[Xen-devel] Xen attention key

[Bin Ren <br260@xxxxxxxxx>]

Xen internally registers a series of key handlers. When a key is 
pressed,
the corresponding key handler is invoked, which 'printk' (not 'printf' 
to stdout)
internal statistical information, very useful for debugging.

When you are using a serial line, you directly enter this special mode, 
i.e.
every key you press results in a key handler invoked (if exists).

When you are using the keyboard under Domain0, you need 
XEN_ATTENTION_KEY
to use this function, (currently defined to Scroll Lk).

With PC keyboard (without Fn key), just simultaneously press Scroll Lk 
+ key (such as 'p', 'h' etc)
However, with a laptop keyboard with Fn, it's much much more tricky.

Typically, you need press Fn + Num Lk to 'produce' Scroll Lk. At this 
point,
if you move on to press another key (say, press Fn, Num Lk, 'p' all 
together),
the key_handler is not invoked at all, and your keyboard hangs.

To restore your keyboard, release the previous three keys, and press Fn 
+ Num Lk again.
The reason is: With Fn pressed, the scan code of the key (say 'p') is 
changed so that it's not
recognized by Xen at all.

The solution is:
1. press Fn + Num Lk
2. release Fn but hold Num Lk
3. press another key ('p', 'h', etc)

Last but not least, as I said at the beginning, Xen internal statistical
information is output via 'printk'. If you are using a serial line, you
could see the output immediately. But if you are under Domain0,
you won't see anything: 'printk' is not directed to 'stdout' on Domain0.
Fortunately, you can use 'xi_read_console_ring' to fetch the
'printk' messages from Xen and print them to 'stdout' on Domain0.
'xi_read_console_ring' only exists in Xeno-unstable.bk tree.

FYI.

-- Bin



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