On Fri, Nov 06, 2020 at 10:50:19AM -0500, Eduardo Habkost wrote: > On Fri, Nov 06, 2020 at 10:45:11AM +0100, Kevin Wolf wrote: > > Am 04.11.2020 um 16:59 hat Eduardo Habkost geschrieben: > > > This series refactor the qdev property code so the static > > > property system can be used by any QOM type. As an example, at > > > the end of the series some properties in TYPE_MACHINE are > > > converted to static properties to demonstrate the new API. > > > > > > Changes v1 -> v2 > > > ---------------- > > > > > > * Rename functions and source files to call the new feature > > > "field property" instead of "static property" > > > > > > * Change the API signature from an array-based interface similar > > > to device_class_set_props() to a object_property_add()-like > > > interface. > > > > > > This means instead of doing this: > > > > > > object_class_property_add_static_props(oc, my_array_of_props); > > > > > > properties are registered like this: > > > > > > object_class_property_add_field(oc, "property-name" > > > PROP_XXX(MyState, my_field), > > > prop_allow_set_always); > > > > > > where PROP_XXX is a PROP_* macro like PROP_STRING, PROP_BOOL, > > > etc. > > > > In comparison, I really like the resulting code from the array based > > interface in v1 better. > > > > I think it's mostly for two reasons: First, the array is much more > > compact and easier to read. And maybe even more importantly, you know > > it's static data and only static data. The function based interface can > > be mixed with other code or the parameter list can contain calls to > > other functions with side effects, so there are a lot more opportunities > > for surprises. > > This is a really good point, and I strongly agree with it. > Letting code do funny tricks at runtime is one of the reasons QOM > properties became hard to introspect. > > > > > What I didn't like about the v1 interface is that there is still a > > separate object_class_property_set_description() for each property, but > > I think that could have been fixed by moving the description to the > > definitions in the array, too. > > This would be very easy to implement.
This was implemented at: https://gitlab.com/ehabkost/qemu/-/commits/work/qdev-make-generic This is the interface I'd like to submit as v3: static Property machine_props[] = { DEFINE_PROP_STRING("kernel", MachineState, kernel_filename, .description = "Linux kernel image file"), DEFINE_PROP_STRING("initrd", MachineState, initrd_filename, .description = "Linux initial ramdisk file"), DEFINE_PROP_STRING("append", MachineState, kernel_cmdline, .description = "Linux kernel command line"), DEFINE_PROP_STRING("dtb", MachineState, dtb, .description = "Linux kernel device tree file"), DEFINE_PROP_STRING("dumpdtb", MachineState, dumpdtb, .description = "Dump current dtb to a file and quit"), DEFINE_PROP_STRING("dt-compatible", MachineState, dt_compatible, .description = "Overrides the \"compatible\" " "property of the dt root node"), DEFINE_PROP_STRING("firmware", MachineState, firmware, .description = "Firmware image"), DEFINE_PROP_STRING("memory-backend", MachineState, ram_memdev_id, .description = "ID of memory backend object"), DEFINE_PROP_BOOL("dump-guest-core", MachineState, dump_guest_core, true, .description = "Include guest memory in a core dump"), DEFINE_PROP_BOOL("mem-merge", MachineState, mem_merge, true, .description = "Enable/disable memory merge support"), DEFINE_PROP_BOOL("graphics", MachineState, enable_graphics, true, .description = "Set on/off to enable/disable graphics emulation"), DEFINE_PROP_BOOL("suppress-vmdesc", MachineState, suppress_vmdesc, false, .description = "Set on to disable self-describing migration"), DEFINE_PROP_UINT32("phandle-start", MachineState, phandle_start, 0, .description = "The first phandle ID we may generate dynamically"), DEFINE_PROP_END_OF_LIST(), }; static void machine_class_init(ObjectClass *oc, void *data) { ... object_class_add_field_properties(oc, machine_props, prop_allow_set_always); ... } > > > > > On Fri, Oct 30, 2020 at 06:10:34PM +0100, Paolo Bonzini wrote: > > > On 29/10/20 23:02, Eduardo Habkost wrote: > > > > +static Property machine_props[] = { > > > > + DEFINE_PROP_STRING("kernel", MachineState, kernel_filename), > > > > + DEFINE_PROP_STRING("initrd", MachineState, initrd_filename), > > > > + DEFINE_PROP_STRING("append", MachineState, kernel_cmdline), > > > > + DEFINE_PROP_STRING("dtb", MachineState, dtb), > > > > + DEFINE_PROP_STRING("dumpdtb", MachineState, dumpdtb), > > > > + DEFINE_PROP_STRING("dt-compatible", MachineState, dt_compatible), > > > > + DEFINE_PROP_STRING("firmware", MachineState, firmware), > > > > + DEFINE_PROP_STRING("memory-backend", MachineState, ram_memdev_id), > > > > + DEFINE_PROP_END_OF_LIST(), > > > > +}; > > > > + > > > > > > While I think generalizing the _code_ for static properties is obviously > > > a good idea, I am not sure about generalizing the interface for adding > > > them. > > > > > > The reason is that we already have a place for adding properties in > > > class_init, and having a second makes things "less local", so to speak. > > > > As long as you have the function call to apply the properites array in > > .class_init, it should be obvious enough what you're doing. > > > > Of course, I think we should refrain from mixing both styles in a single > > object, but generally speaking the array feels so much better that I > > don't think we should reject it just because QOM only had a different > > interface so far (and the property array is preexisting in qdev, too, so > > we already have differences between objects - in fact, the majority of > > objects is probably qdev today). > > This is also a strong argument. The QEMU code base has ~500 > matches for "object*_property_add*" calls, and ~2100 for > "DEFINE_PROP*". > > Converting qdev arrays to object_class_property_add_*() calls > would be a huge effort with no gains. The end result would be > two different APIs for registering class field properties > coexisting for a long time, and people still confused on what's > the preferred API. > > -- > Eduardo -- Eduardo
