Re: [Xen-devel] [PATCH v2 20/21] xen: support console_switching between Dom0 and DomUs on ARM

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.07.18 at 23:55, <sstabellini@xxxxxxxxxx> wrote:
> On Mon, 16 Jul 2018, Jan Beulich wrote:
>> >>> On 07.07.18 at 01:12, <sstabellini@xxxxxxxxxx> wrote:
>> > @@ -389,29 +392,49 @@ static void dump_console_ring_key(unsigned char key)
>> >      free_xenheap_pages(buf, order);
>> >  }
>> >  
>> > -/* CTRL-<switch_char> switches input direction between Xen and DOM0. */
>> > +/*
>> > + * CTRL-<switch_char> switches input direction between Xen, Dom0 and
>> > + * DomUs.
>> > + */
>> >  #define switch_code (opt_conswitch[0]-'a'+1)
>> > -static int __read_mostly xen_rx = 1; /* FALSE => input passed to domain 
>> > 0. */
>> > +static int __read_mostly xen_rx = 1; /* 1 => input passed to domain 0. */
>> 
>> I guess this variable wants renaming now.
> 
> Yeah. What about `console_rx'? 

That's reasonable. Another option would be to use rx_domid, and store
actual domain IDs there (DOMID_XEN for Xen). That'll make the switching
logic slightly larger, but perhaps provide a better understandable end
result.

>> > @@ -933,9 +956,6 @@ void __init console_endboot(void)
>> >                              "decrease log level threshold", 0);
>> >      register_irq_keyhandler('G', &do_toggle_guest,
>> >                              "toggle host/guest log level adjustment", 0);
>> > -
>> > -    /* Serial input is directed to DOM0 by default. */
>> > -    switch_serial_input();
>> 
>> This removes an imo helpful boot time message. Is that intentional,
>> and if so why?
>  
> Yes, it was intentional. switch_serial_input increases xen_rx, I thought
> it didn't make too much sense to do that at boot, and would be clearer
> to just initialize xen_rx to the wanted value from the get go (the value
> would be 1 for dom0). Also, in previous implementations of this patch it
> was actually required, but not anymore.
> 
> In fact, if you prefer, I could also keep this switch_serial_input()
> call as-is and change the initial value of xen_rx to 0. That would also
> work, as the increase of xen_rx here would end up selecting still dom0
> for input.

Yes, I'd prefer if you left it untouched. The idea after all is that prior
to reaching here input goes to Xen, and only from here on it goes to
Dom0.

Jan



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