Re: [Qemu-devel] [PATCH RFC v2 3/5] net/filter: Introduce a helper to add a filter to the netdev

[Jason Wang]

On 02/01/2016 05:22 PM, Hailiang Zhang wrote:
> On 2016/2/1 17:04, Jason Wang wrote:
>>
>>
>> On 02/01/2016 03:56 PM, Hailiang Zhang wrote:
>>> On 2016/2/1 15:46, Jason Wang wrote:
>>>>
>>>>
>>>> On 02/01/2016 02:13 PM, Hailiang Zhang wrote:
>>>>> On 2016/2/1 11:14, Jason Wang wrote:
>>>>>>
>>>>>>
>>>>>> On 01/27/2016 04:29 PM, zhanghailiang wrote:
>>>>>>> We add a new helper function netdev_add_filter(), this function
>>>>>>> can help adding a filter object to a netdev.
>>>>>>> Besides, we add a is_default member for struct NetFilterState
>>>>>>> to indicate whether the filter is default or not.
>>>>>>>
>>>>>>> Signed-off-by: zhanghailiang <address@hidden>
>>>>>>> ---
>>>>>>> v2:
>>>>>>>     -Re-implement netdev_add_filter() by re-using object_create()
>>>>>>>      (Jason's suggestion)
>>>>>>> ---
>>>>>>>     include/net/filter.h |  7 +++++
>>>>>>>     net/filter.c         | 80
>>>>>>> ++++++++++++++++++++++++++++++++++++++++++++++++++++
>>>>>>>     2 files changed, 87 insertions(+)
>>>>>>>
>>>>>>>
>>
>> [...]
>>
>>>>>>> +
>>>>>>> +    optarg =
>>>>>>> g_strdup_printf("qom-type=%s,id=%s,netdev=%s,status=%s",
>>>>>>> +            filter_type, id, netdev_id, is_default ? "disable" :
>>>>>>> "enable"
>>>>>>
>>>>>> Instead of this, I wonder maybe it's better to:
>>>>>>
>>>>>> - store the default filter property into a pointer to string
>>>>>
>>>>> Do you mean, pass a string parameter which stores the filter property
>>>>> instead of
>>>>> assemble it in this helper ?
>>>>
>>>> Yes. E.g just a global string which could be changed by any subsystem.
>>>> E.g colo may change it to
>>>> "filter-buffer,interval=0,status=disable". But
>>>> filter ids need to be generated automatically.
>>>>
>>>
>>> Got it. Then we don't need the global default_netfilter_type[] in
>>> patch 5,
>>
>> Yes.
>>
>>> Just use this global string instead ?
>>
>> Right.
>>
>>>
>>>>>
>>>>>> - colo code may change the pointer to "filter-buffer,status=disable"
>>>>>>
>>>>>
>>>>>> Then, there's no need for lots of codes above:
>>>>>> - no need a "is_default" parameter in netdev_add_filter which
>>>>>> does not
>>>>>> scale consider we may want to have more property in the future
>>>>>> - no need to hacking like "qemu_filter_opts"
>>>>>
>>>>> Yes, we can use qemu_find_opts("object") instead of it.
>>>>>
>>>>>> - no need to have a special flag like "is_default"
>>>>>>
>>>>>
>>>>> But we have to distinguish the default filter from the common
>>>>> filter, use the name (id) to distinguish it ?
>>>>
>>>> What's the reason that you want to distinguish default filters from
>>>> others?
>>>>
>>>
>>> The default filters will be used by COLO or MC, (In COLO, we will
>>> use it
>>> to control packets buffering/releasing).
>>
>> A question is how will you do this?
>>
>
> Er, for COLO, we will enable all the default filter in the
> initialization stage,
> then the buffer-filter will buffer all netdev's packets,
> after doing a checkpoint, we will release all the buffered packets
> (Flush all default
> filters' packets).

Right, that's the point. So looks several choices here:

1) Track each default filter explicitly, generate and record the netdev
ids for default filter by COLO.  Walk through the ids list and release
the packet in each filter.
2) Track the default filters implicitly. Link all buffer filters (with
zero interval) in a list during filter buffer initialization. And export
a helper for COLO to walk them and release packets.

Either looks fine, but maybe 2 is easier.

>  If VM is failover, we will set all default filters back to disabled
> status.
> (This is a periodic mode for COLO, different from another mode, which
> we will call it
> hybrid mode, that is based on colo-proxy, which is in developing by
> zhangchen)
>
> Thanks,
> Hailiang

Yes, I see.