On 2018-04-05 20:59, Frank Rowand wrote: > Hi Jan, > > On 04/04/18 15:35, Jan Kiszka 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? > > Thank you for the pointer to the driver - that makes it much easier to > understand the use case and consider solutions. > > If you can make the changes directly on the FDT instead of on the > expanded devicetree, then you could move to the new API. Are there some examples/references on how to edit FDTs in-place in the kernel? I'd like to avoid writing the n-th FDT parser/generator. > > Looking at the driver, I see one potential issue with that approach. > The property "interrupt-map" is added directly to the changeset > instead of being an existing property in the overlay. Is it possible > to have this property in the overlay when needed? Well, the size of that property has a runtime dependency on the gic's #address-cells. If that is easy to account for depends a bit on the available FDT manipulation services. Or it would take multiple templates to handle the different cases (0, 1, or 2 IIRC). > > I'll also reply to other comments in this thread. TIA! 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
