linux-ext4 - Re: [PATCH] fcntl: Add 32bit filesystem mode

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Date:   Mon, 20 Apr 2020 11:13:44 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Andreas Dilger <adilger.kernel@...ger.ca>,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-api@...r.kernel.org, qemu-devel@...gnu.org,
        Florian Weimer <fw@...eb.enyo.de>,
        Peter Maydell <peter.maydell@...aro.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH] fcntl: Add 32bit filesystem mode

On Tue, Mar 31, 2020 at 03:35:36PM +0200, Linus Walleij wrote:
> It was brought to my attention that this bug from 2018 was
> still unresolved: 32 bit emulators like QEMU were given
> 64 bit hashes when running 32 bit emulation on 64 bit systems.
> 
> This adds a fcntl() operation to set the underlying filesystem
> into 32bit mode even if the file hanle was opened using 64bit
> mode without the compat syscalls.

s/hanle/handle/

The API that you've proposed as a way to set the 32-bit mode, but
there is no way to clear the 32-bit mode, nor there is a way to get
the current status mode.

My suggestion is to add a flag bit for F_GETFD and F_SETFD (set and
get file descriptor flags).  Currently the only file descriptor flag
is FD_CLOEXEC, so why not add a FD_32BIT_MODE bit?

Cheers,

						- Ted