1 .. SPDX-License-Identifier: GPL-2.0 1 .. SPDX-License-Identifier: GPL-2.0
2 2
3 Super Block 3 Super Block
4 ----------- 4 -----------
5 5
6 The superblock records various information abo 6 The superblock records various information about the enclosing
7 filesystem, such as block counts, inode counts 7 filesystem, such as block counts, inode counts, supported features,
8 maintenance information, and more. 8 maintenance information, and more.
9 9
10 If the sparse_super feature flag is set, redun !! 10 If the sparse\_super feature flag is set, redundant copies of the
11 superblock and group descriptors are kept only 11 superblock and group descriptors are kept only in the groups whose group
12 number is either 0 or a power of 3, 5, or 7. I 12 number is either 0 or a power of 3, 5, or 7. If the flag is not set,
13 redundant copies are kept in all groups. 13 redundant copies are kept in all groups.
14 14
15 The superblock checksum is calculated against 15 The superblock checksum is calculated against the superblock structure,
16 which includes the FS UUID. 16 which includes the FS UUID.
17 17
18 The ext4 superblock is laid out as follows in 18 The ext4 superblock is laid out as follows in
19 ``struct ext4_super_block``: 19 ``struct ext4_super_block``:
20 20
21 .. list-table:: 21 .. list-table::
22 :widths: 8 8 24 40 22 :widths: 8 8 24 40
23 :header-rows: 1 23 :header-rows: 1
24 24
25 * - Offset 25 * - Offset
26 - Size 26 - Size
27 - Name 27 - Name
28 - Description 28 - Description
29 * - 0x0 29 * - 0x0
30 - __le32 !! 30 - \_\_le32
31 - s_inodes_count !! 31 - s\_inodes\_count
32 - Total inode count. 32 - Total inode count.
33 * - 0x4 33 * - 0x4
34 - __le32 !! 34 - \_\_le32
35 - s_blocks_count_lo !! 35 - s\_blocks\_count\_lo
36 - Total block count. 36 - Total block count.
37 * - 0x8 37 * - 0x8
38 - __le32 !! 38 - \_\_le32
39 - s_r_blocks_count_lo !! 39 - s\_r\_blocks\_count\_lo
40 - This number of blocks can only be alloc 40 - This number of blocks can only be allocated by the super-user.
41 * - 0xC 41 * - 0xC
42 - __le32 !! 42 - \_\_le32
43 - s_free_blocks_count_lo !! 43 - s\_free\_blocks\_count\_lo
44 - Free block count. 44 - Free block count.
45 * - 0x10 45 * - 0x10
46 - __le32 !! 46 - \_\_le32
47 - s_free_inodes_count !! 47 - s\_free\_inodes\_count
48 - Free inode count. 48 - Free inode count.
49 * - 0x14 49 * - 0x14
50 - __le32 !! 50 - \_\_le32
51 - s_first_data_block !! 51 - s\_first\_data\_block
52 - First data block. This must be at least 52 - First data block. This must be at least 1 for 1k-block filesystems and
53 is typically 0 for all other block size 53 is typically 0 for all other block sizes.
54 * - 0x18 54 * - 0x18
55 - __le32 !! 55 - \_\_le32
56 - s_log_block_size !! 56 - s\_log\_block\_size
57 - Block size is 2 ^ (10 + s_log_block_siz !! 57 - Block size is 2 ^ (10 + s\_log\_block\_size).
58 * - 0x1C 58 * - 0x1C
59 - __le32 !! 59 - \_\_le32
60 - s_log_cluster_size !! 60 - s\_log\_cluster\_size
61 - Cluster size is 2 ^ (10 + s_log_cluster !! 61 - Cluster size is (2 ^ s\_log\_cluster\_size) blocks if bigalloc is
62 enabled. Otherwise s_log_cluster_size m !! 62 enabled. Otherwise s\_log\_cluster\_size must equal s\_log\_block\_size.
63 * - 0x20 63 * - 0x20
64 - __le32 !! 64 - \_\_le32
65 - s_blocks_per_group !! 65 - s\_blocks\_per\_group
66 - Blocks per group. 66 - Blocks per group.
67 * - 0x24 67 * - 0x24
68 - __le32 !! 68 - \_\_le32
69 - s_clusters_per_group !! 69 - s\_clusters\_per\_group
70 - Clusters per group, if bigalloc is enab 70 - Clusters per group, if bigalloc is enabled. Otherwise
71 s_clusters_per_group must equal s_block !! 71 s\_clusters\_per\_group must equal s\_blocks\_per\_group.
72 * - 0x28 72 * - 0x28
73 - __le32 !! 73 - \_\_le32
74 - s_inodes_per_group !! 74 - s\_inodes\_per\_group
75 - Inodes per group. 75 - Inodes per group.
76 * - 0x2C 76 * - 0x2C
77 - __le32 !! 77 - \_\_le32
78 - s_mtime !! 78 - s\_mtime
79 - Mount time, in seconds since the epoch. 79 - Mount time, in seconds since the epoch.
80 * - 0x30 80 * - 0x30
81 - __le32 !! 81 - \_\_le32
82 - s_wtime !! 82 - s\_wtime
83 - Write time, in seconds since the epoch. 83 - Write time, in seconds since the epoch.
84 * - 0x34 84 * - 0x34
85 - __le16 !! 85 - \_\_le16
86 - s_mnt_count !! 86 - s\_mnt\_count
87 - Number of mounts since the last fsck. 87 - Number of mounts since the last fsck.
88 * - 0x36 88 * - 0x36
89 - __le16 !! 89 - \_\_le16
90 - s_max_mnt_count !! 90 - s\_max\_mnt\_count
91 - Number of mounts beyond which a fsck is 91 - Number of mounts beyond which a fsck is needed.
92 * - 0x38 92 * - 0x38
93 - __le16 !! 93 - \_\_le16
94 - s_magic !! 94 - s\_magic
95 - Magic signature, 0xEF53 95 - Magic signature, 0xEF53
96 * - 0x3A 96 * - 0x3A
97 - __le16 !! 97 - \_\_le16
98 - s_state !! 98 - s\_state
99 - File system state. See super_state_ for 99 - File system state. See super_state_ for more info.
100 * - 0x3C 100 * - 0x3C
101 - __le16 !! 101 - \_\_le16
102 - s_errors !! 102 - s\_errors
103 - Behaviour when detecting errors. See su 103 - Behaviour when detecting errors. See super_errors_ for more info.
104 * - 0x3E 104 * - 0x3E
105 - __le16 !! 105 - \_\_le16
106 - s_minor_rev_level !! 106 - s\_minor\_rev\_level
107 - Minor revision level. 107 - Minor revision level.
108 * - 0x40 108 * - 0x40
109 - __le32 !! 109 - \_\_le32
110 - s_lastcheck !! 110 - s\_lastcheck
111 - Time of last check, in seconds since th 111 - Time of last check, in seconds since the epoch.
