On 04/05/18 00:22, Jan Kiszka wrote: > On 2018-04-05 02:55, Rob Herring wrote: >> On Wed, Apr 4, 2018 at 5:35 PM, Jan Kiszka <jan.kiszka@xxxxxx> wrote: >>> Hi Frank, >>> >>> On 2018-03-04 01:17, frowand.list@xxxxxxxxx wrote: >>>> From: Frank Rowand <frank.rowand@xxxxxxxx> >>>> >>>> Move duplicating and unflattening of an overlay flattened devicetree >>>> (FDT) into the overlay application code. To accomplish this, >>>> of_overlay_apply() is replaced by of_overlay_fdt_apply(). >>>> >>>> The copy of the FDT (aka "duplicate FDT") now belongs to devicetree >>>> code, which is thus responsible for freeing the duplicate FDT. The >>>> caller of of_overlay_fdt_apply() remains responsible for freeing the >>>> original FDT. >>>> >>>> The unflattened devicetree now belongs to devicetree code, which is >>>> thus responsible for freeing the unflattened devicetree. >>>> >>>> These ownership changes prevent early freeing of the duplicated FDT >>>> or the unflattened devicetree, which could result in use after free >>>> errors. >>>> >>>> of_overlay_fdt_apply() is a private function for the anticipated >>>> overlay loader. >>> >>> We are using of_fdt_unflatten_tree + of_overlay_apply in the >>> (out-of-tree) Jailhouse loader driver in order to register a virtual >>> device during hypervisor activation with Linux. The DT overlay is >>> created from a a template but modified prior to application to account >>> for runtime-specific parameters. See [1] for the current implementation. >>> >>> I'm now wondering how to model that scenario best with the new API. >>> Given that the loader lost ownership of the unflattened tree but the >>> modification API exist only for the that DT state, I'm not yet seeing a >>> clear solution. Should we apply the template in disabled form (status = >>> "disabled"), modify it, and then activate it while it is already applied? >> >> No. I don't think that will work. >> >> The of_overlay_apply() function is still there, but static. We can >> export it again if the need arises. > > That would be the simplest solution from our perspective, but I'm not > sure if that is in the original spirit of this change. For short term out of tree usage, exporting of_overlay_apply() is ok. Yes, for in-tree, exporting it again defeats the attempted process to solve the overlay issues to make them acceptable in main line. >> >> Another option is there is a notifier callback OF_OVERLAY_PRE_APPLY, >> but I'm not sure we want to make that be the normal interface to make >> modifications. > > And would calling modification functions from that callback be legal at all? It might work in some specific cases, but the result is undefined. > > Jan > -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
