Cleanup generic_osync_inode?

[Jan Kara <jack@suse.cz>]

  Hi,

  I was looking at generic_osync_inode() and found out it's kind of
inconsistent with what we have in fsync() path and does not work in all
cases e.g. on ext3 / ext4. The problem is that filesystem never actually
gets to know that it should sync all metadata needed to reach the data -
generic_osync_inode() only does sync_mapping_buffers() but e.g. ext3 / ext4
don't track metadata buffers there. Then it does write_inode_now() which
would actually flush the journal, but it does so only in case inode is
I_DIRTY_DATASYNC... So there are cases where we sync the data but leave
metadata uncommitted.
  What I'd imagine is that generic_osync_inode() would be just like
fdatasync call, only we'd have to add a possibility to avoid fdatawrite /
fdatawait as some callers submit / wait for data themselves. That would
nicely unify those syncing paths.
  The only small problem is with an interface since ->fsync() callback
takes preferably struct file * and at least struct dentry *, while
generic_osync_inode takes just inode. Most of the callers actually have
a struct file * pointer but sync_page_range[_nolock]() do not, so that
would have to be solved somehow.
  Any opinions / ideas?

								Honza
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR