Re: [PATCH] btrfs: inode: Don't compress if NODATASUM or NODATACOW set

[Roman Mamedov <rm@romanrm.net>]

On Mon, 14 May 2018 11:36:26 +0300
Nikolay Borisov <nborisov@suse.com> wrote:

> So what made you have these expectation, is it codified somewhere
> (docs/man pages etc)? I'm fine with that semantics IF this is what
> people expect.

"Compression ...does not work for NOCOW files":
https://btrfs.wiki.kernel.org/index.php/Compression

The mount options man page does not say that the NOCOW attribute of files will
be disregarded with compress-force.  It only mentions interaction with the
nodatacow and nodatasum mount options. So I'd expect the attribute to still
work and prevent compression of NOCOW files.

> Now the question is why people grew up to have this expectation and not the
> other way round? IMO force_compress should really disregard everything else

Both are knobs that the user needs to explicitly set, the difference is that
the +C attribute is fine-grained and the mount option is global. If they are
set by the user to conflicting values, it seems more useful to have the
fine-grained control override the global one, not the other way round.

-- 
With respect,
Roman