112 * - 0x44 112 * - 0x44
113 - __le32 !! 113 - \_\_le32
114 - s_checkinterval !! 114 - s\_checkinterval
115 - Maximum time between checks, in seconds 115 - Maximum time between checks, in seconds.
116 * - 0x48 116 * - 0x48
117 - __le32 !! 117 - \_\_le32
118 - s_creator_os !! 118 - s\_creator\_os
119 - Creator OS. See the table super_creator 119 - Creator OS. See the table super_creator_ for more info.
120 * - 0x4C 120 * - 0x4C
121 - __le32 !! 121 - \_\_le32
122 - s_rev_level !! 122 - s\_rev\_level
123 - Revision level. See the table super_rev 123 - Revision level. See the table super_revision_ for more info.
124 * - 0x50 124 * - 0x50
125 - __le16 !! 125 - \_\_le16
126 - s_def_resuid !! 126 - s\_def\_resuid
127 - Default uid for reserved blocks. 127 - Default uid for reserved blocks.
128 * - 0x52 128 * - 0x52
129 - __le16 !! 129 - \_\_le16
130 - s_def_resgid !! 130 - s\_def\_resgid
131 - Default gid for reserved blocks. 131 - Default gid for reserved blocks.
132 * - 132 * -
133 - 133 -
134 - 134 -
135 - These fields are for EXT4_DYNAMIC_REV s 135 - These fields are for EXT4_DYNAMIC_REV superblocks only.
136 136
137 Note: the difference between the compat 137 Note: the difference between the compatible feature set and the
138 incompatible feature set is that if the 138 incompatible feature set is that if there is a bit set in the
139 incompatible feature set that the kerne 139 incompatible feature set that the kernel doesn't know about, it should
140 refuse to mount the filesystem. 140 refuse to mount the filesystem.
141 141
142 e2fsck's requirements are more strict; 142 e2fsck's requirements are more strict; if it doesn't know
143 about a feature in either the compatibl 143 about a feature in either the compatible or incompatible feature set, it
144 must abort and not try to meddle with t 144 must abort and not try to meddle with things it doesn't understand...
145 * - 0x54 145 * - 0x54
146 - __le32 !! 146 - \_\_le32
147 - s_first_ino !! 147 - s\_first\_ino
148 - First non-reserved inode. 148 - First non-reserved inode.
149 * - 0x58 149 * - 0x58
150 - __le16 !! 150 - \_\_le16
151 - s_inode_size !! 151 - s\_inode\_size
152 - Size of inode structure, in bytes. 152 - Size of inode structure, in bytes.
153 * - 0x5A 153 * - 0x5A
154 - __le16 !! 154 - \_\_le16
155 - s_block_group_nr !! 155 - s\_block\_group\_nr
156 - Block group # of this superblock. 156 - Block group # of this superblock.
157 * - 0x5C 157 * - 0x5C
158 - __le32 !! 158 - \_\_le32
159 - s_feature_compat !! 159 - s\_feature\_compat
160 - Compatible feature set flags. Kernel ca 160 - Compatible feature set flags. Kernel can still read/write this fs even
161 if it doesn't understand a flag; fsck s 161 if it doesn't understand a flag; fsck should not do that. See the
162 super_compat_ table for more info. 162 super_compat_ table for more info.
163 * - 0x60 163 * - 0x60
164 - __le32 !! 164 - \_\_le32
165 - s_feature_incompat !! 165 - s\_feature\_incompat
166 - Incompatible feature set. If the kernel 166 - Incompatible feature set. If the kernel or fsck doesn't understand one
167 of these bits, it should stop. See the 167 of these bits, it should stop. See the super_incompat_ table for more
168 info. 168 info.
169 * - 0x64 169 * - 0x64
170 - __le32 !! 170 - \_\_le32
171 - s_feature_ro_compat !! 171 - s\_feature\_ro\_compat
172 - Readonly-compatible feature set. If the 172 - Readonly-compatible feature set. If the kernel doesn't understand one of
173 these bits, it can still mount read-onl 173 these bits, it can still mount read-only. See the super_rocompat_ table
174 for more info. 174 for more info.
175 * - 0x68 175 * - 0x68
176 - __u8 !! 176 - \_\_u8
177 - s_uuid[16] !! 177 - s\_uuid[16]
178 - 128-bit UUID for volume. 178 - 128-bit UUID for volume.
179 * - 0x78 179 * - 0x78
180 - char 180 - char
181 - s_volume_name[16] !! 181 - s\_volume\_name[16]
182 - Volume label. 182 - Volume label.
183 * - 0x88 183 * - 0x88
184 - char 184 - char
185 - s_last_mounted[64] !! 185 - s\_last\_mounted[64]
186 - Directory where filesystem was last mou 186 - Directory where filesystem was last mounted.
187 * - 0xC8 187 * - 0xC8
188 - __le32 !! 188 - \_\_le32
189 - s_algorithm_usage_bitmap !! 189 - s\_algorithm\_usage\_bitmap
190 - For compression (Not used in e2fsprogs/ 190 - For compression (Not used in e2fsprogs/Linux)
191 * - 191 * -
192 - 192 -
193 - 193 -
194 - Performance hints. Directory prealloca 194 - Performance hints. Directory preallocation should only happen if the
195 EXT4_FEATURE_COMPAT_DIR_PREALLOC flag i 195 EXT4_FEATURE_COMPAT_DIR_PREALLOC flag is on.
196 * - 0xCC 196 * - 0xCC
197 - __u8 !! 197 - \_\_u8
198 - s_prealloc_blocks !! 198 - s\_prealloc\_blocks
199 - #. of blocks to try to preallocate for 199 - #. of blocks to try to preallocate for ... files? (Not used in
200 e2fsprogs/Linux) 200 e2fsprogs/Linux)
201 * - 0xCD 201 * - 0xCD
202 - __u8 !! 202 - \_\_u8
203 - s_prealloc_dir_blocks !! 203 - s\_prealloc\_dir\_blocks
204 - #. of blocks to preallocate for directo 204 - #. of blocks to preallocate for directories. (Not used in
205 e2fsprogs/Linux) 205 e2fsprogs/Linux)
206 * - 0xCE 206 * - 0xCE
207 - __le16 !! 207 - \_\_le16
208 - s_reserved_gdt_blocks !! 208 - s\_reserved\_gdt\_blocks
209 - Number of reserved GDT entries for futu 209 - Number of reserved GDT entries for future filesystem expansion.
210 * - 210 * -
211 - 211 -
212 - 212 -
213 - Journalling support is valid only if EX 213 - Journalling support is valid only if EXT4_FEATURE_COMPAT_HAS_JOURNAL is
214 set. 214 set.
