[pve-devel] [PATCH pve-storage v3 3/3] lvmthin: disable autoactivation for new logical volumes

[Friedrich Weber <f.weber@proxmox.com>]

When discovering a new volume group (VG), for example on boot, LVM
triggers autoactivation. With the default settings, this activates all
logical volumes (LVs) in the VG. Activating an LV creates a
device-mapper device and a block device under /dev/mapper.

Autoactivation is problematic for shared LVM storages, see #4997 [1].
For the inherently local LVM-thin storage it is less problematic, but
it still makes sense to avoid unnecessarily activating LVs and thus
making them visible on the host at boot.

Hence, disable autoactivation after creating new LVs. As lvcreate
doesn't accept the --setautoactivation flag for thin LVs, this is done
with an additional lvchange command. With this setting, LVM
autoactivation will not activate these LVs, and the storage stack will
take care of activating/deactivating LVs when needed.

[1] https://bugzilla.proxmox.com/show_bug.cgi?id=4997

Signed-off-by: Friedrich Weber <f.weber@proxmox.com>
---

Notes:
    - would be great to get your opinion on whether we should consider
      LVM-thin storages in this series or not.
    
    - passing --setautoactivation n to lvcreate for a thin volume says:
    
        Option --setautoactivation is unsupported with thins.
    
      But lvchange --setautoactivation seems to work on thin LVs, so the
      fact that lvcreate doesn't accept it may be a bug. I reported it
      upstream [1].
    
    new in v3
    
    [1] https://gitlab.com/lvmteam/lvm2/-/issues/32

 src/PVE/Storage/LvmThinPlugin.pm | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/src/PVE/Storage/LvmThinPlugin.pm b/src/PVE/Storage/LvmThinPlugin.pm
index 49a4dcb..3f75ba1 100644
--- a/src/PVE/Storage/LvmThinPlugin.pm
+++ b/src/PVE/Storage/LvmThinPlugin.pm
@@ -82,6 +82,19 @@ sub filesystem_path {
     return wantarray ? ($path, $vmid, $vtype) : $path;
 }
 
+# lvcreate refuses --setautoactivation for thin volumes, so set it via lvchange
+my $set_lv_autoactivation = sub {
+    my ($vg, $lv, $autoactivation) = @_;
+
+    my $cmd = [
+	'/sbin/lvchange',
+	'--setautoactivation', $autoactivation ? 'y' : 'n',
+	"$vg/$lv"
+    ];
+    eval { run_command($cmd); };
+    warn "could not set autoactivation: $@" if $@;
+};
+
 sub alloc_image {
     my ($class, $storeid, $scfg, $vmid, $fmt, $name, $size) = @_;
 
@@ -103,6 +116,7 @@ sub alloc_image {
 	       '--thinpool', "$vg/$scfg->{thinpool}" ];
 
     run_command($cmd, errmsg => "lvcreate '$vg/$name' error");
+    $set_lv_autoactivation->($vg, $name, 0);
 
     return $name;
 }
@@ -283,6 +297,7 @@ sub clone_image {
 
     my $cmd = ['/sbin/lvcreate', '-n', $name, '-prw', '-kn', '-s', $lv];
     run_command($cmd, errmsg => "clone image '$lv' error");
+    $set_lv_autoactivation->($vg, $name, 0);
 
     return $name;
 }
@@ -332,7 +347,7 @@ sub volume_snapshot {
 
     my $cmd = ['/sbin/lvcreate', '-n', $snapvol, '-pr', '-s', "$vg/$volname"];
     run_command($cmd, errmsg => "lvcreate snapshot '$vg/$snapvol' error");
-
+    # disabling autoactivation not needed, as -s defaults to --setautoactivationskip y
 }
 
 sub volume_snapshot_rollback {
@@ -346,6 +361,7 @@ sub volume_snapshot_rollback {
 
     $cmd = ['/sbin/lvcreate', '-kn', '-n', $volname, '-s', "$vg/$snapvol"];
     run_command($cmd, errmsg => "lvm rollback '$vg/$snapvol' error");
+    $set_lv_autoactivation->($vg, $volname, 0);
 }
 
 sub volume_snapshot_delete {
-- 
2.39.5



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