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| author | Nicolas Pitre <nicolas.pitre@linaro.org> | 2017-10-12 02:16:13 -0400 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2017-10-15 00:47:23 -0400 |
| commit | 8d59598c35dc1071e6c36f86c9a95f26dd08b4e5 (patch) | |
| tree | 4890441289c7b514702eac01a67967004fd4af2d /Documentation/filesystems/cramfs.txt | |
| parent | eddcd97659e31f59fc99c6c3ca3dcce403585f7e (diff) | |
| download | lwn-8d59598c35dc1071e6c36f86c9a95f26dd08b4e5.tar.gz lwn-8d59598c35dc1071e6c36f86c9a95f26dd08b4e5.zip | |
cramfs: rehabilitate it
Update documentation, pointer to latest tools, appoint myself as
maintainer. Given it's been unloved for so long, I don't expect anyone
will protest.
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Tested-by: Chris Brandt <chris.brandt@renesas.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'Documentation/filesystems/cramfs.txt')
| -rw-r--r-- | Documentation/filesystems/cramfs.txt | 42 |
1 files changed, 42 insertions, 0 deletions
diff --git a/Documentation/filesystems/cramfs.txt b/Documentation/filesystems/cramfs.txt index 4006298f6707..8e19a53d648b 100644 --- a/Documentation/filesystems/cramfs.txt +++ b/Documentation/filesystems/cramfs.txt @@ -45,6 +45,48 @@ you can just change the #define in mkcramfs.c, so long as you don't mind the filesystem becoming unreadable to future kernels. +Memory Mapped cramfs image +-------------------------- + +The CRAMFS_MTD Kconfig option adds support for loading data directly from +a physical linear memory range (usually non volatile memory like Flash) +instead of going through the block device layer. This saves some memory +since no intermediate buffering is necessary to hold the data before +decompressing. + +And when data blocks are kept uncompressed and properly aligned, they will +automatically be mapped directly into user space whenever possible providing +eXecute-In-Place (XIP) from ROM of read-only segments. Data segments mapped +read-write (hence they have to be copied to RAM) may still be compressed in +the cramfs image in the same file along with non compressed read-only +segments. Both MMU and no-MMU systems are supported. This is particularly +handy for tiny embedded systems with very tight memory constraints. + +The location of the cramfs image in memory is system dependent. You must +know the proper physical address where the cramfs image is located and +configure an MTD device for it. Also, that MTD device must be supported +by a map driver that implements the "point" method. Examples of such +MTD drivers are cfi_cmdset_0001 (Intel/Sharp CFI flash) or physmap +(Flash device in physical memory map). MTD partitions based on such devices +are fine too. Then that device should be specified with the "mtd:" prefix +as the mount device argument. For example, to mount the MTD device named +"fs_partition" on the /mnt directory: + +$ mount -t cramfs mtd:fs_partition /mnt + +To boot a kernel with this as root filesystem, suffice to specify +something like "root=mtd:fs_partition" on the kernel command line. + + +Tools +----- + +A version of mkcramfs that can take advantage of the latest capabilities +described above can be found here: + +https://github.com/npitre/cramfs-tools + + For /usr/share/magic -------------------- |