From: Peter Maydell <peter.maydell@linaro.org>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: "Theodore Ts'o" <tytso@mit.edu>,
Andreas Dilger <adilger.kernel@dilger.ca>,
Ext4 Developers List <linux-ext4@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
QEMU Developers <qemu-devel@nongnu.org>,
Florian Weimer <fw@deneb.enyo.de>,
Andy Lutomirski <luto@kernel.org>,
stable@vger.kernel.org
Subject: Re: [PATCH] ext4: Give 32bit personalities 32bit hashes
Date: Tue, 17 Mar 2020 11:58:09 +0000 [thread overview]
Message-ID: <CAFEAcA9mXE+gPnvM6HZ-w0+BhbpeuH=osFH-9NUzCLv=w-c7HQ@mail.gmail.com> (raw)
In-Reply-To: <20200317113153.7945-1-linus.walleij@linaro.org>
On Tue, 17 Mar 2020 at 11:31, Linus Walleij <linus.walleij@linaro.org> 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.
>
> The personality(2) system call supports to let processes
> indicate that they are 32 bit Linux to the kernel. This
> was suggested by Teo in the original thread, so I just wired
> it up and it solves the problem.
Thanks for having a look at this. I'm not sure this is what
QEMU needs, though. When QEMU runs, it is not a 32-bit
process, it's a 64-bit process. Some of the syscalls
it makes are on behalf of the guest and would need 32-bit
semantics (including this one of wanting 32-bit hash sizes
in directory reads). But some syscalls it makes for itself
(either directly, or via libraries it's linked against
including glibc and glib) -- those would still want the
usual 64-bit semantics, I would have thought.
> Programs that need the 32 bit hash only need to issue the
> personality(PER_LINUX32) call and things start working.
What in particular does this personality setting affect?
My copy of the personality(2) manpage just says:
PER_LINUX32 (since Linux 2.2)
[To be documented.]
which isn't very informative.
thanks
-- PMM
next prev parent reply other threads:[~2020-03-17 11:58 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-17 11:31 [PATCH] ext4: Give 32bit personalities 32bit hashes Linus Walleij
2020-03-17 11:52 ` Florian Weimer
2020-03-17 12:38 ` Linus Walleij
2020-03-17 11:58 ` Peter Maydell [this message]
2020-03-19 15:13 ` Linus Walleij
2020-03-19 15:25 ` Peter Maydell
2020-03-19 22:23 ` Linus Walleij
2020-03-24 2:34 ` Theodore Y. Ts'o
2020-03-24 9:29 ` Peter Maydell
2020-03-24 18:47 ` Theodore Y. Ts'o
2020-03-24 21:17 ` Linus Walleij
2020-03-17 22:28 ` Andreas Dilger
2020-03-19 15:18 ` Linus Walleij
2020-03-17 22:30 ` Sasha Levin
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