scripts/analyze-migration: Support mapped-ram snapshot format

The script has not been updated to read mapped-ram snapshots and is currently
crashing when trying to read such a file.

With this commit, it can now read a snapshot created with:

    (qemu) migrate_set_capability x-ignore-shared on
    (qemu) migrate_set_capability mapped-ram on
    (qemu) migrate -d file:vm.state

Signed-off-by: Pawel Zmarzly <pzmarzly0@gmail.com>
Link: https://lore.kernel.org/r/20251126155015.941129-1-pzmarzly0@gmail.com
[peterx: space fixes, introduce parseMappedRamBlob(), add comments, etc.]
Signed-off-by: Peter Xu <peterx@redhat.com>

scripts/analyze-migration.py

@@ -19,6 +19,7 @@
 
 import json
 import os
+import math
 import argparse
 import collections
 import struct
@@ -127,6 +128,7 @@ class RamSection(object):
         self.dump_memory = ramargs['dump_memory']
         self.write_memory = ramargs['write_memory']
         self.ignore_shared = ramargs['ignore_shared']
+        self.mapped_ram = ramargs['mapped_ram']
         self.sizeinfo = collections.OrderedDict()
         self.data = collections.OrderedDict()
         self.data['section sizes'] = self.sizeinfo
@@ -146,6 +148,57 @@ class RamSection(object):
     def getDict(self):
         return self.data
 
+    def parseMappedRamBlob(self, len):
+        version = self.file.read32()
+        if version != 1:
+            raise Exception("Unsupported MappedRamHeader version %s" % version)
+
+        page_size = self.file.read64()
+        if page_size != self.TARGET_PAGE_SIZE:
+            raise Exception("Page size mismatch in MappedRamHeader")
+
+        bitmap_offset = self.file.read64()
+        pages_offset = self.file.read64()
+
+        if self.ignore_shared and bitmap_offset == 0 and pages_offset == 0:
+            # This is a shared ramblock, x-ignore-share must have been
+            # enabled, and mapped-ram didn't allocate bitmap or page blob
+            # for it.
+            return
+
+        if self.dump_memory or self.write_memory:
+            num_pages = len // page_size
+
+            self.file.seek(bitmap_offset, os.SEEK_SET)
+            bitmap_len = int(math.ceil(num_pages / 8))
+            bitmap = self.file.readvar(size=bitmap_len)
+
+            self.file.seek(pages_offset, os.SEEK_SET)
+            for page_num in range(num_pages):
+                page_addr = page_num * page_size
+
+                is_filled = (bitmap[page_num // 8] >> page_num % 8) & 1
+                if is_filled:
+                    data = self.file.readvar(size=self.TARGET_PAGE_SIZE)
+                    if self.write_memory:
+                        self.files[self.name].seek(page_addr, os.SEEK_SET)
+                        self.files[self.name].write(data)
+                    if self.dump_memory:
+                        hexdata = " ".join("{0:02x}".format(c) for c in data)
+                        self.memory['%s (0x%016x)' %
+                                    (self.name, page_addr)] = hexdata
+                else:
+                    self.file.seek(self.TARGET_PAGE_SIZE, os.SEEK_CUR)
+                    if self.write_memory:
+                        self.files[self.name].seek(page_addr, os.SEEK_SET)
+                        self.files[self.name].write(
+                            b'\x00' * self.TARGET_PAGE_SIZE)
+                    if self.dump_memory:
+                        self.memory['%s (0x%016x)' %
+                                    (self.name, page_addr)] = 'Filled with 0x00'
+
+        self.file.seek(pages_offset + len, os.SEEK_SET)
+
     def read(self):
         # Read all RAM sections
         while True:
@@ -170,6 +223,8 @@ class RamSection(object):
                         self.files[self.name] = f
                     if self.ignore_shared:
                         mr_addr = self.file.read64()
+                    if self.mapped_ram:
+                        self.parseMappedRamBlob(len)
                 flags &= ~self.RAM_SAVE_FLAG_MEM_SIZE
 
             if flags & self.RAM_SAVE_FLAG_ZERO:
@@ -660,6 +715,7 @@ class MigrationDump(object):
         ramargs['dump_memory'] = dump_memory
         ramargs['write_memory'] = write_memory
         ramargs['ignore_shared'] = False
+        ramargs['mapped_ram'] = False
         self.section_classes[('ram',0)][1] = ramargs
 
         while True:
@@ -671,6 +727,7 @@ class MigrationDump(object):
                 section = ConfigurationSection(file, config_desc)
                 section.read()
                 ramargs['ignore_shared'] = section.has_capability('x-ignore-shared')
+                ramargs['mapped_ram'] = section.has_capability('mapped-ram')
             elif section_type == self.QEMU_VM_SECTION_START or section_type == self.QEMU_VM_SECTION_FULL:
                 section_id = file.read32()
                 name = file.readstr()