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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 0F669C32771 for ; Wed, 22 Jan 2020 08:12:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D221C2253D for ; Wed, 22 Jan 2020 08:12:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579680729; bh=6D02fB/ORVNBlFCnxqx9b9CQszWcygA7uSglzQEb/xQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=tKxTzN5lJmaeoVV4eNK8+znniojqi7PrD0mhzgZ6pZQYaPZ47J8iOESU3l1Tc4rd7 6ZA4Hw8LsCIKT6zEj2KWAan7dO6YRmDv5+7sVYZfZ/VDxJcVKd6zBPMkUVK+wQwa6v plNuV7DuhdWvmrvW1seTvv6YtcvIBsvFKcrsvVac= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727141AbgAVIMJ (ORCPT ); Wed, 22 Jan 2020 03:12:09 -0500 Received: from mail.kernel.org ([198.145.29.99]:45940 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725900AbgAVIMI (ORCPT ); Wed, 22 Jan 2020 03:12:08 -0500 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 181542253D; Wed, 22 Jan 2020 08:12:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579680727; bh=6D02fB/ORVNBlFCnxqx9b9CQszWcygA7uSglzQEb/xQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=dp0AgDqLgwPPElizWGTDWJSiRgvVOQuAc/zWgUVlaoypafeLzeLfauukXzS2IjGeO ZZPhmaqr/G/HChws2nw9HGn0S/uqAX1gGKDF0xTlEmPy+3KNX3zNHcvx+b+YoAgVC2 dBOnligizNSEyE3ij13rxCOQ5p0G2xKrJM94ioBA= Date: Wed, 22 Jan 2020 09:12:05 +0100 From: Greg Kroah-Hartman To: Will Deacon Cc: Jason Baron , linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH] dynamic_debug: allow to work if debugfs is disabled Message-ID: <20200122081205.GA2227985@kroah.com> References: <20200122074343.GA2099098@kroah.com> <20200122080352.GA15354@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200122080352.GA15354@willie-the-truck> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 22, 2020 at 08:03:53AM +0000, Will Deacon wrote: > On Wed, Jan 22, 2020 at 08:43:43AM +0100, Greg Kroah-Hartman wrote: > > With the realization that having debugfs enabled on "production" systems is > > generally not a good idea, debugfs is being disabled from more and more > > platforms over time. However, the functionality of dynamic debugging still is > > needed at times, and since it relies on debugfs for its user api, having > > debugfs disabled also forces dynamic debug to be disabled. > > Why is the dyndbg= command-line option not sufficient for these use-cases? They want to enable things after booting, and changing the kernel command line is not something you can do on many systems (i.e. locked-down-bootloaders like embedded systems). Also, the whole option is prevented to be booted if debugfs is not enabled, so the command line wouldn't even work in that situation :) > > To get around this, move the "control" file for dynamic_debug to procfs IFF > > debugfs is disabled. This lets people turn on debugging as needed at runtime > > for individual driverfs and subsystems. > > Hmm. If something called "dynamic_debug" is getting moved out of debugfs, > this does raise the question as to what (if anything) should be left behind. > I worry this is a bit of a slippery slope... I totally agree, but dynamic_debug is independant of debugfs with the exception of the control file itself. > > Reported-by: many different companies > > Cc: Jason Baron > > Signed-off-by: Greg Kroah-Hartman > > --- > > .../admin-guide/dynamic-debug-howto.rst | 3 +++ > > lib/Kconfig.debug | 2 +- > > lib/dynamic_debug.c | 17 ++++++++++++++--- > > 3 files changed, 18 insertions(+), 4 deletions(-) > > > > diff --git a/Documentation/admin-guide/dynamic-debug-howto.rst b/Documentation/admin-guide/dynamic-debug-howto.rst > > index 252e5ef324e5..41f43a373a6a 100644 > > --- a/Documentation/admin-guide/dynamic-debug-howto.rst > > +++ b/Documentation/admin-guide/dynamic-debug-howto.rst > > @@ -54,6 +54,9 @@ If you make a mistake with the syntax, the write will fail thus:: > > /dynamic_debug/control > > -bash: echo: write error: Invalid argument > > > > +Note, for systems without 'debugfs' enabled, the control file can be > > +also found in ``/proc/dynamic_debug/control``. > > + > > Viewing Dynamic Debug Behaviour > > =============================== > > > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > > index 5ffe144c9794..01d4add8b963 100644 > > --- a/lib/Kconfig.debug > > +++ b/lib/Kconfig.debug > > @@ -98,7 +98,7 @@ config DYNAMIC_DEBUG > > bool "Enable dynamic printk() support" > > default n > > depends on PRINTK > > - depends on DEBUG_FS > > + depends on (DEBUG_FS || PROC_FS) > > help > > > > Compiles debug level messages into the kernel, which would noti > > The help text here also needs updating, since it refers to debugfs. Oops, missed that, thanks! > > diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c > > index c60409138e13..077b2d6623ac 100644 > > --- a/lib/dynamic_debug.c > > +++ b/lib/dynamic_debug.c > > @@ -993,13 +993,24 @@ static __initdata int ddebug_init_success; > > > > static int __init dynamic_debug_init_debugfs(void) > > { > > - struct dentry *dir; > > + struct dentry *debugfs_dir; > > + struct proc_dir_entry *procfs_dir; > > > > if (!ddebug_init_success) > > return -ENODEV; > > > > - dir = debugfs_create_dir("dynamic_debug", NULL); > > - debugfs_create_file("control", 0644, dir, NULL, &ddebug_proc_fops); > > + /* Create the control file in debugfs if it is enabled */ > > + if (debugfs_initialized) { > > + debugfs_dir = debugfs_create_dir("dynamic_debug", NULL); > > + debugfs_create_file("control", 0644, debugfs_dir, NULL, > > + &ddebug_proc_fops); > > + return 0; > > + } > > + > > + /* No debugfs so put it in procfs instead */ > > + procfs_dir = proc_mkdir("dynamic_debug", NULL); > > + if (procfs_dir) > > + proc_create("control", 0x644, procfs_dir, &ddebug_proc_fops); > > Shouldn't this be octal rather than hex? Even then, I don't understand what > use it is being able to read but not write to this file. Perhaps make it > 0600 for /proc ? Argh, my fault, fingers are used to typing hex. You can read from the file to see what the current settings are, I was just trying to mirror the debugfs permissions. thanks, greg k-h