Re: [PATCH v3 21/33] qemu-socket: pass monitor link to socket_get_fd directly

[Roman Kagan <rvkagan@yandex-team.ru>]

On Mon, Apr 19, 2021 at 10:34:49AM +0100, Daniel P. Berrangé wrote:
> On Fri, Apr 16, 2021 at 11:08:59AM +0300, Vladimir Sementsov-Ogievskiy wrote:
> > Detecting monitor by current coroutine works bad when we are not in
> > coroutine context. And that's exactly so in nbd reconnect code, where
> > qio_channel_socket_connect_sync() is called from thread.
> > 
> > Add a possibility to pass monitor by hand, to be used in the following
> > commit.
> > 
> > Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> > ---
> >  include/io/channel-socket.h    | 20 ++++++++++++++++++++
> >  include/qemu/sockets.h         |  2 +-
> >  io/channel-socket.c            | 17 +++++++++++++----
> >  tests/unit/test-util-sockets.c | 16 ++++++++--------
> >  util/qemu-sockets.c            | 10 +++++-----
> >  5 files changed, 47 insertions(+), 18 deletions(-)
> > 
> > diff --git a/include/io/channel-socket.h b/include/io/channel-socket.h
> > index e747e63514..6d0915420d 100644
> > --- a/include/io/channel-socket.h
> > +++ b/include/io/channel-socket.h
> > @@ -78,6 +78,23 @@ qio_channel_socket_new_fd(int fd,
> >                            Error **errp);
> >  
> >  
> > +/**
> > + * qio_channel_socket_connect_sync_mon:
> > + * @ioc: the socket channel object
> > + * @addr: the address to connect to
> > + * @mon: current monitor. If NULL, it will be detected by
> > + *       current coroutine.
> > + * @errp: pointer to a NULL-initialized error object
> > + *
> > + * Attempt to connect to the address @addr. This method
> > + * will run in the foreground so the caller will not regain
> > + * execution control until the connection is established or
> > + * an error occurs.
> > + */
> > +int qio_channel_socket_connect_sync_mon(QIOChannelSocket *ioc,
> > +                                        SocketAddress *addr,
> > +                                        Monitor *mon,
> > +                                        Error **errp);
> 
> I don't really like exposing the concept of the QEMU monitor in
> the IO layer APIs. IMHO these ought to remain completely separate
> subsystems from the API pov,

Agreed. 

> and we ought to fix this problem by
> making monitor_cur() work better in the scenario required.

Would it make sense instead to resolve the fdstr into actual file
descriptor number in the context where monitor_cur() works and makes
sense, prior to passing it to the connection thread?

Roman.