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diff --git a/Documentation/filesystems/nilfs2.txt b/Documentation/filesystems/nilfs2.txt deleted file mode 100644 index f2f3f8592a6f..000000000000 --- a/Documentation/filesystems/nilfs2.txt +++ /dev/null @@ -1,276 +0,0 @@ -NILFS2 ------- - -NILFS2 is a log-structured file system (LFS) supporting continuous -snapshotting. In addition to versioning capability of the entire file -system, users can even restore files mistakenly overwritten or -destroyed just a few seconds ago. Since NILFS2 can keep consistency -like conventional LFS, it achieves quick recovery after system -crashes. - -NILFS2 creates a number of checkpoints every few seconds or per -synchronous write basis (unless there is no change). Users can select -significant versions among continuously created checkpoints, and can -change them into snapshots which will be preserved until they are -changed back to checkpoints. - -There is no limit on the number of snapshots until the volume gets -full. Each snapshot is mountable as a read-only file system -concurrently with its writable mount, and this feature is convenient -for online backup. - -The userland tools are included in nilfs-utils package, which is -available from the following download page. At least "mkfs.nilfs2", -"mount.nilfs2", "umount.nilfs2", and "nilfs_cleanerd" (so called -cleaner or garbage collector) are required. Details on the tools are -described in the man pages included in the package. - -Project web page: https://nilfs.sourceforge.io/ -Download page: https://nilfs.sourceforge.io/en/download.html -List info: http://vger.kernel.org/vger-lists.html#linux-nilfs - -Caveats -======= - -Features which NILFS2 does not support yet: - - - atime - - extended attributes - - POSIX ACLs - - quotas - - fsck - - defragmentation - -Mount options -============= - -NILFS2 supports the following mount options: -(*) == default - -barrier(*) This enables/disables the use of write barriers. This -nobarrier requires an IO stack which can support barriers, and - if nilfs gets an error on a barrier write, it will - disable again with a warning. -errors=continue Keep going on a filesystem error. -errors=remount-ro(*) Remount the filesystem read-only on an error. -errors=panic Panic and halt the machine if an error occurs. -cp=n Specify the checkpoint-number of the snapshot to be - mounted. Checkpoints and snapshots are listed by lscp - user command. Only the checkpoints marked as snapshot - are mountable with this option. Snapshot is read-only, - so a read-only mount option must be specified together. -order=relaxed(*) Apply relaxed order semantics that allows modified data - blocks to be written to disk without making a - checkpoint if no metadata update is going. This mode - is equivalent to the ordered data mode of the ext3 - filesystem except for the updates on data blocks still - conserve atomicity. This will improve synchronous - write performance for overwriting. -order=strict Apply strict in-order semantics that preserves sequence - of all file operations including overwriting of data - blocks. That means, it is guaranteed that no - overtaking of events occurs in the recovered file - system after a crash. -norecovery Disable recovery of the filesystem on mount. - This disables every write access on the device for - read-only mounts or snapshots. This option will fail - for r/w mounts on an unclean volume. -discard This enables/disables the use of discard/TRIM commands. -nodiscard(*) The discard/TRIM commands are sent to the underlying - block device when blocks are freed. This is useful - for SSD devices and sparse/thinly-provisioned LUNs. - -Ioctls -====== - -There is some NILFS2 specific functionality which can be accessed by applications -through the system call interfaces. The list of all NILFS2 specific ioctls are -shown in the table below. - -Table of NILFS2 specific ioctls -.............................................................................. - Ioctl Description - NILFS_IOCTL_CHANGE_CPMODE Change mode of given checkpoint between - checkpoint and snapshot state. This ioctl is - used in chcp and mkcp utilities. - - NILFS_IOCTL_DELETE_CHECKPOINT Remove checkpoint from NILFS2 file system. - This ioctl is used in rmcp utility. - - NILFS_IOCTL_GET_CPINFO Return info about requested checkpoints. This - ioctl is used in lscp utility and by - nilfs_cleanerd daemon. - - NILFS_IOCTL_GET_CPSTAT Return checkpoints statistics. This ioctl is - used by lscp, rmcp utilities and by - nilfs_cleanerd daemon. - - NILFS_IOCTL_GET_SUINFO Return segment usage info about requested - segments. This ioctl is used in lssu, - nilfs_resize utilities and by nilfs_cleanerd - daemon. - - NILFS_IOCTL_SET_SUINFO Modify segment usage info of requested - segments. This ioctl is used by - nilfs_cleanerd daemon to skip unnecessary - cleaning operation of segments and reduce - performance penalty or wear of flash device - due to redundant move of in-use blocks. - - NILFS_IOCTL_GET_SUSTAT Return segment usage statistics. This ioctl - is used in lssu, nilfs_resize utilities and - by nilfs_cleanerd daemon. - - NILFS_IOCTL_GET_VINFO Return information on virtual block addresses. - This ioctl is used by nilfs_cleanerd daemon. - - NILFS_IOCTL_GET_BDESCS Return information about descriptors of disk - block numbers. This