Re: [Qemu-devel] [PATCH 07/14] qio/chardev: update net listener gcontext

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Feb 28, 2018 at 01:06:26PM +0800, Peter Xu wrote:
> TCP chardevs can be using QIO network listeners working in the
> background when in listening mode.  However the network listeners are
> always running in main context.  This can race with chardevs that are
> running in non-main contexts.
> 
> To solve this: firstly introduce qio_net_listener_set_context() to allow
> caller to set gcontext for network listeners.  Then call it in
> tcp_chr_update_read_handler(), with the newly cached gcontext.
> 
> It's fairly straightforward after we have introduced some net listener
> helper functions - basically we unregister the GSources and add them
> back with the correct context.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  chardev/char-socket.c     |  9 +++++++++
>  include/io/net-listener.h | 12 ++++++++++++
>  io/net-listener.c         |  7 +++++++
>  3 files changed, 28 insertions(+)
> 
> diff --git a/chardev/char-socket.c b/chardev/char-socket.c
> index 43a2cc2c1c..8f0935cd15 100644
> --- a/chardev/char-socket.c
> +++ b/chardev/char-socket.c
> @@ -559,6 +559,15 @@ static void tcp_chr_update_read_handler(Chardev *chr)
>  {
>      SocketChardev *s = SOCKET_CHARDEV(chr);
>  
> +    if (s->listener) {
> +        /*
> +         * It's possible that chardev context is changed in
> +         * qemu_chr_be_update_read_handlers().  Reset it for QIO net
> +         * listener if there is.
> +         */
> +        qio_net_listener_set_context(s->listener, chr->gcontext);
> +    }
> +
>      if (!s->connected) {
>          return;
>      }
> diff --git a/include/io/net-listener.h b/include/io/net-listener.h
> index 566be283b3..39dede9d6f 100644
> --- a/include/io/net-listener.h
> +++ b/include/io/net-listener.h
> @@ -106,6 +106,18 @@ int qio_net_listener_open_sync(QIONetListener *listener,
>                                 SocketAddress *addr,
>                                 Error **errp);
>  
> +/**
> + * qio_net_listener_set_context:
> + * @listener: the net listener object
> + * @context: the context that we'd like to bind the sources to
> + *
> + * This helper does not do anything but moves existing net listener
> + * sources from the old one to the new one.  It can be seen as a
> + * no-operation if there is no listening source at all.
> + */
> +void qio_net_listener_set_context(QIONetListener *listener,
> +                                  GMainContext *context);

I don't think this is a good design. The GMainContext should be provided
to the qio_net_listener_set_client_func method immediately, not updated
after the fact


Regards,
Daniel
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