[pve-devel] NACK: [PATCH storage 2/3] krbd: remove 'exclusive-lock' from blacklist, kernel-4.13

[Fabian Grünbichler]

this is problematic because it potentially hides bugs in our application
logic, with currently no benefit.

with exclusive-locks disabled, mapping on multiple hosts is possible,
but mounting the same image is not (e.g., when attempting to mount, all
but the first successful node will fail).

with exclusive-locks enabled, mapping and accessing/mounting is
sometimes possible (it seems a bit racy?), but since ext4 is not a
cluster FS, this will cause undesired behaviour / inconsistencies /
corruption.

OTOH, with exclusive-locks enabled we would have the option of exclusive
mapping - if we find a way to make this work with Qemu live-migration it
might solve all of our problems

TL;DR: I think we should postpone this pending further investigations
into potential pros and cons

On Wed, Feb 28, 2018 at 06:50:01PM +0100, Alwin Antreich wrote:
> Signed-off-by: Alwin Antreich <a.antreich at proxmox.com>
> ---
>  PVE/Storage/RBDPlugin.pm | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/PVE/Storage/RBDPlugin.pm b/PVE/Storage/RBDPlugin.pm
> index 804dded..ef9fc4a 100644
> --- a/PVE/Storage/RBDPlugin.pm
> +++ b/PVE/Storage/RBDPlugin.pm
> @@ -109,7 +109,7 @@ my $krdb_feature_disable = sub {
>      my ($major, undef, undef, undef) = ceph_version();
>      return 1 if $major < 10;
>  
> -    my $krbd_feature_blacklist = ['deep-flatten', 'fast-diff', 'object-map', 'exclusive-lock'];
> +    my $krbd_feature_blacklist = ['deep-flatten', 'fast-diff', 'object-map'];
>      my (undef, undef, undef, undef, $features) = rbd_volume_info($scfg, $storeid, $name);
>  
>      my $active_features = { map { $_ => 1 } PVE::Tools::split_list($features)};
> -- 
> 2.11.0
> 
> 
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