From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from list by lists.gnu.org with archive (Exim 4.71) id 1aVicK-0006IT-CU for mharc-qemu-trivial@gnu.org; Tue, 16 Feb 2016 11:36:48 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43501) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aVicE-00065G-3n for qemu-trivial@nongnu.org; Tue, 16 Feb 2016 11:36:46 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aVicC-0007s9-Ou for qemu-trivial@nongnu.org; Tue, 16 Feb 2016 11:36:42 -0500 Received: from mx1.redhat.com ([209.132.183.28]:55254) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aVic7-0007oG-8N; Tue, 16 Feb 2016 11:36:35 -0500 Received: from int-mx11.intmail.prod.int.phx2.redhat.com (int-mx11.intmail.prod.int.phx2.redhat.com [10.5.11.24]) by mx1.redhat.com (Postfix) with ESMTPS id 58049A2C34; Tue, 16 Feb 2016 16:36:34 +0000 (UTC) Received: from tesla.localdomain (ovpn-116-71.ams2.redhat.com [10.36.116.71]) by int-mx11.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u1GGaWGo030451 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Tue, 16 Feb 2016 11:36:34 -0500 Received: by tesla.localdomain (Postfix, from userid 1000) id 2A27D24191F; Tue, 16 Feb 2016 17:36:31 +0100 (CET) Date: Tue, 16 Feb 2016 17:36:31 +0100 From: Kashyap Chamarthy To: Peter Maydell Message-ID: <20160216163631.GD19823@tesla.redhat.com> References: <1455638581-5912-1-git-send-email-peter.maydell@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1455638581-5912-1-git-send-email-peter.maydell@linaro.org> User-Agent: Mutt/1.5.23.1 (2014-03-12) X-Scanned-By: MIMEDefang 2.68 on 10.5.11.24 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 209.132.183.28 Cc: qemu-trivial@nongnu.org, Paolo Bonzini , qemu-devel@nongnu.org, Stefan Hajnoczi , patches@linaro.org Subject: Re: [Qemu-trivial] [PATCH] qemu-options.hx: Improve documentation of chardev multiplexing mode X-BeenThere: qemu-trivial@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 16 Feb 2016 16:36:46 -0000 On Tue, Feb 16, 2016 at 04:03:01PM +0000, Peter Maydell wrote: > The current documentation of chardev mux=on is rather brief and opaque; > expand it to hopefully be a bit more helpful. > > Signed-off-by: Peter Maydell > > --- > There was some discussion on #qemu yesterday evening about multiplexing, > and "make the docs a bit less confusing" was one suggestion... > --- Thanks for following up with the clarifying write-up. > qemu-options.hx | 20 +++++++++++++++++++- > 1 file changed, 19 insertions(+), 1 deletion(-) > > diff --git a/qemu-options.hx b/qemu-options.hx > index 2f0465e..6b46dd4 100644 > --- a/qemu-options.hx > +++ b/qemu-options.hx > @@ -2162,8 +2162,26 @@ All devices must have an id, which can be any string up to 127 characters long. > It is used to uniquely identify this device in other command line directives. > > A character device may be used in multiplexing mode by multiple front-ends. > +Specify @option{mux=on} to enable this mode. > +A multiplexer is a "1:N" device, and here the "1" end is your specified chardev > +backend, and the "N" end is the various parts of QEMU that can talk to a chardev. > +If you create a chardev with @option{id=myid} and @option{mux=on}, QEMU will > +create a multiplexer with your specified ID, and you can then configure multiple > +front ends to use that chardev ID for their input/output. Up to four different > +front ends can be connected to a single multiplexed chardev. (Without > +multiplexing enabled, a chardev can only be used by a single front end.) > +For instance you could use this to allow a single stdio chardev to be used by > +two serial ports and the QEMU monitor. Just noting for convenience here, looking at an old commit[1 that notes the syntax for multiplexing 'stdio', which you mention above in prose: [...] Muxing can be done this way: -chardev stdio,id=mux,mux=on -serial chardev:mux -monitor chardev:mux" [...] [1] http://git.qemu.org/?p=qemu.git;a=commitdiff;h=c845f40 > + > The key sequence of @key{Control-a} and @key{c} will rotate the input focus > -between attached front-ends. Specify @option{mux=on} to enable this mode. > +of a multiplexed character device between attached front-ends. > + > +You can have more than one multiplexer in a system configuration; for instance > +you could have a TCP port multiplexed between UART 0 and UART 1, and stdio > +multiplexed between the QEMU monitor and a parallel port. > + > +There is currently no support for multiplexing in the other direction > +(where a single QEMU front end takes input and output from multiple chardevs). > > Every backend supports the @option{logfile} option, which supplies the path > to a file to record all data transmitted via the backend. The @option{logappend} Reviewed-by: Kashyap Chamarthy -- /kashyap