linux-kernel - Re: [PATCH tty-next 14/22] tty: Remove tty_wait_until_sent_from

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Date:	Fri, 10 Oct 2014 09:58:28 +0100
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	David Laight <David.Laight@...LAB.COM>,
	Arnd Bergmann <arnd@...db.de>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Karsten Keil <isdn@...ux-pingi.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>
Subject: Re: [PATCH tty-next 14/22] tty: Remove
 tty_wait_until_sent_from_close()

> The point being that holding the tty lock across the _entire_ close
> is equivalent to the current outcome, regardless of O_NONBLOCK.
> 
> I'm reluctant to start returning EGAIN for non-blocking tty opens
> because no tty driver does that now, and I don't think userspace will
> deal well with new return codes from tty opens.

I do not know about the non blocking case mattering. The blocking open
does need to wait, when I broke that case before I broke the console
login drivers (mingetty).

Returning EAGAIN would also only work if poll/select did the right thing.
Currently Linux can't support a System5 style ttymon process because of
this limitation, which means, for example, that systemd can't implement a
single thread to manage all console prompts/setup

Alan
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