215 * - 0xD0 215 * - 0xD0
216 - __u8 !! 216 - \_\_u8
217 - s_journal_uuid[16] !! 217 - s\_journal\_uuid[16]
218 - UUID of journal superblock 218 - UUID of journal superblock
219 * - 0xE0 219 * - 0xE0
220 - __le32 !! 220 - \_\_le32
221 - s_journal_inum !! 221 - s\_journal\_inum
222 - inode number of journal file. 222 - inode number of journal file.
223 * - 0xE4 223 * - 0xE4
224 - __le32 !! 224 - \_\_le32
225 - s_journal_dev !! 225 - s\_journal\_dev
226 - Device number of journal file, if the e 226 - Device number of journal file, if the external journal feature flag is
227 set. 227 set.
228 * - 0xE8 228 * - 0xE8
229 - __le32 !! 229 - \_\_le32
230 - s_last_orphan !! 230 - s\_last\_orphan
231 - Start of list of orphaned inodes to del 231 - Start of list of orphaned inodes to delete.
232 * - 0xEC 232 * - 0xEC
233 - __le32 !! 233 - \_\_le32
234 - s_hash_seed[4] !! 234 - s\_hash\_seed[4]
235 - HTREE hash seed. 235 - HTREE hash seed.
236 * - 0xFC 236 * - 0xFC
237 - __u8 !! 237 - \_\_u8
238 - s_def_hash_version !! 238 - s\_def\_hash\_version
239 - Default hash algorithm to use for direc 239 - Default hash algorithm to use for directory hashes. See super_def_hash_
240 for more info. 240 for more info.
241 * - 0xFD 241 * - 0xFD
242 - __u8 !! 242 - \_\_u8
243 - s_jnl_backup_type !! 243 - s\_jnl\_backup\_type
244 - If this value is 0 or EXT3_JNL_BACKUP_B !! 244 - If this value is 0 or EXT3\_JNL\_BACKUP\_BLOCKS (1), then the
245 ``s_jnl_blocks`` field contains a dupli 245 ``s_jnl_blocks`` field contains a duplicate copy of the inode's
246 ``i_block[]`` array and ``i_size``. 246 ``i_block[]`` array and ``i_size``.
247 * - 0xFE 247 * - 0xFE
248 - __le16 !! 248 - \_\_le16
249 - s_desc_size !! 249 - s\_desc\_size
250 - Size of group descriptors, in bytes, if 250 - Size of group descriptors, in bytes, if the 64bit incompat feature flag
251 is set. 251 is set.
252 * - 0x100 252 * - 0x100
253 - __le32 !! 253 - \_\_le32
254 - s_default_mount_opts !! 254 - s\_default\_mount\_opts
255 - Default mount options. See the super_mo 255 - Default mount options. See the super_mountopts_ table for more info.
256 * - 0x104 256 * - 0x104
257 - __le32 !! 257 - \_\_le32
258 - s_first_meta_bg !! 258 - s\_first\_meta\_bg
259 - First metablock block group, if the met !! 259 - First metablock block group, if the meta\_bg feature is enabled.
260 * - 0x108 260 * - 0x108
261 - __le32 !! 261 - \_\_le32
262 - s_mkfs_time !! 262 - s\_mkfs\_time
263 - When the filesystem was created, in sec 263 - When the filesystem was created, in seconds since the epoch.
264 * - 0x10C 264 * - 0x10C
265 - __le32 !! 265 - \_\_le32
266 - s_jnl_blocks[17] !! 266 - s\_jnl\_blocks[17]
267 - Backup copy of the journal inode's ``i_ 267 - Backup copy of the journal inode's ``i_block[]`` array in the first 15
268 elements and i_size_high and i_size in !! 268 elements and i\_size\_high and i\_size in the 16th and 17th elements,
269 respectively. 269 respectively.
270 * - 270 * -
271 - 271 -
272 - 272 -
273 - 64bit support is valid only if EXT4_FEA 273 - 64bit support is valid only if EXT4_FEATURE_COMPAT_64BIT is set.
274 * - 0x150 274 * - 0x150
275 - __le32 !! 275 - \_\_le32
276 - s_blocks_count_hi !! 276 - s\_blocks\_count\_hi
277 - High 32-bits of the block count. 277 - High 32-bits of the block count.
278 * - 0x154 278 * - 0x154
279 - __le32 !! 279 - \_\_le32
280 - s_r_blocks_count_hi !! 280 - s\_r\_blocks\_count\_hi
281 - High 32-bits of the reserved block coun 281 - High 32-bits of the reserved block count.
282 * - 0x158 282 * - 0x158
283 - __le32 !! 283 - \_\_le32
284 - s_free_blocks_count_hi !! 284 - s\_free\_blocks\_count\_hi
285 - High 32-bits of the free block count. 285 - High 32-bits of the free block count.
286 * - 0x15C 286 * - 0x15C
287 - __le16 !! 287 - \_\_le16
288 - s_min_extra_isize !! 288 - s\_min\_extra\_isize
289 - All inodes have at least # bytes. 289 - All inodes have at least # bytes.
290 * - 0x15E 290 * - 0x15E
291 - __le16 !! 291 - \_\_le16
292 - s_want_extra_isize !! 292 - s\_want\_extra\_isize
293 - New inodes should reserve # bytes. 293 - New inodes should reserve # bytes.
294 * - 0x160 294 * - 0x160
295 - __le32 !! 295 - \_\_le32
296 - s_flags !! 296 - s\_flags
297 - Miscellaneous flags. See the super_flag 297 - Miscellaneous flags. See the super_flags_ table for more info.
298 * - 0x164 298 * - 0x164
299 - __le16 !! 299 - \_\_le16
300 - s_raid_stride !! 300 - s\_raid\_stride
301 - RAID stride. This is the number of logi 301 - RAID stride. This is the number of logical blocks read from or written
302 to the disk before moving to the next d 302 to the disk before moving to the next disk. This affects the placement
303 of filesystem metadata, which will hope 303 of filesystem metadata, which will hopefully make RAID storage faster.
304 * - 0x166 304 * - 0x166
305 - __le16 !! 305 - \_\_le16
306 - s_mmp_interval !! 306 - s\_mmp\_interval
307 - #. seconds to wait in multi-mount preve 307 - #. seconds to wait in multi-mount prevention (MMP) checking. In theory,
308 MMP is a mechanism to record in the sup 308 MMP is a mechanism to record in the superblock which host and device
309 have mounted the filesystem, in order t 309 have mounted the filesystem, in order to prevent multiple mounts. This
310 feature does not seem to be implemented 310 feature does not seem to be implemented...
311 * - 0x168 311 * - 0x168
312 - __le64 !! 312 - \_\_le64
313 - s_mmp_block !! 313 - s\_mmp\_block
314 - Block # for multi-mount protection data 314 - Block # for multi-mount protection data.
