Re: Deprecated mandatory file locking

[Jan Kara <jack@suse.cz>]

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!

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