[pve-devel] [RFC v3 storage 8/9] plugin: qemu block device: add support for snapshot option

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

This is mostly in preparation for external qcow2 snapshot support.

For internal qcow2 snapshots, which currently are the only supported
variant, it is not possible to attach the snapshot only. If access to
that is required it will need to be handled differently, e.g. via a
FUSE/NBD export.

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

No changes in v3. RFC, because it depends on the previous one.

 src/PVE/Storage/ISCSIDirectPlugin.pm |  3 +++
 src/PVE/Storage/Plugin.pm            | 13 ++++++++++++-
 src/PVE/Storage/RBDPlugin.pm         |  2 ++
 src/PVE/Storage/ZFSPlugin.pm         |  3 +++
 src/PVE/Storage/ZFSPoolPlugin.pm     |  2 ++
 5 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/src/PVE/Storage/ISCSIDirectPlugin.pm b/src/PVE/Storage/ISCSIDirectPlugin.pm
index 12b894d..e0f8a62 100644
--- a/src/PVE/Storage/ISCSIDirectPlugin.pm
+++ b/src/PVE/Storage/ISCSIDirectPlugin.pm
@@ -113,6 +113,9 @@ sub path {
 sub qemu_blockdev_options {
     my ($class, $scfg, $storeid, $volname, $options) = @_;
 
+    die "volume snapshot is not possible on iscsi device\n"
+        if $options->{'snapshot-name'};
+
     my $lun = ($class->parse_volname($volname))[1];
 
     return {
diff --git a/src/PVE/Storage/Plugin.pm b/src/PVE/Storage/Plugin.pm
index 7a274a3..e6892ec 100644
--- a/src/PVE/Storage/Plugin.pm
+++ b/src/PVE/Storage/Plugin.pm
@@ -2004,6 +2004,11 @@ A hash reference with additional options.
 
 =over
 
+=item C<< $options->{'snapshot-name'} >>
+
+(optional) The snapshot name. Set when the associated snapshot should be opened rather than the
+volume itself.
+
 =item C<< $options->{hints} >>
 
 A hash reference with hints indicating what the volume will be used for. This can be safely ignored
@@ -2030,9 +2035,15 @@ sub qemu_blockdev_options {
 
     my $blockdev = {};
 
-    my ($path) = $class->filesystem_path($scfg, $volname);
+    my ($path) = $class->filesystem_path($scfg, $volname, $options->{'snapshot-name'});
 
     if ($path =~ m|^/|) {
+        # For qcow2 and qed the path of a snapshot will be the same, but it's not possible to attach
+        # the snapshot alone.
+        my $format = ($class->parse_volname($volname))[6];
+        die "cannot attach only the snapshot of a '$format' image\n"
+            if $options->{'snapshot-name'} && ($format eq 'qcow2' || $format eq 'qed');
+
         # The 'file' driver only works for regular files. The check below is taken from
         # block/file-posix.c:hdev_probe_device() in QEMU. Do not bother with detecting 'host_cdrom'
         # devices here, those are not managed by the storage layer.
diff --git a/src/PVE/Storage/RBDPlugin.pm b/src/PVE/Storage/RBDPlugin.pm
index 6b37ba3..cf3d354 100644
--- a/src/PVE/Storage/RBDPlugin.pm
+++ b/src/PVE/Storage/RBDPlugin.pm
@@ -530,6 +530,7 @@ sub qemu_blockdev_options {
     my ($name) = ($class->parse_volname($volname))[1];
 
     if ($scfg->{krbd}) {
+        $name .= '@' . $options->{'snapshot-name'} if $options->{'snapshot-name'};
         my $rbd_dev_path = get_rbd_dev_path($scfg, $storeid, $name);
         return { driver => 'host_device', filename => $rbd_dev_path };
     }
@@ -540,6 +541,7 @@ sub qemu_blockdev_options {
         image => "$name",
     };
     $blockdev->{namespace} = "$scfg->{namespace}" if defined($scfg->{namespace});
+    $blockdev->{snapshot} = $options->{'snapshot-name'} if $options->{'snapshot-name'};
 
     $blockdev->{conf} = $cmd_option->{ceph_conf} if $cmd_option->{ceph_conf};
 
diff --git a/src/PVE/Storage/ZFSPlugin.pm b/src/PVE/Storage/ZFSPlugin.pm
index 0f64898..940d4f0 100644
--- a/src/PVE/Storage/ZFSPlugin.pm
+++ b/src/PVE/Storage/ZFSPlugin.pm
@@ -250,6 +250,9 @@ sub path {
 sub qemu_blockdev_options {
     my ($class, $scfg, $storeid, $volname, $options) = @_;
 
+    die "direct access to snapshots not implemented\n"
+        if $options->{'snapshot-name'};
+
     my $name = ($class->parse_volname($volname))[1];
     my $guid = $class->zfs_get_lu_name($scfg, $name);
     my $lun = $class->zfs_get_lun_number($scfg, $guid);
diff --git a/src/PVE/Storage/ZFSPoolPlugin.pm b/src/PVE/Storage/ZFSPoolPlugin.pm
index 677f88c..86f83a2 100644
--- a/src/PVE/Storage/ZFSPoolPlugin.pm
+++ b/src/PVE/Storage/ZFSPoolPlugin.pm
@@ -165,6 +165,8 @@ sub path {
 sub qemu_blockdev_options {
     my ($class, $scfg, $storeid, $volname, $options) = @_;
 
+    die "cannot attach only the snapshot of a zvol\n" if $options->{'snapshot-name'};
+
     my ($path) = $class->path($scfg, $volname, $storeid);
 
     my $blockdev = { driver => 'host_device', filename => $path };
-- 
2.47.2



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