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

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

On Thu Apr 3, 2025 at 9:23 AM CEST, Fabian Grünbichler wrote:
> On April 2, 2025 6:32 pm, Max Carrara wrote:
> > 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.
>
> in case that wasn't obvious - I know what $vmid is (and also what it
> does) - it should be explained to readers that don't (yet).
>
> So I think this should say something like:
>
> If C<$vmid> is set, only images owned by that VMID must be included in
> the return value.
>
> If C<\@vollist> is set and not empty, the return value must be filtered
> using the contained volids.
>
> If both C<$vmid> and C<\@vollist> are set, only C<\@vollist> should be
> honored.

Thanks for the suggestion, that's actually much better. I also agree
with the other suggestions further below.

>
> and about that last part - do we actually have callers that set both? if
> not, should we instead recommend treating it as an error and document it
> as such?

I'll revisit the call sites again and see whether we actually do, just
to be sure. The current code at least doesn't treat it as an error.

>
> >> > +
> >> > +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 $vmid mean?
> > 
> > See above; the guest's ID. Since it was unclear, the parameter should
> > probably be explained here (and also above) instead of (just) in the
> > DESCRIPTION section.
>
> I know what a vmid is ;) the question is what does this parameter *mean*
> for this particular method?
>
> C<$vmid> contains the owner of the new volume, which must be encoded in
> the returned volid.
>
> or something like that?
>
> >> > +
> >> > +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?
>
> here as well, similar to clone_image above
>
>
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