From patchwork Thu Aug 31 03:09:32 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nicolas Pitre X-Patchwork-Id: 9931057 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 099D4603B5 for ; Thu, 31 Aug 2017 03:10:45 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 067632880C for ; Thu, 31 Aug 2017 03:10:45 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id ED0BC287F3; Thu, 31 Aug 2017 03:10:44 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 4783F287D5 for ; Thu, 31 Aug 2017 03:10:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751286AbdHaDKZ (ORCPT ); Wed, 30 Aug 2017 23:10:25 -0400 Received: from pb-smtp2.pobox.com ([64.147.108.71]:60148 "EHLO sasl.smtp.pobox.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751333AbdHaDJj (ORCPT ); Wed, 30 Aug 2017 23:09:39 -0400 Received: from sasl.smtp.pobox.com (unknown [127.0.0.1]) by pb-smtp2.pobox.com (Postfix) with ESMTP id 6716791C25; Wed, 30 Aug 2017 23:09:38 -0400 (EDT) DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=pobox.com; h=from:to:cc :subject:date:message-id:in-reply-to:references; s=sasl; bh=jjdb ApHS+DL+SRJSQEg6GRJAQ3M=; b=UxWBnUEY+nJVyjGpGEuYMauTADBm/UAXYRdX /kP/aD1LoFIehlClxB9jI+c4Q7RKbtei07DIjcq1Tzd223aVMM2fYdprqUSclnwL Ng54Y6L1rrcR3RyaOOfSLBjcJmtHQgMnZlBV17xGxcSNpgeHp/EB+AmwmtNJSqE5 n/vm/xo= Received: from pb-smtp2.nyi.icgroup.com (unknown [127.0.0.1]) by pb-smtp2.pobox.com (Postfix) with ESMTP id 5EE1591C24; Wed, 30 Aug 2017 23:09:38 -0400 (EDT) Received: from yoda.home (unknown [70.80.200.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by pb-smtp2.pobox.com (Postfix) with ESMTPSA id A642991C20; Wed, 30 Aug 2017 23:09:37 -0400 (EDT) Received: from xanadu.home (xanadu.home [192.168.2.2]) by yoda.home (Postfix) with ESMTP id 817392DA06F2; Wed, 30 Aug 2017 23:09:36 -0400 (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 v3 5/5] cramfs: rehabilitate it Date: Wed, 30 Aug 2017 23:09:32 -0400 Message-Id: <20170831030932.26979-6-nicolas.pitre@linaro.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20170831030932.26979-1-nicolas.pitre@linaro.org> References: <20170831030932.26979-1-nicolas.pitre@linaro.org> X-Pobox-Relay-ID: D28DFA5C-8DF9-11E7-A4CB-9D2B0D78B957-78420484!pb-smtp2.pobox.com Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP 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 Tested-by: Chris Brandt --- Documentation/filesystems/cramfs.txt | 42 ++++++++++++++++++++++++++++++++++++ MAINTAINERS | 4 ++-- fs/cramfs/Kconfig | 9 +++++--- 3 files changed, 50 insertions(+), 5 deletions(-) diff --git a/Documentation/filesystems/cramfs.txt b/Documentation/filesystems/cramfs.txt index 4006298f67..8875d306bc 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_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 -------------------- 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 5b4e0b7e13..ae1fe6c795 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.