1 .. SPDX-License-Identifier: GPL-2.0 1 .. SPDX-License-Identifier: GPL-2.0
2 2
3 Index Nodes 3 Index Nodes
4 ----------- 4 -----------
5 5
6 In a regular UNIX filesystem, the inode stores 6 In a regular UNIX filesystem, the inode stores all the metadata
7 pertaining to the file (time stamps, block map 7 pertaining to the file (time stamps, block maps, extended attributes,
8 etc), not the directory entry. To find the inf 8 etc), not the directory entry. To find the information associated with a
9 file, one must traverse the directory files to 9 file, one must traverse the directory files to find the directory entry
10 associated with a file, then load the inode to 10 associated with a file, then load the inode to find the metadata for
11 that file. ext4 appears to cheat (for performa 11 that file. ext4 appears to cheat (for performance reasons) a little bit
12 by storing a copy of the file type (normally s 12 by storing a copy of the file type (normally stored in the inode) in the
13 directory entry. (Compare all this to FAT, whi 13 directory entry. (Compare all this to FAT, which stores all the file
14 information directly in the directory entry, b 14 information directly in the directory entry, but does not support hard
15 links and is in general more seek-happy than e 15 links and is in general more seek-happy than ext4 due to its simpler
16 block allocator and extensive use of linked li 16 block allocator and extensive use of linked lists.)
17 17
18 The inode table is a linear array of ``struct 18 The inode table is a linear array of ``struct ext4_inode``. The table is
19 sized to have enough blocks to store at least 19 sized to have enough blocks to store at least
20 ``sb.s_inode_size * sb.s_inodes_per_group`` by 20 ``sb.s_inode_size * sb.s_inodes_per_group`` bytes. The number of the
21 block group containing an inode can be calcula 21 block group containing an inode can be calculated as
22 ``(inode_number - 1) / sb.s_inodes_per_group`` 22 ``(inode_number - 1) / sb.s_inodes_per_group``, and the offset into the
23 group's table is ``(inode_number - 1) % sb.s_i 23 group's table is ``(inode_number - 1) % sb.s_inodes_per_group``. There
24 is no inode 0. 24 is no inode 0.
25 25
26 The inode checksum is calculated against the F 26 The inode checksum is calculated against the FS UUID, the inode number,
27 and the inode structure itself. 27 and the inode structure itself.
28 28
29 The inode table entry is laid out in ``struct 29 The inode table entry is laid out in ``struct ext4_inode``.
30 30
31 .. list-table:: 31 .. list-table::
32 :widths: 8 8 24 40 32 :widths: 8 8 24 40
33 :header-rows: 1 33 :header-rows: 1
34 :class: longtable 34 :class: longtable
35 35
36 * - Offset 36 * - Offset
37 - Size 37 - Size
38 - Name 38 - Name
39 - Description 39 - Description
40 * - 0x0 40 * - 0x0
41 - __le16 41 - __le16
42 - i_mode 42 - i_mode
43 - File mode. See the table i_mode_ below. 43 - File mode. See the table i_mode_ below.
44 * - 0x2 44 * - 0x2
45 - __le16 45 - __le16
46 - i_uid 46 - i_uid
47 - Lower 16-bits of Owner UID. 47 - Lower 16-bits of Owner UID.
48 * - 0x4 48 * - 0x4
49 - __le32 49 - __le32
50 - i_size_lo 50 - i_size_lo
51 - Lower 32-bits of size in bytes. 51 - Lower 32-bits of size in bytes.
52 * - 0x8 52 * - 0x8
53 - __le32 53 - __le32
54 - i_atime 54 - i_atime
55 - Last access time, in seconds since the 55 - Last access time, in seconds since the epoch. However, if the EA_INODE
56 inode flag is set, this inode stores an 56 inode flag is set, this inode stores an extended attribute value and
57 this field contains the checksum of the 57 this field contains the checksum of the value.
58 * - 0xC 58 * - 0xC
59 - __le32 59 - __le32
60 - i_ctime 60 - i_ctime
61 - Last inode change time, in seconds sinc 61 - Last inode change time, in seconds since the epoch. However, if the
62 EA_INODE inode flag is set, this inode 62 EA_INODE inode flag is set, this inode stores an extended attribute
63 value and this field contains the lower 63 value and this field contains the lower 32 bits of the attribute value's
64 reference count. 64 reference count.
65 * - 0x10 65 * - 0x10
66 - __le32 66 - __le32
67 - i_mtime 67 - i_mtime
68 - Last data modification time, in seconds 68 - Last data modification time, in seconds since the epoch. However, if the
69 EA_INODE inode flag is set, this inode 69 EA_INODE inode flag is set, this inode stores an extended attribute
70 value and this field contains the numbe 70 value and this field contains the number of the inode that owns the
71 extended attribute. 71 extended attribute.
