From patchwork Wed Sep 27 23:32:19 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nicolas Pitre X-Patchwork-Id: 114380 Delivered-To: patch@linaro.org Received: by 10.140.106.117 with SMTP id d108csp60557qgf; Wed, 27 Sep 2017 16:32:38 -0700 (PDT) X-Google-Smtp-Source: AOwi7QBoF/ZjSCHdEYc1dDYVJ9hSWAaFMpGluGZsSrQyBT35G+7qddWnUM7zDjSRiovM8BSlDy5W X-Received: by 10.99.96.10 with SMTP id u10mr2633783pgb.370.1506555158437; Wed, 27 Sep 2017 16:32:38 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1506555158; cv=none; d=google.com; s=arc-20160816; b=daL6D2EKt4nP208LhhW13hGHMglRguFBpgsZoRF1W5H5QayC14tAy4RRScZA+/aYfN TIAYn1YeErVxAvS2HO8cdbDG6WH20sU9LoY12vJeZ1qY3H4l6vDWBXy5cQcy+XEbyNrg X5KRC5iwjFiMBMxfDckzF0wEGU++/SL0iFkgeqg7mgEUaEX1GL/BPc8dlQcrUuz72xuV oN7MCDTfAHN30HjiPzh1Hee99IxmGWnKn9d1L7ZRBAVV9wyWILT5SJxFKAfxnRUgny5F AehNMiJJUG17Lm3t2JMUD+kHv8fJeHpgCxRRFmW5W9N6P1LdRvoNRdmHFdsk4Fvltjhh ULgg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:sender:message-id:date:subject:cc:to:from :dkim-signature:arc-authentication-results; bh=rOeuN0GxKrN14XBq5IgmkuO4NrMlGNRE9yijYJIrsqI=; b=xR6avZ9UoM0GS8wHGlEBLcBrAL5EjA/p1N6xdtFRTgc6zGEx1rW0fbBsJ50pTax7xJ RzQ98gJc3i6qmGNzDoWPr2zY7WX92T2JEcvi9NSs1cPaCHbfikzAigB9C8yrXJn8oZgE OHEAHLxUFSeFdelIzuGsAtQOX4EHHDJhd1uib1enluoz9PKqJ1ZMi++9294auyBCQxOh Fw88/+ItsF8UacDLv/Pz714Sh++dZWrd2IZhymQkX8wzvKAJNS0W4CaIlu/DhDpqQcBt 4GmbxO1tF1i+VMvgrPEe29+KKw+iUTduM0Ph9k+QZSiYDoz+K0W2t0lr6VxuKT/5ceGz Dy0g== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@pobox.com header.s=sasl header.b=HY6kwGyF; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=linaro.org Return-Path: Received: from vger.kernel.org (vger.kernel.org. [209.132.180.67]) by mx.google.com with ESMTP id y7si111215pln.60.2017.09.27.16.32.38; Wed, 27 Sep 2017 16:32:38 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@pobox.com header.s=sasl header.b=HY6kwGyF; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=linaro.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752537AbdI0Xcf (ORCPT + 26 others); Wed, 27 Sep 2017 19:32:35 -0400 Received: from pb-smtp1.pobox.com ([64.147.108.70]:61301 "EHLO sasl.smtp.pobox.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752152AbdI0Xca (ORCPT ); Wed, 27 Sep 2017 19:32:30 -0400 Received: from sasl.smtp.pobox.com (unknown [127.0.0.1]) by pb-smtp1.pobox.com (Postfix) with ESMTP id 0A27E9954D; Wed, 27 Sep 2017 19:32:30 -0400 (EDT) DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=pobox.com; h=from:to:cc :subject:date:message-id; s=sasl; bh=Pz1AL0uWhn/dQkGSrv7kOkCDst8 =; b=HY6kwGyF4SLAmSfiYVvupd04FulXhXMd5z2ezJQdg7blfy7HoTktghbQsD5 4MBDH9LalOChroSKHqrbhUKGYdj+AYZ89aaDtCyDjG//YjwhcJ6yPZ9hhmnJcjd7 P2UgvHGIExiIJWHDNWwbJrXsQDBr9ez7U7CUXMcvC7vKgV3M= Received: from pb-smtp1.nyi.icgroup.com (unknown [127.0.0.1]) by pb-smtp1.pobox.com (Postfix) with ESMTP id 01B459954C; Wed, 27 Sep 2017 19:32:30 -0400 (EDT) Received: from yoda.home (unknown [137.175.234.45]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by pb-smtp1.pobox.com (Postfix) with ESMTPSA id 75BC499547; Wed, 27 Sep 2017 19:32:29 -0400 (EDT) Received: from xanadu.home (xanadu.home [192.168.2.2]) by yoda.home (Postfix) with ESMTP id C31F32DA041D; Wed, 27 Sep 2017 19:32:28 -0400 (EDT) From: Nicolas Pitre To: Alexander Viro , linux-mm@kvack.org Cc: linux-fsdevel@vger.kernel.org, linux-embedded@vger.kernel.org, linux-kernel@vger.kernel.org, Chris Brandt Subject: [PATCH v4 0/5] cramfs refresh for embedded usage Date: Wed, 27 Sep 2017 19:32:19 -0400 Message-Id: <20170927233224.31676-1-nicolas.pitre@linaro.org> X-Mailer: git-send-email 2.9.5 X-Pobox-Relay-ID: 20B5E9F4-A3DC-11E7-B33C-FE4B1A68708C-78420484!pb-smtp1.pobox.com Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org To memory management people: please review patch #4 of this series. This series brings a nice refresh to the cramfs filesystem, adding