315 * - 0x170 315 * - 0x170
316 - __le32 !! 316 - \_\_le32
317 - s_raid_stripe_width !! 317 - s\_raid\_stripe\_width
318 - RAID stripe width. This is the number o 318 - RAID stripe width. This is the number of logical blocks read from or
319 written to the disk before coming back 319 written to the disk before coming back to the current disk. This is used
320 by the block allocator to try to reduce 320 by the block allocator to try to reduce the number of read-modify-write
321 operations in a RAID5/6. 321 operations in a RAID5/6.
322 * - 0x174 322 * - 0x174
323 - __u8 !! 323 - \_\_u8
324 - s_log_groups_per_flex !! 324 - s\_log\_groups\_per\_flex
325 - Size of a flexible block group is 2 ^ ` 325 - Size of a flexible block group is 2 ^ ``s_log_groups_per_flex``.
326 * - 0x175 326 * - 0x175
327 - __u8 !! 327 - \_\_u8
328 - s_checksum_type !! 328 - s\_checksum\_type
329 - Metadata checksum algorithm type. The o 329 - Metadata checksum algorithm type. The only valid value is 1 (crc32c).
330 * - 0x176 330 * - 0x176
331 - __le16 !! 331 - \_\_le16
332 - s_reserved_pad !! 332 - s\_reserved\_pad
333 - 333 -
334 * - 0x178 334 * - 0x178
335 - __le64 !! 335 - \_\_le64
336 - s_kbytes_written !! 336 - s\_kbytes\_written
337 - Number of KiB written to this filesyste 337 - Number of KiB written to this filesystem over its lifetime.
338 * - 0x180 338 * - 0x180
339 - __le32 !! 339 - \_\_le32
340 - s_snapshot_inum !! 340 - s\_snapshot\_inum
341 - inode number of active snapshot. (Not u 341 - inode number of active snapshot. (Not used in e2fsprogs/Linux.)
342 * - 0x184 342 * - 0x184
343 - __le32 !! 343 - \_\_le32
344 - s_snapshot_id !! 344 - s\_snapshot\_id
345 - Sequential ID of active snapshot. (Not 345 - Sequential ID of active snapshot. (Not used in e2fsprogs/Linux.)
346 * - 0x188 346 * - 0x188
347 - __le64 !! 347 - \_\_le64
348 - s_snapshot_r_blocks_count !! 348 - s\_snapshot\_r\_blocks\_count
349 - Number of blocks reserved for active sn 349 - Number of blocks reserved for active snapshot's future use. (Not used in
350 e2fsprogs/Linux.) 350 e2fsprogs/Linux.)
351 * - 0x190 351 * - 0x190
352 - __le32 !! 352 - \_\_le32
353 - s_snapshot_list !! 353 - s\_snapshot\_list
354 - inode number of the head of the on-disk 354 - inode number of the head of the on-disk snapshot list. (Not used in
355 e2fsprogs/Linux.) 355 e2fsprogs/Linux.)
356 * - 0x194 356 * - 0x194
357 - __le32 !! 357 - \_\_le32
358 - s_error_count !! 358 - s\_error\_count
359 - Number of errors seen. 359 - Number of errors seen.
360 * - 0x198 360 * - 0x198
361 - __le32 !! 361 - \_\_le32
362 - s_first_error_time !! 362 - s\_first\_error\_time
363 - First time an error happened, in second 363 - First time an error happened, in seconds since the epoch.
364 * - 0x19C 364 * - 0x19C
365 - __le32 !! 365 - \_\_le32
366 - s_first_error_ino !! 366 - s\_first\_error\_ino
367 - inode involved in first error. 367 - inode involved in first error.
368 * - 0x1A0 368 * - 0x1A0
369 - __le64 !! 369 - \_\_le64
370 - s_first_error_block !! 370 - s\_first\_error\_block
371 - Number of block involved of first error 371 - Number of block involved of first error.
372 * - 0x1A8 372 * - 0x1A8
373 - __u8 !! 373 - \_\_u8
374 - s_first_error_func[32] !! 374 - s\_first\_error\_func[32]
375 - Name of function where the error happen 375 - Name of function where the error happened.
376 * - 0x1C8 376 * - 0x1C8
377 - __le32 !! 377 - \_\_le32
378 - s_first_error_line !! 378 - s\_first\_error\_line
379 - Line number where error happened. 379 - Line number where error happened.
380 * - 0x1CC 380 * - 0x1CC
381 - __le32 !! 381 - \_\_le32
382 - s_last_error_time !! 382 - s\_last\_error\_time
383 - Time of most recent error, in seconds s 383 - Time of most recent error, in seconds since the epoch.
384 * - 0x1D0 384 * - 0x1D0
385 - __le32 !! 385 - \_\_le32
386 - s_last_error_ino !! 386 - s\_last\_error\_ino
387 - inode involved in most recent error. 387 - inode involved in most recent error.
388 * - 0x1D4 388 * - 0x1D4
389 - __le32 !! 389 - \_\_le32
390 - s_last_error_line !! 390 - s\_last\_error\_line
391 - Line number where most recent error hap 391 - Line number where most recent error happened.
392 * - 0x1D8 392 * - 0x1D8
393 - __le64 !! 393 - \_\_le64
394 - s_last_error_block !! 394 - s\_last\_error\_block
395 - Number of block involved in most recent 395 - Number of block involved in most recent error.
396 * - 0x1E0 396 * - 0x1E0
397 - __u8 !! 397 - \_\_u8
398 - s_last_error_func[32] !! 398 - s\_last\_error\_func[32]
399 - Name of function where the most recent 399 - Name of function where the most recent error happened.
400 * - 0x200 400 * - 0x200
401 - __u8 !! 401 - \_\_u8
402 - s_mount_opts[64] !! 402 - s\_mount\_opts[64]
403 - ASCIIZ string of mount options. 403 - ASCIIZ string of mount options.
404 * - 0x240 404 * - 0x240
405 - __le32 !! 405 - \_\_le32
406 - s_usr_quota_inum !! 406 - s\_usr\_quota\_inum
407 - Inode number of user `quota <quota>`__ 407 - Inode number of user `quota <quota>`__ file.
408 * - 0x244 408 * - 0x244
409 - __le32 !! 409 - \_\_le32
410 - s_grp_quota_inum !! 410 - s\_grp\_quota\_inum
411 - Inode number of group `quota <quota>`__ 411 - Inode number of group `quota <quota>`__ file.
412 * - 0x248 412 * - 0x248
413 - __le32 !! 413 - \_\_le32
414 - s_overhead_blocks !! 414 - s\_overhead\_blocks
415 - Overhead blocks/clusters in fs. (Huh? T 415 - Overhead blocks/clusters in fs. (Huh? This field is always zero, which
416 means that the kernel calculates it dyn 416 means that the kernel calculates it dynamically.)
