On Thu, Jan 21, 2021 at 03:27:56PM -0500, J. Bruce Fields wrote:

quoted

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.

quoted

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'd much prefer to just keep consulting the I_VERSION flag and only
add the new op as an override for the NFS export.

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.)

Even without the ctime i_version never goes backward, what is the
problem here?