1 .. SPDX-License-Identifier: GPL-2.0 1 .. SPDX-License-Identifier: GPL-2.0
2 2
3 ====== 3 ======
4 NILFS2 4 NILFS2
5 ====== 5 ======
6 6
7 NILFS2 is a log-structured file system (LFS) s 7 NILFS2 is a log-structured file system (LFS) supporting continuous
8 snapshotting. In addition to versioning capab 8 snapshotting. In addition to versioning capability of the entire file
9 system, users can even restore files mistakenl 9 system, users can even restore files mistakenly overwritten or
10 destroyed just a few seconds ago. Since NILFS 10 destroyed just a few seconds ago. Since NILFS2 can keep consistency
11 like conventional LFS, it achieves quick recov 11 like conventional LFS, it achieves quick recovery after system
12 crashes. 12 crashes.
13 13
14 NILFS2 creates a number of checkpoints every f 14 NILFS2 creates a number of checkpoints every few seconds or per
15 synchronous write basis (unless there is no ch 15 synchronous write basis (unless there is no change). Users can select
16 significant versions among continuously create 16 significant versions among continuously created checkpoints, and can
17 change them into snapshots which will be prese 17 change them into snapshots which will be preserved until they are
18 changed back to checkpoints. 18 changed back to checkpoints.
19 19
20 There is no limit on the number of snapshots u 20 There is no limit on the number of snapshots until the volume gets
21 full. Each snapshot is mountable as a read-on 21 full. Each snapshot is mountable as a read-only file system
22 concurrently with its writable mount, and this 22 concurrently with its writable mount, and this feature is convenient
23 for online backup. 23 for online backup.
24 24
25 The userland tools are included in nilfs-utils 25 The userland tools are included in nilfs-utils package, which is
26 available from the following download page. A 26 available from the following download page. At least "mkfs.nilfs2",
27 "mount.nilfs2", "umount.nilfs2", and "nilfs_cl 27 "mount.nilfs2", "umount.nilfs2", and "nilfs_cleanerd" (so called
28 cleaner or garbage collector) are required. D 28 cleaner or garbage collector) are required. Details on the tools are
29 described in the man pages included in the pac 29 described in the man pages included in the package.
30 30
31 :Project web page: https://nilfs.sourceforg 31 :Project web page: https://nilfs.sourceforge.io/
32 :Download page: https://nilfs.sourceforg 32 :Download page: https://nilfs.sourceforge.io/en/download.html
33 :List info: http://vger.kernel.org/v 33 :List info: http://vger.kernel.org/vger-lists.html#linux-nilfs
34 34
35 Caveats 35 Caveats
36 ======= 36 =======
37 37
38 Features which NILFS2 does not support yet: 38 Features which NILFS2 does not support yet:
39 39
40 - atime 40 - atime
41 - extended attributes 41 - extended attributes
42 - POSIX ACLs 42 - POSIX ACLs
43 - quotas 43 - quotas
44 - fsck 44 - fsck
45 - defragmentation 45 - defragmentation
46 46
47 Mount options 47 Mount options
48 ============= 48 =============
49 49
50 NILFS2 supports the following mount options: 50 NILFS2 supports the following mount options:
51 (*) == default 51 (*) == default
52 52
53 ======================= ====================== 53 ======================= =======================================================
54 barrier(*) This enables/disables 54 barrier(*) This enables/disables the use of write barriers. This
55 nobarrier requires an IO stack w 55 nobarrier requires an IO stack which can support barriers, and
56 if nilfs gets an error 56 if nilfs gets an error on a barrier write, it will
57 disable again with a w 57 disable again with a warning.
58 errors=continue Keep going on a filesy 58 errors=continue Keep going on a filesystem error.
59 errors=remount-ro(*) Remount the filesystem 59 errors=remount-ro(*) Remount the filesystem read-only on an error.
60 errors=panic Panic and halt the mac 60 errors=panic Panic and halt the machine if an error occurs.