417 * - 0x24C 417 * - 0x24C
418 - __le32 !! 418 - \_\_le32
419 - s_backup_bgs[2] !! 419 - s\_backup\_bgs[2]
420 - Block groups containing superblock back !! 420 - Block groups containing superblock backups (if sparse\_super2)
421 * - 0x254 421 * - 0x254
422 - __u8 !! 422 - \_\_u8
423 - s_encrypt_algos[4] !! 423 - s\_encrypt\_algos[4]
424 - Encryption algorithms in use. There can 424 - Encryption algorithms in use. There can be up to four algorithms in use
425 at any time; valid algorithm codes are 425 at any time; valid algorithm codes are given in the super_encrypt_ table
426 below. 426 below.
427 * - 0x258 427 * - 0x258
428 - __u8 !! 428 - \_\_u8
429 - s_encrypt_pw_salt[16] !! 429 - s\_encrypt\_pw\_salt[16]
430 - Salt for the string2key algorithm for e 430 - Salt for the string2key algorithm for encryption.
431 * - 0x268 431 * - 0x268
432 - __le32 !! 432 - \_\_le32
433 - s_lpf_ino !! 433 - s\_lpf\_ino
434 - Inode number of lost+found 434 - Inode number of lost+found
435 * - 0x26C 435 * - 0x26C
436 - __le32 !! 436 - \_\_le32
437 - s_prj_quota_inum !! 437 - s\_prj\_quota\_inum
438 - Inode that tracks project quotas. 438 - Inode that tracks project quotas.
439 * - 0x270 439 * - 0x270
440 - __le32 !! 440 - \_\_le32
441 - s_checksum_seed !! 441 - s\_checksum\_seed
442 - Checksum seed used for metadata_csum ca !! 442 - Checksum seed used for metadata\_csum calculations. This value is
443 crc32c(~0, $orig_fs_uuid). !! 443 crc32c(~0, $orig\_fs\_uuid).
444 * - 0x274 444 * - 0x274
445 - __u8 !! 445 - \_\_u8
446 - s_wtime_hi !! 446 - s\_wtime_hi
447 - Upper 8 bits of the s_wtime field. 447 - Upper 8 bits of the s_wtime field.
448 * - 0x275 448 * - 0x275
449 - __u8 !! 449 - \_\_u8
450 - s_mtime_hi !! 450 - s\_wtime_hi
451 - Upper 8 bits of the s_mtime field. 451 - Upper 8 bits of the s_mtime field.
452 * - 0x276 452 * - 0x276
453 - __u8 !! 453 - \_\_u8
454 - s_mkfs_time_hi !! 454 - s\_mkfs_time_hi
455 - Upper 8 bits of the s_mkfs_time field. 455 - Upper 8 bits of the s_mkfs_time field.
456 * - 0x277 456 * - 0x277
457 - __u8 !! 457 - \_\_u8
458 - s_lastcheck_hi !! 458 - s\_lastcheck_hi
459 - Upper 8 bits of the s_lastcheck field. !! 459 - Upper 8 bits of the s_lastcheck_hi field.
460 * - 0x278 460 * - 0x278
461 - __u8 !! 461 - \_\_u8
462 - s_first_error_time_hi !! 462 - s\_first_error_time_hi
463 - Upper 8 bits of the s_first_error_time !! 463 - Upper 8 bits of the s_first_error_time_hi field.
464 * - 0x279 464 * - 0x279
465 - __u8 !! 465 - \_\_u8
466 - s_last_error_time_hi !! 466 - s\_last_error_time_hi
467 - Upper 8 bits of the s_last_error_time f !! 467 - Upper 8 bits of the s_last_error_time_hi field.
468 * - 0x27A 468 * - 0x27A
469 - __u8 !! 469 - \_\_u8[2]
470 - s_pad[2] !! 470 - s\_pad
471 - Zero padding. 471 - Zero padding.
472 * - 0x27C 472 * - 0x27C
473 - __le16 !! 473 - \_\_le32
474 - s_encoding !! 474 - s\_reserved[96]
475 - Filename charset encoding. <<
476 * - 0x27E <<
477 - __le16 <<
478 - s_encoding_flags <<
479 - Filename charset encoding flags. <<
480 * - 0x280 <<
481 - __le32 <<
482 - s_orphan_file_inum <<
483 - Orphan file inode number. <<
484 * - 0x284 <<
485 - __le32 <<
486 - s_reserved[94] <<
487 - Padding to the end of the block. 475 - Padding to the end of the block.
488 * - 0x3FC 476 * - 0x3FC
489 - __le32 !! 477 - \_\_le32
490 - s_checksum !! 478 - s\_checksum
491 - Superblock checksum. 479 - Superblock checksum.
492 480
493 .. _super_state: 481 .. _super_state:
494 482
495 The superblock state is some combination of th 483 The superblock state is some combination of the following:
496 484
497 .. list-table:: 485 .. list-table::
498 :widths: 8 72 486 :widths: 8 72
499 :header-rows: 1 487 :header-rows: 1
500 488
501 * - Value 489 * - Value
502 - Description 490 - Description
503 * - 0x0001 491 * - 0x0001
504 - Cleanly umounted 492 - Cleanly umounted
505 * - 0x0002 493 * - 0x0002
506 - Errors detected 494 - Errors detected
507 * - 0x0004 495 * - 0x0004
508 - Orphans being recovered 496 - Orphans being recovered
509 497
510 .. _super_errors: 498 .. _super_errors:
511 499
512 The superblock error policy is one of the foll 500 The superblock error policy is one of the following:
513 501
514 .. list-table:: 502 .. list-table::
515 :widths: 8 72 503 :widths: 8 72
516 :header-rows: 1 504 :header-rows: 1
517 505
518 * - Value 506 * - Value
519 - Description 507 - Description
520 * - 1 508 * - 1
521 - Continue 509 - Continue
522 * - 2 510 * - 2
523 - Remount read-only 511 - Remount read-only
524 * - 3 512 * - 3
525 - Panic 513 - Panic
526 514
527 .. _super_creator: 515 .. _super_creator:
528 516
529 The filesystem creator is one of the following 517 The filesystem creator is one of the following:
530 518
531 .. list-table:: 519 .. list-table::
532 :widths: 8 72 520 :widths: 8 72
533 :header-rows: 1 521 :header-rows: 1
534 522
535 * - Value 523 * - Value
536 - Description 524 - Description
537 * - 0 525 * - 0
538 - Linux 526 - Linux
539 * - 1 527 * - 1
540 - Hurd 528 - Hurd
541 * - 2 529 * - 2
542 - Masix 530 - Masix
543 * - 3 531 * - 3
544 - FreeBSD 532 - FreeBSD
545 * - 4 533 * - 4
546 - Lites 534 - Lites
547 535
548 .. _super_revision: 536 .. _super_revision:
549 537
550 The superblock revision is one of the followin 538 The superblock revision is one of the following:
551 539
552 .. list-table:: 540 .. list-table::
553 :widths: 8 72 541 :widths: 8 72
554 :header-rows: 1 542 :header-rows: 1
555 543
556 * - Value 544 * - Value
557 - Description 545 - Description
558 * - 0 546 * - 0
559 - Original format 547 - Original format
560 * - 1 548 * - 1
561 - v2 format w/ dynamic inode sizes 549 - v2 format w/ dynamic inode sizes
562 550
563 Note that ``EXT4_DYNAMIC_REV`` refers to a rev 551 Note that ``EXT4_DYNAMIC_REV`` refers to a revision 1 or newer filesystem.
