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Date:   Sun, 10 Oct 2021 14:36:39 +0200
From:   Pali =?utf-8?B?Um9ow6Fy?= <pali@kernel.org>
To:     Martin Kepplinger <martink@posteo.de>
Cc:     OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>, angus@akkea.ca,
        linux-kernel@vger.kernel.org, kay.sievers@vrfy.org,
        lennart@poettering.net, gregkh@linuxfoundation.org, david@fubar.dk,
        tytso@mit.edu, alan@lxorguk.ukuu.org.uk, akpm@linux-foundation.org
Subject: Re: [PATCH] fs: fat: Make the volume label writable when mounted
Message-ID: <20211010123639.ubjvilz5fe3nlmau@pali>
References: <20211007095639.5002-1-martink@posteo.de>
 <874k9pccdf.fsf@mail.parknet.co.jp>
 <20211010121816.fdvn6uiiteszbnql@pali>
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On Sunday 10 October 2021 14:18:16 Pali Rohár wrote:
> 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/

Also look at important details about encoding in discussion:
https://lore.kernel.org/lkml/20200107231522.GC472641@magnolia/

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