61 cp=n Specify the checkpoint 61 cp=n Specify the checkpoint-number of the snapshot to be
62 mounted. Checkpoints 62 mounted. Checkpoints and snapshots are listed by lscp
63 user command. Only th 63 user command. Only the checkpoints marked as snapshot
64 are mountable with thi 64 are mountable with this option. Snapshot is read-only,
65 so a read-only mount o 65 so a read-only mount option must be specified together.
66 order=relaxed(*) Apply relaxed order se 66 order=relaxed(*) Apply relaxed order semantics that allows modified data
67 blocks to be written t 67 blocks to be written to disk without making a
68 checkpoint if no metad 68 checkpoint if no metadata update is going. This mode
69 is equivalent to the o 69 is equivalent to the ordered data mode of the ext3
70 filesystem except for 70 filesystem except for the updates on data blocks still
71 conserve atomicity. T 71 conserve atomicity. This will improve synchronous
72 write performance for 72 write performance for overwriting.
73 order=strict Apply strict in-order 73 order=strict Apply strict in-order semantics that preserves sequence
74 of all file operations 74 of all file operations including overwriting of data
75 blocks. That means, i 75 blocks. That means, it is guaranteed that no
76 overtaking of events o 76 overtaking of events occurs in the recovered file
77 system after a crash. 77 system after a crash.
78 norecovery Disable recovery of th 78 norecovery Disable recovery of the filesystem on mount.
79 This disables every wr 79 This disables every write access on the device for
80 read-only mounts or sn 80 read-only mounts or snapshots. This option will fail
81 for r/w mounts on an u 81 for r/w mounts on an unclean volume.
82 discard This enables/disables 82 discard This enables/disables the use of discard/TRIM commands.
83 nodiscard(*) The discard/TRIM comma 83 nodiscard(*) The discard/TRIM commands are sent to the underlying
84 block device when bloc 84 block device when blocks are freed. This is useful
85 for SSD devices and sp 85 for SSD devices and sparse/thinly-provisioned LUNs.
86 ======================= ====================== 86 ======================= =======================================================
87 87
88 Ioctls 88 Ioctls
89 ====== 89 ======
90 90
91 There is some NILFS2 specific functionality wh 91 There is some NILFS2 specific functionality which can be accessed by applications
92 through the system call interfaces. The list o 92 through the system call interfaces. The list of all NILFS2 specific ioctls are
93 shown in the table below. 93 shown in the table below.
94 94
95 Table of NILFS2 specific ioctls: 95 Table of NILFS2 specific ioctls:
96 96
97 ============================== ============== 97 ============================== ===============================================
98 Ioctl Description 98 Ioctl Description
99 ============================== ============== 99 ============================== ===============================================
100 NILFS_IOCTL_CHANGE_CPMODE Change mode of 100 NILFS_IOCTL_CHANGE_CPMODE Change mode of given checkpoint between
101 checkpoint and 101 checkpoint and snapshot state. This ioctl is
102 used in chcp a 102 used in chcp and mkcp utilities.
103 103
104 NILFS_IOCTL_DELETE_CHECKPOINT Remove checkpo 104 NILFS_IOCTL_DELETE_CHECKPOINT Remove checkpoint from NILFS2 file system.
105 This ioctl is 105 This ioctl is used in rmcp utility.
106 106
107 NILFS_IOCTL_GET_CPINFO Return info ab 107 NILFS_IOCTL_GET_CPINFO Return info about requested checkpoints. This
108 ioctl is used 108 ioctl is used in lscp utility and by
109 nilfs_cleanerd 109 nilfs_cleanerd daemon.
110 110
111 NILFS_IOCTL_GET_CPSTAT Return checkpo 111 NILFS_IOCTL_GET_CPSTAT Return checkpoints statistics. This ioctl is
112 used by lscp, 112 used by lscp, rmcp utilities and by
113 nilfs_cleanerd 113 nilfs_cleanerd daemon.
114 114
115 NILFS_IOCTL_GET_SUINFO Return segment 115 NILFS_IOCTL_GET_SUINFO Return segment usage info about requested
116 segments. This 116 segments. This ioctl is used in lssu,
117 nilfs_resize u 117 nilfs_resize utilities and by nilfs_cleanerd
118 daemon. 118 daemon.
