From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Thomas Pfaff <tpfaff@pcs.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Question about TTY_DO_WRITE_WAKEUP
Date: Thu, 20 Nov 2008 16:47:19 +0000 [thread overview]
Message-ID: <20081120164719.13daa129@lxorguk.ukuu.org.uk> (raw)
In-Reply-To: <Pine.LNX.4.64.0811201700320.1274@lxtpfaff.pcs.ditec.de>
> > The base code should probably really use test_and_clear_bit() when
> > calling that method.
>
> Why should you test it, clear it and set it again in n_tty_write_wakeup ?
Because it should only be set again if a wakeup is needed. If the fasync
list for the tty is now empty it should stay clear.
> IMHO a SIGIO on write possible should always be generated if the user wants it,
> currently it is generated when the user wants it and the tty driver enables the
> TTY_DO_WRITE_WAKEUP flag. Unfortunately most drivers don't set it.
It is nothing to do with the driver. The line discipline sets it - or
rather should set it. If you have a case where you get an EAGAIN or short
write and the line discipline is not setting it then that is what needs
fixing not the drivers.
> Once a write fails with EAGAIN a flag can be set and only in that case a SIGIO is
> generated, afterwards the bit is cleared. Maybe that is what TTY_DO_WRITE_WAKEUP
> was intended for.
Correct.
next prev parent reply other threads:[~2008-11-20 16:47 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-11-20 10:06 Thomas Pfaff
2008-11-20 13:17 ` Alan Cox
2008-11-20 14:09 ` Thomas Pfaff
2008-11-20 14:31 ` Alan Cox
2008-11-20 15:12 ` Thomas Pfaff
2008-11-20 15:55 ` Alan Cox
2008-11-20 16:39 ` Thomas Pfaff
2008-11-20 16:47 ` Alan Cox [this message]
2008-11-20 16:58 ` Alan Cox
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