filesystems/ext4/attributes.rst

1 .. SPDX-License-Identifier: GPL-2.0
4 -------------------
17 sb.inode_size = 256, then there are 256 - (128 + 28) = 100 bytes
18 available for in-inode extended attribute storage. The second place
26 Keys are generally assumed to be ASCIIZ strings, whereas values can be
27 strings or binary data.
32 .. list-table::
34    :header-rows: 1
36    * - Offset
37      - Type
38      - Name
39      - Description
40    * - 0x0
41      - __le32
42      - h_magic
43      - Magic number for identification, 0xEA020000. This value is set by the
49 .. list-table::
51    :header-rows: 1
53    * - Offset
54      - Type
55      - Name
56      - Description
57    * - 0x0
58      - __le32
59      - h_magic
60      - Magic number for identification, 0xEA020000.
61    * - 0x4
62      - __le32
63      - h_refcount
64      - Reference count.
65    * - 0x8
66      - __le32
67      - h_blocks
68      - Number of disk blocks used.
69    * - 0xC
70      - __le32
71      - h_hash
72      - Hash value of all attributes.
73    * - 0x10
74      - __le32
75      - h_checksum
76      - Checksum of the extended attribute block.
77    * - 0x14
78      - __u32
79      - h_reserved[3]
80      - Zero.
82 The checksum is calculated against the FS UUID, the 64-bit block number
94 .. list-table::
96    :header-rows: 1
98    * - Offset
99      - Type
100      - Name
101      - Description
102    * - 0x0
103      - __u8
104      - e_name_len
105      - Length of name.
106    * - 0x1
107      - __u8
108      - e_name_index
109      - Attribute name index. There is a discussion of this below.
110    * - 0x2
111      - __le16
112      - e_value_offs
113      - Location of this attribute's value on the disk block where it is stored.
117    * - 0x4
118      - __le32
119      - e_value_inum
120      - The inode where the value is stored. Zero indicates the value is in the
122        INCOMPAT_EA_INODE feature is enabled.
123    * - 0x8
124      - __le32
125      - e_value_size
126      - Length of attribute value.
127    * - 0xC
128      - __le32
129      - e_hash
130      - Hash value of attribute name and attribute value. The kernel doesn't
131        update the hash for in-inode attributes, so for that case this value
132        must be zero, because e2fsck validates any non-zero hash regardless of
134    * - 0x10
135      - char
136      - e_name[e_name_len]
137      - Attribute name. Does not include trailing NULL.
140 be a requirement that they be aligned to 4-byte boundaries. The values
144 filesystem returns -ENOSPC.
153 The keys are assumed to be NULL-terminated strings. To reduce the amount
154 of on-disk space that the keys consume, the beginning of the key string
159 .. list-table::
161    :header-rows: 1
163    * - Name Index
164      - Key Prefix
165    * - 0
166      - (no prefix)
167    * - 1
168      - “user.”
169    * - 2
170      - “system.posix_acl_access”
171    * - 3
172      - “system.posix_acl_default”
173    * - 4
174      - “trusted.”
175    * - 6
176      - “security.”
177    * - 7
178      - “system.” (inline_data only?)
179    * - 8
180      - “system.richacl” (SuSE kernels only?)