119 119
120 NILFS_IOCTL_SET_SUINFO Modify segment 120 NILFS_IOCTL_SET_SUINFO Modify segment usage info of requested
121 segments. This 121 segments. This ioctl is used by
122 nilfs_cleanerd 122 nilfs_cleanerd daemon to skip unnecessary
123 cleaning opera 123 cleaning operation of segments and reduce
124 performance pe 124 performance penalty or wear of flash device
125 due to redunda 125 due to redundant move of in-use blocks.
126 126
127 NILFS_IOCTL_GET_SUSTAT Return segment 127 NILFS_IOCTL_GET_SUSTAT Return segment usage statistics. This ioctl
128 is used in lss 128 is used in lssu, nilfs_resize utilities and
129 by nilfs_clean 129 by nilfs_cleanerd daemon.
130 130
131 NILFS_IOCTL_GET_VINFO Return informa 131 NILFS_IOCTL_GET_VINFO Return information on virtual block addresses.
132 This ioctl is 132 This ioctl is used by nilfs_cleanerd daemon.
133 133
134 NILFS_IOCTL_GET_BDESCS Return informa 134 NILFS_IOCTL_GET_BDESCS Return information about descriptors of disk
135 block numbers. 135 block numbers. This ioctl is used by
136 nilfs_cleanerd 136 nilfs_cleanerd daemon.
137 137
138 NILFS_IOCTL_CLEAN_SEGMENTS Do garbage col 138 NILFS_IOCTL_CLEAN_SEGMENTS Do garbage collection operation in the
139 environment of 139 environment of requested parameters from
140 userspace. Thi 140 userspace. This ioctl is used by
141 nilfs_cleanerd 141 nilfs_cleanerd daemon.
142 142
143 NILFS_IOCTL_SYNC Make a checkpo 143 NILFS_IOCTL_SYNC Make a checkpoint. This ioctl is used in
144 mkcp utility. 144 mkcp utility.
145 145
146 NILFS_IOCTL_RESIZE Resize NILFS2 146 NILFS_IOCTL_RESIZE Resize NILFS2 volume. This ioctl is used
147 by nilfs_resiz 147 by nilfs_resize utility.
148 148
149 NILFS_IOCTL_SET_ALLOC_RANGE Define lower l 149 NILFS_IOCTL_SET_ALLOC_RANGE Define lower limit of segments in bytes and
150 upper limit of 150 upper limit of segments in bytes. This ioctl
151 is used by nil 151 is used by nilfs_resize utility.
152 ============================== ============== 152 ============================== ===============================================
153 153
154 NILFS2 usage 154 NILFS2 usage
155 ============ 155 ============
156 156
157 To use nilfs2 as a local file system, simply:: 157 To use nilfs2 as a local file system, simply::
158 158
159 # mkfs -t nilfs2 /dev/block_device 159 # mkfs -t nilfs2 /dev/block_device
160 # mount -t nilfs2 /dev/block_device /dir 160 # mount -t nilfs2 /dev/block_device /dir
161 161
162 This will also invoke the cleaner through the 162 This will also invoke the cleaner through the mount helper program
163 (mount.nilfs2). 163 (mount.nilfs2).
164 164
165 Checkpoints and snapshots are managed by the f 165 Checkpoints and snapshots are managed by the following commands.
166 Their manpages are included in the nilfs-utils 166 Their manpages are included in the nilfs-utils package above.
167 167
168 ==== =================================== 168 ==== ===========================================================
169 lscp list checkpoints or snapshots. 169 lscp list checkpoints or snapshots.
170 mkcp make a checkpoint or a snapshot. 170 mkcp make a checkpoint or a snapshot.
171 chcp change an existing checkpoint to a 171 chcp change an existing checkpoint to a snapshot or vice versa.
172 rmcp invalidate specified checkpoint(s). 172 rmcp invalidate specified checkpoint(s).
