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[24.6.192.50]) by smtp.gmail.com with ESMTPSA id l71-v6sm20353451pge.89.2018.10.15.19.47.16 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 15 Oct 2018 19:47:17 -0700 (PDT) Subject: Re: [PATCH v2] of: overlay: user space synchronization To: valdis.kletnieks@vt.edu Cc: Rob Herring , pantelis.antoniou@konsulko.com, Pantelis Antoniou , devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, geert@linux-m68k.org, Alan Tull References: <1539649621-5518-1-git-send-email-frowand.list@gmail.com> <5408.1539650158@turing-police.cc.vt.edu> From: Frank Rowand Message-ID: <294737e8-f94e-5d53-acaf-ecb9a4ef42af@gmail.com> Date: Mon, 15 Oct 2018 19:47:16 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <5408.1539650158@turing-police.cc.vt.edu> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/15/18 17:35, valdis.kletnieks@vt.edu wrote: > On Mon, 15 Oct 2018 17:27:01 -0700, frowand.list@gmail.com said: >> From: Frank Rowand >> >> When an overlay is applied or removed, the live devicetree visible in >> /proc/device-tree/, aka /sys/firmware/devicetree/base/, reflects the >> changes. There is no method for user space to determine whether the >> live devicetree was modified by overlay actions. >> >> Provide a sysfs file, /sys/firmware/devicetree/tree_version, to allow >> user space to determine if the live devicetree has remained unchanged >> while a series of one or more accesses of /proc/device-tree/ occur. >> >> The use of both dynamic devicetree modifications and overlay apply and >> removal are not supported during the same boot cycle. Thus non-overlay >> dynamic modifications are not reflected in the value of tree_version. > > Is there an easy way from userspace to detect "yes/no dynamic modifications > have been done since boot"? > Unfortunately not. I considered adding detecting dynamic modifications in another patch, making this a two patch series, but that feature will be much more intrusive than detecting modifications made by overlays. I may add that feature in the future, but not anytime soon. If you want to understand a little bit about why dynamic modifications occur, please see my reply to Geert in the thread about version 1 of this patch.