introduce a new monitor command 'dump-guest-memory' to dump guest's memory

The command's usage:
   dump-guest-memory [-p] protocol [begin] [length]
The supported protocol can be file or fd:
1. file: the protocol starts with "file:", and the following string is
   the file's path.
2. fd: the protocol starts with "fd:", and the following string is the
   fd's name.

Note:
  1. If you want to use gdb to process the core, please specify -p option.
     The reason why the -p option is not default is:
       a. guest machine in a catastrophic state can have corrupted memory,
          which we cannot trust.
       b. The guest machine can be in read-mode even if paging is enabled.
          For example: the guest machine uses ACPI to sleep, and ACPI sleep
          state goes in real-mode.
  2. If you don't want to dump all guest's memory, please specify the start
     physical address and the length.

Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>

memory_mapping.c

@@ -220,3 +220,30 @@ void qemu_get_guest_simple_memory_mapping(MemoryMappingList *list)
         create_new_memory_mapping(list, block->offset, 0, block->length);
     }
 }
+
+void memory_mapping_filter(MemoryMappingList *list, int64_t begin,
+                           int64_t length)
+{
+    MemoryMapping *cur, *next;
+
+    QTAILQ_FOREACH_SAFE(cur, &list->head, next, next) {
+        if (cur->phys_addr >= begin + length ||
+            cur->phys_addr + cur->length <= begin) {
+            QTAILQ_REMOVE(&list->head, cur, next);
+            list->num--;
+            continue;
+        }
+
+        if (cur->phys_addr < begin) {
+            cur->length -= begin - cur->phys_addr;
+            if (cur->virt_addr) {
+                cur->virt_addr += begin - cur->phys_addr;
+            }
+            cur->phys_addr = begin;
+        }
+
+        if (cur->phys_addr + cur->length > begin + length) {
+            cur->length -= cur->phys_addr + cur->length - begin - length;
+        }
+    }
+}