173 ==== =================================== 173 ==== ===========================================================
174 174
175 To mount a snapshot:: 175 To mount a snapshot::
176 176
177 # mount -t nilfs2 -r -o cp=<cno> /dev/block_d 177 # mount -t nilfs2 -r -o cp=<cno> /dev/block_device /snap_dir
178 178
179 where <cno> is the checkpoint number of the sn 179 where <cno> is the checkpoint number of the snapshot.
180 180
181 To unmount the NILFS2 mount point or snapshot, 181 To unmount the NILFS2 mount point or snapshot, simply::
182 182
183 # umount /dir 183 # umount /dir
184 184
185 Then, the cleaner daemon is automatically shut 185 Then, the cleaner daemon is automatically shut down by the umount
186 helper program (umount.nilfs2). 186 helper program (umount.nilfs2).
187 187
188 Disk format 188 Disk format
189 =========== 189 ===========
190 190
191 A nilfs2 volume is equally divided into a numb 191 A nilfs2 volume is equally divided into a number of segments except
192 for the super block (SB) and segment #0. A se 192 for the super block (SB) and segment #0. A segment is the container
193 of logs. Each log is composed of summary info 193 of logs. Each log is composed of summary information blocks, payload
194 blocks, and an optional super root block (SR): 194 blocks, and an optional super root block (SR)::
195 195
196 ___________________________________________ 196 ______________________________________________________
197 | |SB| | Segment | Segment | Segment | ... | 197 | |SB| | Segment | Segment | Segment | ... | Segment | |
198 |_|__|_|____0____|____1____|____2____|_____| 198 |_|__|_|____0____|____1____|____2____|_____|____N____|_|
199 0 +1K +4K +8M +16M +24M +( 199 0 +1K +4K +8M +16M +24M +(8MB x N)
200 . . (Typical off 200 . . (Typical offsets for 4KB-block)
201 . . 201 . .
202 .______________________. 202 .______________________.
203 | log | log |... | log | 203 | log | log |... | log |
204 |__1__|__2__|____|__m__| 204 |__1__|__2__|____|__m__|
205 . . 205 . .
206 . . 206 . .
207 . . 207 . .
208 .______________________________. 208 .______________________________.
209 | Summary | Payload blocks |SR| 209 | Summary | Payload blocks |SR|
210 |_blocks__|_________________|__| 210 |_blocks__|_________________|__|
211 211
212 The payload blocks are organized per file, and 212 The payload blocks are organized per file, and each file consists of
213 data blocks and B-tree node blocks:: 213 data blocks and B-tree node blocks::
214 214
215 |<--- File-A --->|<--- 215 |<--- File-A --->|<--- File-B --->|
216 ___________________________________________ 216 _______________________________________________________________
217 | Data blocks | B-tree blocks | Data block 217 | Data blocks | B-tree blocks | Data blocks | B-tree blocks | ...
218 _|_____________|_______________|___________ 218 _|_____________|_______________|_____________|_______________|_
219 219
220 220
221 Since only the modified blocks are written in 221 Since only the modified blocks are written in the log, it may have
222 files without data blocks or B-tree node block 222 files without data blocks or B-tree node blocks.
223 223
224 The organization of the blocks is recorded in 224 The organization of the blocks is recorded in the summary information
225 blocks, which contains a header structure (nil 225 blocks, which contains a header structure (nilfs_segment_summary), per
226 file structures (nilfs_finfo), and per block s 226 file structures (nilfs_finfo), and per block structures (nilfs_binfo)::
227 227
228 ____________________________________________ 228 _________________________________________________________________________
229 | Summary | finfo | binfo | ... | binfo | fin 229 | Summary | finfo | binfo | ... | binfo | finfo | binfo | ... | binfo |...
