pc-dimm: get_memory_region() will not fail after realize

Let's try to reduce error handling a bit. In the plug/unplug case, the
device was realized and therefore we can assume that getting access to
the memory region will not fail.

For get_vmstate_memory_region() this is already handled that way.
Document both cases.

Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20180619134141.29478-13-david@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/i386/pc.c

@@ -1706,15 +1706,10 @@ static void pc_memory_plug(HotplugHandler *hotplug_dev,
     PCMachineClass *pcmc = PC_MACHINE_GET_CLASS(pcms);
     PCDIMMDevice *dimm = PC_DIMM(dev);
     PCDIMMDeviceClass *ddc = PC_DIMM_GET_CLASS(dimm);
-    MemoryRegion *mr;
+    MemoryRegion *mr = ddc->get_memory_region(dimm, &error_abort);
     uint64_t align = TARGET_PAGE_SIZE;
     bool is_nvdimm = object_dynamic_cast(OBJECT(dev), TYPE_NVDIMM);
 
-    mr = ddc->get_memory_region(dimm, &local_err);
-    if (local_err) {
-        goto out;
-    }
-
     if (memory_region_get_alignment(mr) && pcmc->enforce_aligned_dimm) {
         align = memory_region_get_alignment(mr);
     }

hw/mem/pc-dimm.c

@@ -37,15 +37,10 @@ void pc_dimm_plug(DeviceState *dev, MachineState *machine, uint64_t align,
     PCDIMMDeviceClass *ddc = PC_DIMM_GET_CLASS(dimm);
     MemoryRegion *vmstate_mr = ddc->get_vmstate_memory_region(dimm,
                                                               &error_abort);
+    MemoryRegion *mr = ddc->get_memory_region(dimm, &error_abort);
     Error *local_err = NULL;
-    MemoryRegion *mr;
     uint64_t addr;
 
-    mr = ddc->get_memory_region(dimm, &local_err);
-    if (local_err) {
-        goto out;
-    }
-
     addr = object_property_get_uint(OBJECT(dimm),
                                     PC_DIMM_ADDR_PROP, &local_err);
     if (local_err) {

hw/ppc/spapr.c

@@ -3149,14 +3149,10 @@ static void spapr_memory_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
     sPAPRMachineState *ms = SPAPR_MACHINE(hotplug_dev);
     PCDIMMDevice *dimm = PC_DIMM(dev);
     PCDIMMDeviceClass *ddc = PC_DIMM_GET_CLASS(dimm);
-    MemoryRegion *mr;
+    MemoryRegion *mr = ddc->get_memory_region(dimm, &error_abort);
     uint64_t align, size, addr;
     uint32_t node;
 
-    mr = ddc->get_memory_region(dimm, &local_err);
-    if (local_err) {
-        goto out;
-    }
     align = memory_region_get_alignment(mr);
     size = memory_region_size(mr);
 
@@ -3344,16 +3340,12 @@ static void spapr_memory_unplug_request(HotplugHandler *hotplug_dev,
     Error *local_err = NULL;
     PCDIMMDevice *dimm = PC_DIMM(dev);
     PCDIMMDeviceClass *ddc = PC_DIMM_GET_CLASS(dimm);
-    MemoryRegion *mr;
+    MemoryRegion *mr = ddc->get_memory_region(dimm, &error_abort);
     uint32_t nr_lmbs;
     uint64_t size, addr_start, addr;
     int i;
     sPAPRDRConnector *drc;
 
-    mr = ddc->get_memory_region(dimm, &local_err);
-    if (local_err) {
-        goto out;
-    }
     size = memory_region_size(mr);
     nr_lmbs = size / SPAPR_MEMORY_BLOCK_SIZE;
 

include/hw/mem/pc-dimm.h

@@ -62,9 +62,11 @@ typedef struct PCDIMMDevice {
  * @realize: called after common dimm is realized so that the dimm based
  * devices get the chance to do specified operations.
  * @get_memory_region: returns #MemoryRegion associated with @dimm which
- * is directly mapped into the physical address space of guest.
+ * is directly mapped into the physical address space of guest. Will not
+ * fail after the device was realized.
  * @get_vmstate_memory_region: returns #MemoryRegion which indicates the
- * memory of @dimm should be kept during live migration.
+ * memory of @dimm should be kept during live migration. Will not fail
+ * after the device was realized.
  */
 typedef struct PCDIMMDeviceClass {
     /* private */