Re: [PATCH] btrfs: do not allow -o compress-force to override per-inode settings

[Hugo Mills <hugo@carfax.org.uk>]

On Mon, Nov 30, 2020 at 09:50:13AM -0500, Josef Bacik wrote:
> On 11/30/20 9:08 AM, Roman Mamedov wrote:
> > On Mon, 30 Nov 2020 08:46:21 -0500
> > Josef Bacik <josef@toxicpanda.com> wrote:
> > 
> > > However some time later we got chattr -c, which is a user way of
> > > indicating that the file shouldn't be compressed.  This is at odds with
> > > -o compress-force.  We should be honoring what the user wants, which is
> > > to disable compression.
> > 
> > But chattr -c only removes the previously set chattr +c. There's no
> > "negative-c" to be forced by user in attributes. And +c is already unset on all
> > files by default. Unless I'm missing something? Thanks
> > 
> 
> The thing you're missing is that when we do chattr -c we're setting
> NOCOMPRESS on the file.  The thing that I'm missing is what exactly we're
> trying to allow.  If chattr -c is supposed to just be the removal of +c,
> then btrfs is doing the wrong thing by setting NOCOMPRESS.  We also do the
> same thing when we clear a btrfs.compression property.

   If I'm understanding this right, there's more than two states
here. There's a "default", and there's two "force" options -- forcing
nocompress, and forcing/allowing compression. If there's no c flag
set, the file could be in one of two states: default behaviour
(presumably defined by the value of the mount options), and
NOCOMPRESS. How do I tell which it is?

> I guess the question is what do we want?  Do we want to only allow the user
> to indicate we want compression, or do we want to allow them to also
> indicate that they don't want compression?  If we don't want to enable them
> to disable compression for a file, then this patch needs to be thrown away,
> but then we also need to fix up all the places we set NOCOMPRESS when we
> clear these flags.  Thanks,

   Hugo.

-- 
Hugo Mills             | The last man on Earth sat in a room. Suddenly, there
hugo@... carfax.org.uk | was a knock at the door.
http://carfax.org.uk/  |
PGP: E2AB1DE4          |                                        Frederic Brown