[lkml]   [2017]   [Aug]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
Subject[PATCH 5/5] 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 <>
Documentation/filesystems/cramfs.txt | 35 +++++++++++++++++++++++++++++++++++
fs/cramfs/Kconfig | 9 ++++++---
3 files changed, 43 insertions(+), 5 deletions(-)

diff --git a/Documentation/filesystems/cramfs.txt b/Documentation/filesystems/cramfs.txt
index 4006298f67..5955c23bac 100644
--- a/Documentation/filesystems/cramfs.txt
+++ b/Documentation/filesystems/cramfs.txt
@@ -45,6 +45,41 @@ 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
+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:
+$ mount -t cramfs_physmem -o physaddr=0x80100000 none /mnt
+A version of mkcramfs that can take advantage of the latest capabilities
+described above can be found here:
For /usr/share/magic

index 44cb004c76..12f8155cfe 100644
@@ -3612,8 +3612,8 @@ F: drivers/cpuidle/*
F: include/linux/cpuidle.h

-S: Orphan / Obsolete
+M: Nicolas Pitre <>
+S: Maintained
F: Documentation/filesystems/cramfs.txt
F: fs/cramfs/

diff --git a/fs/cramfs/Kconfig b/fs/cramfs/Kconfig
index 5eed4ad2d5..8ed27e41bd 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)"
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.

 \ /
  Last update: 2017-08-11 21:31    [W:0.101 / U:0.460 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site