[PATCH 1/2 for 8.0] Add the port allocation logic for isa-serial devices.

[Ani Sinha]

> > > index 144ba4dd12..a8f41dc8c2 100644
> > > --- a/src/conf/domain_conf.h
> > > +++ b/src/conf/domain_conf.h
> > > @@ -1187,6 +1187,12 @@ typedef enum {
> > >      VIR_DOMAIN_CHR_CONSOLE_TARGET_TYPE_LAST
> > >  } virDomainChrConsoleTargetType;
> > >
> > > +/*
> > > + * The value of VIR_MAX_ISA_SERIAL_PORTS corresponds to MAX_ISA_SERIAL_PORTS
> > > + * set in qemu code base.
> >
> > We prefer upper case spelling of QEMU. And it's been a long time since
> > I've last booted up my machine with ISA, but IIRC it could only have 4
> > COM ports, so maybe the limit doesn't come from QEMU really but BIOS of
> > that time? What I'm trying to say is, if this is a limit shared across
> > other hypervisors then it can live under src/conf/ but if isn't shared
> > then it has to go under hypervisor specific dir (src/qemu/ in this case).
> >
> > I'm just going to assume the limit is shared and not QEMU specific.

Ok I spoke to Peter about the following commit on @qemu-devel. The
underlying limitation is indeed dictated by the hw it is emulating. Fair
enough! I still think though that we should leave the above comment as is
because this validation in libvirt is dependent on what Qemu allows today.
The reference is important IMHO.

>
> Maybe I read this wrong but I interpreted this commit message in QEMU
> repo to mean that the limitation is qemu specific :
>
> commit def337ffda34d331404bd7f1a42726b71500df22
> Author: Peter Maydell <peter.maydell at linaro.org>
> Date:   Fri Apr 20 15:52:46 2018 +0100
>
>     serial-isa: Use MAX_ISA_SERIAL_PORTS instead of MAX_SERIAL_PORTS
>
>     The ISA serial port handling in serial-isa.c imposes a limit
>     of 4 serial ports. This is because we only know of 4 IO port
>     and IRQ settings for them, and is unrelated to the generic
>     MAX_SERIAL_PORTS limit, though they happen to both be set at
>     4 currently.
>
>     Use a new MAX_ISA_SERIAL_PORTS wherever that is the correct
>     limit to be checking against.
>
>     Signed-off-by: Peter Maydell <peter.maydell at linaro.org>
>     Reviewed-by: Philippe Mathieu-Daudé <f4bug at amsat.org>
>     Reviewed-by: Thomas Huth <thuth at redhat.com>
>     Tested-by: Philippe Mathieu-Daudé <f4bug at amsat.org>
>     Message-id: 20180420145249.32435-11-peter.maydell at linaro.org
>
>