On Fri, Jul 05, 2019 at 03:29:58PM +0100, Andre Przywara wrote: > On Fri, 5 Jul 2019 12:04:41 +0100 > Dave Martin <Dave.Martin@xxxxxxx> wrote: [...] > > Output to a pty master before the slave is opened just disappears. > > Not always, it seems. When I do: > $ lkvm run -k Image --tty 0 > then wait for a bit and open the pseudo-terminal, I get the full boot log > "replayed". Not sure who in the chain is actually buffering this, though? FYI, after a bit of experimentation, it looks like the tty layer will buffer some data (maybe 64K, didn't check exactly), after which further writes silently disappear. Writing doesn't yield an error in either case. When the slave is opened, you get actual backpressure and writes to the master block if insufficient data has been read from the slave. So we may lose data, depending on how much dmesg there is, and anyway screen seems to flush pending input when opening a terminal, so I see nothing if connecting with screen with a bunch of data already written to the pty master. Not sure whether this matters. Once the slave is connected, communiction seems reliable. (Tons of software would likely break if it weren't.) [...] Cheers ---Dave
