[PATCH 5/5] cramfs: rehabilitate it
- Date: Fri, 11 Aug 2017 15:22:52 -0400
- From: Nicolas Pitre <nicolas.pitre@xxxxxxxxxx>
- 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 <nico@xxxxxxxxxx>
Documentation/filesystems/cramfs.txt | 35 +++++++++++++++++++++++++++++++++++
MAINTAINERS | 4 ++--
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
@@ -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:
diff --git a/MAINTAINERS b/MAINTAINERS
index 44cb004c76..12f8155cfe 100644
@@ -3612,8 +3612,8 @@ F: drivers/cpuidle/*
-S: Orphan / Obsolete
+M: Nicolas Pitre <nico@xxxxxxxxxx>
diff --git a/fs/cramfs/Kconfig b/fs/cramfs/Kconfig
index 5eed4ad2d5..8ed27e41bd 100644
@@ -1,5 +1,5 @@
- 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.