linux-kernel - Re: [PATCH] fs: fat: Make the volume label writable when mounted

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Date:   Sun, 10 Oct 2021 14:18:16 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Martin Kepplinger <martink@...teo.de>
Cc:     OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>, angus@...ea.ca,
        linux-kernel@...r.kernel.org, kay.sievers@...y.org,
        lennart@...ttering.net, harald@...hat.com,
        gregkh@...uxfoundation.org, david@...ar.dk, tytso@....edu,
        alan@...rguk.ukuu.org.uk, akpm@...ux-foundation.org
Subject: Re: [PATCH] fs: fat: Make the volume label writable when mounted

Hello!

On Sunday 10 October 2021 21:06:52 OGAWA Hirofumi wrote:
> > diff --git a/include/uapi/linux/msdos_fs.h b/include/uapi/linux/msdos_fs.h
> > index a5773899f4d9..b666bca09238 100644
> > --- a/include/uapi/linux/msdos_fs.h
> > +++ b/include/uapi/linux/msdos_fs.h
> > @@ -104,6 +104,7 @@ struct __fat_dirent {
> >  #define FAT_IOCTL_SET_ATTRIBUTES	_IOW('r', 0x11, __u32)
> >  /*Android kernel has used 0x12, so we use 0x13*/
> >  #define FAT_IOCTL_GET_VOLUME_ID		_IOR('r', 0x13, __u32)
> > +#define VFAT_IOCTL_SET_LABEL		_IOW('r', 0x14, __u32)
> 
> maybe FAT_IOCTL_SET_LABEL is better.

Please do not introduce a new fs specific ioctls. There is already
vfs-agnostic FS_IOC_SETFSLABEL ioctl, look at manpage:
https://man7.org/linux/man-pages/man2/ioctl_fslabel.2.html

I have WIP patches which adds support for FS_IOC_SETFSLABEL ioctl into
kernel vfat driver. But it is not possible to implement this ioctl
properly until issues with encoding are fixed in vfat driver. Some of
dependency patches I have sent to ML as RFC series:
https://lore.kernel.org/lkml/20210808162453.1653-1-pali@kernel.org/

If you have a time and motivation, I can send you my unfinished WIP
patches which implements FS_IOC_SETFSLABEL ioctl for vfat.