On Mon, 22 Jan 2024 at 17:46, Philippe Mathieu-Daudé <phi...@linaro.org> wrote: > > Hi, > > On 22/1/24 17:36, Peter Maydell wrote: > > 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.mayd...@linaro.org> > > --- > > qemu-options.hx | 14 +++++++++++--- > > 1 file changed, 11 insertions(+), 3 deletions(-) > > > > diff --git a/qemu-options.hx b/qemu-options.hx > > index ced82848637..d8c3fe91de1 100644 > > --- a/qemu-options.hx > > +++ b/qemu-options.hx > > @@ -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. > > Should we deprecate this broken case, suggesting to use ``null`` > instead?
It's machine specific. On systems with pluggable serial devices it makes sense to use '-serial none' to get rid of them entirely. On systems where the UARTs are hardwired into the board, having '-serial none' literally delete the UART device just breaks guests, which is why those boards make it behave like '-serial null'. But users should still be able to use '-serial none' to say "I don't really care about serial here". (This is why in commit 12051d82f004024d5d we made the chardev frontend functions cope with having a NULL backend, to avoid boards having to say "oh, serial_hd(n) is NULL, I must create a 'null' backend for it", which half of them didn't do.) thanks -- PMM
