Re: [Qemu-devel] [PATCH v2 08/15] chardev: allow telnet gsource to switch gcontext
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. NB, the chardev will emit the CHR_EVENT_OPENED event once the connection is successfully established, which includes completion of the telnet and/or TLS handshake. I'm just not seeing what code in QEMU would actually trigger a decision to change the GMainContext, in between the accept() of the socket, and the CHR_EVENT_OPENED, since we don't tell anyone that the accept() has actually taken place - they first they'll know of a new client being connected is when the CHR_EVENT_OPENED is emitted. Regards, Daniel -- |: https://berrange.com -o-https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o-https://fstop138.berrange.com :| |: https://entangle-photo.org-o-https://www.instagram.com/dberrange :|
Re: [Qemu-devel] [PATCH v2 08/15] chardev: allow telnet gsource to switch gcontext
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
Re: [Qemu-devel] [PATCH v2 08/15] chardev: allow telnet gsource to switch gcontext
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. Paolo
Re: [Qemu-devel] [PATCH v2 08/15] chardev: allow telnet gsource to switch gcontext
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. Regards, Daniel -- |: https://berrange.com -o-https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o-https://fstop138.berrange.com :| |: https://entangle-photo.org-o-https://www.instagram.com/dberrange :|
