On 10/18/18 12:32, Rob Herring wrote: > On Tue, Oct 16, 2018 at 05:34:26PM -0700, frowand.list@xxxxxxxxx wrote: >> From: Frank Rowand <frank.rowand@xxxxxxxx> >> >> 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. > > Because userspace has no way to modify the DT and the ways the kernel > can do modifications is limited. > > Do you have an actually need for this outside of testing/development? I do not know if anyone uses /proc/device-tree for anything outside of testing/development. If we believe that there is no other use of /proc/device-tree we can simply document that there is no expectation that accessors will see a consistent, unchanging /proc/device-tree. That would be a much smaller patch. >> 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 (1) dynamic devicetree modifications and (2) 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. > > I'd prefer to see some sort of information on overlays exported and user > space can check if that changed. IIRC, Pantelis had a series to do that > along with a kill switch to prevent further modifications. At least some > of that series only had minor issues to fix. The kill switch addresses a different concern, which was from the security community. The kill switch is on my todo list. I don't remember exactly what info the overlay information export patch provided. I'll have to go find it and re-read it. > Also, shouldn't we get uevents if the tree changes? Maybe that's not Yes (off the top of my head). But a shell script accessing /proc/device-tree is not going to get uevents. > guaranteed, but I'd bet we can't handle cases where we don't get events. > A property added to an existing node comes to mind.> > Rob >
