Documentation: ext4: Add fields to ext4_super_block documentation

Documentation and implementation of the ext4 super block have
slightly diverged: Padding has been removed in order to make room for
new fields that are still missing in the documentation.

Add the new fields s_encryption_level, s_first_error_errorcode,
s_last_error_errorcode to the documentation of the ext4 super block.

Fixes: f542fbe8d5 ("ext4 crypto: reserve codepoints used by the ext4 encryption feature")
Fixes: 878520ac45 ("ext4: save the error code which triggered an ext4_error() in the superblock")

Signed-off-by: Tom Vierjahn <tom.vierjahn@acm.org>
Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Link: https://patch.msgid.link/20250324221004.5268-1-tom.vierjahn@acm.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Documentation/filesystems/ext4/super.rst

@@ -328,9 +328,13 @@ The ext4 superblock is laid out as follows in
      - s_checksum_type
      - Metadata checksum algorithm type. The only valid value is 1 (crc32c).
    * - 0x176
-     - __le16
-     - s_reserved_pad
-     -
+     - \_\_u8
+     - s\_encryption\_level
+     - Versioning level for encryption.
+   * - 0x177
+     - \_\_u8
+     - s\_reserved\_pad
+     - Padding to next 32bits.
    * - 0x178
      - __le64
      - s_kbytes_written
@@ -466,9 +470,13 @@ The ext4 superblock is laid out as follows in
      - s_last_error_time_hi
      - Upper 8 bits of the s_last_error_time field.
    * - 0x27A
-     - __u8
-     - s_pad[2]
-     - Zero padding.
+     - \_\_u8
+     - s\_first\_error\_errcode
+     -
+   * - 0x27B
+     - \_\_u8
+     - s\_last\_error\_errcode
+     -
    * - 0x27C
      - __le16
      - s_encoding