Re: [Qemu-devel] [RFC PATCH V3 1/4] colo-compare: introduce colo compare initlization

[Jason Wang <jasowang@redhat.com>]

On 2016年05月13日 11:48, Jason Wang wrote:
>
>
> On 2016年05月12日 16:16, Zhang Chen wrote:
>>
>>
>> On 05/12/2016 04:01 PM, Jason Wang wrote:
>>>
>>>
>>> On 2016年05月12日 14:49, Zhang Chen wrote:
>>>>
>>>>
>>>> On 05/09/2016 06:49 PM, Zhang Chen wrote:
>>>>>
>>>>>> +
>>>>>> +    s->chr_sec_in = qemu_chr_find(s->sec_indev);
>>>>>> +    if (s->chr_sec_in == NULL) {
>>>>>> +        error_setg(errp, "Secondary IN Device '%s' not found",
>>>>>> +                   s->sec_indev);
>>>>>> +        return;
>>>>>> +    }
>>>>>> +
>>>>>> +    s->chr_out = qemu_chr_find(s->outdev);
>>>>>> +    if (s->chr_out == NULL) {
>>>>>> +        error_setg(errp, "OUT Device '%s' not found", s->outdev);
>>>>>> +        return;
>>>>>> +    }
>>>>>> +
>>>>>> +    qemu_chr_fe_claim_no_fail(s->chr_pri_in);
>>>>>> +    qemu_chr_add_handlers(s->chr_pri_in, compare_chr_can_read,
>>>>>> +                          compare_pri_chr_in, NULL, s);
>>>>>> +
>>>>>> +    qemu_chr_fe_claim_no_fail(s->chr_sec_in);
>>>>>> +    qemu_chr_add_handlers(s->chr_sec_in, compare_chr_can_read,
>>>>>> +                          compare_sec_chr_in, NULL, s);
>>>>>> +
>>>>>>>>>>>> Btw, what's the reason of handling this in main loop? I 
>>>>>>>>>>>> thought it
>>>>>>>>>>>> would
>>>>>>>>>>>> be better to do this in colo thread? Otherwise, you need 
>>>>>>>>>>>> lots of
>>>>>>>>>>>> extra
>>>>>>>>>>>> synchronizations?
>>>>>>>>>>> Do you mean we should start/stop/do checkpoint it by 
>>>>>>>>>>> colo-frame?
>>>>>>>>>> I mean we probably want to handle pri_in and sec_in in colo 
>>>>>>>>>> compare
>>>>>>>>>> thread. Through this way, there's no need for extra 
>>>>>>>>>> synchronization
>>>>>>>>>> with
>>>>>>>>>> main loop.
>>>>>>>>> I get your point, but how to do this.
>>>>>>>>> Now, we use qemu_chr_add_handlers to do this job.
>>>>>>>> You probably want to start a new main loop in colo comparing 
>>>>>>>> thread.
>>>>>>>
>>>>>>> IIUC, do you mean
>>>>>>> - remove char device read_handler
>>>>>>>
>>>>>>>   ↓at colo comparing thread↓
>>>>>>> while (true) {
>>>>>>> - blocking read packet from char device with select(2)/poll(2)...
>>>>>>> - compare packet
>>>>>>> }
>>>>>> Yes, something like this.
>>>>>>
>>>>>
>>>>> But remove qemu_chr_add_handlers I can't get fd to select/poll.
>>>>>
>>>>> How to get fd from all kinds of chardev?
>>>>>
>>>>
>>>> Hi~ jason.
>>>>
>>>> If we use chardev socket the fd save in QIOChannelSocket.
>>>>
>>>> and if we use chardev file the fd save in QIOChannelFile.
>>>>
>>>> Have any common method to get fd?
>>>
>>> I'm not sure I get the question. But you probably can call 
>>> qemu_chr_add_handlers() in colo comparing thread to solve this I think?
>>>
>>
>> I have tested call qemu_chr_add_handlers() in colo comparing thread, 
>> but when data come,
>> the handler always running in main loop.
>>
>> Thanks
>> Zhang Chen 
>
> Cc Amit for the help.
>
> Amit, we want to poll and handle chardev in another thread other than 
> main loop. But looks like qemu_chr_add_handlers() can only work for 
> default context other than thread default context. Any other solution 
> for this?
>
> Thanks
>

Cc Fam for more thought.