Re: [Qemu-devel] [PULL 05/15] qmp/hmp: add query-vm-generation-id and 'info vm-generation-id' commands

[Laszlo Ersek <lersek@redhat.com>]

On 03/02/17 09:42, Markus Armbruster wrote:
> Laszlo Ersek <lersek@redhat.com> writes:
> 
>> On 03/02/17 09:11, Markus Armbruster wrote:
>>> Crash bug, I'm afraid...
>>>
>>> "Michael S. Tsirkin" <mst@redhat.com> writes:
>>>
>>>> From: Igor Mammedov <imammedo@redhat.com>
>>>>
>>>> Add commands to query Virtual Machine Generation ID counter.
>>>>
>>>> QMP command example:
>>>>     { "execute": "query-vm-generation-id" }
>>>>
>>>> HMP command example:
>>>>     info vm-generation-id
>>>>
>>>> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
>>>> Reviewed-by: Eric Blake <eblake@redhat.com>
>>>> Signed-off-by: Ben Warren <ben@skyportsystems.com>
>>>> Reviewed-by: Laszlo Ersek <lersek@redhat.com>
>>>> Tested-by: Laszlo Ersek <lersek@redhat.com>
>>>> Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
>>>> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
>>>> ---
>>>>  qapi-schema.json     | 20 ++++++++++++++++++++
>>>>  hmp.h                |  1 +
>>>>  hmp.c                |  9 +++++++++
>>>>  hw/acpi/vmgenid.c    | 16 ++++++++++++++++
>>>>  stubs/vmgenid.c      |  9 +++++++++
>>>>  hmp-commands-info.hx | 14 ++++++++++++++
>>>>  stubs/Makefile.objs  |  1 +
>>>>  7 files changed, 70 insertions(+)
>>>>  create mode 100644 stubs/vmgenid.c
>>>>
>>>> diff --git a/qapi-schema.json b/qapi-schema.json
>>>> index d6186d4..84692da 100644
>>>> --- a/qapi-schema.json
>>>> +++ b/qapi-schema.json
>>>> @@ -6188,3 +6188,23 @@
>>>>  #
>>>>  ##
>>>>  { 'command': 'query-hotpluggable-cpus', 'returns': ['HotpluggableCPU'] }
>>>> +
>>>> +##
>>>> +# @GuidInfo:
>>>> +#
>>>> +# GUID information.
>>>> +#
>>>> +# @guid: the globally unique identifier
>>>> +#
>>>> +# Since: 2.9
>>>> +##
>>>> +{ 'struct': 'GuidInfo', 'data': {'guid': 'str'} }
>>>> +
>>>> +##
>>>> +# @query-vm-generation-id:
>>>> +#
>>>> +# Show Virtual Machine Generation ID
>>>> +#
>>>> +# Since 2.9
>>>> +##
>>>> +{ 'command': 'query-vm-generation-id', 'returns': 'GuidInfo' }
>>> [...]
>>>> diff --git a/hw/acpi/vmgenid.c b/hw/acpi/vmgenid.c
>>>> index c8465df..744f284 100644
>>>> --- a/hw/acpi/vmgenid.c
>>>> +++ b/hw/acpi/vmgenid.c
>>>> @@ -240,3 +240,19 @@ static void vmgenid_register_types(void)
>>>>  }
>>>>  
>>>>  type_init(vmgenid_register_types)
>>>> +
>>>> +GuidInfo *qmp_query_vm_generation_id(Error **errp)
>>>> +{
>>>> +    GuidInfo *info;
>>>> +    VmGenIdState *vms;
>>>> +    Object *obj = find_vmgenid_dev();
>>>> +
>>>> +    if (!obj) {
>>>> +        return NULL;
>>>> +    }
>>>> +    vms = VMGENID(obj);
>>>> +
>>>> +    info = g_malloc0(sizeof(*info));
>>>> +    info->guid = qemu_uuid_unparse_strdup(&vms->guid);
>>>> +    return info;
>>>> +}
>>>
>>> This either returns a GuidInfo or NULL.
>>>
>>> If it returns NULL, the generated qmp_marshal_output_GuidInfo() will
>>> crash like this:
>>>
>>> #0  0x00007fffdb4c7765 in raise () at /lib64/libc.so.6
>>> #1  0x00007fffdb4c936a in abort () at /lib64/libc.so.6
