On Fri, Aug 17, 2018 at 03:52:20PM +0200, Marc-André Lureau wrote: > Hi, > > In commit 25679e5d58e "chardev: tcp: postpone async connection setup" > (and its follow up 99f2f54174a59), Peter moved chardev socket > connection to machine_done event. However, chardev created later will > no longer attempt to connect, and chardev created in tests do not have > machine_done event (breaking some of vhost-user-test). > > The goal was to move the "connect" source to the chardev frontend > context (the monitor thread context in his case). chr->gcontext is set > with qemu_chr_fe_set_handlers(). But there is no guarantee that the > function will be called in general,
Could you hint a case where we didn't use qemu_chr_fe_set_handlers() upon a chardev backend? I thought it was always used in chardev frontends, and what the backend could do if without a frontend? [1] > so we can't delay connection until > then: the chardev should still attempt to connect during open(), using > the main context. > > An alternative would be to specify the iothread during chardev > creation. Setting up monitor OOB would be quite different too, it > would take the same iothread as argument. > > 99f2f54174a595e is also a bit problematic, since it will behave > differently before and after machine_done (the first case gives a > chance to use a different context reliably, the second looks racy) > > In the end, I am not sure this is all necessary, as chardev callbacks > are called after qemu_chr_fe_set_handlers(), at which point the > context of sources are updated. In "char-socket: update all ioc > handlers when changing context", I moved also the hup handler to the > updated context. So unless the main thread is already stuck, we can > setup a different context for the chardev at that time. Or not? IMHO the two patches that you reverted are special-cases for reasons. The TLS handshake is carried out with an TLS internal GSource which is not owned by the chardev code, so the qemu_chr_fe_set_handlers() won't update that GSource (please refer to qio_channel_tls_handshake_task). The async connection is carried out in a standalone thread that calls connect(). IMHO we'd better not update the gcontext bound to the async task since otherwise there'll be a race (IIRC I proposed something before using a mutex to update the gcontext, but Dan would prefer not to, and I followed with the suggestion which makes sense to me). Could we just postpone these machine done tasks into qemu_chr_fe_set_handlers() (or say, chr_update_read_handler() hook, just like what I mentioned in the other thread)? Though we'll be sure qemu_chr_fe_set_handlers() will be called for all chardev backends hence I asked question [1] above. Regards, -- Peter Xu
