Re: [PATCH 6/8] quota: port quota helpers mount ids

[Christian Brauner <brauner@kernel.org>]

On Tue, Jun 21, 2022 at 12:20:27PM +0200, Jan Kara wrote:
> On Mon 20-06-22 15:49:45, Christian Brauner wrote:
> > Port the is_quota_modification() and dqout_transfer() helper to type
> > safe kmnt{g,u}id_t. Since these helpers are only called by a few
> > filesystems don't introduce a new helper but simply extend the existing
> > helpers to pass down the mount's idmapping.
> > 
> > Note, that this is a non-functional change, i.e. nothing will have
> > happened here or at the end of this series to how quota are done! This
> > a change necessary because we will at the end of this series make
> > ownership changes easier to reason about by keeping the original value
> > in struct iattr for both non-idmapped and idmapped mounts.
> > 
> > For now we always pass the initial idmapping which makes the idmapping
> > functions these helpers call nops.
> > 
> > This is done because we currently always pass the actual value to be
> > written to i_{g,u}id via struct iattr. While this allowed us to treat
> > the {g,u}id values in struct iattr as values that can be directly
> > written to inode->i_{g,u}id it also increases the potential for
> > confusion for filesystems.
> > 
> > Now that we are about to introduce dedicated types to prevent this
> > confusion we will ultimately only map the value from the idmapped mount
> > into a filesystem value that can be written to inode->i_{g,u}id when the
> > filesystem actually updates the inode. So pass down the initial
> > idmapping until we finished that conversion.
> > 
> > Since struct iattr uses an anonymous union with overlapping types as
> > supported by the C filesystems that haven't converted to ia_mnt{g,u}id
> > won't see any difference and things will continue to work as before.
> > In other words, no functional changes intended with this change.
> > 
> > Cc: Seth Forshee <sforshee@digitalocean.com>
> > Cc: Christoph Hellwig <hch@lst.de>
> > Cc: Jan Kara <jack@suse.cz>
> > Cc: Aleksa Sarai <cyphar@cyphar.com>
> > Cc: Linus Torvalds <torvalds@linux-foundation.org>
> > Cc: Al Viro <viro@zeniv.linux.org.uk>
> > CC: linux-fsdevel@vger.kernel.org
> > Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
> 
> Yeah, this looks fairly innocent. Feel free to add:
> 
> Reviewed-by: Jan Kara <jack@suse.cz>
> 
> Just when do you plan to make changes actually using the passed namespace?

Hey Jan,

Thank you for the review!
The changes are in the last patch of the series. But it is all unrelated
to quotas and doesn't alter them in any way. We really just change how
ia_{vfs}uid is set up to get type safety which requires the generic
codepaths like here to calculate the correct value when they actually
perform a write instead of having performed that calculation when we
set up iattr. That's really all.

Thanks!
Christian