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

["Max Carrara" <m.carrara@proxmox.com>]

On Mon Mar 31, 2025 at 5:12 PM CEST, Fabian Grünbichler wrote:
> 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@proxmox.com>
> > Co-authored-by: Maximiliano Sandoval <m.sandoval@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>.

Upfront note: Unless I otherwise comment something, I agree with you.
Just sparing myself from writing and you from reading too many ACKs :P

>
> what does usually mean? what does $vmid do?

Sorry, this got lost when tossing out some redundant paragraphs here.

The "usually" can be dropped; C<$vmid> is the guest's ID (mentioned in
the DESCRIPTION in patch 01) and unless C<\@vollist> is provided, the
images that the given C<$vmid> owns will be returned.

>
> > +
> > +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!

Oh dang, thanks for pointing this out! Sorry for the oversight.

>
> > +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?

See above; the guest's ID. Since it was unclear, the parameter should
probably be explained here (and also above) instead of (just) in the
DESCRIPTION section.

>
> > +
> > +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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> > 
> > 
> > 
>
>
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