[pve-devel] [PATCH v1 pve-storage 8/8] pluginbase: document import and export methods

[Max Carrara]

Adapt the previous description, slightly rewording it and formatting
it for POD under the IMPORTS AND EXPORTS section.

Also add docstrings for the following methods:
- volume_export
- volume_export_formats
- volume_import
- volume_import_formats

Signed-off-by: Max Carrara <m.carrara at proxmox.com>
Co-authored-by: Maximiliano Sandoval <m.sandoval at proxmox.com>
---
 src/PVE/Storage/PluginBase.pm | 134 ++++++++++++++++++++++++++--------
 1 file changed, 105 insertions(+), 29 deletions(-)

diff --git a/src/PVE/Storage/PluginBase.pm b/src/PVE/Storage/PluginBase.pm
index a1bfc8d..cfa5087 100644
--- a/src/PVE/Storage/PluginBase.pm
+++ b/src/PVE/Storage/PluginBase.pm
@@ -1345,55 +1345,131 @@ sub prune_backups {
 
 =head2 IMPORTS AND EXPORTS
 
+Any path-based storage is assumed to support C<raw> and C<tar> streams, so
+the default implementations in C<L<PVE::Storage::Plugin>> will return this if
+C<< $scfg->{path} >> is set (thereby mimicking the old C<< PVE::Storage::storage_migrate() >>
+function).
+
+Plugins may fall back to methods like C<volume_export>, C<volume_import>, etc.
+of C<L<PVE::Storage::Plugin>> in case the format doesn't match their
+specialized implementations to reuse the C<raw>/C<tar> code.
+
+=head3 FORMATS
+
+The following formats are all prefixed with image information in the form of a
+64 bit little endian unsigned integer (C<< pack('Q\<') >>) in order to be able
+to preallocate the image on storages which require it.
+
+=over
+
+=item * C<< raw+size >> (image files only)
+
+A raw binary data stream as produced via C<< dd if=$IMAGE_FILE >>.
+
+=item * C<< qcow2+size >>, C<< vmdk >> (image files only)
+
+A raw C<qcow2>/C<vmdk>/... file as produced via C<< dd if=some_file.qcow2 >>
+for files which are already in C<qcow2> format, or via C<qemu-img convert>.
+
+B<NOTE:> These formats are only valid with C<$with_snapshots> being true (C<1>).
+
+=item * C<< tar+size >> (subvolumes only)
+
+A GNU C<tar> stream containing just the inner contents of the subvolume. This
+does not distinguish between the contents of a privileged or unprivileged
+container. In other words, this is from the root user namespace's point of view
+with no uid-mapping in effect. As produced via e.g.
+C<< tar -C vm-100-disk-1.subvol -cpf output_file.dat . >>
+
+=back
+
 =cut
 
-# Import/Export interface:
-#   Any path based storage is assumed to support 'raw' and 'tar' streams, so
-#   the default implementations will return this if $scfg->{path} is set,
-#   mimicking the old PVE::Storage::storage_migrate() function.
-#
-# Plugins may fall back to PVE::Storage::Plugin::volume_{export,import}...
-#   functions in case the format doesn't match their specialized
-#   implementations to reuse the raw/tar code.
-#
-# Format specification:
-#   The following formats are all prefixed with image information in the form
-#   of a 64 bit little endian unsigned integer (pack('Q<')) in order to be able
-#   to preallocate the image on storages which require it.
-#
-#   raw+size: (image files only)
-#     A raw binary data stream such as produced via `dd if=TheImageFile`.
-#   qcow2+size, vmdk: (image files only)
-#     A raw qcow2/vmdk/... file such as produced via `dd if=some.qcow2` for
-#     files which are already in qcow2 format, or via `qemu-img convert`.
-#     Note that these formats are only valid with $with_snapshots being true.
-#   tar+size: (subvolumes only)
-#     A GNU tar stream containing just the inner contents of the subvolume.
-#     This does not distinguish between the contents of a privileged or
-#     unprivileged container. In other words, this is from the root user
-#     namespace's point of view with no uid-mapping in effect.
-#     As produced via `tar -C vm-100-disk-1.subvol -cpf TheOutputFile.dat .`
+=head3 $plugin->volume_export(\%scfg, $storeid, $fh, $volname, $format [, $snapshot, $base_snapshot, $with_snapshots])
+
+=head3 $plugin->volume_export(...)
+
+Exports a volume or a volume's C<$snapshot> into a file handle C<$fh> as a
+stream with a desired export C<$format>. See L<FORMATS> for all import/export
+formats.
+
+Optionally, C<$snapshot> (if provided) may have a C<$base_snapshot>, and
+C<$with_snapshots> states whether the volume has snapshots overall.
+
+C<die>s in order to abort the export if there are (grave) problems, if the
+given C<$format> is not supported, or if exporting volumes is not supported as
+a whole.
+
+=cut
 
