linux-kernel - [PATCH 0/2] hvc_console: Add DTR/RTS callbacks to handle HUPCL conditions

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Date:	Tue,  2 Jul 2013 17:07:13 +0200
From:	Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>
To:	benh@...nel.crashing.org, jslaby@...e.cz,
	gregkh@...uxfoundation.org
Cc:	brueckner@...ux.vnet.com, heiko.carstens@...ibm.com,
	schwidefsky@...ibm.com, linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Subject: [PATCH 0/2] hvc_console: Add DTR/RTS callbacks to handle HUPCL conditions

Hi folks,

this series resolves an issue for hvc back-ends that transfer
terminal data over an established communication path.

The current implementation of the hvc_console layer notifies its
back-ends for tty open, close, and hangups.  However, there are
conditions where the hangup-on-close (HUPCL) termios flag must be
considered, for example, when doing a vhangup().

For the hvc_iucv back-end, users perceives disconnects at their
login which are triggered by a modified vhangup() invocation as
described in https://lkml.org/lkml/2012/6/5/145.
(The kernel change implied also a change in the login program).

However, this also necessitates to inform back-ends about changes
in the DTR/RTS control lines which actually depend on the setting
of the HUPCL termios flag.  Like in the old days for modems,
network-based back-ends need to know when to hang-up and drop off
an established communication path.  Without this new notification,
back-ends can only use the tty open, close, hangup notifiers to
decide whether to disconnect.  This is not sufficient because the
HUPCL flag can be cleared (i.e. not to hang-up a connection) when
last tty file descriptor is closed.

This series adds the dtr_rts() callback to the hvc_console layer
and modifies the hvc_iucv device driver to disconnect an established
IUCV connection only when the DTR/RTS is lowered.

Feedback is very welcome.  Thanks in advance!

Kind regards,
  Hendrik

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