Re: [PATCH] vfs: ensure mount source is set to "none" if empty string specified
From: Prakash Sangappa
Date: Tue Jul 16 2024 - 19:13:07 EST
> On Jul 15, 2024, at 5:35 AM, Christian Brauner <brauner@xxxxxxxxxx> wrote:
>
>> The issue can be easily reproduced.
>> #mount -t tmpfs "" /tmp/tdir
>> #grep "/tmp/tdir" /proc/$$/mountinfo
>
> The kernel has accepted "" before the new mount api was introduced. So
> the regression was showing "none" when userspace requested "" which got
> fixed. The patch proposed right here would reintroduce the regression:
The commit messages do not indicate that ’none’ caused a regression and was changed back to being empty string again, unless I missed it.
I was under the impression ’none’ was added to address issues with parsing mount entries in /proc/<pid>mountinfo.
Below was a patch proposal describing the parsing issues with libmount and other software because the mount source is empty. Don’t think this patch was merged.
https://patchwork.kernel.org/project/linux-fsdevel/patch/1524109641-45617-1-git-send-email-cofyc.jackson@xxxxxxxxx/
Due to changes in v5.4 timeframe the mount entry started showing ’none’ for source name.
Our Database application ran into an issue with libmount when moving from running on v5.4* kernel to v5.15* kernel version.
>
> (1) 4.15
> root@b1:~# cat /proc/self/mountinfo | grep mnt
> 386 28 0:52 / /mnt rw,relatime shared:223 - tmpfs rw
>
> (2) 5.4
> root@f1:~# cat /proc/self/mountinfo | grep mnt
> 584 31 0:55 / /mnt rw,relatime shared:336 - tmpfs none rw
>
> (3) 6.10-rc6
> root@localhost:~# cat /proc/self/mountinfo | grep mnt
> 62 130 0:60 / /mnt rw,relatime shared:135 - tmpfs rw,inode64