230 |_blocks__|___A___|_(A,1)_|_____|(A,Na)_|___B 230 |_blocks__|___A___|_(A,1)_|_____|(A,Na)_|___B___|_(B,1)_|_____|(B,Nb)_|___
231 231
232 232
233 The logs include regular files, directory file 233 The logs include regular files, directory files, symbolic link files
234 and several meta data files. The meta data fi !! 234 and several meta data files. The mata data files are the files used
235 to maintain file system meta data. The curren 235 to maintain file system meta data. The current version of NILFS2 uses
236 the following meta data files:: 236 the following meta data files::
237 237
238 1) Inode file (ifile) -- Stores o 238 1) Inode file (ifile) -- Stores on-disk inodes
239 2) Checkpoint file (cpfile) -- Stores c 239 2) Checkpoint file (cpfile) -- Stores checkpoints
240 3) Segment usage file (sufile) -- Stores a 240 3) Segment usage file (sufile) -- Stores allocation state of segments
241 4) Data address translation file -- Maps vir 241 4) Data address translation file -- Maps virtual block numbers to usual
242 (DAT) block nu 242 (DAT) block numbers. This file serves to
243 make on- 243 make on-disk blocks relocatable.
244 244
245 The following figure shows a typical organizat 245 The following figure shows a typical organization of the logs::
246 246
247 ____________________________________________ 247 _________________________________________________________________________
248 | Summary | regular file | file | ... | ifil 248 | Summary | regular file | file | ... | ifile | cpfile | sufile | DAT |SR|
249 |_blocks__|_or_directory_|_______|_____|_____ 249 |_blocks__|_or_directory_|_______|_____|_______|________|________|_____|__|
250 250
251 251
252 To stride over segment boundaries, this sequen 252 To stride over segment boundaries, this sequence of files may be split
253 into multiple logs. The sequence of logs that 253 into multiple logs. The sequence of logs that should be treated as
254 logically one log, is delimited with flags mar 254 logically one log, is delimited with flags marked in the segment
255 summary. The recovery code of nilfs2 looks th 255 summary. The recovery code of nilfs2 looks this boundary information
256 to ensure atomicity of updates. 256 to ensure atomicity of updates.
257 257
258 The super root block is inserted for every che 258 The super root block is inserted for every checkpoints. It includes
259 three special inodes, inodes for the DAT, cpfi 259 three special inodes, inodes for the DAT, cpfile, and sufile. Inodes
260 of regular files, directories, symlinks and ot 260 of regular files, directories, symlinks and other special files, are
261 included in the ifile. The inode of ifile its 261 included in the ifile. The inode of ifile itself is included in the
262 corresponding checkpoint entry in the cpfile. 262 corresponding checkpoint entry in the cpfile. Thus, the hierarchy
263 among NILFS2 files can be depicted as follows: 263 among NILFS2 files can be depicted as follows::
264 264
265 Super block (SB) 265 Super block (SB)
266 | 266 |
267 v 267 v
268 Super root block (the latest cno=xx) 268 Super root block (the latest cno=xx)
269 |-- DAT 269 |-- DAT
270 |-- sufile 270 |-- sufile
271 `-- cpfile 271 `-- cpfile
272 |-- ifile (cno=c1) 272 |-- ifile (cno=c1)
273 |-- ifile (cno=c2) ---- file (in 273 |-- ifile (cno=c2) ---- file (ino=i1)
274 : : |-- file (in 274 : : |-- file (ino=i2)
275 `-- ifile (cno=xx) |-- file (in 275 `-- ifile (cno=xx) |-- file (ino=i3)
276 : : 276 : :
277 `-- file (in 277 `-- file (ino=yy)
278 ( regular 278 ( regular file, directory, or symlink )
279 279
280 For detail on the format of each file, please 280 For detail on the format of each file, please see nilfs2_ondisk.h
281 located at include/uapi/linux directory. 281 located at include/uapi/linux directory.
282 282
283 There are no patents or other intellectual pro 283 There are no patents or other intellectual property that we protect
284 with regard to the design of NILFS2. It is al 284 with regard to the design of NILFS2. It is allowed to replicate the
285 design in hopes that other operating systems c 285 design in hopes that other operating systems could share (mount, read,
286 write, etc.) data stored in this format. 286 write, etc.) data stored in this format.
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