ioctl is used by - nilfs_cleanerd daemon. - - NILFS_IOCTL_CLEAN_SEGMENTS Do garbage collection operation in the - environment of requested parameters from - userspace. This ioctl is used by - nilfs_cleanerd daemon. - - NILFS_IOCTL_SYNC Make a checkpoint. This ioctl is used in - mkcp utility. - - NILFS_IOCTL_RESIZE Resize NILFS2 volume. This ioctl is used - by nilfs_resize utility. - - NILFS_IOCTL_SET_ALLOC_RANGE Define lower limit of segments in bytes and - upper limit of segments in bytes. This ioctl - is used by nilfs_resize utility. - -NILFS2 usage -============ - -To use nilfs2 as a local file system, simply: - - # mkfs -t nilfs2 /dev/block_device - # mount -t nilfs2 /dev/block_device /dir - -This will also invoke the cleaner through the mount helper program -(mount.nilfs2). - -Checkpoints and snapshots are managed by the following commands. -Their manpages are included in the nilfs-utils package above. - - lscp list checkpoints or snapshots. - mkcp make a checkpoint or a snapshot. - chcp change an existing checkpoint to a snapshot or vice versa. - rmcp invalidate specified checkpoint(s). - -To mount a snapshot, - - # mount -t nilfs2 -r -o cp=<cno> /dev/block_device /snap_dir - -where <cno> is the checkpoint number of the snapshot. - -To unmount the NILFS2 mount point or snapshot, simply: - - # umount /dir - -Then, the cleaner daemon is automatically shut down by the umount -helper program (umount.nilfs2). - -Disk format -=========== - -A nilfs2 volume is equally divided into a number of segments except -for the super block (SB) and segment #0. A segment is the container -of logs. Each log is composed of summary information blocks, payload -blocks, and an optional super root block (SR): - - ______________________________________________________ - | |SB| | Segment | Segment | Segment | ... | Segment | | - |_|__|_|____0____|____1____|____2____|_____|____N____|_| - 0 +1K +4K +8M +16M +24M +(8MB x N) - . . (Typical offsets for 4KB-block) - . . - .______________________. - | log | log |... | log | - |__1__|__2__|____|__m__| - . . - . . - . . - .______________________________. - | Summary | Payload blocks |SR| - |_blocks__|_________________|__| - -The payload blocks are organized per file, and each file consists of -data blocks and B-tree node blocks: - - |<--- File-A --->|<--- File-B --->| - _______________________________________________________________ - | Data blocks | B-tree blocks | Data blocks | B-tree blocks | ... - _|_____________|_______________|_____________|_______________|_ - - -Since only the modified blocks are written in the log, it may have -files without data blocks or B-tree node blocks. - -The organization of the blocks is recorded in the summary information -blocks, which contains a header structure (nilfs_segment_summary), per -file structures (nilfs_finfo), and per block structures (nilfs_binfo): - - _________________________________________________________________________ - | Summary | finfo | binfo | ... | binfo | finfo | binfo | ... | binfo |... - |_blocks__|___A___|_(A,1)_|_____|(A,Na)_|___B___|_(B,1)_|_____|(B,Nb)_|___ - - -The logs include regular files, directory files, symbolic link files -and several meta data files. The mata data files are the files used -to maintain file system meta data. The current version of NILFS2 uses -the following meta data files: - - 1) Inode file (ifile) -- Stores on-disk inodes - 2) Checkpoint file (cpfile) -- Stores checkpoints - 3) Segment usage file (sufile) -- Stores allocation state of segments - 4) Data address translation file -- Maps virtual block numbers to usual - (DAT) block numbers. This file serves to - make on-disk blocks relocatable. - -The following figure shows a typical organization of the logs: - - _________________________________________________________________________ - | Summary | regular file | file | ... | ifile | cpfile | sufile | DAT |SR| - |_blocks__|_or_directory_|_______|_____|_______|________|________|_____|__| - - -To stride over segment boundaries, this sequence of files may be split -into multiple logs. The sequence of logs that should be treated as -logically one log, is delimited with flags marked in the segment -summary. The recovery code of nilfs2 looks this boundary information -to ensure atomicity of updates. - -The super root block is inserted for every checkpoints. It includes -three special inodes, inodes for the DAT, cpfile, and sufile. Inodes -of regular files, directories, symlinks and other special files, are -included in the ifile. The inode of ifile itself is included in the -corresponding checkpoint entry in the cpfile. Thus, the hierarchy -among NILFS2 files can be depicted as follows: - - Super block (SB) - | - v - Super root block (the latest cno=xx) - |-- DAT - |-- sufile - `-- cpfile - |-- ifile (cno=c1) - |-- ifile (cno=c2) ---- file (ino=i1) - : : |-- file (ino=i2) - `-- ifile (cno=xx) |-- file (ino=i3) - : : - `-- file (ino=yy) - ( regular file, directory, or symlink ) - -For detail on the format of each file, please see nilfs2_ondisk.h -located at include/uapi/linux directory. - -There are no patents or other intellectual property that we protect -with regard to the design of NILFS2. It is allowed to replicate the -design in hopes that other operating systems could share (mount, read, -write, etc.) data stored in this format. |