From: Theodore Ts'o <tytso@mit.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@mit.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));
+}

@@ -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));