72 * - 0x14 72 * - 0x14
73 - __le32 73 - __le32
74 - i_dtime 74 - i_dtime
75 - Deletion Time, in seconds since the epo 75 - Deletion Time, in seconds since the epoch.
76 * - 0x18 76 * - 0x18
77 - __le16 77 - __le16
78 - i_gid 78 - i_gid
79 - Lower 16-bits of GID. 79 - Lower 16-bits of GID.
80 * - 0x1A 80 * - 0x1A
81 - __le16 81 - __le16
82 - i_links_count 82 - i_links_count
83 - Hard link count. Normally, ext4 does no 83 - Hard link count. Normally, ext4 does not permit an inode to have more
84 than 65,000 hard links. This applies to 84 than 65,000 hard links. This applies to files as well as directories,
85 which means that there cannot be more t 85 which means that there cannot be more than 64,998 subdirectories in a
86 directory (each subdirectory's '..' ent 86 directory (each subdirectory's '..' entry counts as a hard link, as does
87 the '.' entry in the directory itself). 87 the '.' entry in the directory itself). With the DIR_NLINK feature
88 enabled, ext4 supports more than 64,998 88 enabled, ext4 supports more than 64,998 subdirectories by setting this
89 field to 1 to indicate that the number 89 field to 1 to indicate that the number of hard links is not known.
90 * - 0x1C 90 * - 0x1C
91 - __le32 91 - __le32
92 - i_blocks_lo 92 - i_blocks_lo
93 - Lower 32-bits of “block” count. If 93 - Lower 32-bits of “block” count. If the huge_file feature flag is not
94 set on the filesystem, the file consume 94 set on the filesystem, the file consumes ``i_blocks_lo`` 512-byte blocks
95 on disk. If huge_file is set and EXT4_H 95 on disk. If huge_file is set and EXT4_HUGE_FILE_FL is NOT set in
96 ``inode.i_flags``, then the file consum 96 ``inode.i_flags``, then the file consumes ``i_blocks_lo + (i_blocks_hi
97 << 32)`` 512-byte blocks on disk. If hu 97 << 32)`` 512-byte blocks on disk. If huge_file is set and
98 EXT4_HUGE_FILE_FL IS set in ``inode.i_f 98 EXT4_HUGE_FILE_FL IS set in ``inode.i_flags``, then this file
99 consumes (``i_blocks_lo + i_blocks_hi`` 99 consumes (``i_blocks_lo + i_blocks_hi`` << 32) filesystem blocks on
100 disk. 100 disk.
101 * - 0x20 101 * - 0x20
102 - __le32 102 - __le32
103 - i_flags 103 - i_flags
104 - Inode flags. See the table i_flags_ bel 104 - Inode flags. See the table i_flags_ below.
105 * - 0x24 105 * - 0x24
106 - 4 bytes 106 - 4 bytes
107 - i_osd1 107 - i_osd1
108 - See the table i_osd1_ for more details. 108 - See the table i_osd1_ for more details.
109 * - 0x28 109 * - 0x28
110 - 60 bytes 110 - 60 bytes
111 - i_block[EXT4_N_BLOCKS=15] 111 - i_block[EXT4_N_BLOCKS=15]
112 - Block map or extent tree. See the secti 112 - Block map or extent tree. See the section “The Contents of inode.i_block”.
113 * - 0x64 113 * - 0x64
114 - __le32 114 - __le32
115 - i_generation 115 - i_generation
116 - File version (for NFS). 116 - File version (for NFS).
117 * - 0x68 117 * - 0x68
118 - __le32 118 - __le32
119 - i_file_acl_lo 119 - i_file_acl_lo
120 - Lower 32-bits of extended attribute blo 120 - Lower 32-bits of extended attribute block. ACLs are of course one of
121 many possible extended attributes; I th 121 many possible extended attributes; I think the name of this field is a
122 result of the first use of extended att 122 result of the first use of extended attributes being for ACLs.
123 * - 0x6C 123 * - 0x6C
124 - __le32 124 - __le32
125 - i_size_high / i_dir_acl 125 - i_size_high / i_dir_acl
126 - Upper 32-bits of file/directory size. I 126 - Upper 32-bits of file/directory size. In ext2/3 this field was named
127 i_dir_acl, though it was usually set to 127 i_dir_acl, though it was usually set to zero and never used.
128 * - 0x70 128 * - 0x70
129 - __le32 129 - __le32
130 - i_obso_faddr 130 - i_obso_faddr
131 - (Obsolete) fragment address. 131 - (Obsolete) fragment address.
132 * - 0x74 132 * - 0x74
133 - 12 bytes 133 - 12 bytes
134 - i_osd2 134 - i_osd2
135 - See the table i_osd2_ for more details. 135 - See the table i_osd2_ for more details.
