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 <[email protected]> --- 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