564 552
565 .. _super_compat: 553 .. _super_compat:
566 554
567 The superblock compatible features field is a 555 The superblock compatible features field is a combination of any of the
568 following: 556 following:
569 557
570 .. list-table:: 558 .. list-table::
571 :widths: 16 64 559 :widths: 16 64
572 :header-rows: 1 560 :header-rows: 1
573 561
574 * - Value 562 * - Value
575 - Description 563 - Description
576 * - 0x1 564 * - 0x1
577 - Directory preallocation (COMPAT_DIR_PRE !! 565 - Directory preallocation (COMPAT\_DIR\_PREALLOC).
578 * - 0x2 566 * - 0x2
579 - “imagic inodes”. Not clear from the 567 - “imagic inodes”. Not clear from the code what this does
580 (COMPAT_IMAGIC_INODES). !! 568 (COMPAT\_IMAGIC\_INODES).
581 * - 0x4 569 * - 0x4
582 - Has a journal (COMPAT_HAS_JOURNAL). !! 570 - Has a journal (COMPAT\_HAS\_JOURNAL).
583 * - 0x8 571 * - 0x8
584 - Supports extended attributes (COMPAT_EX !! 572 - Supports extended attributes (COMPAT\_EXT\_ATTR).
585 * - 0x10 573 * - 0x10
586 - Has reserved GDT blocks for filesystem 574 - Has reserved GDT blocks for filesystem expansion
587 (COMPAT_RESIZE_INODE). Requires RO_COMP !! 575 (COMPAT\_RESIZE\_INODE). Requires RO\_COMPAT\_SPARSE\_SUPER.
588 * - 0x20 576 * - 0x20
589 - Has directory indices (COMPAT_DIR_INDEX !! 577 - Has directory indices (COMPAT\_DIR\_INDEX).
590 * - 0x40 578 * - 0x40
591 - “Lazy BG”. Not in Linux kernel, see 579 - “Lazy BG”. Not in Linux kernel, seems to have been for uninitialized
592 block groups? (COMPAT_LAZY_BG) !! 580 block groups? (COMPAT\_LAZY\_BG)
593 * - 0x80 581 * - 0x80
594 - “Exclude inode”. Not used. (COMPAT_ !! 582 - “Exclude inode”. Not used. (COMPAT\_EXCLUDE\_INODE).
595 * - 0x100 583 * - 0x100
596 - “Exclude bitmap”. Seems to be used 584 - “Exclude bitmap”. Seems to be used to indicate the presence of
597 snapshot-related exclude bitmaps? Not d 585 snapshot-related exclude bitmaps? Not defined in kernel or used in
598 e2fsprogs (COMPAT_EXCLUDE_BITMAP). !! 586 e2fsprogs (COMPAT\_EXCLUDE\_BITMAP).
599 * - 0x200 587 * - 0x200
600 - Sparse Super Block, v2. If this flag is !! 588 - Sparse Super Block, v2. If this flag is set, the SB field s\_backup\_bgs
601 points to the two block groups that con 589 points to the two block groups that contain backup superblocks
602 (COMPAT_SPARSE_SUPER2). !! 590 (COMPAT\_SPARSE\_SUPER2).
603 * - 0x400 <<
604 - Fast commits supported. Although fast c <<
605 backward incompatible, fast commit bloc <<
606 present in the journal. If fast commit <<
607 the journal, JBD2 incompat feature <<
608 (JBD2_FEATURE_INCOMPAT_FAST_COMMIT) get <<
609 set (COMPAT_FAST_COMMIT). <<
610 * - 0x1000 <<
611 - Orphan file allocated. This is the spec <<
612 tracking of unlinked but still open ino <<
613 entries in the file, we additionally se <<
614 (RO_COMPAT_ORPHAN_PRESENT). <<
615 591
616 .. _super_incompat: 592 .. _super_incompat:
617 593
618 The superblock incompatible features field is 594 The superblock incompatible features field is a combination of any of the
619 following: 595 following:
620 596
621 .. list-table:: 597 .. list-table::
622 :widths: 16 64 598 :widths: 16 64
623 :header-rows: 1 599 :header-rows: 1
624 600
625 * - Value 601 * - Value
626 - Description 602 - Description
627 * - 0x1 603 * - 0x1
628 - Compression (INCOMPAT_COMPRESSION). !! 604 - Compression (INCOMPAT\_COMPRESSION).
629 * - 0x2 605 * - 0x2
630 - Directory entries record the file type. !! 606 - Directory entries record the file type. See ext4\_dir\_entry\_2 below
631 (INCOMPAT_FILETYPE). !! 607 (INCOMPAT\_FILETYPE).
632 * - 0x4 608 * - 0x4
633 - Filesystem needs recovery (INCOMPAT_REC !! 609 - Filesystem needs recovery (INCOMPAT\_RECOVER).
634 * - 0x8 610 * - 0x8
635 - Filesystem has a separate journal devic !! 611 - Filesystem has a separate journal device (INCOMPAT\_JOURNAL\_DEV).
636 * - 0x10 612 * - 0x10
637 - Meta block groups. See the earlier disc 613 - Meta block groups. See the earlier discussion of this feature
638 (INCOMPAT_META_BG). !! 614 (INCOMPAT\_META\_BG).
639 * - 0x40 615 * - 0x40
640 - Files in this filesystem use extents (I !! 616 - Files in this filesystem use extents (INCOMPAT\_EXTENTS).
641 * - 0x80 617 * - 0x80
642 - Enable a filesystem size of 2^64 blocks !! 618 - Enable a filesystem size of 2^64 blocks (INCOMPAT\_64BIT).
643 * - 0x100 619 * - 0x100
644 - Multiple mount protection (INCOMPAT_MMP !! 620 - Multiple mount protection. Not implemented (INCOMPAT\_MMP).
645 * - 0x200 621 * - 0x200
646 - Flexible block groups. See the earlier 622 - Flexible block groups. See the earlier discussion of this feature
647 (INCOMPAT_FLEX_BG). !! 623 (INCOMPAT\_FLEX\_BG).
