On Wed, Jan 20, 2021 at 08:46:38AM +0000, Christoph Hellwig wrote: > On Tue, Jan 19, 2021 at 02:24:56PM -0500, J. Bruce Fields wrote: > > From: "J. Bruce Fields" <bfields@xxxxxxxxxx> > > > > After this, only filesystems lacking change attribute support will leave > > the fetch_iversion export op NULL. > > > > This seems cleaner to me, and will allow some minor optimizations in the > > nfsd code. > > Another indirect call just to fetch the change attribute (which happens > a lot IIRC) does not seem very optimal to me. In the next patch we're removing an fh_getattr (vfs_getattr) in the case we call the new op, so that's typically a net decrease in indirect calls. Though maybe we could use a flag here and do without either. > And the fact that we need three duplicate implementations also is not > very nice. Ext4 and xfs are identical, btrfs is a little different since it doesn't consult I_VERSION. (And then there's nfs, which uses the origin server's i_version if it can.) I also have a vague idea that some filesystem-specific improvements might be possible. (E.g., if a filesystem had some kind of boot count in the superblock, maybe that would be a better way to prevent the change attribute from going backwards on reboot than the thing generic_fetch_iversion is currently doing with ctime. But I have no concrete plan there, maybe I'm dreaming.) --b.
