3.1.1 平衡二叉树中改变区块属性，并分裂区块保持属性一致:MmSplitRegion（）

MmSplitRegion函数

//改变区块属性，并分裂区块保持属性一致:

---

MmSplitRegion

//改变区块属性，并分裂区块保持属性一致:

PMM_REGION static
MmSplitRegion(PMM_REGION InitialRegion, PVOID InitialBaseAddress,
              PVOID StartAddress, ULONG Length, ULONG NewType,
              ULONG NewProtect, PMADDRESS_SPACE AddressSpace,
              PMM_ALTER_REGION_FUNC AlterFunc)
{
   PMM_REGION NewRegion1;
   PMM_REGION NewRegion2;
   ULONG InternalLength;

   /* Allocate this in front otherwise the failure case is too difficult. */
   NewRegion2 = ExAllocatePoolWithTag(NonPagedPool, sizeof(MM_REGION),
                                      TAG_MM_REGION);
   if (NewRegion2 == NULL)
   {
      return(NULL);
   }

   /* Create the new region. */
   NewRegion1 = ExAllocatePoolWithTag(NonPagedPool, sizeof(MM_REGION),
                                      TAG_MM_REGION);
   if (NewRegion1 == NULL)
   {
      ExFreePool(NewRegion2);
      return(NULL);
   }
   NewRegion1->Type = NewType;
   NewRegion1->Protect = NewProtect;
   InternalLength = ((char*)InitialBaseAddress + InitialRegion->Length) - (char*)StartAddress;
   InternalLength = min(InternalLength, Length);
   NewRegion1->Length = InternalLength;
   InsertAfterEntry(&InitialRegion->RegionListEntry,
                    &NewRegion1->RegionListEntry);

   /*
    * Call our helper function to do the changes on the addresses contained
    * in the initial region.
    */
   AlterFunc(AddressSpace, StartAddress, InternalLength, InitialRegion->Type,
             InitialRegion->Protect, NewType, NewProtect);

   /*
    * If necessary create a new region for the portion of the initial region
    * beyond the range of addresses to alter.
    */
   if (((char*)InitialBaseAddress + InitialRegion->Length) > ((char*)StartAddress + Length))
   {
      NewRegion2->Type = InitialRegion->Type;
      NewRegion2->Protect = InitialRegion->Protect;
      NewRegion2->Length = ((char*)InitialBaseAddress + InitialRegion->Length) -
                           ((char*)StartAddress + Length);
      InsertAfterEntry(&NewRegion1->RegionListEntry,
                       &NewRegion2->RegionListEntry);
   }
   else
   {
      ExFreePool(NewRegion2);
   }

   /* Either remove or shrink the initial region. */
   if (InitialBaseAddress == StartAddress)
   {
      RemoveEntryList(&InitialRegion->RegionListEntry);
      ExFreePool(InitialRegion);
   }
   else
   {
      InitialRegion->Length = (char*)StartAddress - (char*)InitialBaseAddress;
   }

   return(NewRegion1);
}