[pve-devel] [PATCH pve-storage 3/4] lvmplugin: add thin volume support for LVM external snapshots

[Tiago Sousa via pve-devel <pve-devel@lists.proxmox.com>]

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From: Tiago Sousa <joao.sousa@eurotux.com>
To: pve-devel@lists.proxmox.com
Subject: [PATCH pve-storage 3/4] lvmplugin: add thin volume support for LVM external snapshots
Date: Fri, 17 Oct 2025 12:25:28 +0100
Message-ID: <20251017112539.26471-4-joao.sousa@eurotux.com>

Signed-off-by: Tiago Sousa <joao.sousa@eurotux.com>
---
 src/PVE/Storage/Common.pm    |  4 ++--
 src/PVE/Storage/LVMPlugin.pm | 19 +++++++++++++++----
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/src/PVE/Storage/Common.pm b/src/PVE/Storage/Common.pm
index 222dc76..1e5d4c6 100644
--- a/src/PVE/Storage/Common.pm
+++ b/src/PVE/Storage/Common.pm
@@ -170,7 +170,7 @@ C<$options> currently allows setting the C<preallocation> value.
 =cut
 
 sub qemu_img_create_qcow2_backed {
-    my ($path, $backing_path, $backing_format, $options) = @_;
+    my ($path, $backing_path, $backing_format, $options, $thin) = @_;
 
     my $cmd = [
         '/usr/bin/qemu-img',
@@ -188,7 +188,7 @@ sub qemu_img_create_qcow2_backed {
     my $opts = ['extended_l2=on', 'cluster_size=128k'];
 
     push @$opts, "preallocation=$options->{preallocation}"
-        if defined($options->{preallocation});
+        if defined($options->{preallocation}) && !$thin;
     push @$cmd, '-o', join(',', @$opts) if @$opts > 0;
 
     run_command($cmd, errmsg => "unable to create image");
diff --git a/src/PVE/Storage/LVMPlugin.pm b/src/PVE/Storage/LVMPlugin.pm
index 0416c9e..dc5e648 100644
--- a/src/PVE/Storage/LVMPlugin.pm
+++ b/src/PVE/Storage/LVMPlugin.pm
@@ -575,7 +575,7 @@ sub lvrename {
 }
 
 my sub lvm_qcow2_format {
-    my ($class, $storeid, $scfg, $name, $fmt, $backing_snap, $size) = @_;
+    my ($class, $storeid, $scfg, $name, $fmt, $backing_snap, $size, $thin) = @_;
 
     $class->activate_volume($storeid, $scfg, $name);
     my $path = $class->path($scfg, $name, $storeid);
@@ -585,7 +585,9 @@ my sub lvm_qcow2_format {
     };
     if ($backing_snap) {
         my $backing_volname = get_snap_name($class, $name, $backing_snap);
-        PVE::Storage::Common::qemu_img_create_qcow2_backed($path, $backing_volname, $fmt, $options);
+        PVE::Storage::Common::qemu_img_create_qcow2_backed(
+            $path, $backing_volname, $fmt, $options, $thin,
+        );
     } else {
         PVE::Storage::Common::qemu_img_create($fmt, $size, $path, $options);
     }
@@ -629,7 +631,16 @@ my sub alloc_lvm_image {
     die "no such volume group '$vg'\n" if !defined($vgs->{$vg});
 
     my $free = int($vgs->{$vg}->{free});
-    my $lvmsize = calculate_lvm_size($size, $fmt, $backing_snap);
+    my $lvmsize;
+
+    # FIX: make this variable a check box when taking a snapshot
+    # right now all snapshots are created thin for testing purposes
+    my $thin = $backing_snap ? 1 : 0;
+    if ($thin) {
+        $lvmsize = 2 * 1024 * 1024;
+    } else {
+        $lvmsize = calculate_lvm_size($size, $fmt, $backing_snap);
+    }
 
     die "not enough free space ($free < $size)\n" if $free < $size;
 
@@ -641,7 +652,7 @@ my sub alloc_lvm_image {
     return if $fmt ne 'qcow2';
 
     #format the lvm volume with qcow2 format
-    eval { lvm_qcow2_format($class, $storeid, $scfg, $name, $fmt, $backing_snap, $size) };
+    eval { lvm_qcow2_format($class, $storeid, $scfg, $name, $fmt, $backing_snap, $size, $thin) };
     if ($@) {
         my $err = $@;
         #no need to safe cleanup as the volume is still empty
-- 
2.47.3



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