[pve-devel] [PATCH v1 pve-storage 6/8] pluginbase: document image operation methods

[Fabian Grünbichler]

On March 26, 2025 3:20 pm, Max Carrara wrote:
> Add documentation for the following methods:
> - list_images
> - create_base
> - clone_image
> - alloc_image
> - free_image
> 
> 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 | 111 ++++++++++++++++++++++++++++++++++
>  1 file changed, 111 insertions(+)
> 
> diff --git a/src/PVE/Storage/PluginBase.pm b/src/PVE/Storage/PluginBase.pm
> index b3ce684..37b1471 100644
> --- a/src/PVE/Storage/PluginBase.pm
> +++ b/src/PVE/Storage/PluginBase.pm
> @@ -721,26 +721,137 @@ sub on_delete_hook {
>  
>  =cut
>  
> +=head3 $plugin->list_images($storeid, \%scfg [, $vmid, \@vollist, \%cache])
> +
> +B<REQUIRED:> Must be implemented in every storage plugin.
> +
> +Returns a listref of all disk images of a storage. If the storage does not
> +support storing disk images, returns an empty listref.
> +
> +Optionally, if C<\@vollist> is provided, return only disks whose volume ID is
> +within C<\@vollist>. Note that this usually has higher precedence than
> +C<$vmid>.

what does usually mean? what does $vmid do?

> +
> +C<die>s in case of errors.
> +
> +This method may reuse L<< cached information via C<\%cache>|/"CACHING EXPENSIVE OPERATIONS" >>.
> +
> +The returned listref has the following structure:
> +
> +    [
> +	{
> +	    ctime => "1689163322", # creation time as unix timestamp
> +	    format => "raw",
> +	    size => 8589934592, # in bytes!
> +	    vmid => 101,
> +	    volid => "local-lvm:base-101-disk-0", # volume ID, storage-specific
> +	},
> +	# [...]
> +    ]
> +
> +=cut
> +
>  sub list_images {
>      my ($class, $storeid, $scfg, $vmid, $vollist, $cache) = @_;
>      croak "implement me in sub-class\n";
>  }
>  
> +=head3 $plugin->create_base($storeid, \%scfg, $volname)
> +
> +B<OPTIONAL:> May be implemented in a storage plugin.
> +
> +Creates a base volume from an existing volume, allowing the volume to be

this is misleading - it doesn't create a base volume from an existing
volume, it *converts* an existing volume into a base volume!

> +L<< cloned|/"$plugin->clone_image(...)" >>. This cloned volume (usually
> +a disk image) may then be used as a base for the purpose of creating linked

this is wrong? there is no cloned volume yet? and all of this only
applies to images and not other volumes?

> +clones. See L<C<PVE::Storage::LvmThinPlugin>> and
> +L<C<PVE::Storage::ZFSPoolPlugin>> for example implementations.
> +
> +On completion, returns the name of the new base volume (the new C<$volname>).
> +
> +This method is called in the context of C<L<< cluster_lock_storage()|/"cluster_lock_storage(...)" >>>,
> +i.e. when the storage is B<locked>.

Shouldn't this say that it *should* be called in a locked context?

> +
> +=cut
> +
>  sub create_base {
>      my ($class, $storeid, $scfg, $volname) = @_;
>      croak "implement me in sub-class\n";
>  }
>  
> +=head3 $plugin->clone_image($scfg, $storeid, $volname, $vmid [, $snap])
> +
> +=head3 $plugin->clone_image(...)
> +
> +B<REQUIRED:> Must be implemented in every storage plugin.

not really? there's a feature guard for it, so only storage plugins that
support it should ever get it called anyway..

what does $vmid mean?

> +
> +Clones a disk image or a snapshot of an image, returning the name of the new
> +image (the new C<$volname>). Note that I<cloning> here means to create a linked
> +clone and not duplicating an image. See L<C<PVE::Storage::LvmThinPlugin>> and
> +L<C<PVE::Storage::ZFSPoolPlugin>> for example implementations.

then why not start with

"Creates a linked clone of an existing disk image or snapshot of an
image"

? maybe also include that unless the linked clone is 100% independent
from the base (only true for LVM thin atm?), the new volid should encode
the base->clone relation in the volname?

> +
> +C<die>s in case of an error of if the underlying storage doesn't support

s/of/or/

> +cloning images.
> +
> +This method is called in the context of C<L<< cluster_lock_storage()|/"cluster_lock_storage(...)" >>>,
> +i.e. when the storage is B<locked>.

same as above

> +
> +=cut
> +
>  sub clone_image {
>      my ($class, $scfg, $storeid, $volname, $vmid, $snap) = @_;
>      croak "implement me in sub-class\n";
>  }
>  
> +=head3 $plugin->alloc_image($storeid, $scfg, $vmid, $fmt, $name, $size)
> +
> +B<REQUIRED:> Must be implemented in every storage plugin.
> +
> +Allocates a disk image with the given format C<$fmt> and C<$size> in bytes,
> +returning the name of the new image (the new C<$volname>). See
> +C<L<< plugindata()|/"$plugin->plugindata()" >>> for all disk formats.
> +
> +Optionally, if given, set the name of the image to C<$name>. If C<$name> isn't
> +provided, the next name should be determined via C<L<< find_free_diskname()|/"$plugin->find_free_diskname(...)" >>>.

a suitable name should be automatically generated, unless we really want
to stabilize find_free_diskname as part of the API..

what does $vmid mean?

> +
> +C<die>s in case of an error of if the underlying storage doesn't support
> +allocating images.
> +
> +This method is called in the context of C<L<< cluster_lock_storage()|/"cluster_lock_storage(...)" >>>,
> +i.e. when the storage is B<locked>.
> +
> +=cut
> +
>  sub alloc_image {
>      my ($class, $storeid, $scfg, $vmid, $fmt, $name, $size) = @_;
>      croak "implement me in sub-class\n";
>  }
>  
> +=head3 $plugin->free_image($storeid, $scfg, $volname [, $isBase, $format])
> +
> +=head3 $plugin->free_image(...)
> +
> +B<REQUIRED:> Must be implemented in every storage plugin.
> +
> +Frees (deletes) the disk image given by C<$volname>. Optionally, the image may
> +be a base image (C<$isBase>) and have a certain C<$format>. See
> +C<L<< plugindata()|/"$plugin->plugindata()" >>> for all disk formats.
> +
> +If a cleanup is required after freeing the image, returns a reference to a
> +subroutine that performs the cleanup, and C<undef> otherwise.

might be a good idea to explain why? also, what do $isBase and $format
mean?

> +
> +C<die>s in case of errors, if the image has a L<< C<protected> attribute|/"$plugin->get_volume_attribute(...)" >>
> +(and may thus not be freed), or if the underlying storage implementation
> +doesn't support freeing images.
> +
> +This method is called in the context of C<L<< cluster_lock_storage()|/"cluster_lock_storage(...)" >>>,
> +i.e. when the storage is B<locked>.
> +
> +B<NOTE:> The returned cleanup subroutine is called in a separate worker and
> +should L<< lock|/"$plugin->cluster_lock_storage(...)" >> the underlying storage
> +separately.

it should? or it must?

> +
> +=cut
> +
>  sub free_image {
>      my ($class, $storeid, $scfg, $volname, $isBase, $format) = @_;
>      croak "implement me in sub-class\n";
> -- 
> 2.39.5
> 
> 
> 
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