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

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Message-ID: <20200107003944.GN23195@dread.disaster.area>
Date:   Tue, 7 Jan 2020 11:39:44 +1100
From:   Dave Chinner <david@...morbit.com>
To:     Chris Down <chris@...isdown.name>
Cc:     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>,
        Amir Goldstein <amir73il@...il.com>,
        Jeff Layton <jlayton@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Tejun Heo <tj@...nel.org>, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH v5 2/2] tmpfs: Support 64-bit inums per-sb

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.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com