linux-kernel - Re: Q: how to control the TTY output queue in real time?

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 10 Aug 2012 20:33:55 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Stas Sergeev <stsp@...t.ru>
Cc:	Linux kernel <linux-kernel@...r.kernel.org>,
	linux-serial@...r.kernel.org
Subject: Re: Q: how to control the TTY output queue in real time?

> I am writing an app that needs to control the
> serial xmit in real-time. What I need is a notification
> that the TTY output queue fillup (returned by TIOCOUTQ
> ioctl) have dropped below the specified value.

Not a supported feature basically.

> I haven't found anything that can help implementing
> this. If I can't get an async notification, the sync
> notification will do too, like, for instance, the tcdrain()
> call, but with the argument to specify the needed fillup,
> below which the function will return.
> If there is nothing like this, then even the notification
> on every transmitted char will do.
> But I've found nothing of the above. :(
> 
> Any suggestions how the real-time control can be
> implemented?

Bascially even on the hardware that knows with this degree of granularity
we don't propogate the information back in the manner you want.

I'm not sure its a total loss however. Currently all the code basically
does stuff in the tx path or tx irq handler along the line of


	if (bytes_left < constant)
		write_wakeup


and I suspect if you made that adjustable and turned off the fifo and any
other funnies you'd at least make it work for a sufficiently rigged demo.

We could in theory put it in the tty_port in future too if its general
purpose useful.

Alan
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/