>>> #2  0x00007fffdb4bff97 in __assert_fail_base () at /lib64/libc.so.6
>>> #3  0x00007fffdb4c0042 in  () at /lib64/libc.so.6
>>> #4  0x0000555555c800a0 in visit_start_struct (v=
>>>     0x555557727000, name=0x555555cf29e8 "unused", obj=0x7fffffffc7c8, size=8, errp=0x7fffffffc790) at /work/armbru/qemu/qapi/qapi-visit-core.c:49
>>> #5  0x0000555555c5d398 in visit_type_GuidInfo (v=
>>>     0x555557727000, name=0x555555cf29e8 "unused", obj=0x7fffffffc7c8, errp=0x7fffffffc7d8) at qapi-visit.c:6038
>>> #6  0x0000555555922fc0 in qmp_marshal_output_GuidInfo (ret_in=0x0, ret_out=0x7fffffffc870, errp=0x7fffffffc820) at qmp-marshal.c:5148
>>> #7  0x0000555555923123 in qmp_marshal_query_vm_generation_id (args=0x555557a67500, ret=0x7fffffffc870, errp=0x7fffffffc868) at qmp-marshal.c:5186
>>> #8  0x0000555555c83a73 in do_qmp_dispatch (request=0x555556ab3200, errp=0x7fffffffc8c0) at /work/armbru/qemu/qapi/qmp-dispatch.c:97
>>> #9  0x0000555555c83ba3 in qmp_dispatch (request=0x555556ab3200)
>>>     at /work/armbru/qemu/qapi/qmp-dispatch.c:124
>>> #10 0x00005555557bb671 in handle_qmp_command (parser=
>>>     0x5555568776b0, tokens=0x555556858520) at /work/armbru/qemu/monitor.c:3789
>>> #11 0x0000555555c8af2f in json_message_process_token (lexer=0x5555568776b8, input=0x5555568582e0, type=JSON_RCURLY, x=48, y=1)
>>>     at /work/armbru/qemu/qobject/json-streamer.c:105
>>>
>>> Sorry for not having reviewed this earlier.  On the other hand, how come
>>> this survived testing?
>>
>> We primarily focused on testing the functionality, not the failure /
>> corner cases, I think.
> 
> That's as natural as it is wrong :)
> 
> I'm a lackluster tester myself.  The only way I can bring myself to test
> systematically is write automated tests.  Fortunately, our
> infrastructure for that is much better than it used to be.  Our habits
> still seem to be trailing the infrastructure, though.
> 
> See also "New QMP command without a test -> automatic NAK", Message-ID:
> <871sugkrw5.fsf@dusky.pond.sub.org>.
> 
>>                        (There are at least two other known startup
>> scenarios that are not handled correctly just yet, although they don't
>> crash -- multiple vmgenid devices, and vmgenid on machtypes without
>> writeable fw_cfg.)
>>
>> Also, in my testing I only called the monitor command via HMP (from
>> virsh), and AFAICS that one doesn't crash even if the device is missing.
> 
> Correct.
> 
>> Nonetheless, qmp_query_vm_generation_id() should set an error when it
>> returns NULL, yes.
> 
> That's the obvious fix.  It's a one-liner.
> 
>> I think Ben wants to post a followup series with those fixes mentioned
>> above, in time for 2.9, perhaps this crash can be addressed in there
>> too. Ben?
> 
> Since the fix is a one-liner, I'd like you guys to consider respinning
> this pull request with the fix.

If Ben & Michael send out a new pull with the above fixed, I'd like to
point out that the updated SeaBIOS blob is now in the tree (see commit
8779fccbef0c, "seabios: update to 1.10.2 release", 2017-02-28), so the
unit test patch can be included as well.

Thanks
Laszlo