[people/ms/u-boot.git] / doc / README.JFFS2

JFFS2 options and usage.
-----------------------

JFFS2 in U-Boot is a read only implementation of the file system in
Linux with the same name. To use JFFS2 define CONFIG_CMD_JFFS2.

The module adds three new commands.
fsload  - load binary file from a file system image
fsinfo  - print information about file systems
ls      - list files in a directory
chpart  - change active partition

If you do now need the commands, you can enable the filesystem separately
with CONFIG_FS_JFFS2 and call the jffs2 functions yourself.

If you boot from a partition which is mounted writable, and you
update your boot environment by replacing single files on that
partition, you should also define CONFIG_SYS_JFFS2_SORT_FRAGMENTS. Scanning
the JFFS2 filesystem takes *much* longer with this feature, though.
Sorting is done while inserting into the fragment list, which is
more or less a bubble sort. That algorithm is known to be O(n^2),
thus you should really consider if you can avoid it!


There only one way for JFFS2 to find the disk. It uses the flash_info
structure to find the start of a JFFS2 disk (called partition in the code)
and you can change where the partition is with two defines.

CONFIG_SYS_JFFS2_FIRST_BANK
	defined the first flash bank to use

CONFIG_SYS_JFFS2_FIRST_SECTOR
	defines the first sector to use
---

TODO.

	Remove the assumption that JFFS can dereference a pointer
	into the disk. The current code do not work with memory holes
	or hardware with a sliding window (PCMCIA).
Commit	Line	Data
	1	JFFS2 options and usage.
	2	-----------------------
	3
	4	JFFS2 in U-Boot is a read only implementation of the file system in
	5	Linux with the same name. To use JFFS2 define CONFIG_CMD_JFFS2.
	6
	7	The module adds three new commands.
	8	fsload - load binary file from a file system image
	9	fsinfo - print information about file systems
	10	ls - list files in a directory
	11	chpart - change active partition
	12
	13	If you do now need the commands, you can enable the filesystem separately
	14	with CONFIG_FS_JFFS2 and call the jffs2 functions yourself.
	15
	16	If you boot from a partition which is mounted writable, and you
	17	update your boot environment by replacing single files on that
	18	partition, you should also define CONFIG_SYS_JFFS2_SORT_FRAGMENTS. Scanning
	19	the JFFS2 filesystem takes much longer with this feature, though.
	20	Sorting is done while inserting into the fragment list, which is
	21	more or less a bubble sort. That algorithm is known to be O(n^2),
	22	thus you should really consider if you can avoid it!
	23
	24
	25	There only one way for JFFS2 to find the disk. It uses the flash_info
	26	structure to find the start of a JFFS2 disk (called partition in the code)
	27	and you can change where the partition is with two defines.
	28
	29	CONFIG_SYS_JFFS2_FIRST_BANK
	30	defined the first flash bank to use
	31
	32	CONFIG_SYS_JFFS2_FIRST_SECTOR
	33	defines the first sector to use
	34	---
	35
	36	TODO.
	37
	38	Remove the assumption that JFFS can dereference a pointer
	39	into the disk. The current code do not work with memory holes
	40	or hardware with a sliding window (PCMCIA).