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Date: Mon, 08 Nov 2021 16:21:15 +0100
From: Fabian =?iso-8859-1?q?Gr=FCnbichler?= <f.gruenbichler@proxmox.com>
To: Proxmox VE development discussion <pve-devel@lists.proxmox.com>
References: <20211102150335.2371545-1-a.lauterer@proxmox.com>
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Subject: Re: [pve-devel] [PATCH v4 storage 1/9] storage: add new
find_free_volname
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On November 2, 2021 4:03 pm, Aaron Lauterer wrote:
> This new method exposes the functionality to request a new, not yet
> used, volname for a storage.
>=20
> The default implementation will return the result from
> 'find_free_diskname' prefixed with "<VMID>/" if $scfg->{path} exists.
> Otherwise it will only return the result from 'find_free_diskname'.
>=20
> If the format suffix is added also depends on the existence of
> $scfg->{path}.
>=20
> $scfg->{path} will be present for directory based storage types.
>=20
> Should a storage need to return different volname, it needs to override
> the 'find_free_volname' method.
>=20
> Signed-off-by: Aaron Lauterer <a.lauterer@proxmox.com>
as discussed off-list (I am sorry I didn't read through the full=20
discussion on-list of all 10 versions of this and the previous series=20
;)) - IMHO this is not a backwards compatible addition since it's not=20
guarded by any feature flag, so external plugins fall into two=20
categories:
- derived from Plugin.pm, so automatically implement it via=20
find_free_diskname -> get_next_vm_diskname, which might or might not=20
be correct for that plugin
- not derived from Plugin.pm, don't implement it, no safeguard to handle=20
that
RIGHT NOW, the only callers are guarded by the rename feature so there=20
can't be any problems in practice - but there is no guarantee that this=20
will be remembered down the line, and it also breaks the=20
modularization/layering of the code to rely on this fact ;)
while we could argue about whether we really want to be that strict,=20
another point against exposing this method for me is that it's also=20
prone to mis-use, since it encourages code patterns like in this=20
series with:
get_free_volname
do_something_that_allocates_that_volname
without holding a storage lock over both calls, since the storage lock=20
is only available on the plugin level and not exposed in PVE::Storage=20
itself.
an interface like
$plugin->rename_volume($scfg, $storeid, $source, $new_owner, $new_name)
with at least $new_owner or $new_name set would also cover both cases=20
(reassign with just $new_owner, rename with just $new_name) and can be=20
feature-guarded while keeping the locking in PVE::Storage for the full=20
operation including finding a free slot if needed.
alternatively, just implementing
$plugin->reassign_volume($scfg, $storeid, $source, $new_owner)
for now (guarded by a 'reassign' feature), and postponing the rename=20
feature for a future series that handles 'custom suffix/volname'=20
across the board of our stack would also be an option.
> ---
>=20
> v3 -> v4:
> * fix style nit
>=20
> v2 -> v3:
> * dropped exists() check
> * fixed base image handling
> * fixed smaller code style issues
>=20
> v1 -> v2:
> * many small fixes and improvements
> * rename_volume now accepts $source_volname instead of $source_volid
> helps us to avoid to parse the volid a second time
>=20
> rfc -> v1:
> * reduced number of parameters to minimum needed, plugins infer needed
> information themselves
> * added storage locking and checking if volume already exists
> * parse target_volname prior to renaming to check if valid
>=20
> old dedicated API endpoint -> rfc:
> only do rename now but the rename function handles templates and returns
> the new volid as this can be differently handled on some storages.
> =20
> PVE/Storage.pm | 9 +++++++++
> PVE/Storage/Plugin.pm | 8 ++++++++
> 2 files changed, 17 insertions(+)
>=20
> diff --git a/PVE/Storage.pm b/PVE/Storage.pm
> index 71d6ad7..4fbeaea 100755
> --- a/PVE/Storage.pm
> +++ b/PVE/Storage.pm
> @@ -203,6 +203,15 @@ sub storage_can_replicate {
> return $plugin->storage_can_replicate($scfg, $storeid, $format);
> }
> =20
> +sub find_free_volname {
> + my ($cfg, $storeid, $vmid, $fmt) =3D @_;
> +
> + my $scfg =3D storage_config($cfg, $storeid);
> + my $plugin =3D PVE::Storage::Plugin->lookup($scfg->{type});
> +
> + return $plugin->find_free_volname($storeid, $scfg, $vmid, $fmt);
> +}
> +
> sub storage_ids {
> my ($cfg) =3D @_;
> =20
> diff --git a/PVE/Storage/Plugin.pm b/PVE/Storage/Plugin.pm
> index aeb4fff..d21c874 100644
> --- a/PVE/Storage/Plugin.pm
> +++ b/PVE/Storage/Plugin.pm
> @@ -732,6 +732,14 @@ sub find_free_diskname {
> return get_next_vm_diskname($disk_list, $storeid, $vmid, $fmt, $scfg=
, $add_fmt_suffix);
> }
> =20
> +sub find_free_volname {
> + my ($class, $storeid, $scfg, $vmid, $fmt) =3D @_;
> +
> + my $diskname =3D $class->find_free_diskname($storeid, $scfg, $vmid, =
$fmt, $scfg->{path});
> +
> + return $scfg->{path} ? "${vmid}/$diskname" : $diskname;
> +}
> +
> sub clone_image {
> my ($class, $scfg, $storeid, $volname, $vmid, $snap) =3D @_;
> =20
> --=20
> 2.30.2
>=20
>=20
>=20
> _______________________________________________
> pve-devel mailing list
> pve-devel@lists.proxmox.com
> https://lists.proxmox.com/cgi-bin/mailman/listinfo/pve-devel
>=20
>=20
>=20