|
From: | Eric Blake |
Subject: | Re: [PATCH] fcntl: Add 32bit filesystem mode |
Date: | Mon, 20 Apr 2020 10:23:46 -0500 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 |
On 4/20/20 10:13 AM, Theodore Y. Ts'o wrote:
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?
Also, POSIX is proposing standardizing FD_CLOFORK, which would be another file descriptor flag worth considering in Linux (Solaris and BSD already have it):
https://www.austingroupbugs.net/view.php?id=1318It will be interesting to find how much code (wrongly) assumes it can use a blind assignment of fcntl(fd, F_SETFD, 1) and thereby accidentally wipes out other existing flags, when it should have instead been doing a read-modify-write to protect flags other than FD_CLOEXEC.
-- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
[Prev in Thread] | Current Thread | [Next in Thread] |