From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33003) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aVi5k-0005ey-Hw for qemu-devel@nongnu.org; Tue, 16 Feb 2016 11:03:09 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aVi5g-0006th-0F for qemu-devel@nongnu.org; Tue, 16 Feb 2016 11:03:08 -0500 Received: from mnementh.archaic.org.uk ([2001:8b0:1d0::1]:57386) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aVi5f-0006tJ-Pf for qemu-devel@nongnu.org; Tue, 16 Feb 2016 11:03:03 -0500 From: Peter Maydell Date: Tue, 16 Feb 2016 16:03:01 +0000 Message-Id: <1455638581-5912-1-git-send-email-peter.maydell@linaro.org> Subject: [Qemu-devel] [PATCH] qemu-options.hx: Improve documentation of chardev multiplexing mode List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: qemu-trivial@nongnu.org, Paolo Bonzini , Stefan Hajnoczi , patches@linaro.org 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