-# Export a volume into a file handle as a stream of desired format.
 sub volume_export {
     my ($class, $scfg, $storeid, $fh, $volname, $format, $snapshot, $base_snapshot, $with_snapshots) = @_;
     croak "implement me in sub-class\n";
 }
 
+=head3 $plugin->volume_export_formats(\%scfg, $storeid, $volname [, $snapshot, $base_snapshot, $with_snapshot])
+
+=head3 $plugin->volume_export_formats(...)
+
+B<OPTIONAL:> May be implemented in a storage plugin.
+
+Returns a list of supported export formats for the given volume or snapshot.
+
+Optionally, C<$snapshot> (if provided) may have a C<$base_snapshot>, and
+C<$with_snapshots> states whether the volume has snapshots overall.
+
+If the storage does not support exporting volumes at all, and empty list should
+be returned.
+
+=cut
+
 sub volume_export_formats {
     my ($class, $scfg, $storeid, $volname, $snapshot, $base_snapshot, $with_snapshots) = @_;
     croak "implement me in sub-class\n";
 }
 
-# Import data from a stream, creating a new or replacing or adding to an existing volume.
+=head3 $plugin->volume_import(\%scfg, $storeid, $fh, $volname, $format [, $snapshot, $base_snapshot, $with_snapshots, $allow_rename])
+
+=head3 $plugin->volume_import(...)
+
+B<OPTIONAL:> May be implemented in a storage plugin.
+
+Imports data with the given C<$format> from a stream / filehandle C<$fh>,
+creating a new volume, or replacing or adding to an existing one. Returns the
+volume ID of the imported volume.
+
+Optionally, C<$snapshot> (if provided) may have a C<$base_snapshot>, and
+C<$with_snapshots> states whether the volume has snapshots overall. Renaming an
+existing volume may also optionally be allowed via C<$allow_rename>
+
+C<die>s if the import fails, if the given C<$format> is not supported, or if
+importing volumes is not supported as a whole.
+
+=cut
+
 sub volume_import {
     my ($class, $scfg, $storeid, $fh, $volname, $format, $snapshot, $base_snapshot, $with_snapshots, $allow_rename) = @_;
     croak "implement me in sub-class\n";
 }
 
+=head3 $plugin->volume_import_formats(\%scfg, $storeid, $volname [, $snapshot, $base_snapshot, $with_snapshot])
+
+=head3 $plugin->volume_import_formats(...)
+
+B<OPTIONAL:> May be implemented in a storage plugin.
+
+Returns a list of supported import formats for the given volume or snapshot.
+
+Optionally, C<$snapshot> (if provided) may have a C<$base_snapshot>, and
+C<$with_snapshots> states whether the volume has snapshots overall.
+
+If the storage does not support importing volumes at all, and empty list should
+be returned.
+
+=cut
+
 sub volume_import_formats {
     my ($class, $scfg, $storeid, $volname, $snapshot, $base_snapshot, $with_snapshots) = @_;
     croak "implement me in sub-class\n";
 }
-
 1;
-- 
2.39.5