On Tue, Oct 21, 2014 at 04:38:26PM +0200, Jan Kara wrote:

Currently all filesystems supporting VFS quota support user and group
quotas. With introduction of project quotas this is going to change so
make sure filesystem isn't called for quota type it doesn't support by
introduction of a bitmask determining which quota types each filesystem
supports.

Why don't you keep this bitmask in the dquot.c instead of pushing it
to the caller?  So far usage of s_dquot is mostly confined to dquot.c
(with a few leaks to the filesystems using it), so keeping it that
way seems like a good idea.