qemu-options.hx: Improve -serial option documentation

The -serial option documentation is a bit brief about '-serial none'
and '-serial null'. In particular it's not very clear about the
difference between them, and it doesn't mention that it's up to
the machine model whether '-serial none' means "don't create the
serial port" or "don't wire the serial port up to anything".

Expand on these points.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20240122163607.459769-3-peter.maydell@linaro.org
This commit is contained in:
Peter Maydell 2024-01-22 16:36:07 +00:00
parent d2019a9d0c
commit 747bfaf3a9

View File

@ -4129,7 +4129,8 @@ SRST
This option can be used several times to simulate up to 4 serial
ports.
Use ``-serial none`` to disable all serial ports.
You can use ``-serial none`` to suppress the creation of default
serial devices.
Available character devices are:
@ -4151,10 +4152,17 @@ SRST
[Linux only] Pseudo TTY (a new PTY is automatically allocated)
``none``
No device is allocated.
No device is allocated. Note that for machine types which
emulate systems where a serial device is always present in
real hardware, this may be equivalent to the ``null`` option,
in that the serial device is still present but all output
is discarded. For boards where the number of serial ports is
truly variable, this suppresses the creation of the device.
``null``
void device
A guest will see the UART or serial device as present in the
machine, but all output is discarded, and there is no input.
Conceptually equivalent to redirecting the output to ``/dev/null``.
``chardev:id``
Use a named character device defined with the ``-chardev``