diff options
| -rw-r--r-- | Documentation/filesystems/cramfs.txt | 42 | ||||
| -rw-r--r-- | MAINTAINERS | 4 | ||||
| -rw-r--r-- | fs/cramfs/Kconfig | 9 |
3 files changed, 50 insertions, 5 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 -------------------- diff --git a/MAINTAINERS b/MAINTAINERS index 2d3d750b19c0..3438aaa20b73 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -3676,8 +3676,8 @@ F: drivers/cpuidle/* F: include/linux/cpuidle.h CRAMFS FILESYSTEM -W: http://sourceforge.net/projects/cramfs/ -S: Orphan / Obsolete +M: Nicolas Pitre <nico@linaro.org> +S: Maintained F: Documentation/filesystems/cramfs.txt F: fs/cramfs/ diff --git a/fs/cramfs/Kconfig b/fs/cramfs/Kconfig index ef86b06bc064..f937082f3244 100644 --- a/fs/cramfs/Kconfig +++ b/fs/cramfs/Kconfig @@ -1,5 +1,5 @@ config CRAMFS - tristate "Compressed ROM file system support (cramfs) (OBSOLETE)" + tristate "Compressed ROM file system support (cramfs)" select ZLIB_INFLATE help Saying Y here includes support for CramFs (Compressed ROM File @@ -15,8 +15,11 @@ config CRAMFS cramfs. Note that the root file system (the one containing the directory /) cannot be compiled as a module. - This filesystem is obsoleted by SquashFS, which is much better - in terms of performance and features. + This filesystem is limited in capabilities and performance on + purpose to remain small and low on RAM usage. It is most suitable + for small embedded systems. If you have ample RAM to spare, you may + consider a more capable compressed filesystem such as SquashFS + which is much better in terms of performance and features. If unsure, say N. |