Hi Lennart, >>>> To facility the feature of doing an asynchronous sending of messages >>>> when the bus is idle, make sure to return POLLOUT | POLLWRNORM from >>>> kdbus_handle_poll. >>>> >>>> Signed-off-by: Marcel Holtmann <mar...@holtmann.org> >>>> --- >>>> handle.c | 2 ++ >>>> 1 file changed, 2 insertions(+) >>>> >>>> diff --git a/handle.c b/handle.c >>>> index ac6868133280..fc15d28351b3 100644 >>>> --- a/handle.c >>>> +++ b/handle.c >>>> @@ -884,6 +884,8 @@ static unsigned int kdbus_handle_poll(struct file >>>> *file, >>>> mask |= POLLERR | POLLHUP; >>>> else if (!list_empty(&conn->msg_list)) >>>> mask |= POLLIN | POLLRDNORM; >>>> + else >>>> + mask |= POLLOUT | POLLWRNORM; >>> >>> Hmm, what's your use case here? list_empty(&conn->msg_list) only checks >>> the incoming list of the current connection for pending messages. That >>> doesn't tell you whether the bus is idle, or if your receiving end has >>> messages pending ... >> >> if you are a good client citizen, then you only send messages when >> POLLOUT gets signaled. That is what this is allowing now. >> >> Blindly sending messages is never a good idea. You want to poll for >> POLLOUT first. This does not make a big difference for current kernel, >> but it allows future extensions when the clients are well behaving and >> just waiting for POLLOUT. Meaning once the kernel does not signal >> POLLOUT, no new messages will come from the client. >> >> Current code does not do this POLLOUT before sending a messages, but >> our kdbus client actually does that. It is the right thing to do. And >> we have been doing this with all of our protocols that are using >> asynchronous IO. No point in kdbus being any different. > > Well, kdbus keeps per-reciever buffers only, hence signalling on the > kdbus fd when you are able to write is not really possible, since this > information is not bound to the sender fd but only to the receiever of > which there are many... If I understand you correctly you hence want the > kdbus fd to always return EPOLLOUT then, because if a client wants to > send something it can do that at any time? > > If that's the case then POLLOUT should really be ORed into the mask > unconditionally, not just in some cases... > > So, I can sympathize with what you are trying to do. However, I think > your patch doesn't do the right thing... It should really OR the POLLOUT > into all masks always.
always returning POLLOUT is also fine. As long as the fd signals POLLOUT and not just swallows it. Regards Marcel _______________________________________________ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
