replace volume_support_qemu_snapshot with volume_qemu_snapshot

This also changes the return values, since their meanings are rather
weird from the storage point of view. For instance, "internal" meant
it is *not* the storage which does the snapshot, while "external"
meant a mixture of storage and qemu-server side actions. `undef` meant
the storage does it all...

┌────────────┬───────────┐
│ previous   │ new       │
├────────────┼───────────┤
│ "internal" │ "qemu"    │
│ "external" │ "mixed"   │
│ undef      │ "storage" │
└────────────┴───────────┘

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>

ApiChangeLog

@@ -25,13 +25,27 @@ Future changes should be documented in here.
 * Introduce rename_snapshot() plugin method
     This method allow to rename a vm disk snapshot name to a different snapshot name.
 
-* Introduce volume_support_qemu_snapshot() plugin method
+* Introduce volume_qemu_snapshot_method() plugin method
-    This method is used to known if the a snapshot need to be done by qemu
+    This method declares how snapshots should be handled for *running* VMs.
-    or by the storage api.
+    This should return one of the following:
-    returned values are :
+    'qemu':
-    'internal' : support snapshot with qemu internal snapshot
+      Qemu must perform the snapshot. The storage plugin does nothing.
-    'external' : support snapshot with qemu external snapshot
+    'storage':
-    undef      : don't support qemu snapshot
+      The storage plugin *transparently* performs the snapshot and the running VM does not need to
+      do anything.
+    'mixed': 
+      For taking a snapshot: The storage performs an offline snapshot and qemu then has to reopen
+      the volume.
+      For removing a snapshot: One of 2 things will happen (both must be supported):
+      a) Qemu will "unhook" the snapshot by moving its data into the child snapshot, and then call
+         `volume_snapshot_delete` with `running` set, in which case the storage should delete only
+         the snapshot without touching the surrounding snapshots.
+      b) Qemu will "commit" the child snapshot to the one which is being removed, then call
+         `volume_snapshot_delete()` on the child snapshot, then call `rename_snapshot()` to move the
+         merged snapshot into place.
+      NOTE: Storages must support using "current" as a special name in `rename_snapshot()` to
+      cheaply convert a snapshot into the current disk state and back.
+
 
 ##  Version 11:
 

src/PVE/Storage.pm

@@ -2370,7 +2370,7 @@ sub rename_snapshot {
     );
 }
 
-sub volume_support_qemu_snapshot {
+sub volume_qemu_snapshot_method {
     my ($cfg, $volid) = @_;
 
     my ($storeid, $volname) = parse_volume_id($volid, 1);
@@ -2380,7 +2380,7 @@ sub volume_support_qemu_snapshot {
 
         my $plugin = PVE::Storage::Plugin->lookup($scfg->{type});
 
-        return $plugin->volume_support_qemu_snapshot($storeid, $scfg, $volname);
+        return $plugin->volume_qemu_snapshot_method($storeid, $scfg, $volname);
     }
     return undef;
 }

src/PVE/Storage/DirPlugin.pm

@@ -315,14 +315,13 @@ sub get_import_metadata {
     };
 }
 
-sub volume_support_qemu_snapshot {
+sub volume_qemu_snapshot_method {
     my ($class, $storeid, $scfg, $volname) = @_;
 
     my $format = ($class->parse_volname($volname))[6];
-    return if $format ne 'qcow2';
+    return 'storage' if $format ne 'qcow2';
 
-    my $type = $scfg->{'external-snapshots'} ? 'external' : 'internal';
+    return $scfg->{'external-snapshots'} ? 'mixed' : 'qemu';
-    return $type;
 }
 
 1;

src/PVE/Storage/LVMPlugin.pm

@@ -1301,11 +1301,12 @@ sub rename_snapshot {
     lvrename($scfg, $source_snap_volname, $target_snap_volname);
 }
 
-sub volume_support_qemu_snapshot {
+sub volume_qemu_snapshot_method {
     my ($class, $storeid, $scfg, $volname) = @_;
 
     my $format = ($class->parse_volname($volname))[6];
-    return 'external' if $format eq 'qcow2';
+    return 'mixed' if $format eq 'qcow2';
+    return 'storage';
 }
 
 1;

src/PVE/Storage/Plugin.pm

@@ -2428,9 +2428,9 @@ sub new_backup_provider {
 
 =pod
 
-=head3 volume_support_qemu_snapshot
+=head3 volume_qemu_snapshot_method
 
-    $blockdev = $plugin->volume_support_qemu_snapshot($storeid, $scfg, $volname)
+    $blockdev = $plugin->volume_qemu_snapshot_method($storeid, $scfg, $volname)
 
 Returns a string with the type of snapshot that qemu can do for a specific volume
 
@@ -2439,11 +2439,12 @@ Returns a string with the type of snapshot that qemu can do for a specific volum
 undef      : don't support qemu snapshot
 =cut
 
-sub volume_support_qemu_snapshot {
+sub volume_qemu_snapshot_method {
     my ($class, $storeid, $scfg, $volname) = @_;
 
     my $format = ($class->parse_volname($volname))[6];
-    return 'internal' if $format eq 'qcow2';
+    return 'qemu' if $format eq 'qcow2';
+    return 'storage';
 }
 
 sub config_aware_base_mkdir {

src/PVE/Storage/RBDPlugin.pm

@@ -1063,10 +1063,11 @@ sub rename_snapshot {
     die "rename_snapshot is not implemented for $class";
 }
 
-sub volume_support_qemu_snapshot {
+sub volume_qemu_snapshot_method {
     my ($class, $storeid, $scfg, $volname) = @_;
 
-    return 'internal' if !$scfg->{krbd};
+    return 'qemu' if !$scfg->{krbd};
+    return 'storage';
 }
 
 1;