Re: [Qemu-devel] [PATCH v3 1/3] pc-dimm: factor out MemoryDevice interface

[David Hildenbrand]

On 22.04.2018 12:10, David Gibson wrote:
> On Sun, Apr 22, 2018 at 10:21:34AM +0200, David Hildenbrand wrote:
>> On 22.04.2018 06:26, David Gibson wrote:
>>> On Fri, Apr 20, 2018 at 02:34:54PM +0200, David Hildenbrand wrote:
>>>> On the qmp level, we already have the concept of memory devices:
>>>>     "query-memory-devices"
>>>> Right now, we only support NVDIMM and PCDIMM.
>>>>
>>>> We want to map other devices later into the address space of the guest.
>>>> Such device could e.g. be virtio devices. These devices will have a
>>>> guest memory range assigned but won't be exposed via e.g. ACPI. We want
>>>> to make them look like memory device, but not glued to pc-dimm.
>>>>
>>>> Especially, it will not always be possible to have TYPE_PC_DIMM as a parent
>>>> class (e.g. virtio devices). Let's use an interface instead. As a first
>>>> part, convert handling of
>>>> - qmp_pc_dimm_device_list
>>>> - get_plugged_memory_size
>>>> to our new model. plug/unplug stuff etc. will follow later.
>>>>
>>>> A memory device will have to provide the following functions:
>>>> - get_addr(): Necessary, as the property "addr" can e.g. not be used for
>>>>               virtio devices (already defined).
>>>> - get_plugged_size(): The amount this device offers to the guest as of
>>>>                       now.
>>>> - get_region_size(): Because this can later on be bigger than the
>>>>                      plugged size.
>>>> - fill_device_info(): Fill MemoryDeviceInfo, e.g. for qmp.
>>>>
>>>> Signed-off-by: David Hildenbrand <address@hidden>
>>>
>>> Reviewed-by: David Gibson <address@hidden>
>>>
>>> with the exception of some tiny nits..
>>>
>>> [snip]
>>>> +static gint memory_device_addr_sort(gconstpointer a, gconstpointer b)
>>>> +{
>>>> +    MemoryDeviceState *md_a = MEMORY_DEVICE(a);
>>>> +    MemoryDeviceState *md_b = MEMORY_DEVICE(b);
>>>
>>> These probably should be const MemoryDeviceState *.
>>
>> Yes, that could work (depends on what the functions getting called
>> internally expect). Will look into it
> 
> Well, the only thing being called here is the ->get_addr() hook, which
> you can redefine if necessary.  Discarding the const in the passed in
> pointers seems like bad idea, even though it won't explicitly warn due
> to the existing MEMORY_DEVICE() cast.

I converted all MemoryDevice functions to eat "const MemoryDeviceState *md".

The only problematic part now is

static uint64_t pc_dimm_md_get_region_size(const MemoryDeviceState *md)

It calls "ddc->get_memory_region(dimm, &error_abort);", and it looks
like we cannot convert this to eat a const DIMM pointer (as it has to
return a !const pointer to the memory region).

So we will actually drop the const here - which is fine because we don't
modify anything.

> 
>>>> +    MemoryDeviceClass *mdc_a = MEMORY_DEVICE_GET_CLASS(a);
>>>> +    MemoryDeviceClass *mdc_b = MEMORY_DEVICE_GET_CLASS(b);
>>>> +    const uint64_t addr_a = mdc_a->get_addr(md_a);
>>>> +    const uint64_t addr_b = mdc_b->get_addr(md_b);
>>>> +
>>>> +    if (addr_a > addr_b) {
>>>> +        return 1;
>>>> +    } else if (addr_a < addr_b) {
>>>> +        return -1;
>>>> +    }
>>>> +    return 0;
>>>> +}
>>>> +
>>>> +static int memory_device_built_list(Object *obj, void *opaque)
>>>
>>> s/built/build/ will read a bit more clearly I think.
>>>
>>
>> Indeed, thanks!
>>
> 


-- 

Thanks,

David / dhildenb