Re: Deprecated mandatory file locking

[Jan Kara <jack@suse.cz>]

On Thu 07-11-19 13:34:21, Jeff Layton wrote:
> On Thu, 2019-11-07 at 17:15 +0100, Jan Kara wrote:
> > Hi Jeff,
> > 
> > On Fri 16-08-19 17:31:49, Jan Kara wrote:
> > > On Thu 15-08-19 15:18:45, Jeff Layton wrote:
> > > > On Wed, 2019-08-14 at 19:46 +0200, Jan Kara wrote:
> > > > > Resending to proper Jeff's address...
> > > > > 
> > > > > On Wed 14-08-19 19:33:45, Jan Kara wrote:
> > > > > > Hello Jeff,
> > > > > > 
> > > > > > we've got a report from user
> > > > > > (https://bugzilla.suse.com/show_bug.cgi?id=1145007) wondering why his fstab
> > > > > > entry (for root filesystem!) using 'mand' mount option stopped working.
> > > > > > Now I understand your rationale in 9e8925b67a "locks: Allow disabling
> > > > > > mandatory locking at compile time" but I guess there's some work to do wrt
> > > > > > documentation. At least mount(8) manpage could mention that mandatory
> > > > > > locking is broken and may be disabled referencing the rationale in fcntl
> > > > > > manpage? Or the kernel could mention something in the log about failing
> > > > > > mount because of 'mand' mount option?  What do you think? Because it took
> > > > > > me some code searching to understand why the mount is actually failing
> > > > > > which we can hardly expect from a normal sysadmin...
> > > > > > 
> > > > > > 								Honza
> > > > 
> > > > Wow, I think this is the first actual user fallout we've ever had from
> > > > that change! Why was he setting that option? Does he actually use
> > > > mandatory locking?
> > > 
> > > Yeah, reportedly they had an application that required mandatory locking.
> > > But they don't use it anymore so they just removed the mount option.
> > > 
> > > > I think a pr_notice() or pr_warn() at mount time when someone tries to
> > > > use it sounds like a very reasonable thing to do. Perhaps we can just
> > > > stick one in may_mandlock()?
> > > 
> > > Yeah, sounds reasonable to me.
> > > 
> > > > I'll draft up a patch, and also update
> > > > Documentation/filesystems/mandatory-locking.txt with the current
> > > > situation.
> > > 
> > > Thanks!
> > 
> > Did you ever get to this?
> > 
> > 								Honza
> 
> Yes. It went into v5.4-rc1. You even reviewed it! ;)

Bah ;) I completely forgot and somehow didn't realize the section 7. in
Documentation/filesystems/mandatory-locking.txt is describing what I
wanted when I looked at it yesterday. Sorry for the noise!

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