[pve-devel] [PATCH v3 qemu-server 1/7] migration: only migrate disks used by the guest

[Fiona Ebner]

Am 02.06.23 um 11:45 schrieb Fiona Ebner:
> Am 01.06.23 um 15:53 schrieb Aaron Lauterer:
>> When scanning all configured storages for disk images belonging to the
>> VM, the migration could easily fail if a storage is not available, but
>> enabled. That storage might not even be used by the VM at all.
>>
>> By not doing that and only looking at the disk images referenced in the
>> VM config, we can avoid that.
>> Extra handling is needed for disk images currently in the 'pending'
>> section of the VM config. These disk images used to be detected by
>> scanning all storages before.
>> It is also necessary to fetch some information (size, format) about the
>> disk images explicitly that used to be provided by the initial scan of
>> all storages.
>>
>> The big change regarding behavior is that disk images not referenced in
>> the VM config file will be ignored.  They are already orphans that used
>> to be migrated as well, but are now left where they are.  The tests have
>> been adapted to that changed behavior.
>>
>> Signed-off-by: Aaron Lauterer <a.lauterer at proxmox.com>
>> ---
>> changes sind v2:
>> - move handling of pending changes into QemuSerer::foreach_volid
>>     Seems to not have any bad side-effects
> 
> This should really be its own patch and talk about what the side effects
> actually are and why they are okay in the commit message.
> 
> Maybe even keep old behavior for replication at first and then add a
> second patch which explicitly enables replication for pending volumes by
> removing the filtering initially added. Easiest probably is an option
> $exclude_pending for foreach_volid() used only by replication and then
> remove it in the following patch.
> 
> Like that, each patch has its own clear purpose and effect.
> 
>> - style fixes
>> - use 'volume_size_info()' to get format and size of the image
>>
>>  PVE/QemuMigrate.pm                    | 88 ++++++++-------------------
>>  PVE/QemuServer.pm                     |  9 ++-
>>  test/MigrationTest/QemuMigrateMock.pm |  9 +++
>>  test/run_qemu_migrate_tests.pl        | 12 ++--
>>  4 files changed, 50 insertions(+), 68 deletions(-)
>>
>> diff --git a/PVE/QemuMigrate.pm b/PVE/QemuMigrate.pm
>> index 09cc1d8..163a721 100644
>> --- a/PVE/QemuMigrate.pm
>> +++ b/PVE/QemuMigrate.pm
>> @@ -149,6 +149,22 @@ sub lock_vm {
>>      return PVE::QemuConfig->lock_config($vmid, $code, @param);
>>  }
>>  
>> +sub target_storage_check_available {
>> +    my ($self, $storecfg, $targetsid, $volid) = @_;
>> +
>> +    if (!$self->{opts}->{remote}) {
>> +	# check if storage is available on target node
>> +	my $target_scfg = PVE::Storage::storage_check_enabled(
>> +	    $storecfg,
>> +	    $targetsid,
>> +	    $self->{node},
>> +	);
>> +	my ($vtype) = PVE::Storage::parse_volname($storecfg, $volid);
>> +	die "$volid: content type '$vtype' is not available on storage '$targetsid'\n"
>> +	    if !$target_scfg->{content}->{$vtype};
>> +    }
>> +}
> 
> This should also be its own patch, please.
> 
>> +
>>  sub prepare {
>>      my ($self, $vmid) = @_;
>>  
>> @@ -396,17 +358,21 @@ sub scan_local_volumes {
>>  		$targetsid = PVE::JSONSchema::map_id($self->{opts}->{storagemap}, $sid);
>>  	    }
>>  
>> -	    # check target storage on target node if intra-cluster migration
>> -	    if (!$self->{opts}->{remote}) {
>> -		PVE::Storage::storage_check_enabled($storecfg, $targetsid, $self->{node});
>> -
>> -		return if $scfg->{shared};
>> -	    }
>> +	    return if $scfg->{shared} && !$self->{opts}->{remote};
>> +	    $self->target_storage_check_available($storecfg, $targetsid, $volid);
> 
> Shouldn't these two lines be switched?
> 
> Before, the enabled check would be done if !$self->{opts}->{remote} and
> then early return.
> 
> But now, if $scfg->{shared} && !$self->{opts}->{remote};, you early
> return without doing the check at all.
> 
> With switched lines, you call the helper, which does the check if
> !$self->{opts}->{remote} and then you do the early return like before.
> 
>>  
>>  	    $local_volumes->{$volid}->{ref} = $attr->{referenced_in_config} ? 'config' : 'snapshot';
>>  	    $local_volumes->{$volid}->{ref} = 'storage' if $attr->{is_unused};
> 
> Not yours, but this is actually wrong, because if the same volume is
> already referenced in a snapshot, the reference will be overwritten to
> be 'storage' here :P
> 
>> +	    $local_volumes->{$volid}->{ref} = 'storage' if $attr->{is_pending};
> 
> But yours is also not correct ;) It should only be done for volumes that
> are only referenced in pending, but not in the current config. You don't
> touch the...
> 
>> @@ -4888,6 +4888,8 @@ sub foreach_volid {
> 
> $volhash->{$volid}->{referenced_in_config} = 1 if !defined($snapname);
> 
> ...line in PVE/QemuServer.pm's foreach_volid(), so is_pending being 1
> means referenced_in_config is also 1 and there's no way to distinguish
> via attributes if a volume is only in pending or both in pending and the
> current config.
> 
> Not sure if we should even bother to distinguish between more than
> 'config' and 'snapshot' anymore. Everything that's just in a snapshot
> gets 'snapshot' and everything that's in the current config (including
> pending) gets 'config'. No need for 'storage' at all.
> 

Argh, it's actually not just used informationally, but affects real
logic too :(

        foreach my $volid (sort keys %$local_volumes) {
            my $ref = $local_volumes->{$volid}->{ref};
            if ($self->{running} && $ref eq 'config') {
                $local_volumes->{$volid}->{migration_mode} = 'online';

So we do need a real way to distinguish 'only in pending' and 'both in
pending and current config' after all here.