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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 19 Aug 2021 13:31:35 -0700
Message-ID: <CAHk-=wgD-SNxB=2iCurEoP=RjrciRgLtXZ7R_DejK+mXF2etfg@mail.gmail.com>
Subject: Re: Removing Mandatory Locks
To:     Jeff Layton <jlayton@kernel.org>
Cc:     "Eric W. Biederman" <ebiederm@xmission.com>,
        Matthew Wilcox <willy@infradead.org>,
        Andy Lutomirski <luto@kernel.org>,
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On Thu, Aug 19, 2021 at 1:18 PM Jeff Layton <jlayton@kernel.org> wrote:
>
> Now that I think about it a little more, I actually did get one
> complaint a few years ago:
>
> Someone had upgraded from an earlier distro that supported the -o mand
> mount option to a later one that had disabled it, and they had an (old)
> fstab entry that specified it.

Hmm. We might be able to turn the "return -EINVAL" into just a warning.

Yes, yes, currently if you turn off CONFIG_MANDATORY_FILE_LOCKING, we
already do that

        VFS: "mand" mount option not supported

warning print, but then we fail the mount.

If CONFIG_MANDATORY_FILE_LOCKING goes away entirely, it might make
sense to turn that warning into something bigger, but then let the
mount continue - since now that "mand" flag would be purely a legacy
thing.

And yes, if we do that, we'd want the warning to be a big ugly thing,
just to make people very aware of it happening. Right now it's a
one-liner that is easy to miss, and the "oh, the mount failed" is the
thing that hopefully informs people about the fact that they need to
enable CONFIG_MANDATORY_FILE_LOCKING.

The logic being that if you can no longer enable mandatory locking in
the kernel, the current hard failure seems overly aggressive (and
might cause boot failures and inability to fix/report things when it
possibly keeps you from using the system at all).

              Linus