136 * - 0x80 136 * - 0x80
137 - __le16 137 - __le16
138 - i_extra_isize 138 - i_extra_isize
139 - Size of this inode - 128. Alternately, 139 - Size of this inode - 128. Alternately, the size of the extended inode
140 fields beyond the original ext2 inode, 140 fields beyond the original ext2 inode, including this field.
141 * - 0x82 141 * - 0x82
142 - __le16 142 - __le16
143 - i_checksum_hi 143 - i_checksum_hi
144 - Upper 16-bits of the inode checksum. 144 - Upper 16-bits of the inode checksum.
145 * - 0x84 145 * - 0x84
146 - __le32 146 - __le32
147 - i_ctime_extra 147 - i_ctime_extra
148 - Extra change time bits. This provides s 148 - Extra change time bits. This provides sub-second precision. See Inode
149 Timestamps section. 149 Timestamps section.
150 * - 0x88 150 * - 0x88
151 - __le32 151 - __le32
152 - i_mtime_extra 152 - i_mtime_extra
153 - Extra modification time bits. This prov 153 - Extra modification time bits. This provides sub-second precision.
154 * - 0x8C 154 * - 0x8C
155 - __le32 155 - __le32
156 - i_atime_extra 156 - i_atime_extra
157 - Extra access time bits. This provides s 157 - Extra access time bits. This provides sub-second precision.
158 * - 0x90 158 * - 0x90
159 - __le32 159 - __le32
160 - i_crtime 160 - i_crtime
161 - File creation time, in seconds since th 161 - File creation time, in seconds since the epoch.
162 * - 0x94 162 * - 0x94
163 - __le32 163 - __le32
164 - i_crtime_extra 164 - i_crtime_extra
165 - Extra file creation time bits. This pro 165 - Extra file creation time bits. This provides sub-second precision.
166 * - 0x98 166 * - 0x98
167 - __le32 167 - __le32
168 - i_version_hi 168 - i_version_hi
169 - Upper 32-bits for version number. 169 - Upper 32-bits for version number.
170 * - 0x9C 170 * - 0x9C
171 - __le32 171 - __le32
172 - i_projid 172 - i_projid
173 - Project ID. 173 - Project ID.
174 174
175 .. _i_mode: 175 .. _i_mode:
176 176
177 The ``i_mode`` value is a combination of the f 177 The ``i_mode`` value is a combination of the following flags:
178 178
179 .. list-table:: 179 .. list-table::
180 :widths: 16 64 180 :widths: 16 64
181 :header-rows: 1 181 :header-rows: 1
182 182
183 * - Value 183 * - Value
184 - Description 184 - Description
185 * - 0x1 185 * - 0x1
186 - S_IXOTH (Others may execute) 186 - S_IXOTH (Others may execute)
187 * - 0x2 187 * - 0x2
188 - S_IWOTH (Others may write) 188 - S_IWOTH (Others may write)
189 * - 0x4 189 * - 0x4
190 - S_IROTH (Others may read) 190 - S_IROTH (Others may read)
191 * - 0x8 191 * - 0x8
192 - S_IXGRP (Group members may execute) 192 - S_IXGRP (Group members may execute)
193 * - 0x10 193 * - 0x10
194 - S_IWGRP (Group members may write) 194 - S_IWGRP (Group members may write)
195 * - 0x20 195 * - 0x20
196 - S_IRGRP (Group members may read) 196 - S_IRGRP (Group members may read)
197 * - 0x40 197 * - 0x40
198 - S_IXUSR (Owner may execute) 198 - S_IXUSR (Owner may execute)
199 * - 0x80 199 * - 0x80
200 - S_IWUSR (Owner may write) 200 - S_IWUSR (Owner may write)
201 * - 0x100 201 * - 0x100
202 - S_IRUSR (Owner may read) 202 - S_IRUSR (Owner may read)
203 * - 0x200 203 * - 0x200
204 - S_ISVTX (Sticky bit) 204 - S_ISVTX (Sticky bit)
205 * - 0x400 205 * - 0x400
206 - S_ISGID (Set GID) 206 - S_ISGID (Set GID)
207 * - 0x800 207 * - 0x800
208 - S_ISUID (Set UID) 208 - S_ISUID (Set UID)
209 * - 209 * -
210 - These are mutually-exclusive file types 210 - These are mutually-exclusive file types:
211 * - 0x1000 211 * - 0x1000
212 - S_IFIFO (FIFO) 212 - S_IFIFO (FIFO)
213 * - 0x2000 213 * - 0x2000
214 - S_IFCHR (Character device) 214 - S_IFCHR (Character device)
215 * - 0x4000 215 * - 0x4000
216 - S_IFDIR (Directory) 216 - S_IFDIR (Directory)
217 * - 0x6000 217 * - 0x6000
218 - S_IFBLK (Block device) 218 - S_IFBLK (Block device)
219 * - 0x8000 219 * - 0x8000
220 - S_IFREG (Regular file) 220 - S_IFREG (Regular file)
221 * - 0xA000 221 * - 0xA000
222 - S_IFLNK (Symbolic link) 222 - S_IFLNK (Symbolic link)
223 * - 0xC000 223 * - 0xC000
224 - S_IFSOCK (Socket) 224 - S_IFSOCK (Socket)
225 225
226 .. _i_flags: 226 .. _i_flags:
227 227
228 The ``i_flags`` field is a combination of thes 228 The ``i_flags`` field is a combination of these values:
229 229
230 .. list-table:: 230 .. list-table::
231 :widths: 16 64 231 :widths: 16 64
232 :header-rows: 1 232 :header-rows: 1
233 233
234 * - Value 234 * - Value
235 - Description 235 - Description
236 * - 0x1 236 * - 0x1
237 - This file requires secure deletion (EXT 237 - This file requires secure deletion (EXT4_SECRM_FL). (not implemented)
238 * - 0x2 238 * - 0x2
239 - This file should be preserved, should u 239 - This file should be preserved, should undeletion be desired
240 (EXT4_UNRM_FL). (not implemented) 240 (EXT4_UNRM_FL). (not implemented)
241 * - 0x4 241 * - 0x4
242 - File is compressed (EXT4_COMPR_FL). (no 242 - File is compressed (EXT4_COMPR_FL). (not really implemented)
243 * - 0x8 243 * - 0x8
244 - All writes to the file must be synchron 244 - All writes to the file must be synchronous (EXT4_SYNC_FL).
