Re: [pve-devel] [PATCH pve-storage v4 2/2] fix #1611: implement import of base-images for LVM-thin Storage

["Hannes Dürr" <h.duerr@proxmox.com>]

On 1/30/24 11:00, Fabian Grünbichler wrote:
> On December 19, 2023 3:03 pm, Hannes Duerr wrote:
>> for base images we call the volume_import of the parent plugin and pass
>> it as vm-image instead of base-image, then convert it back as base-image
>>
>> Signed-off-by: Hannes Duerr <h.duerr@proxmox.com>
>> ---
>>   src/PVE/Storage/LvmThinPlugin.pm | 50 ++++++++++++++++++++++++++++++++
>>   1 file changed, 50 insertions(+)
>>
>> diff --git a/src/PVE/Storage/LvmThinPlugin.pm b/src/PVE/Storage/LvmThinPlugin.pm
>> index 1d2e37c..96f619b 100644
>> --- a/src/PVE/Storage/LvmThinPlugin.pm
>> +++ b/src/PVE/Storage/LvmThinPlugin.pm
>> @@ -383,6 +383,56 @@ sub volume_has_feature {
>>       return undef;
>>   }
>>   
>> +sub volume_import {
>> +    my ($class, $scfg, $storeid, $fh, $volname, $format, $snapshot, $base_snapshot, $with_snapshots, $allow_rename) = @_;
>> +
>> +    my ($vtype, $name, $vmid, $basename, $basevmid, $isBase, $file_format) =
>> +	$class->parse_volname($volname);
>> +
>> +    if (!$isBase) {
>> +	return $class->SUPER::volume_import(
>> +	    $scfg,
>> +	    $storeid,
>> +	    $fh,
>> +	    $volname,
>> +	    $format,
>> +	    $snapshot,
>> +	    $base_snapshot,
>> +	    $with_snapshots,
>> +	    $allow_rename
>> +	);
>> +    } else {
>> +	my $tempname;
>> +	my $vg = $scfg->{vgname};
>> +	my $lvs = PVE::Storage::LVMPlugin::lvm_list_volumes($vg);
>> +	if ($lvs->{$vg}->{$volname}) {
>> +	    die "volume $vg/$volname already exists\n" if !$allow_rename;
>> +	    warn "volume $vg/$volname already exists - importing with a different name\n";
>> +
>> +	    $tempname = $class->find_free_diskname($storeid, $scfg, $vmid);
>> +	} else {
>> +	    $tempname = $volname;
>> +	    $tempname =~ s/base/vm/;
> couldn't we simply do this part unconditionally, and then call the SUPER
> method? that one already checks whether $volname exists, does the same
> die/warn and then unsets $volname in case of a collision, so that
> alloc_image gets to pick a free one? then we just need to create_base on
> the returned $volid and be done, making this a very thin wrapper..

If we simply rename base-image-x to vm-image-x and pass it on to the parent

image, we may not be able to create a base image of the imported volume

vm-image-x, as there may already be a base-image-x, which we have not 
checked

before.


The patch still applies on master

> but, I just realized a bigger issue with all of this code here - AFAICT
> nothing ensures the storage is actually locked, so two parallel
> imports (or an import racing with an alloc/..) could actually end up
> trying to use the same volname. but we don't want to hold the lock for
> the full duration of the import, just for the part covering the "find
> free slot -> alloc_image" time span. this is not limited to LVM, but
> properly handling it would require splitting up volume_import into two
> plugin methods (breaking the storage plugin ABI) which might not even
> work for all storage types.
>
Created a patch for this issue:
https://lists.proxmox.com/pipermail/pve-devel/2024-April/062581.html

>> +	}
>> +
>> +	($storeid,my $newname) = PVE::Storage::parse_volume_id($class->SUPER::volume_import(
>> +	    $scfg,
>> +	    $storeid,
>> +	    $fh,
>> +	    $tempname,
>> +	    $format,
>> +	    $snapshot,
>> +	    $base_snapshot,
>> +	    $with_snapshots,
>> +	    $allow_rename
>> +	));
>> +
>> +	$volname = $class->create_base($storeid, $scfg, $newname);
>> +    }
>> +
>> +    return "$storeid:$volname";
>> +}
>> +
>>   # used in LVMPlugin->volume_import
>>   sub volume_import_write {
>>       my ($class, $input_fh, $output_file) = @_;
>> -- 
>> 2.39.2
>>
>>
>>
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>>
>>
>
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