Re: [Qemu-devel] [PATCH v2 08/15] chardev: allow telnet gsource to switch gcontext

[Peter Xu]

On Thu, Mar 01, 2018 at 06:16:53PM +0100, Paolo Bonzini wrote:
> On 01/03/2018 16:46, Daniel P. Berrangé wrote:
> > On Thu, Mar 01, 2018 at 04:44:31PM +0800, Peter Xu wrote:
> >> It was originally created by qio_channel_add_watch() so it's always
> >> assigning the task to main context.  Now we use the new API called
> >> qio_channel_add_watch_source() so that we get the GSource handle rather
> >> than the tag ID.
> >>
> >> Meanwhile, caching the gsource in SocketChardev.telnet_source so that we
> >> can also do dynamic context switch when update read handlers.
> > I don't see why we would ever want to dynamically switch the
> > GMainContext in use while in middle of reading the telnet greeting.
> 
> Maybe because the remote client hangs in the middle of the telnet
> greeting?  The user of the Chardev can't know that the initial handshake
> hasn't been done yet.

Ah, this reminded me that I should better cache the
TCPChardevTelnetInit struct, otherwise when context changes we'll
possibly restart a telnet handshake.

Actually if only considering the monitor-OOB series (which is the only
one now who may change the context) it's not really necessary, since
the context will only be changed once when init monitors. But it's
easy to even achieve a higher goal to support real dynamic switch for
telnet connections.  So I think I'll try that in my next post.

Thanks,

-- 
Peter Xu