245 * - 0x10 245 * - 0x10
246 - File is immutable (EXT4_IMMUTABLE_FL). 246 - File is immutable (EXT4_IMMUTABLE_FL).
247 * - 0x20 247 * - 0x20
248 - File can only be appended (EXT4_APPEND_ 248 - File can only be appended (EXT4_APPEND_FL).
249 * - 0x40 249 * - 0x40
250 - The dump(1) utility should not dump thi 250 - The dump(1) utility should not dump this file (EXT4_NODUMP_FL).
251 * - 0x80 251 * - 0x80
252 - Do not update access time (EXT4_NOATIME 252 - Do not update access time (EXT4_NOATIME_FL).
253 * - 0x100 253 * - 0x100
254 - Dirty compressed file (EXT4_DIRTY_FL). 254 - Dirty compressed file (EXT4_DIRTY_FL). (not used)
255 * - 0x200 255 * - 0x200
256 - File has one or more compressed cluster 256 - File has one or more compressed clusters (EXT4_COMPRBLK_FL). (not used)
257 * - 0x400 257 * - 0x400
258 - Do not compress file (EXT4_NOCOMPR_FL). 258 - Do not compress file (EXT4_NOCOMPR_FL). (not used)
259 * - 0x800 259 * - 0x800
260 - Encrypted inode (EXT4_ENCRYPT_FL). This 260 - Encrypted inode (EXT4_ENCRYPT_FL). This bit value previously was
261 EXT4_ECOMPR_FL (compression error), whi 261 EXT4_ECOMPR_FL (compression error), which was never used.
262 * - 0x1000 262 * - 0x1000
263 - Directory has hashed indexes (EXT4_INDE 263 - Directory has hashed indexes (EXT4_INDEX_FL).
264 * - 0x2000 264 * - 0x2000
265 - AFS magic directory (EXT4_IMAGIC_FL). 265 - AFS magic directory (EXT4_IMAGIC_FL).
266 * - 0x4000 266 * - 0x4000
267 - File data must always be written throug 267 - File data must always be written through the journal
268 (EXT4_JOURNAL_DATA_FL). 268 (EXT4_JOURNAL_DATA_FL).
269 * - 0x8000 269 * - 0x8000
270 - File tail should not be merged (EXT4_NO 270 - File tail should not be merged (EXT4_NOTAIL_FL). (not used by ext4)
271 * - 0x10000 271 * - 0x10000
272 - All directory entry data should be writ 272 - All directory entry data should be written synchronously (see
273 ``dirsync``) (EXT4_DIRSYNC_FL). 273 ``dirsync``) (EXT4_DIRSYNC_FL).
274 * - 0x20000 274 * - 0x20000
275 - Top of directory hierarchy (EXT4_TOPDIR 275 - Top of directory hierarchy (EXT4_TOPDIR_FL).
276 * - 0x40000 276 * - 0x40000
277 - This is a huge file (EXT4_HUGE_FILE_FL) 277 - This is a huge file (EXT4_HUGE_FILE_FL).
278 * - 0x80000 278 * - 0x80000
279 - Inode uses extents (EXT4_EXTENTS_FL). 279 - Inode uses extents (EXT4_EXTENTS_FL).
280 * - 0x100000 280 * - 0x100000
281 - Verity protected file (EXT4_VERITY_FL). 281 - Verity protected file (EXT4_VERITY_FL).
