@@ -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_PHYSMEM Kconfig option adds support for loading data directly
+from a physical linear memory range (usually non volatile memory like Flash)
+to cramfs 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 filesystem type for this feature is "cramfs_physmem" to distinguish it
+from the block device (or MTD) based access. 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 specify it using the
+physaddr=0x******** mount option (for example, if the physical address
+of the cramfs image is 0x80100000, the following command would mount it
+on /mnt:
+
+$ mount -t cramfs_physmem -o physaddr=0x80100000 none /mnt
+
+To boot such an image as the root filesystem, the following kernel
+commandline parameters must be provided:
+
+ "rootfstype=cramfs_physmem rootflags=physaddr=0x80100000"
+
+
+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
--------------------
@@ -3612,8 +3612,8 @@ 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/
@@ -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. For a more capable compressed filesystem
+ you should look at SquashFS which is much better in terms of
+ performance and features.
If unsure, say N.
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> --- Documentation/filesystems/cramfs.txt | 42 ++++++++++++++++++++++++++++++++++++ MAINTAINERS | 4 ++-- fs/cramfs/Kconfig | 9 +++++--- 3 files changed, 50 insertions(+), 5 deletions(-) -- 2.9.5