migration: Fix analyze-migration.py when ignore-shared is used

The script is currently broken when the x-ignore-shared capability is
used:

Traceback (most recent call last):
  File "./scripts/analyze-migration.py", line 656, in <module>
    dump.read(dump_memory = args.memory)
  File "./scripts/analyze-migration.py", line 593, in read
    section.read()
  File "./scripts/analyze-migration.py", line 163, in read
    self.name = self.file.readstr(len = namelen)
  File "./scripts/analyze-migration.py", line 53, in readstr
    return self.readvar(len).decode('utf-8')
UnicodeDecodeError: 'utf-8' codec can't decode byte 0x82 in position 55: invalid start byte

We're currently adding data to the middle of the ram section depending
on the presence of the capability. As a consequence, any code loading
the ram section needs to know about capabilities so it can interpret
the stream.

Skip the byte that's added when x-ignore-shared is used to fix the
script.

Signed-off-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Message-ID: <20231009184326.15777-5-farosas@suse.de>

scripts/analyze-migration.py

@@ -123,6 +123,7 @@ def __init__(self, file, version_id, ramargs, section_key):
         self.TARGET_PAGE_SIZE = ramargs['page_size']
         self.dump_memory = ramargs['dump_memory']
         self.write_memory = ramargs['write_memory']
+        self.ignore_shared = ramargs['ignore_shared']
         self.sizeinfo = collections.OrderedDict()
         self.data = collections.OrderedDict()
         self.data['section sizes'] = self.sizeinfo
@@ -169,6 +170,8 @@ def read(self):
                         f.truncate(0)
                         f.truncate(len)
                         self.files[self.name] = f
+                    if self.ignore_shared:
+                        mr_addr = self.file.read64()
                 flags &= ~self.RAM_SAVE_FLAG_MEM_SIZE
 
             if flags & self.RAM_SAVE_FLAG_COMPRESS:
@@ -572,6 +575,7 @@ def read(self, desc_only = False, dump_memory = False, write_memory = False):
         ramargs['page_size'] = self.vmsd_desc['page_size']
         ramargs['dump_memory'] = dump_memory
         ramargs['write_memory'] = write_memory
+        ramargs['ignore_shared'] = False
         self.section_classes[('ram',0)][1] = ramargs
 
         while True:
@@ -582,6 +586,7 @@ def read(self, desc_only = False, dump_memory = False, write_memory = False):
                 config_desc = self.vmsd_desc.get('configuration')
                 section = ConfigurationSection(file, config_desc)
                 section.read()
+                ramargs['ignore_shared'] = section.has_capability('x-ignore-shared')
             elif section_type == self.QEMU_VM_SECTION_START or section_type == self.QEMU_VM_SECTION_FULL:
                 section_id = file.read32()
                 name = file.readstr()