linux-kernel - Re: [PATCH v5 2/2] tmpfs: Support 64-bit inums per-sb

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Date:   Tue, 7 Jan 2020 08:54:23 +0200
From:   Amir Goldstein <amir73il@...il.com>
To:     Dave Chinner <david@...morbit.com>
Cc:     Chris Down <chris@...isdown.name>, Linux MM <linux-mm@...ck.org>,
        Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>,
        Jeff Layton <jlayton@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Tejun Heo <tj@...nel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>, kernel-team@...com
Subject: Re: [PATCH v5 2/2] tmpfs: Support 64-bit inums per-sb

On Tue, Jan 7, 2020 at 2:40 AM Dave Chinner <david@...morbit.com> wrote:
>
> On Tue, Jan 07, 2020 at 12:16:43AM +0000, Chris Down wrote:
> > Dave Chinner writes:
> > > It took 15 years for us to be able to essentially deprecate
> > > inode32 (inode64 is the default behaviour), and we were very happy
> > > to get that albatross off our necks.  In reality, almost everything
> > > out there in the world handles 64 bit inodes correctly
> > > including 32 bit machines and 32bit binaries on 64 bit machines.
> > > And, IMNSHO, there no excuse these days for 32 bit binaries that
> > > don't using the *64() syscall variants directly and hence support
> > > 64 bit inodes correctlyi out of the box on all platforms.
> > >
> > > I don't think we should be repeating past mistakes by trying to
> > > cater for broken 32 bit applications on 64 bit machines in this day
> > > and age.
> >
> > I'm very glad to hear that. I strongly support moving to 64-bit inums in all
> > cases if there is precedent that it's not a compatibility issue, but from
> > the comments on my original[0] patch (especially that they strayed from the
> > original patches' change to use ino_t directly into slab reuse), I'd been
> > given the impression that it was known to be one.
> >
> > From my perspective I have no evidence that inode32 is needed other than the
> > comment from Jeff above get_next_ino. If that turns out not to be a problem,
> > I am more than happy to just wholesale migrate 64-bit inodes per-sb in
> > tmpfs.
>
> Well, that's my comment above about 32 bit apps using non-LFS
> compliant interfaces in this day and age. It's essentially a legacy
> interface these days, and anyone trying to access a modern linux
> filesystem (btrfs, XFS, ext4, etc) ion 64 bit systems need to handle
> 64 bit inodes because they all can create >32bit inode numbers
> in their default configurations.
>

Chris,

Following Dave's comment, let's keep the config option, but make it
default to Y and remove the mount option for now.
If somebody shouts, mount option could be re-added later.
This way at least we leave an option for workaround for an unlikely
breakage.

Thanks,
Amir.