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diff --git a/Documentation/filesystems/ubifs.txt b/Documentation/filesystems/ubifs.txt deleted file mode 100644 index ab653b46addc..000000000000 --- a/Documentation/filesystems/ubifs.txt +++ /dev/null @@ -1,163 +0,0 @@ -Introduction -============= - -UBIFS file-system stands for UBI File System. UBI stands for "Unsorted -Block Images". UBIFS is a flash file system, which means it is designed -to work with flash devices. It is important to understand, that UBIFS -is completely different to any traditional file-system in Linux, like -Ext2, XFS, JFS, etc. UBIFS represents a separate class of file-systems -which work with MTD devices, not block devices. The other Linux -file-system of this class is JFFS2. - -To make it more clear, here is a small comparison of MTD devices and -block devices. - -1 MTD devices represent flash devices and they consist of eraseblocks of - rather large size, typically about 128KiB. Block devices consist of - small blocks, typically 512 bytes. -2 MTD devices support 3 main operations - read from some offset within an - eraseblock, write to some offset within an eraseblock, and erase a whole - eraseblock. Block devices support 2 main operations - read a whole - block and write a whole block. -3 The whole eraseblock has to be erased before it becomes possible to - re-write its contents. Blocks may be just re-written. -4 Eraseblocks become worn out after some number of erase cycles - - typically 100K-1G for SLC NAND and NOR flashes, and 1K-10K for MLC - NAND flashes. Blocks do not have the wear-out property. -5 Eraseblocks may become bad (only on NAND flashes) and software should - deal with this. Blocks on hard drives typically do not become bad, - because hardware has mechanisms to substitute bad blocks, at least in - modern LBA disks. - -It should be quite obvious why UBIFS is very different to traditional -file-systems. - -UBIFS works on top of UBI. UBI is a separate software layer which may be -found in drivers/mtd/ubi. UBI is basically a volume management and -wear-leveling layer. It provides so called UBI volumes which is a higher -level abstraction than a MTD device. The programming model of UBI devices -is very similar to MTD devices - they still consist of large eraseblocks, -they have read/write/erase operations, but UBI devices are devoid of -limitations like wear and bad blocks (items 4 and 5 in the above list). - -In a sense, UBIFS is a next generation of JFFS2 file-system, but it is -very different and incompatible to JFFS2. The following are the main -differences. - -* JFFS2 works on top of MTD devices, UBIFS depends on UBI and works on - top of UBI volumes. -* JFFS2 does not have on-media index and has to build it while mounting, - which requires full media scan. UBIFS maintains the FS indexing - information on the flash media and does not require full media scan, - so it mounts many times faster than JFFS2. -* JFFS2 is a write-through file-system, while UBIFS supports write-back, - which makes UBIFS much faster on writes. - -Similarly to JFFS2, UBIFS supports on-the-flight compression which makes -it possible to fit quite a lot of data to the flash. - -Similarly to JFFS2, UBIFS is tolerant of unclean reboots and power-cuts. -It does not need stuff like ckfs.ext2. UBIFS automatically replays its -journal and recovers from crashes, ensuring that the on-flash data -structures are consistent. - -UBIFS scales logarithmically (most of the data structures it uses are -trees), so the mount time and memory consumption do not linearly depend -on the flash size, like in case of JFFS2. This is because UBIFS -maintains the FS index on the flash media. However, UBIFS depends on -UBI, which scales linearly. So overall UBI/UBIFS stack scales linearly. -Nevertheless, UBI/UBIFS scales considerably better than JFFS2. - -The authors of UBIFS believe, that it is possible to develop UBI2 which -would scale logarithmically as well. UBI2 would support the same API as UBI, -but it would be binary incompatible to UBI. So UBIFS would not need to be -changed to use UBI2 - - -Mount options -============= - -(*) == default. - -norm_unmount (*) commit on unmount; the journal is committed - when the file-system is unmounted so that the - next mount does not have to replay the journal - and it becomes very fast; -fast_unmount do not commit on unmount; this option makes - unmount faster, but the next mount slower - because of the need to replay the journal. - - -Quick usage instructions -======================== - -The UBI volume to mount is specified using "ubiX_Y" or "ubiX:NAME" syntax, -where "X" is UBI device number, "Y" is UBI volume number, and "NAME" is -UBI volume name. - -Mount volume 0 on UBI device 0 to /mnt/ubifs: -$ mount -t ubifs ubi0_0 /mnt/ubifs - -Mount "rootfs" volume of UBI device 0 to /mnt/ubifs ("rootfs" is volume -name): -$ mount -t ubifs ubi0:rootfs /mnt/ubifs - -The following is an example of the kernel boot arguments to attach mtd0 -to UBI and mount volume "rootfs": -ubi.mtd=0 root=ubi0:rootfs rootfstype=ubifs - - -Module Parameters for Debugging -=============================== - -When UBIFS has been compiled with debugging enabled, there are 3 module -parameters that are available to control aspects of testing and debugging. -The parameters are unsigned integers where each bit controls an option. -The parameters are: - -debug_msgs Selects which debug messages to display, as follows: - - Message Type Flag value - - General messages 1 - Journal messages 2 - Mount messages 4 - Commit messages 8 - LEB search messages 16 - Budgeting messages 32 - Garbage collection messages 64 - Tree Node Cache (TNC) messages 128 - LEB properties (lprops) messages 256 - Input/output messages 512 - Log messages 1024 - Scan messages 2048 - Recovery messages 4096 - -debug_chks Selects extra checks that UBIFS can do while running: - - Check Flag value - - General checks 1 - Check Tree Node Cache (TNC) 2 - Check indexing tree size 4 - Check orphan area 8 - Check old indexing tree 16 - Check LEB properties (lprops) 32 - -debug_tsts Selects a mode of testing, as follows: - - Test mode Flag value - - Force in-the-gaps method 2 - Failure mode for recovery testing 4 - -For example, set debug_msgs to 5 to display General messages and Mount -messages. - - -References -========== - -UBIFS documentation and FAQ/HOWTO at the MTD web site: -http://www.linux-mtd.infradead.org/doc/ubifs.html -http://www.linux-mtd.infradead.org/faq/ubifs.html |