282 * - 0x200000 282 * - 0x200000
283 - Inode stores a large extended attribute 283 - Inode stores a large extended attribute value in its data blocks
284 (EXT4_EA_INODE_FL). 284 (EXT4_EA_INODE_FL).
285 * - 0x400000 285 * - 0x400000
286 - This file has blocks allocated past EOF 286 - This file has blocks allocated past EOF (EXT4_EOFBLOCKS_FL).
287 (deprecated) 287 (deprecated)
288 * - 0x01000000 288 * - 0x01000000
289 - Inode is a snapshot (``EXT4_SNAPFILE_FL 289 - Inode is a snapshot (``EXT4_SNAPFILE_FL``). (not in mainline)
290 * - 0x04000000 290 * - 0x04000000
291 - Snapshot is being deleted (``EXT4_SNAPF 291 - Snapshot is being deleted (``EXT4_SNAPFILE_DELETED_FL``). (not in
292 mainline) 292 mainline)
293 * - 0x08000000 293 * - 0x08000000
294 - Snapshot shrink has completed (``EXT4_S 294 - Snapshot shrink has completed (``EXT4_SNAPFILE_SHRUNK_FL``). (not in
295 mainline) 295 mainline)
296 * - 0x10000000 296 * - 0x10000000
297 - Inode has inline data (EXT4_INLINE_DATA 297 - Inode has inline data (EXT4_INLINE_DATA_FL).
298 * - 0x20000000 298 * - 0x20000000
299 - Create children with the same project I 299 - Create children with the same project ID (EXT4_PROJINHERIT_FL).
300 * - 0x80000000 300 * - 0x80000000
301 - Reserved for ext4 library (EXT4_RESERVE 301 - Reserved for ext4 library (EXT4_RESERVED_FL).
302 * - 302 * -
303 - Aggregate flags: 303 - Aggregate flags:
304 * - 0x705BDFFF 304 * - 0x705BDFFF
305 - User-visible flags. 305 - User-visible flags.
306 * - 0x604BC0FF 306 * - 0x604BC0FF
307 - User-modifiable flags. Note that while 307 - User-modifiable flags. Note that while EXT4_JOURNAL_DATA_FL and
308 EXT4_EXTENTS_FL can be set with setattr 308 EXT4_EXTENTS_FL can be set with setattr, they are not in the kernel's
309 EXT4_FL_USER_MODIFIABLE mask, since it 309 EXT4_FL_USER_MODIFIABLE mask, since it needs to handle the setting of
310 these flags in a special manner and the 310 these flags in a special manner and they are masked out of the set of
311 flags that are saved directly to i_flag 311 flags that are saved directly to i_flags.
312 312
313 .. _i_osd1: 313 .. _i_osd1:
314 314
315 The ``osd1`` field has multiple meanings depen 315 The ``osd1`` field has multiple meanings depending on the creator:
316 316
317 Linux: 317 Linux:
318 318
319 .. list-table:: 319 .. list-table::
320 :widths: 8 8 24 40 320 :widths: 8 8 24 40
321 :header-rows: 1 321 :header-rows: 1
322 322
323 * - Offset 323 * - Offset
324 - Size 324 - Size
325 - Name 325 - Name
326 - Description 326 - Description
327 * - 0x0 327 * - 0x0
328 - __le32 328 - __le32
329 - l_i_version 329 - l_i_version
330 - Inode version. However, if the EA_INODE 330 - Inode version. However, if the EA_INODE inode flag is set, this inode
331 stores an extended attribute value and 331 stores an extended attribute value and this field contains the upper 32
332 bits of the attribute value's reference 332 bits of the attribute value's reference count.
333 333
334 Hurd: 334 Hurd:
335 335
336 .. list-table:: 336 .. list-table::
337 :widths: 8 8 24 40 337 :widths: 8 8 24 40
338 :header-rows: 1 338 :header-rows: 1
339 339
340 * - Offset 340 * - Offset
341 - Size 341 - Size
342 - Name 342 - Name
343 - Description 343 - Description
344 * - 0x0 344 * - 0x0
345 - __le32 345 - __le32
346 - h_i_translator 346 - h_i_translator
347 - ?? 347 - ??
348 348
349 Masix: 349 Masix:
350 350
351 .. list-table:: 351 .. list-table::
352 :widths: 8 8 24 40 352 :widths: 8 8 24 40
353 :header-rows: 1 353 :header-rows: 1
354 354
355 * - Offset 355 * - Offset
356 - Size 356 - Size
357 - Name 357 - Name
358 - Description 358 - Description
359 * - 0x0 359 * - 0x0
360 - __le32 360 - __le32
361 - m_i_reserved 361 - m_i_reserved
362 - ?? 362 - ??
