Re: Filesystem configuration parsers - (was: Re: [RESEND][PATCH] xfs: add online uevent for mount operation)

Luis R. Rodriguez
2017-08-25T01:20:04Z

On Fri, Aug 25, 2017 at 11:01:55AM +1000, Dave Chinner wrote:
> On Thu, Aug 24, 2017 at 08:04:41PM +0200, Luis R. Rodriguez wrote:
> > While all this is nice, I'm sure we're all aware of the dangers of setting
> > things in stone through sysfs, its likely already decided for the above
> > tunables, but adding a uevent *is* yet another layer of user interface
> > which userspace can *expect* and we should be certain we want this so
> > we won't regress userspace later.
> >
> > Just saying, we better damn be sure this is the way we want to go.
>
> I'm not sure what you are trying to warn us about? :/
>
> These are events on an XFS specific kobj, it's not a generic VFS
> filesystem event we are generating here. It's no different from a
> hardware device generating it's own uevents to tell userspace
> something changed in the device.

I meant that once its sent even if it is XFS specific, it will be
something that some userspace can expect and then we'd always have
to send it later.

> A quick grep would have told you that GFS2 already has it's own
> online/offline uevents (e.g. gfs2_online_uevent()), as does the
> DLM code. Orangefs seems to use quite a few of uevent notifications,
> too. So it's not like we're doing something controversial or unique
> here, nor something that locks us out of a non-existent VFS event
> notification mechanism.

I don't think its controversial *at all*. Just that a mount uevent,
with uuid, sounds like something we could at least agree is pretty generic.

Regardless of what we end up doing with it or how.

Luis