EROFS ("Read-only file system") error is incorretly returned when trying to open already existing file with 'O_CREAT' on a read-only filesystem

04시 25분 2013년 10월 18일 업데이트

문제

¶If given path ends up with a file/symlink residing on a read-only filesystem, an attempt to issue open with that path and 'O_CREAT' flag results in EROFS ("Read-only file system").

¶This affects in particular:
* regular files
* symlinks
* device nodes
* bind mounts

환경

Red Hat Enterprise Linux 6

해결

¶Update to kernel version 2.6.32-358.10.1.el6 or later. See RHSA-2013:0911 for more details.

근본 원인

¶A bug in the do_filp_open() function caused it to exit early if any write access was requested on a read-only file system. This prevented the opening of device nodes on a read-only file system. With this update, the do_filp_open() has been fixed to no longer exit if a write request is made on a read-only file system.

¶The problem has been tracked in Bugzilla #920752.

진단 단계

¶Example steps to confirm this behaviour:

prepare a filesystem:

dd if=/dev/zero of=foo bs=1M count=10
losetup -vf foo
mkfs.ext3 /dev/loop0
mount /dev/loop0 /mnt
mknod /mnt/null c 1 3
umount /mnt

mount the filesystem read-only: mount -o ro /dev/loop0 /mnt
Try to write to the filesystem: echo foo >> /mnt/null

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