648 * - 0x400 624 * - 0x400
649 - Inodes can be used to store large exten 625 - Inodes can be used to store large extended attribute values
650 (INCOMPAT_EA_INODE). !! 626 (INCOMPAT\_EA\_INODE).
651 * - 0x1000 627 * - 0x1000
652 - Data in directory entry (INCOMPAT_DIRDA !! 628 - Data in directory entry (INCOMPAT\_DIRDATA). (Not implemented?)
653 * - 0x2000 629 * - 0x2000
654 - Metadata checksum seed is stored in the 630 - Metadata checksum seed is stored in the superblock. This feature enables
655 the administrator to change the UUID of !! 631 the administrator to change the UUID of a metadata\_csum filesystem
656 while the filesystem is mounted; withou 632 while the filesystem is mounted; without it, the checksum definition
657 requires all metadata blocks to be rewr !! 633 requires all metadata blocks to be rewritten (INCOMPAT\_CSUM\_SEED).
658 * - 0x4000 634 * - 0x4000
659 - Large directory >2GB or 3-level htree ( !! 635 - Large directory >2GB or 3-level htree (INCOMPAT\_LARGEDIR). Prior to
660 this feature, directories could not be 636 this feature, directories could not be larger than 4GiB and could not
661 have an htree more than 2 levels deep. 637 have an htree more than 2 levels deep. If this feature is enabled,
662 directories can be larger than 4GiB and 638 directories can be larger than 4GiB and have a maximum htree depth of 3.
663 * - 0x8000 639 * - 0x8000
664 - Data in inode (INCOMPAT_INLINE_DATA). !! 640 - Data in inode (INCOMPAT\_INLINE\_DATA).
665 * - 0x10000 641 * - 0x10000
666 - Encrypted inodes are present on the fil !! 642 - Encrypted inodes are present on the filesystem. (INCOMPAT\_ENCRYPT).
667 643
668 .. _super_rocompat: 644 .. _super_rocompat:
669 645
670 The superblock read-only compatible features f 646 The superblock read-only compatible features field is a combination of any of
671 the following: 647 the following:
672 648
673 .. list-table:: 649 .. list-table::
674 :widths: 16 64 650 :widths: 16 64
675 :header-rows: 1 651 :header-rows: 1
676 652
677 * - Value 653 * - Value
678 - Description 654 - Description
679 * - 0x1 655 * - 0x1
680 - Sparse superblocks. See the earlier dis 656 - Sparse superblocks. See the earlier discussion of this feature
681 (RO_COMPAT_SPARSE_SUPER). !! 657 (RO\_COMPAT\_SPARSE\_SUPER).
682 * - 0x2 658 * - 0x2
683 - This filesystem has been used to store 659 - This filesystem has been used to store a file greater than 2GiB
684 (RO_COMPAT_LARGE_FILE). !! 660 (RO\_COMPAT\_LARGE\_FILE).
685 * - 0x4 661 * - 0x4
686 - Not used in kernel or e2fsprogs (RO_COM !! 662 - Not used in kernel or e2fsprogs (RO\_COMPAT\_BTREE\_DIR).
687 * - 0x8 663 * - 0x8
688 - This filesystem has files whose sizes a 664 - This filesystem has files whose sizes are represented in units of
689 logical blocks, not 512-byte sectors. T 665 logical blocks, not 512-byte sectors. This implies a very large file
690 indeed! (RO_COMPAT_HUGE_FILE) !! 666 indeed! (RO\_COMPAT\_HUGE\_FILE)
691 * - 0x10 667 * - 0x10
692 - Group descriptors have checksums. In ad 668 - Group descriptors have checksums. In addition to detecting corruption,
693 this is useful for lazy formatting with 669 this is useful for lazy formatting with uninitialized groups
694 (RO_COMPAT_GDT_CSUM). !! 670 (RO\_COMPAT\_GDT\_CSUM).
695 * - 0x20 671 * - 0x20
696 - Indicates that the old ext3 32,000 subd 672 - Indicates that the old ext3 32,000 subdirectory limit no longer applies
697 (RO_COMPAT_DIR_NLINK). A directory's i_ !! 673 (RO\_COMPAT\_DIR\_NLINK). A directory's i\_links\_count will be set to 1
698 if it is incremented past 64,999. 674 if it is incremented past 64,999.
699 * - 0x40 675 * - 0x40
700 - Indicates that large inodes exist on th 676 - Indicates that large inodes exist on this filesystem
701 (RO_COMPAT_EXTRA_ISIZE). !! 677 (RO\_COMPAT\_EXTRA\_ISIZE).
702 * - 0x80 678 * - 0x80
703 - This filesystem has a snapshot (RO_COMP !! 679 - This filesystem has a snapshot (RO\_COMPAT\_HAS\_SNAPSHOT).
704 * - 0x100 680 * - 0x100
705 - `Quota <Quota>`__ (RO_COMPAT_QUOTA). !! 681 - `Quota <Quota>`__ (RO\_COMPAT\_QUOTA).
706 * - 0x200 682 * - 0x200
707 - This filesystem supports “bigalloc” 683 - This filesystem supports “bigalloc”, which means that file extents are
708 tracked in units of clusters (of blocks 684 tracked in units of clusters (of blocks) instead of blocks
709 (RO_COMPAT_BIGALLOC). !! 685 (RO\_COMPAT\_BIGALLOC).
710 * - 0x400 686 * - 0x400
711 - This filesystem supports metadata check 687 - This filesystem supports metadata checksumming.
712 (RO_COMPAT_METADATA_CSUM; implies RO_CO !! 688 (RO\_COMPAT\_METADATA\_CSUM; implies RO\_COMPAT\_GDT\_CSUM, though
713 GDT_CSUM must not be set) !! 689 GDT\_CSUM must not be set)
714 * - 0x800 690 * - 0x800
715 - Filesystem supports replicas. This feat 691 - Filesystem supports replicas. This feature is neither in the kernel nor
716 e2fsprogs. (RO_COMPAT_REPLICA) !! 692 e2fsprogs. (RO\_COMPAT\_REPLICA)
717 * - 0x1000 693 * - 0x1000
718 - Read-only filesystem image; the kernel 694 - Read-only filesystem image; the kernel will not mount this image
719 read-write and most tools will refuse t 695 read-write and most tools will refuse to write to the image.
