Re: Deprecated mandatory file locking

[Jeff Layton <jlayton@kernel.org>]

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?

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()?

I'll draft up a patch, and also update
Documentation/filesystems/mandatory-locking.txt with the current
situation.

Thanks,
-- 
Jeff Layton <jlayton@kernel.org>