Re: [man-pages RFC PATCH v4] statx, inode: document the new STATX_INO_VERSION field

Jeff Layton
2022-09-12T14:02:44Z

On Mon, 2022-09-12 at 09:51 -0400, J. Bruce Fields wrote:
> On Mon, Sep 12, 2022 at 08:55:04AM -0400, Jeff Layton wrote:
> > Because of the "seen" flag, we have a 63 bit counter to play with. Could
> > we use a similar scheme to the one we use to handle when "jiffies"
> > wraps? Assume that we'd never compare two values that were more than
> > 2^62 apart? We could add i_version_before/i_version_after macros to make
> > it simple to handle this.
>
> As far as I recall the protocol just assumes it can never wrap. I guess
> you could add a new change_attr_type that works the way you describe.
> But without some new protocol clients aren't going to know what to do
> with a change attribute that wraps.
>

Right, I think that's the case now, and with contemporary hardware that
shouldn't ever happen, but in 10 years when we're looking at femtosecond
latencies, could this be different? I don't know.

> I think this just needs to be designed so that wrapping is impossible in
> any realistic scenario. I feel like that's doable?
>
> If we feel we have to catch that case, the only 100% correct behavior
> would probably be to make the filesystem readonly.

What would be the recourse at that point? Rebuild the fs from scratch, I
guess?
--
Jeff Layton <jlayton@kernel.org>