Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753688AbdHKTa7 (ORCPT ); Fri, 11 Aug 2017 15:30:59 -0400 Received: from pb-smtp2.pobox.com ([64.147.108.71]:59658 "EHLO sasl.smtp.pobox.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753181AbdHKTa5 (ORCPT ); Fri, 11 Aug 2017 15:30:57 -0400 X-Greylist: delayed 474 seconds by postgrey-1.27 at vger.kernel.org; Fri, 11 Aug 2017 15:30:56 EDT From: Nicolas Pitre To: Alexander Viro Cc: linux-fsdevel@vger.kernel.org, linux-embedded@vger.kernel.org, linux-kernel@vger.kernel.org, Chris Brandt Subject: [PATCH 5/5] cramfs: rehabilitate it Date: Fri, 11 Aug 2017 15:22:52 -0400 Message-Id: <20170811192252.19062-6-nicolas.pitre@linaro.org> X-Mailer: git-send-email 2.9.4 In-Reply-To: <20170811192252.19062-1-nicolas.pitre@linaro.org> References: <20170811192252.19062-1-nicolas.pitre@linaro.org> X-Pobox-Relay-ID: 7D9D4360-7ECA-11E7-BAA9-9D2B0D78B957-78420484!pb-smtp2.pobox.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3689 Lines: 98 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 +++++++++++++++++++++++++++++++++++ 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 --- 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 +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: + +$ mount -t cramfs_physmem -o physaddr=0x80100000 none /mnt + + +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 44cb004c76..12f8155cfe 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -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 +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)" 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. -- 2.9.4