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Re: [PATCH] ext4: Give 32bit personalities 32bit hashes
From: |
Peter Maydell |
Subject: |
Re: [PATCH] ext4: Give 32bit personalities 32bit hashes |
Date: |
Tue, 17 Mar 2020 11:58:09 +0000 |
On Tue, 17 Mar 2020 at 11:31, Linus Walleij <address@hidden> 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
- [PATCH] ext4: Give 32bit personalities 32bit hashes, Linus Walleij, 2020/03/17
- Re: [PATCH] ext4: Give 32bit personalities 32bit hashes, Florian Weimer, 2020/03/17
- Re: [PATCH] ext4: Give 32bit personalities 32bit hashes,
Peter Maydell <=
- Re: [PATCH] ext4: Give 32bit personalities 32bit hashes, Linus Walleij, 2020/03/19
- Re: [PATCH] ext4: Give 32bit personalities 32bit hashes, Peter Maydell, 2020/03/19
- Re: [PATCH] ext4: Give 32bit personalities 32bit hashes, Linus Walleij, 2020/03/19
- Re: [PATCH] ext4: Give 32bit personalities 32bit hashes, Theodore Y. Ts'o, 2020/03/23
- Re: [PATCH] ext4: Give 32bit personalities 32bit hashes, Peter Maydell, 2020/03/24
- Re: [PATCH] ext4: Give 32bit personalities 32bit hashes, Theodore Y. Ts'o, 2020/03/24
- Re: [PATCH] ext4: Give 32bit personalities 32bit hashes, Linus Walleij, 2020/03/24
Re: [PATCH] ext4: Give 32bit personalities 32bit hashes, Andreas Dilger, 2020/03/17