On 3/16/21 8:00 AM, Norman Maurer wrote: > Hi there, > > I think I found a bug in the current io_uring implementation. It seems > like recvmsg currently not respect when a fd is set to non-blocking. > At the moment recvmsg never returns in this case. I can work around > this by using MSG_DONTWAIT but I don’t think this should be needed. > > I am using the latest 5.12 code base atm. This is actually "by design" in that system calls that offer a "don't block for this operation" (like MSG_DONTWAIT here) will not be looking at the O_NONBLOCK flag. Though it is a bit confusing and potentially inconsistent, my argument here is that this is the case for system calls in general, where even O_NONBLOCK has very hazy semantics depending on what system call you are looking at. The issue is mostly around when to use -EAGAIN to arm async retry, and when to return -EAGAIN to the application. I'd like to hear from others here, but as far as io_uring is concerned, we _should_ be consistent in how we treat O_NONBLOCK _depending_ on if that system call allows a flags method of passing in nonblock behavior. -- Jens Axboe
