Hi On Mon, Aug 18, 2014 at 4:15 PM, Marcel Holtmann <mar...@holtmann.org> wrote: > 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.
Yes, we should add POLLOUT unconditionally. I will push the fix. Thanks David _______________________________________________ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
