From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7720AC43219 for ; Sat, 27 Apr 2019 13:38:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4996C208C2 for ; Sat, 27 Apr 2019 13:38:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1556372331; bh=CQcLLq5g0BGJbtU32SVU6f5FrjJ1oFNOfzb5TjWhoQw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=RcVhx25A5k7roNnHhoJXUlMBvqzkacEBl+37VKOPV9kLbXBnRQFBXgrLWqJdXtMQ4 POpKY2sO+3E6IQi0mqsGyrNl0Zjf62rvDXXml1Wo0F061+GDt1SP9NPpQzTMz/2fn8 4p3HvOnLx8ESZFnCAXSdneB8aCuX/QrUj4zFRPQY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726079AbfD0Nis (ORCPT ); Sat, 27 Apr 2019 09:38:48 -0400 Received: from mail.kernel.org ([198.145.29.99]:37754 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725902AbfD0Nir (ORCPT ); Sat, 27 Apr 2019 09:38:47 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 690622087C; Sat, 27 Apr 2019 13:38:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1556372326; bh=CQcLLq5g0BGJbtU32SVU6f5FrjJ1oFNOfzb5TjWhoQw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=VrSZOaxD3J8Y9bd0i/Ao20cxuGAUkc5xtteQQaQTLR0SqpT+eBj9scMUlWJ7z30Fd Cr6LcQyukHusNdWX794WdFdVxxZ/ehgIxOqu8Qt63U4KpulEeRq6zOSISMhciNF/g6 kJScp46Ejq962tIRsV7hJzVQJWveers8pjTvNflI= Date: Sat, 27 Apr 2019 15:38:44 +0200 From: Greg KH To: "Joel Fernandes (Google)" Cc: linux-kernel@vger.kernel.org, Masahiro Yamada , Andrew Morton , ast@kernel.org, atishp04@gmail.com, dancol@google.com, Dan Williams , dietmar.eggemann@arm.com, Guenter Roeck , Jonathan Corbet , karim.yaghmour@opersys.com, Kees Cook , kernel-team@android.com, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-trace-devel@vger.kernel.org, Manoj Rao , mhiramat@kernel.org, qais.yousef@arm.com, rdunlap@infradead.org, rostedt@goodmis.org, Shuah Khan , yhs@fb.com Subject: Re: [PATCH v7 resend 1/2] Provide in-kernel headers to make extending kernel easier Message-ID: <20190427133844.GA29366@kroah.com> References: <20190426190430.172543-1-joel@joelfernandes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190426190430.172543-1-joel@joelfernandes.org> User-Agent: Mutt/1.11.4 (2019-03-13) Sender: linux-trace-devel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-trace-devel@vger.kernel.org On Fri, Apr 26, 2019 at 03:04:29PM -0400, Joel Fernandes (Google) wrote: > Introduce in-kernel headers which are made available as an archive > through proc (/proc/kheaders.tar.xz file). This archive makes it > possible to run eBPF and other tracing programs that need to extend the > kernel for tracing purposes without any dependency on the file system > having headers. > > A github PR is sent for the corresponding BCC patch at: > https://github.com/iovisor/bcc/pull/2312 > > On Android and embedded systems, it is common to switch kernels but not > have kernel headers available on the file system. Further once a > different kernel is booted, any headers stored on the file system will > no longer be useful. This is an issue even well known to distros. > By storing the headers as a compressed archive within the kernel, we can > avoid these issues that have been a hindrance for a long time. > > The best way to use this feature is by building it in. Several users > have a need for this, when they switch debug kernels, they do not want to > update the filesystem or worry about it where to store the headers on > it. However, the feature is also buildable as a module in case the user > desires it not being part of the kernel image. This makes it possible to > load and unload the headers from memory on demand. A tracing program can > load the module, do its operations, and then unload the module to save > kernel memory. The total memory needed is 3.3MB. > > By having the archive available at a fixed location independent of > filesystem dependencies and conventions, all debugging tools can > directly refer to the fixed location for the archive, without concerning > with where the headers on a typical filesystem which significantly > simplifies tooling that needs kernel headers. > > The code to read the headers is based on /proc/config.gz code and uses > the same technique to embed the headers. > > Other approaches were discussed such as having an in-memory mountable > filesystem, but that has drawbacks such as requiring an in-kernel xz > decompressor which we don't have today, and requiring usage of 42 MB of > kernel memory to host the decompressed headers at anytime. Also this > approach is simpler than such approaches. > > Reviewed-by: Masahiro Yamada > Signed-off-by: Joel Fernandes (Google) Reviewed-by: Greg Kroah-Hartman