Re: [Qemu-devel] [PATCH] qemu-char: Allow a chardev to reconnect if disconnected

[Gerd Hoffmann <kraxel@redhat.com>]

  Hi,

> > This patch is modified according to corey's patch. Some changes below:
> > 1. IMO it's unnecessary that chardev reconnect if it fails to connect at startup.
> > Qemu exit in this scene. In this way the patch does not change interface of chardev.
> > It would be much more simple.
> 
> I believe that it should not stop qemu if it fails at startup. 
> Otherwise you constrain the start order and you can prevent a server
> from coming up because of a missing resource that may not be that
> critical at the moment.

With reconnect being implemented (and active, guess we should add a
option for it) it we might rethink this indeed.

> With the current implementation, client sockets
> really aren't that useful for a critical system.  Reconnecting makes it
> usable in a critical system.

I consider client sockets not very useful at all, I always put my
sockets into server mode.  YMMV though.

> > 2. I set the reconnect timer one second, just like pty.
> 
> I'm not too picky about the time.  A couple of things about this:

Well, sockets and pty are different.  pty is a local thing.  sockets (at
least tcp) goes out to the network.  After each failed reconnect the
time to retry should be increased a bit so you don't flood the
non-responding server with connect requests.

> With this patch, the default behavior changes to reconnect.  That might
> cause issues for some users.  Adding a configurable timeout is easy if
> you have to specify something on the command line, that's why I did it.

Specifying the timeout (best with min+max) could enable reconnect at the
same time, i.e. something like

  -chardev socket,host=1.2.3.4,port=5678,reconnect=1-300

would turn on reconnect, with 1 second min and 300 seconds (5min) max
delay.

cheers,
  Gerd