linux-kernel - Re: Changing FAT label of mounted file system

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Date:   Wed, 06 Sep 2017 00:35:10 +0900
From:   OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:     Pali Rohár <pali.rohar@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: Changing FAT label of mounted file system

Pali Rohár <pali.rohar@...il.com> writes:

> Hello!

Hi,

> On most file system it is possible to change its label at anytime, when 
> mounted or unmounted. But FAT is such special file system on which is 
> label stored in two location, plus one is in directory structure (which 
> cannot be modified when file system is mounted).
>
> I would like to ask what about providing FAT specific IOCTL for vfat 
> kernel driver which would allow to change volume label?

I have no objection to add this ioctl though, there is really needs of
apps?

For example, ext4's volume name is sb->s_volume_name, right? And no
ioctl to change it, so I guess the app does read-modify-write
superblock. If so, there is theoretical race with umount and super block
update of ext4 (yes, although updating superblock is rare timing).  So
ext4 is unsafe actually to rewrite volume_name on the mounted fs.

Well, anyway, if there is the patch to add ioctl, again, I have no
objection.

Thanks.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>