From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from list by lists.gnu.org with archive (Exim 4.71) id 1aVi5s-0005nv-9v for mharc-qemu-trivial@gnu.org; Tue, 16 Feb 2016 11:03:16 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33004) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aVi5k-0005ez-I1 for qemu-trivial@nongnu.org; Tue, 16 Feb 2016 11:03:14 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aVi5g-0006tr-OT for qemu-trivial@nongnu.org; Tue, 16 Feb 2016 11:03:08 -0500 Received: from mnementh.archaic.org.uk ([81.2.115.146]:41242) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aVi5g-0006tm-FU for qemu-trivial@nongnu.org; Tue, 16 Feb 2016 11:03:04 -0500 Received: from pm215 by mnementh.archaic.org.uk with local (Exim 4.84) (envelope-from ) id 1aVi5d-0001Xu-5X; Tue, 16 Feb 2016 16:03:01 +0000 From: Peter Maydell To: qemu-devel@nongnu.org Date: Tue, 16 Feb 2016 16:03:01 +0000 Message-Id: <1455638581-5912-1-git-send-email-peter.maydell@linaro.org> X-Mailer: git-send-email 2.1.4 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 81.2.115.146 Cc: qemu-trivial@nongnu.org, Paolo Bonzini , Kashyap Chamarthy , Stefan Hajnoczi , patches@linaro.org Subject: [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 16:03:14 -0000 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} -- 1.9.1