Re: [Qemu-devel] [PATCH] migration: fix analyze-migration.py script

[Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>]

On 06/09/15 12:54, Mark Cave-Ayland wrote:

> On 06/09/15 09:36, Alexander Graf wrote:
> 
>> On 05.09.15 21:51, Mark Cave-Ayland wrote:
>>> Commit 61964 "Add configuration section" broke the analyze-migration.py script
>>> which terminates due to the unrecognised section. Fix the script by parsing
>>> the contents of the configuration section directly into a new
>>> ConfigurationSection object (although nothing is done with it yet).
>>>
>>> Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
>>> ---
>>>  scripts/analyze-migration.py |   13 +++++++++++++
>>>  1 file changed, 13 insertions(+)
>>>
>>> diff --git a/scripts/analyze-migration.py b/scripts/analyze-migration.py
>>> index f6894be..1455387 100755
>>> --- a/scripts/analyze-migration.py
>>> +++ b/scripts/analyze-migration.py
>>> @@ -252,6 +252,15 @@ class HTABSection(object):
>>>      def getDict(self):
>>>          return ""
>>>  
>>> +
>>> +class ConfigurationSection(object):
>>> +    def __init__(self, file):
>>> +        self.file = file
>>> +
>>> +    def read(self):
>>> +        name_len = self.file.read32()
>>> +        name = self.file.readstr(len = name_len)
>>> +
>>>  class VMSDFieldGeneric(object):
>>>      def __init__(self, desc, file):
>>>          self.file = file
>>> @@ -474,6 +483,7 @@ class MigrationDump(object):
>>>      QEMU_VM_SECTION_FULL  = 0x04
>>>      QEMU_VM_SUBSECTION    = 0x05
>>>      QEMU_VM_VMDESCRIPTION = 0x06
>>> +    QEMU_VM_CONFIGURATION = 0x07
>>>      QEMU_VM_SECTION_FOOTER= 0x7e
>>>  
>>>      def __init__(self, filename):
>>> @@ -514,6 +524,9 @@ class MigrationDump(object):
>>>              section_type = file.read8()
>>>              if section_type == self.QEMU_VM_EOF:
>>>                  break
>>> +            elif section_type == self.QEMU_VM_CONFIGURATION:
>>> +                section = ConfigurationSection(file)
>>> +                section.read()
>>
>> So since we don't have a normal section header, there is no version
>> field either. That in turn means that the format is determined by the
>> machine version only - bleks.
> 
> Yes :(  I double-checked the output of a migration file with hexdump and
> confirmed that just the raw fields are included without any additional
> metadata, even though the state is held in a VMStateDescription.
> 
>> So if there ever has to be more in the configuration section than the
>> machine name, please move to a more detectable scheme. Ideally something
>> that contains
>>
>>   * version
>>   * length of dynamically sized fields
>>   * lenght of full blob
>>
>> would be ideal, so that we have a chance to at least put code into the
>> analyze script to examine it.
>>
>> For now, I think the hard coded solution in the analyze script is
>> reasonable.
>>
>> However, I think we should print out the name if we find it. It should
>> be as simple as adding a special case for the configuration section in
>> MigrationDump.getDict().
> 
> I did play with adding a separate JSON object for configuration but was
> torn between whether configuration should have its own JSON object
> (better if we include extra fields and metadata as above) or to just
> embed it as a simple "machine" property similar to "page_size". I'll
> wait until we hear back from David/Juan and submit a v2 accordingly.

Ping again from Juan/David? The analyze-migration.py script is currently
broken without this patch (or another equivalent) applied.


ATB,

Mark.