. Using such a pool may lead to data
corruption for various operations like drive mirror.

In the future, a dedicated storage configuration option could be
introduced that can be checked by volume_has_feature() and enforced
upon storage activation.

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

RFC - it is rather noisy since pvestatd will log it every time, OTOH
it may cause data corruption so being noisy can be justified. An
alternative might be to just automatically set it after detecting that
the flag is missing and only warn once, mentioning that that this is
done, but might be too much automagic.

 src/PVE/Storage/LvmThinPlugin.pm | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/src/PVE/Storage/LvmThinPlugin.pm b/src/PVE/Storage/LvmThinPlugin.pm
index 256ec43..dae40b6 100644
--- a/src/PVE/Storage/LvmThinPlugin.pm
+++ b/src/PVE/Storage/LvmThinPlugin.pm
@@ -6,6 +6,7 @@ use warnings;
 use IO::File;
 
 use PVE::JSONSchema qw(get_standard_option);
+use PVE::RESTEnvironment qw(log_warn);
 use PVE::Tools qw(run_command trim);
 
 use PVE::Storage::Plugin;
@@ -263,7 +264,21 @@ sub activate_storage {
 
     $class->SUPER::activate_storage($storeid, $scfg, $cache);
 
-    $activate_lv->($scfg->{vgname}, $scfg->{thinpool}, $cache);
+    my ($vg_name, $thin_pool) = $scfg->@{qw(vgname thinpool)};
+
+    $activate_lv->($vg_name, $thin_pool, $cache);
+
+    if ($scfg->{content}->{images}) {
+        my $lvs = $cache->{lvs} ||= PVE::Storage::LVMPlugin::lvm_list_volumes();
+        my $thin_pool_zero = $lvs->{$vg_name}->{$thin_pool}->{zero};
+        if (!defined($thin_pool_zero) || $thin_pool_zero ne 'zero') {
+            # TODO Add dedicated storage configuration option to support thin pools without zero to
+            # allow cheap checking in volume_has_feature() and check that it matches here.
+            # TODO PVE 10 - enforce?
+            log_warn("$storeid: thin pool without zeroing is not supported for VM images!"
+                . " Use 'lvchange -Z y $vg_name/$thin_pool' to enable zeroing");
+        }
+    }
 }
 
 sub activate_volume {
-- 
2.47.3