720 (RO_COMPAT_READONLY) !! 696 (RO\_COMPAT\_READONLY)
721 * - 0x2000 697 * - 0x2000
722 - Filesystem tracks project quotas. (RO_C !! 698 - Filesystem tracks project quotas. (RO\_COMPAT\_PROJECT)
723 * - 0x8000 <<
724 - Verity inodes may be present on the fil <<
725 * - 0x10000 <<
726 - Indicates orphan file may have valid or <<
727 to clean them up when mounting the file <<
728 (RO_COMPAT_ORPHAN_PRESENT). <<
729 699
730 .. _super_def_hash: 700 .. _super_def_hash:
731 701
732 The ``s_def_hash_version`` field is one of the 702 The ``s_def_hash_version`` field is one of the following:
733 703
734 .. list-table:: 704 .. list-table::
735 :widths: 8 72 705 :widths: 8 72
736 :header-rows: 1 706 :header-rows: 1
737 707
738 * - Value 708 * - Value
739 - Description 709 - Description
740 * - 0x0 710 * - 0x0
741 - Legacy. 711 - Legacy.
742 * - 0x1 712 * - 0x1
743 - Half MD4. 713 - Half MD4.
744 * - 0x2 714 * - 0x2
745 - Tea. 715 - Tea.
746 * - 0x3 716 * - 0x3
747 - Legacy, unsigned. 717 - Legacy, unsigned.
748 * - 0x4 718 * - 0x4
749 - Half MD4, unsigned. 719 - Half MD4, unsigned.
750 * - 0x5 720 * - 0x5
751 - Tea, unsigned. 721 - Tea, unsigned.
752 722
753 .. _super_mountopts: 723 .. _super_mountopts:
754 724
755 The ``s_default_mount_opts`` field is any comb 725 The ``s_default_mount_opts`` field is any combination of the following:
756 726
757 .. list-table:: 727 .. list-table::
758 :widths: 8 72 728 :widths: 8 72
759 :header-rows: 1 729 :header-rows: 1
760 730
761 * - Value 731 * - Value
762 - Description 732 - Description
763 * - 0x0001 733 * - 0x0001
764 - Print debugging info upon (re)mount. (E !! 734 - Print debugging info upon (re)mount. (EXT4\_DEFM\_DEBUG)
765 * - 0x0002 735 * - 0x0002
766 - New files take the gid of the containin 736 - New files take the gid of the containing directory (instead of the fsgid
767 of the current process). (EXT4_DEFM_BSD !! 737 of the current process). (EXT4\_DEFM\_BSDGROUPS)
768 * - 0x0004 738 * - 0x0004
769 - Support userspace-provided extended att !! 739 - Support userspace-provided extended attributes. (EXT4\_DEFM\_XATTR\_USER)
770 * - 0x0008 740 * - 0x0008
771 - Support POSIX access control lists (ACL !! 741 - Support POSIX access control lists (ACLs). (EXT4\_DEFM\_ACL)
772 * - 0x0010 742 * - 0x0010
773 - Do not support 32-bit UIDs. (EXT4_DEFM_ !! 743 - Do not support 32-bit UIDs. (EXT4\_DEFM\_UID16)
774 * - 0x0020 744 * - 0x0020
775 - All data and metadata are committed to !! 745 - All data and metadata are commited to the journal.
776 (EXT4_DEFM_JMODE_DATA) !! 746 (EXT4\_DEFM\_JMODE\_DATA)
777 * - 0x0040 747 * - 0x0040
778 - All data are flushed to the disk before 748 - All data are flushed to the disk before metadata are committed to the
779 journal. (EXT4_DEFM_JMODE_ORDERED) !! 749 journal. (EXT4\_DEFM\_JMODE\_ORDERED)
780 * - 0x0060 750 * - 0x0060
781 - Data ordering is not preserved; data ma 751 - Data ordering is not preserved; data may be written after the metadata
782 has been written. (EXT4_DEFM_JMODE_WBAC !! 752 has been written. (EXT4\_DEFM\_JMODE\_WBACK)
783 * - 0x0100 753 * - 0x0100
784 - Disable write flushes. (EXT4_DEFM_NOBAR !! 754 - Disable write flushes. (EXT4\_DEFM\_NOBARRIER)
785 * - 0x0200 755 * - 0x0200
786 - Track which blocks in a filesystem are 756 - Track which blocks in a filesystem are metadata and therefore should not
787 be used as data blocks. This option wil 757 be used as data blocks. This option will be enabled by default on 3.18,
788 hopefully. (EXT4_DEFM_BLOCK_VALIDITY) !! 758 hopefully. (EXT4\_DEFM\_BLOCK\_VALIDITY)
789 * - 0x0400 759 * - 0x0400
790 - Enable DISCARD support, where the stora 760 - Enable DISCARD support, where the storage device is told about blocks
791 becoming unused. (EXT4_DEFM_DISCARD) !! 761 becoming unused. (EXT4\_DEFM\_DISCARD)
792 * - 0x0800 762 * - 0x0800
793 - Disable delayed allocation. (EXT4_DEFM_ !! 763 - Disable delayed allocation. (EXT4\_DEFM\_NODELALLOC)
794 764
795 .. _super_flags: 765 .. _super_flags:
796 766
797 The ``s_flags`` field is any combination of th 767 The ``s_flags`` field is any combination of the following:
798 768
799 .. list-table:: 769 .. list-table::
800 :widths: 8 72 770 :widths: 8 72
801 :header-rows: 1 771 :header-rows: 1
802 772
803 * - Value 773 * - Value
804 - Description 774 - Description
805 * - 0x0001 775 * - 0x0001
806 - Signed directory hash in use. 776 - Signed directory hash in use.
807 * - 0x0002 777 * - 0x0002
808 - Unsigned directory hash in use. 778 - Unsigned directory hash in use.
809 * - 0x0004 779 * - 0x0004
810 - To test development code. 780 - To test development code.
811 781
812 .. _super_encrypt: 782 .. _super_encrypt:
813 783
814 The ``s_encrypt_algos`` list can contain any o 784 The ``s_encrypt_algos`` list can contain any of the following:
815 785
816 .. list-table:: 786 .. list-table::
817 :widths: 8 72 787 :widths: 8 72
818 :header-rows: 1 788 :header-rows: 1
819 789
820 * - Value 790 * - Value
821 - Description 791 - Description
822 * - 0 792 * - 0
823 - Invalid algorithm (ENCRYPTION_MODE_INVA !! 793 - Invalid algorithm (ENCRYPTION\_MODE\_INVALID).
824 * - 1 794 * - 1
825 - 256-bit AES in XTS mode (ENCRYPTION_MOD !! 795 - 256-bit AES in XTS mode (ENCRYPTION\_MODE\_AES\_256\_XTS).
826 * - 2 796 * - 2
827 - 256-bit AES in GCM mode (ENCRYPTION_MOD !! 797 - 256-bit AES in GCM mode (ENCRYPTION\_MODE\_AES\_256\_GCM).
828 * - 3 798 * - 3
829 - 256-bit AES in CBC mode (ENCRYPTION_MOD !! 799 - 256-bit AES in CBC mode (ENCRYPTION\_MODE\_AES\_256\_CBC).
830 800
831 Total size of the superblock is 1024 bytes. 801 Total size of the superblock is 1024 bytes.
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.