363 363
364 .. _i_osd2: 364 .. _i_osd2:
365 365
366 The ``osd2`` field has multiple meanings depen 366 The ``osd2`` field has multiple meanings depending on the filesystem creator:
367 367
368 Linux: 368 Linux:
369 369
370 .. list-table:: 370 .. list-table::
371 :widths: 8 8 24 40 371 :widths: 8 8 24 40
372 :header-rows: 1 372 :header-rows: 1
373 373
374 * - Offset 374 * - Offset
375 - Size 375 - Size
376 - Name 376 - Name
377 - Description 377 - Description
378 * - 0x0 378 * - 0x0
379 - __le16 379 - __le16
380 - l_i_blocks_high 380 - l_i_blocks_high
381 - Upper 16-bits of the block count. Pleas 381 - Upper 16-bits of the block count. Please see the note attached to
382 i_blocks_lo. 382 i_blocks_lo.
383 * - 0x2 383 * - 0x2
384 - __le16 384 - __le16
385 - l_i_file_acl_high 385 - l_i_file_acl_high
386 - Upper 16-bits of the extended attribute 386 - Upper 16-bits of the extended attribute block (historically, the file
387 ACL location). See the Extended Attribu 387 ACL location). See the Extended Attributes section below.
388 * - 0x4 388 * - 0x4
389 - __le16 389 - __le16
390 - l_i_uid_high 390 - l_i_uid_high
391 - Upper 16-bits of the Owner UID. 391 - Upper 16-bits of the Owner UID.
392 * - 0x6 392 * - 0x6
393 - __le16 393 - __le16
394 - l_i_gid_high 394 - l_i_gid_high
395 - Upper 16-bits of the GID. 395 - Upper 16-bits of the GID.
396 * - 0x8 396 * - 0x8
397 - __le16 397 - __le16
398 - l_i_checksum_lo 398 - l_i_checksum_lo
399 - Lower 16-bits of the inode checksum. 399 - Lower 16-bits of the inode checksum.
400 * - 0xA 400 * - 0xA
401 - __le16 401 - __le16
402 - l_i_reserved 402 - l_i_reserved
403 - Unused. 403 - Unused.
404 404
405 Hurd: 405 Hurd:
406 406
407 .. list-table:: 407 .. list-table::
408 :widths: 8 8 24 40 408 :widths: 8 8 24 40
409 :header-rows: 1 409 :header-rows: 1
410 410
411 * - Offset 411 * - Offset
412 - Size 412 - Size
413 - Name 413 - Name
414 - Description 414 - Description
415 * - 0x0 415 * - 0x0
416 - __le16 416 - __le16
417 - h_i_reserved1 417 - h_i_reserved1
418 - ?? 418 - ??
419 * - 0x2 419 * - 0x2
420 - __u16 420 - __u16
421 - h_i_mode_high 421 - h_i_mode_high
422 - Upper 16-bits of the file mode. 422 - Upper 16-bits of the file mode.
423 * - 0x4 423 * - 0x4
424 - __le16 424 - __le16
425 - h_i_uid_high 425 - h_i_uid_high
426 - Upper 16-bits of the Owner UID. 426 - Upper 16-bits of the Owner UID.
427 * - 0x6 427 * - 0x6
428 - __le16 428 - __le16
429 - h_i_gid_high 429 - h_i_gid_high
430 - Upper 16-bits of the GID. 430 - Upper 16-bits of the GID.
431 * - 0x8 431 * - 0x8
432 - __u32 432 - __u32
433 - h_i_author 433 - h_i_author
434 - Author code? 434 - Author code?
435 435
436 Masix: 436 Masix:
437 437
438 .. list-table:: 438 .. list-table::
439 :widths: 8 8 24 40 439 :widths: 8 8 24 40
440 :header-rows: 1 440 :header-rows: 1
441 441
442 * - Offset 442 * - Offset
443 - Size 443 - Size
444 - Name 444 - Name
445 - Description 445 - Description
446 * - 0x0 446 * - 0x0
447 - __le16 447 - __le16
448 - h_i_reserved1 448 - h_i_reserved1
449 - ?? 449 - ??
450 * - 0x2 450 * - 0x2
451 - __u16 451 - __u16
452 - m_i_file_acl_high 452 - m_i_file_acl_high
453 - Upper 16-bits of the extended attribute 453 - Upper 16-bits of the extended attribute block (historically, the file
454 ACL location). 454 ACL location).
455 * - 0x4 455 * - 0x4
456 - __u32 456 - __u32
457 - m_i_reserved2[2] 457 - m_i_reserved2[2]
458 - ?? 458 - ??
