linux-ext4 - Re: [PATCH v2 2/3] ext4: add support for 32-bit default reserved uid and gid values

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Message-ID: <qer3kr5vjietsze72b47gdw5bk3vkb5phulmpzz3pthpgvf3vu@xwvih5oy2ixe>
Date: Wed, 17 Sep 2025 18:10:14 +0200
From: Jan Kara <jack@...e.cz>
To: tytso@....edu
Cc: linux-ext4@...r.kernel.org, linux-api@...r.kernel.org
Subject: Re: [PATCH v2 2/3] ext4: add support for 32-bit default reserved uid
 and gid values

On Tue 16-09-25 23:22:48, Theodore Ts'o via B4 Relay wrote:
> From: Theodore Ts'o <tytso@....edu>
> 
> Support for specifying the default user id and group id that is
> allowed to use the reserved block space was added way back when Linux
> only supported 16-bit uid's and gid's.  (Yeah, that long ago.)  It's
> not a commonly used feature, but let's add support for 32-bit user and
> group id's.
> 
> Signed-off-by: Theodore Ts'o <tytso@....edu>
> ---
>  fs/ext4/ext4.h  | 16 +++++++++++++++-
>  fs/ext4/super.c |  8 ++++----
>  2 files changed, 19 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 01a6e2de7fc3ef0e20b039d3200b9c9bd656f59f..4bfcd5f0c74fda30db4009ee28fbee00a2f6b76f 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1442,7 +1442,9 @@ struct ext4_super_block {
>  	__le16  s_encoding;		/* Filename charset encoding */
>  	__le16  s_encoding_flags;	/* Filename charset encoding flags */
>  	__le32  s_orphan_file_inum;	/* Inode for tracking orphan inodes */
> -	__le32	s_reserved[94];		/* Padding to the end of the block */
> +	__le16	s_def_resuid_hi;
> +	__le16	s_def_resgid_hi;
> +	__le32	s_reserved[93];		/* Padding to the end of the block */
>  	__le32	s_checksum;		/* crc32c(superblock) */
>  };
>  
> @@ -1812,6 +1814,18 @@ static inline int ext4_valid_inum(struct super_block *sb, unsigned long ino)
>  		 ino <= le32_to_cpu(EXT4_SB(sb)->s_es->s_inodes_count));
>  }
>  
> +static inline int ext4_get_resuid(struct ext4_super_block *es)
> +{
> +	return(le16_to_cpu(es->s_def_resuid) |
> +	       (le16_to_cpu(es->s_def_resuid_hi) << 16));
> +}

I'd prefer a style like:

	return le16_to_cpu(es->s_def_resuid) |
	       (le16_to_cpu(es->s_def_resuid_hi) << 16);

but whatever...

> @@ -5270,8 +5270,8 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
>  
>  	ext4_set_def_opts(sb, es);
>  
> -	sbi->s_resuid = make_kuid(&init_user_ns, le16_to_cpu(es->s_def_resuid));
> -	sbi->s_resgid = make_kgid(&init_user_ns, le16_to_cpu(es->s_def_resgid));
> +	sbi->s_resuid = make_kuid(&init_user_ns, ext4_get_resuid(es));
> +	sbi->s_resgid = make_kgid(&init_user_ns, ext4_get_resuid(es));
						^^^^ ext4_get_resgid() here.

>  	sbi->s_commit_interval = JBD2_DEFAULT_MAX_COMMIT_AGE * HZ;
>  	sbi->s_min_batch_time = EXT4_DEF_MIN_BATCH_TIME;
>  	sbi->s_max_batch_time = EXT4_DEF_MAX_BATCH_TIME;

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR