On 2018-04-05 02:55, Rob Herring wrote: > On Wed, Apr 4, 2018 at 5:35 PM, Jan Kiszka <jan.kis...@web.de> wrote: >> Hi Frank, >> >> On 2018-03-04 01:17, frowand.l...@gmail.com wrote: >>> From: Frank Rowand <frank.row...@sony.com> >>> >>> 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  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. > > 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? Jan