459 459
460 Inode Size 460 Inode Size
461 ~~~~~~~~~~ 461 ~~~~~~~~~~
462 462
463 In ext2 and ext3, the inode structure size was 463 In ext2 and ext3, the inode structure size was fixed at 128 bytes
464 (``EXT2_GOOD_OLD_INODE_SIZE``) and each inode 464 (``EXT2_GOOD_OLD_INODE_SIZE``) and each inode had a disk record size of
465 128 bytes. Starting with ext4, it is possible 465 128 bytes. Starting with ext4, it is possible to allocate a larger
466 on-disk inode at format time for all inodes in 466 on-disk inode at format time for all inodes in the filesystem to provide
467 space beyond the end of the original ext2 inod 467 space beyond the end of the original ext2 inode. The on-disk inode
468 record size is recorded in the superblock as ` 468 record size is recorded in the superblock as ``s_inode_size``. The
469 number of bytes actually used by struct ext4_i 469 number of bytes actually used by struct ext4_inode beyond the original
470 128-byte ext2 inode is recorded in the ``i_ext 470 128-byte ext2 inode is recorded in the ``i_extra_isize`` field for each
471 inode, which allows struct ext4_inode to grow 471 inode, which allows struct ext4_inode to grow for a new kernel without
472 having to upgrade all of the on-disk inodes. A 472 having to upgrade all of the on-disk inodes. Access to fields beyond
473 EXT2_GOOD_OLD_INODE_SIZE should be verified to 473 EXT2_GOOD_OLD_INODE_SIZE should be verified to be within
474 ``i_extra_isize``. By default, ext4 inode reco 474 ``i_extra_isize``. By default, ext4 inode records are 256 bytes, and (as
475 of August 2019) the inode structure is 160 byt 475 of August 2019) the inode structure is 160 bytes
476 (``i_extra_isize = 32``). The extra space betw 476 (``i_extra_isize = 32``). The extra space between the end of the inode
477 structure and the end of the inode record can 477 structure and the end of the inode record can be used to store extended
478 attributes. Each inode record can be as large 478 attributes. Each inode record can be as large as the filesystem block
479 size, though this is not terribly efficient. 479 size, though this is not terribly efficient.
480 480
481 Finding an Inode 481 Finding an Inode
482 ~~~~~~~~~~~~~~~~ 482 ~~~~~~~~~~~~~~~~
483 483
484 Each block group contains ``sb->s_inodes_per_g 484 Each block group contains ``sb->s_inodes_per_group`` inodes. Because
485 inode 0 is defined not to exist, this formula 485 inode 0 is defined not to exist, this formula can be used to find the
486 block group that an inode lives in: 486 block group that an inode lives in:
487 ``bg = (inode_num - 1) / sb->s_inodes_per_grou 487 ``bg = (inode_num - 1) / sb->s_inodes_per_group``. The particular inode
488 can be found within the block group's inode ta 488 can be found within the block group's inode table at
489 ``index = (inode_num - 1) % sb->s_inodes_per_g 489 ``index = (inode_num - 1) % sb->s_inodes_per_group``. To get the byte
490 address within the inode table, use 490 address within the inode table, use
491 ``offset = index * sb->s_inode_size``. 491 ``offset = index * sb->s_inode_size``.
492 492
493 Inode Timestamps 493 Inode Timestamps
494 ~~~~~~~~~~~~~~~~ 494 ~~~~~~~~~~~~~~~~
495 495
496 Four timestamps are recorded in the lower 128 496 Four timestamps are recorded in the lower 128 bytes of the inode
497 structure -- inode change time (ctime), access 497 structure -- inode change time (ctime), access time (atime), data
498 modification time (mtime), and deletion time ( 498 modification time (mtime), and deletion time (dtime). The four fields
499 are 32-bit signed integers that represent seco 499 are 32-bit signed integers that represent seconds since the Unix epoch
500 (1970-01-01 00:00:00 GMT), which means that th 500 (1970-01-01 00:00:00 GMT), which means that the fields will overflow in
501 January 2038. If the filesystem does not have 501 January 2038. If the filesystem does not have orphan_file feature, inodes
502 that are not linked from any directory but are 502 that are not linked from any directory but are still open (orphan inodes) have
503 the dtime field overloaded for use with the or 503 the dtime field overloaded for use with the orphan list. The superblock field
504 ``s_last_orphan`` points to the first inode in 504 ``s_last_orphan`` points to the first inode in the orphan list; dtime is then
505 the number of the next orphaned inode, or zero 505 the number of the next orphaned inode, or zero if there are no more orphans.
506 506
507 If the inode structure size ``sb->s_inode_size 507 If the inode structure size ``sb->s_inode_size`` is larger than 128
508 bytes and the ``i_inode_extra`` field is large 508 bytes and the ``i_inode_extra`` field is large enough to encompass the
509 respective ``i_[cma]time_extra`` field, the ct 509 respective ``i_[cma]time_extra`` field, the ctime, atime, and mtime
510 inode fields are widened to 64 bits. Within th 510 inode fields are widened to 64 bits. Within this “extra” 32-bit field,
511 the lower two bits are used to extend the 32-b 511 the lower two bits are used to extend the 32-bit seconds field to be 34
512 bit wide; the upper 30 bits are used to provid 512 bit wide; the upper 30 bits are used to provide nanosecond timestamp
513 accuracy. Therefore, timestamps should not ove 513 accuracy. Therefore, timestamps should not overflow until May 2446.
