Re: [Qemu-devel] [PATCH v6 18/33] dimm: get mapped memory region from DIMMDeviceClass->get_memory_region

[Xiao Guangrong]

On 10/31/2015 10:15 PM, Xiao Guangrong wrote:
> On 10/31/2015 06:52 PM, Vladimir Sementsov-Ogievskiy wrote:
> > On 30.10.2015 08:56, Xiao Guangrong wrote:
> > > Curretly, the memory region of backed memory is directly mapped to
> > > guest's address space, however, it is not true for nvdimm device
> > >
> > > This patch let dimm device realize this fact and use
> > > DIMMDeviceClass->get_memory_region method to get the mapped memory
> > > region
> > >
> > > Signed-off-by: Xiao Guangrong <address@hidden>
> > > ---
> > >   hw/mem/dimm.c | 3 ++-
> > >   1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/hw/mem/dimm.c b/hw/mem/dimm.c
> > > index 4a63409..498d380 100644
> > > --- a/hw/mem/dimm.c
> > > +++ b/hw/mem/dimm.c
> > > @@ -377,8 +377,9 @@ static void dimm_get_size(Object *obj, Visitor *v, void 
> > > *opaque,
> > >       int64_t value;
> > >       MemoryRegion *mr;
> > >       DIMMDevice *dimm = DIMM(obj);
> > > +    DIMMDeviceClass *ddc = DIMM_GET_CLASS(obj);
> > > -    mr = host_memory_backend_get_memory(dimm->hostmem, errp);
> > > +    mr = ddc->get_memory_region(dimm);
> > >       value = memory_region_size(mr);
> > >       visit_type_int(v, &value, name, errp);
> >
> > Isn't it better to add Error** parameter to get_memory_region and not mix 
> > returning error in errp
> > parameter and aborting through &error_abort?
>
> Yes, it's better, will do. Thanks for your suggestion.

Vladimir,

After checking the current code, the @errp in pc-dimm's get_memory_region() is 
useless
and all its caller did not check the return value as they assumed the backend 
memory of
pc-dimm is always properly initialized.

So we catch the error condition internally instead of propagating it to the 
caller:

 static MemoryRegion *pc_dimm_get_memory_region(DIMMDevice *dimm)
 {
-    return host_memory_backend_get_memory(dimm->hostmem, &error_abort);
+    Error *local_err = NULL;
+    MemoryRegion *mr;
+
+    mr = host_memory_backend_get_memory(dimm->hostmem, &local_err);
+
+    /*
+     * plug a pc-dimm device whose backend memory was not properly
+     * initialized?
+     */
+    assert(!local_err && mr);
+    return mr;
 }

please review it in the new version i have CCed you.

Thanks for your review.