the following capabilities: - Direct memory access, bypassing the block and/or MTD layers entirely. - Ability to store individual data blocks uncompressed. - Ability to locate individual data blocks anywhere in the filesystem. The end result is a very tight filesystem that can be accessed directly from ROM without any other subsystem underneath. This also allows for user space XIP which is a very important feature for tiny embedded systems. This series is also available based on v4.13 via git here: http://git.linaro.org/people/nicolas.pitre/linux xipcramfs Why cramfs? Because cramfs is very simple and small. With CONFIG_CRAMFS_BLOCK=n and CONFIG_CRAMFS_PHYSMEM=y the cramfs driver may use as little as 3704 bytes of code. That's many times smaller than squashfs. And the runtime memory usage is also much less with cramfs than squashfs. It packs very tightly already compared to romfs which has no compression support. And the cramfs format was simple to extend, allowing for both compressed and uncompressed blocks within the same file. Why not accessing ROM via MTD? The MTD layer is nice and flexible. It also represents a huge overhead considering its core with no other enabled options weights 19KB. That's many times the size of the cramfs code for something that essentially boils down to a glorified argument parser and a call to memremap() in this case. And if someone still wants to use cramfs via MTD then it is already possible with mtdblock. Why not using DAX? DAX stands for "Direct Access" and is a generic kernel layer helping with the necessary tasks involved with XIP. It is tailored for large writable filesystems and relies on the presence of an MMU. It also has the following shortcoming: "The DAX code does not work correctly on architectures which have virtually mapped caches such as ARM, MIPS and SPARC." That makes it unsuitable for a large portion of the intended targets for this series. And due to the read-only nature of cramfs, it is possible to achieve the intended result with a much simpler approach making DAX somewhat overkill in this context. The maximum size of a cramfs image can't exceed 272MB. In practice it is likely to be much much less. Given this series is concerned with small memory systems, even in the MMU case there is always plenty of vmalloc space left to map it all and even a 272MB memremap() wouldn't be a problem. If it is then maybe your system is big enough with large resources to manage already and you're pretty unlikely to be using cramfs in the first place. Of course, while this cramfs remains backward compatible with existing filesystem images, a newer mkcramfs version is necessary to take advantage of the extended data layout. I created a version of mkcramfs that detects ELF files and marks text+rodata segments for XIP and compresses the rest of those ELF files automatically. So here it is. I'm also willing to step up as cramfs maintainer given that no sign of any maintenance activities appeared for years. Changes from v3: - Rebased on v4.13. - Made direct access depend on cramfs not being modular due to unexported vma handling functions. - Solicit comments from mm people explicitly. Changes from v2: - Plugged a few races in cramfs_vmasplit_fault(). Thanks to Al Viro for highlighting them. - Fixed some checkpatch warnings Changes from v1: - Improved mmap() support by adding the ability to partially populate a mapping and lazily split the non directly mapable pages to a separate vma at fault time (thanks to Chris Brandt for testing). - Clarified the documentation some more. diffstat: Documentation/filesystems/cramfs.txt | 42 ++ MAINTAINERS | 4 +- fs/cramfs/Kconfig | 38 +- fs/cramfs/README | 31 +- fs/cramfs/inode.c | 646 ++++++++++++++++++++++++++--- include/uapi/linux/cramfs_fs.h | 20 +- init/do_mounts.c | 8 + 7 files changed, 712 insertions(+), 77 deletions(-)