We've come across a problem with 6.4 kernels that we didn't have with
6.2 kernels - which involves writing to a symlink that is on a read-only
file system - but the symlink lands on a read-write file system
The following shows the issue:
mkdir -p /mnt/tmp
mount -t tmpfs -o size=1% none /mnt/tmp
rm -f /tmp/file
ln -s /tmp/file /mnt/tmp/file
mount -o remount,ro /mnt/tmp
echo "some text" > /mnt/tmp/file
On a machine with a 6.2 kernel, the above works fine - the target of the
symlink (/tmp/file) is created etc. with no error
But on a machine with a 6.4 kernel, the above fails with:
/mnt/tmp/file: Read-only file system.
Strace'ing a process that fails gives:
open("/mnt/tmp/file", O_WRONLY|O_CREAT|O_TRUNC, 0666) = -1 EROFS
(Read-only file system)
I don't have a machine with a 6.3 kernel, so I'm not sure when the
change in behaviour happened, but does anyone know as to why this change
was made in the kernel?
I've had a look through the kernel changelog - and the following entry
mentions EROFS and read-only file systems:
- [fs] vfs: prefer EEXIST to EROFS when creating on an RO filesystem
(Eric Sandeen) [878091]
I can't access that BZ (878091) entry - so don't know if the above is
anything to do with what I'm seeing ...
Thanks
James Pearson
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