Il 02/06/2013 18:12, Peter Maydell ha scritto: > On 2 June 2013 16:43, Paolo Bonzini <pbonz...@redhat.com> wrote: >> Reference counting the region piggybacks on reference counting of a QOM >> object, the "owner" of the region. The owner API is designed so that >> it will be called as little as possible. Unowned subregions will get a >> region if memory_region_set_owner is called after the subregion is added. >> This is in general the common case already; often setting the owner can >> be delegated to a bus-specific API that already takes a DeviceState >> (for example pci_register_bar or sysbus_init_mmio). > > This feels a bit fragile to me -- there doesn't seem to be > a clear rule for who has to set the owner of a region or > when they have to do it, or for ensuring that it doesn't > get forgotten altogether.
The best rule would be "who creates it". This would touch half the files in hw/, which I am trying to avoid. So I'm settling for: * in general, the bus sets the owner for regions that are managed by the bus (patches 5/6/9); * if the device plays directly with address_space_memory/io (shouldn't happen except in very special cases, such as patch 7) or if regions are added/deleted dynamically to a container (patches 8/10/11/12), then the device must set the owner itself. All stuff that should be in a comment, I guess... > What happens if I take a MemoryRegion* that another device > has exposed to me as a sysbus mmio region (and so claimed > ownership of) and pass it to pci_register_bar()? You get an assertion failure. > Who owns it at that point? [That's a legitimate thing to do, I think, > though I don't suppose anybody does it at the moment. > Sysbus MMIOs aren't only for mapping in the system address > space, they're a general way for one device to expose a > MemoryRegion * for use by another device.] I don't think it is legitimate, MMIO regions are just for use via sysbus_map_mmio. But the same scenario could apply without sysbus MMIO in the future (e.g. via QOM properties), so it is a good question. The right thing to do is to use a container or alias region, and put the 1st region inside it. Then the 1st region keeps its owner, and the container/alias gets a new one. Paolo
