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

From: Jason Wang
Subject: Re: [Qemu-devel] [RFC PATCH V3 1/4] colo-compare: introduce colo compare initlization
Date: Fri, 20 May 2016 10:46:44 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.2

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
be better to do this in colo thread? Otherwise, you need lots of
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
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.

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?


Cc Fam for more thought.

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