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Date:   Thu, 19 Aug 2021 12:55:08 -0700
From:   Eric Biggers <ebiggers@kernel.org>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Jeff Layton <jlayton@kernel.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
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Subject: Re: Removing Mandatory Locks
Message-ID: <YR63HOPASyh21DjK@gmail.com>
References: <CAHk-=wgru1UAm3kAKSOdnbewPXQMOxYkq9PnAsRadAC6pXCCMQ@mail.gmail.com>
 <87eeay8pqx.fsf@disp2133>
 <5b0d7c1e73ca43ef9ce6665fec6c4d7e@AcuMS.aculab.com>
 <87h7ft2j68.fsf@disp2133>
 <CAHk-=whmXTiGUzVrTP=mOPQrg-XOi3R-45hC4dQOqW4JmZdFUQ@mail.gmail.com>
 <b629cda1-becd-4725-b16c-13208ff478d3@www.fastmail.com>
 <YRcyqbpVqwwq3P6n@casper.infradead.org>
 <87k0kkxbjn.fsf_-_@disp2133>
 <0c2af732e4e9f74c9d20b09fc4b6cbae40351085.camel@kernel.org>
 <CAHk-=wgewmbABDC3_ZNn11C+sm4Uz0L9HZ5Kvx0Joho4vsV4DQ@mail.gmail.com>
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On Thu, Aug 19, 2021 at 12:15:08PM -0700, Linus Torvalds wrote:
> On Thu, Aug 19, 2021 at 11:39 AM Jeff Layton <jlayton@kernel.org> wrote:
> >
> > I'm all for ripping it out too. It's an insane interface anyway.
> >
> > I've not heard a single complaint about this being turned off in
> > fedora/rhel or any other distro that has this disabled.
> 
> I'd love to remove it, we could absolutely test it. The fact that
> several major distros have it disabled makes me think it's fine.
> 
> But as always, it would be good to check Android.
> 
> The desktop distros tend to have the same tools and programs, so if
> Fedora and RHEL haven't needed it for years, then it's likely stale in
> Debian too (despite being enabled).
> 
> But Android tends to be very different. Does anybody know?
> 

As far as I know, Android never uses mandatory file locking.  While
CONFIG_MANDATORY_LOCKING=y is typically set (as it's "default y" upstream),
I can't find anywhere in the Android source tree that uses the "mand" mount
option, let alone anything actually using mandatory locks.  (I'm assuming that
Documentation/filesystems/mandatory-locking.rst is up-to-date regarding what
userspace actually has to do to use it.)

- Eric