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Date: Tue, 6 Feb 2024 12:29:36 -0800
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Subject: Re: [PATCH v2 3/7] fs: FS_IOC_GETUUID
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To: Kent Overstreet <kent.overstreet@linux.dev>, brauner@kernel.org,
 linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: Jan Kara <jack@suse.cz>, Dave Chinner <dchinner@redhat.com>,
 "Darrick J. Wong" <djwong@kernel.org>, Theodore Ts'o <tytso@mit.edu>,
 linux-fsdevel@vger.kernel.or
References: <20240206201858.952303-1-kent.overstreet@linux.dev>
 <20240206201858.952303-4-kent.overstreet@linux.dev>
From: Randy Dunlap <rdunlap@infradead.org>
In-Reply-To: <20240206201858.952303-4-kent.overstreet@linux.dev>
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On 2/6/24 12:18, Kent Overstreet wrote:
> Add a new generic ioctls for querying the filesystem UUID.
> 
> These are lifted versions of the ext4 ioctls, with one change: we're not
> using a flexible array member, because UUIDs will never be more than 16
> bytes.
> 
> This patch adds a generic implementation of FS_IOC_GETFSUUID, which
> reads from super_block->s_uuid. We're not lifting SETFSUUID from ext4 -
> that can be done on offline filesystems by the people who need it,
> trying to do it online is just asking for too much trouble.
> 
> Cc: Christian Brauner <brauner@kernel.org>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Dave Chinner <dchinner@redhat.com>
> Cc: "Darrick J. Wong" <djwong@kernel.org>
> Cc: Theodore Ts'o <tytso@mit.edu>
> Cc: linux-fsdevel@vger.kernel.or
> Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
> ---
>  fs/ioctl.c              | 16 ++++++++++++++++
>  include/uapi/linux/fs.h | 17 +++++++++++++++++
>  2 files changed, 33 insertions(+)
> 


> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index 48ad69f7722e..16a6ecadfd8d 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -64,6 +64,19 @@ struct fstrim_range {
>  	__u64 minlen;
>  };
>  
> +/*
> + * We include a length field because some filesystems (vfat) have an identifier
> + * that we do want to expose as a UUID, but doesn't have the standard length.
> + *
> + * We use a fixed size buffer beacuse this interface will, by fiat, never

                                 because

> + * support "UUIDs" longer than 16 bytes; we don't want to force all downstream
> + * users to have to deal with that.
> + */
> +struct fsuuid2 {
> +	__u8	len;
> +	__u8	uuid[16];
> +};
> +
>  /* extent-same (dedupe) ioctls; these MUST match the btrfs ioctl definitions */
>  #define FILE_DEDUPE_RANGE_SAME		0
>  #define FILE_DEDUPE_RANGE_DIFFERS	1
> @@ -190,6 +203,9 @@ struct fsxattr {
>   * (see uapi/linux/blkzoned.h)
>   */
>  
> +/* Returns the external filesystem UUID, the same one blkid returns */
> +#define FS_IOC_GETFSUUID		_IOR(0x12, 142, struct fsuuid2)
> +
>  #define BMAP_IOCTL 1		/* obsolete - kept for compatibility */
>  #define FIBMAP	   _IO(0x00,1)	/* bmap access */
>  #define FIGETBSZ   _IO(0x00,2)	/* get the block size used for bmap */
> @@ -198,6 +214,7 @@ struct fsxattr {
>  #define FITRIM		_IOWR('X', 121, struct fstrim_range)	/* Trim */
>  #define FICLONE		_IOW(0x94, 9, int)
>  #define FICLONERANGE	_IOW(0x94, 13, struct file_clone_range)
> +
>  #define FIDEDUPERANGE	_IOWR(0x94, 54, struct file_dedupe_range)

Why the additional blank line? (nit)

>  
>  #define FSLABEL_MAX 256	/* Max chars for the interface; each fs may differ */

-- 
#Randy