From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from list by lists.gnu.org with archive (Exim 4.71) id 1aViYH-0007SU-Pi for mharc-qemu-trivial@gnu.org; Tue, 16 Feb 2016 11:32:37 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:41692) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aViYE-0007Nv-U5 for qemu-trivial@nongnu.org; Tue, 16 Feb 2016 11:32:35 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aViYD-0006dj-U4 for qemu-trivial@nongnu.org; Tue, 16 Feb 2016 11:32:34 -0500 Received: from mx1.redhat.com ([209.132.183.28]:53698) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aViY6-0006cq-RF; Tue, 16 Feb 2016 11:32:27 -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 788B75A43; Tue, 16 Feb 2016 16:32:26 +0000 (UTC) Received: from lacos-laptop-7.usersys.redhat.com (ovpn-113-108.phx2.redhat.com [10.3.113.108]) by int-mx11.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u1GGWOqu026890; Tue, 16 Feb 2016 11:32:25 -0500 To: Peter Maydell , qemu-devel@nongnu.org References: <1455638581-5912-1-git-send-email-peter.maydell@linaro.org> From: Laszlo Ersek Message-ID: <56C34F18.7090006@redhat.com> Date: Tue, 16 Feb 2016 17:32:24 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: <1455638581-5912-1-git-send-email-peter.maydell@linaro.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit 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 , Stefan Hajnoczi , patches@linaro.org Subject: Re: [Qemu-trivial] [Qemu-devel] [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 16:32:36 -0000 On 02/16/16 17:03, 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... > --- > 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. > + > 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} > I'm a big fan of muxing the stdio backend between the (human) monitor and the guest's serial console: -chardev stdio,signal=off,mux=on,id=char0 \ -mon chardev=char0,mode=readline,default \ -serial chardev:char0 \ I think if you could mention the following in the above, that would be even more helpful: - how to enter a real Control-A character (relevant when typing at the guest's shell prompt, over serial) - not strictly related, but a warning about using this in "screen" (I use "screen" all the time to capture serial IO) -- Control-A is also piggy-backed by "screen" - how the initially active frontend gets selected - the fact that frontends use different syntaxes to refer to the backend. You have two examples in the text being added ("for instance, ..."), so I think it would be really helpful to provide actual command line options for those. Just my two cents. The patch looks great. Thanks Laszlo