Re: [Xen-users] Is it possible to have two serial consoles?

[Andy Smith <andy@xxxxxxxxxxxxxx>]

On Thu, Nov 12, 2015 at 11:45:50AM +0000, Andy Smith wrote:
> On Thu, Nov 12, 2015 at 11:24:27AM +0000, Ian Campbell wrote:
> > There is a com2 as well, so you should be able to do com2=stuff just like
> > with com1.
> > 
> > I've no idea what console=com1,com2 will do though I'm afraid, but it'd be
> > interesting to try for sure.
> 
> Thanks, I'll give it a go and let you know. :)

When booting with Xen command line:

com1=115200,8n1,0x2f8,10 com2=115200,8n1,0x3f8,4 console=com1,com2,vga

No output on ttyS1 (com1 / IPMI). On both VGA and ttyS0 there is
output from Xen up to:

(XEN) Detected 2000.067 MHz processor.
(XEN) Initing memory sharing.
(XEN) xstate_init: using cntxt_size: 0x340 and states: 0x7
(XEN) Intel VT-d iommu 0 supported page sizes: 4kB, 2MB, 1GB.
(XEN) Intel VT-d Snoop Control enabled.
(XEN) Intel VT-d Dom0 DMA Passthrough not enabled.
(XEN) Intel VT-d Queued Invalidation enabled.
(XEN) Intel VT-d Interrupt Remapping enabled.
(XEN) Intel VT-d Shared EPT tables enabled.
(XEN) I/O virtualisation enabled
(XEN)  - Dom0 mode: Relaxed
(XEN) Interrupt remapping enabled
(XEN) Enabled directed EOI with ioapic_ack_old on!
(XEN) ENABLING IO-APIC IRQs
(XEN)  -> Using old ACK method
(XEN) Platform timer is 14.318MHz HPET

âand then there is no further output on either. Boot appears to
stall there.

When booting with Xen command line:

com1=115200,8n1,0x2f8,10 com2=115200,8n1,0x3f8,4 console=com1,com2

No output on ttyS1 or vga, output appears on ttyS0.

ttyS0 gets all Xen and Linux kernel output right up until boot is
complete and a getty starts. Once gettys have started, a login
prompt appears on vga also, so vga is useless between end of grub
and start of getty.

A getty never appears on ttyS1.

When booting with Xen command line:

com1=115200,8n1,0x2f8,10 com2=115200,8n1,0x3f8,4 console=com1,vga

ttyS1 and vga get all output and a getty, ttyS0 gets nothing and no
getty.

When booting with Xen command line:

com1=115200,8n1,0x2f8,10 console=com1,vga

ttyS1 and vga get all output and eventually a getty. ttyS0 gets no
output but does have a getty once dom0 is booted.

In an ideal world I would like for everything that goes to the
console to end up going to vga, the real serial port and the IPMI
serial. However, I cannot manage this with vanilla linux which I
think is either by design or a wishlist item:

    https://www.kernel.org/doc/Documentation/serial-console.txt

    "Note that you can only define one console per device type
    (serial, video)."

I take this to mean that Linux can only use one ttyS* as its
console, and the best you could do with any extra ones is put a
getty on them.

So, if I can't do any better in Xen I suppose I'll take the last
command line I listed, so I have a console on vga and IPMI serial,
and a getty on the real serial as well.

If anyone has a better setup then I'd like to hear how you've done
it.

Cheers,
Andy

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