514 dtime was not widened. There is also a fifth t 514 dtime was not widened. There is also a fifth timestamp to record inode
515 creation time (crtime); this field is 64-bits 515 creation time (crtime); this field is 64-bits wide and decoded in the
516 same manner as 64-bit [cma]time. Neither crtim 516 same manner as 64-bit [cma]time. Neither crtime nor dtime are accessible
517 through the regular stat() interface, though d 517 through the regular stat() interface, though debugfs will report them.
518 518
519 We use the 32-bit signed time value plus (2^32 519 We use the 32-bit signed time value plus (2^32 * (extra epoch bits)).
520 In other words: 520 In other words:
521 521
522 .. list-table:: 522 .. list-table::
523 :widths: 20 20 20 20 20 523 :widths: 20 20 20 20 20
524 :header-rows: 1 524 :header-rows: 1
525 525
526 * - Extra epoch bits 526 * - Extra epoch bits
527 - MSB of 32-bit time 527 - MSB of 32-bit time
528 - Adjustment for signed 32-bit to 64-bit 528 - Adjustment for signed 32-bit to 64-bit tv_sec
529 - Decoded 64-bit tv_sec 529 - Decoded 64-bit tv_sec
530 - valid time range 530 - valid time range
531 * - 0 0 531 * - 0 0
532 - 1 532 - 1
533 - 0 533 - 0
534 - ``-0x80000000 - -0x00000001`` 534 - ``-0x80000000 - -0x00000001``
535 - 1901-12-13 to 1969-12-31 535 - 1901-12-13 to 1969-12-31
536 * - 0 0 536 * - 0 0
537 - 0 537 - 0
538 - 0 538 - 0
539 - ``0x000000000 - 0x07fffffff`` 539 - ``0x000000000 - 0x07fffffff``
540 - 1970-01-01 to 2038-01-19 540 - 1970-01-01 to 2038-01-19
541 * - 0 1 541 * - 0 1
542 - 1 542 - 1
543 - 0x100000000 543 - 0x100000000
544 - ``0x080000000 - 0x0ffffffff`` 544 - ``0x080000000 - 0x0ffffffff``
545 - 2038-01-19 to 2106-02-07 545 - 2038-01-19 to 2106-02-07
546 * - 0 1 546 * - 0 1
547 - 0 547 - 0
548 - 0x100000000 548 - 0x100000000
549 - ``0x100000000 - 0x17fffffff`` 549 - ``0x100000000 - 0x17fffffff``
550 - 2106-02-07 to 2174-02-25 550 - 2106-02-07 to 2174-02-25
551 * - 1 0 551 * - 1 0
552 - 1 552 - 1
553 - 0x200000000 553 - 0x200000000
554 - ``0x180000000 - 0x1ffffffff`` 554 - ``0x180000000 - 0x1ffffffff``
555 - 2174-02-25 to 2242-03-16 555 - 2174-02-25 to 2242-03-16
556 * - 1 0 556 * - 1 0
557 - 0 557 - 0
558 - 0x200000000 558 - 0x200000000
559 - ``0x200000000 - 0x27fffffff`` 559 - ``0x200000000 - 0x27fffffff``
560 - 2242-03-16 to 2310-04-04 560 - 2242-03-16 to 2310-04-04
561 * - 1 1 561 * - 1 1
562 - 1 562 - 1
563 - 0x300000000 563 - 0x300000000
564 - ``0x280000000 - 0x2ffffffff`` 564 - ``0x280000000 - 0x2ffffffff``
565 - 2310-04-04 to 2378-04-22 565 - 2310-04-04 to 2378-04-22
566 * - 1 1 566 * - 1 1
567 - 0 567 - 0
568 - 0x300000000 568 - 0x300000000
569 - ``0x300000000 - 0x37fffffff`` 569 - ``0x300000000 - 0x37fffffff``
570 - 2378-04-22 to 2446-05-10 570 - 2378-04-22 to 2446-05-10
571 571
572 This is a somewhat odd encoding since there ar 572 This is a somewhat odd encoding since there are effectively seven times
573 as many positive values as negative values. Th 573 as many positive values as negative values. There have also been
574 long-standing bugs decoding and encoding dates 574 long-standing bugs decoding and encoding dates beyond 2038, which don't
575 seem to be fixed as of kernel 3.12 and e2fspro 575 seem to be fixed as of kernel 3.12 and e2fsprogs 1.42.8. 64-bit kernels
576 incorrectly use the extra epoch bits 1,1 for d 576 incorrectly use the extra epoch bits 1,1 for dates between 1901 and
577 1970. At some point the kernel will be fixed a 577 1970. At some point the kernel will be fixed and e2fsck will fix this
578 situation, assuming that it is run before 2310 578 situation, assuming that it is run before 2310.
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