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author | Linus Torvalds <torvalds@linux-foundation.org> | 2017-11-17 13:20:41 -0800 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2017-11-17 13:20:41 -0800 |
commit | cbda1b270f7ac23665f25fa513d2a73ea7149cbe (patch) | |
tree | df7d08c6dda69a8a664f8595109874e87f62129c /Documentation/filesystems | |
parent | ca5b857cb0f42986520abd9dbb0c2508067342b2 (diff) | |
parent | 8d59598c35dc1071e6c36f86c9a95f26dd08b4e5 (diff) | |
download | linux-stable-cbda1b270f7ac23665f25fa513d2a73ea7149cbe.tar.gz linux-stable-cbda1b270f7ac23665f25fa513d2a73ea7149cbe.tar.bz2 linux-stable-cbda1b270f7ac23665f25fa513d2a73ea7149cbe.zip |
Merge branch 'work.cramfs' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull cramfs updates from Al Viro:
"Nicolas Pitre's cramfs work"
* 'work.cramfs' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
cramfs: rehabilitate it
cramfs: add mmap support
cramfs: implement uncompressed and arbitrary data block positioning
cramfs: direct memory access support
Diffstat (limited to 'Documentation/filesystems')
-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 -------------------- |