Re: Cnmagic support for wscons

[Nathanial Sloss <nat%netbsd.org@localhost>]

On Tue, 17 Jan 2017 07:32:34 Valery Ushakov wrote:
> On Tue, Jan 17, 2017 at 04:26:48 +1100, Nathanial Sloss wrote:
> > On Mon, 16 Jan 2017 00:44:02 Valery Ushakov wrote:
> > > On Sun, Jan 15, 2017 at 13:30:15 +0100, Martin Husemann wrote:
> > > > On Sun, Jan 15, 2017 at 01:59:06PM +1100, Nathanial Sloss wrote:
> > > > > Mapping KS_Cmd_Debugger would also work but I'm unsure as to how
> > > > > to do this without using wskbd key sequences in the magic.
> > > > 
> > > > I don't understand - if you just assing KS_Cmd_Debugger somewhere,
> > > > why would you need cnmagic?
> > > 
> > > Exactly.  You need cnmagic(9) for detecting debugger _sequence_
> > > in-band like in serial console.
> > > 
> > > Your patch doesn't provide any documentation or an accompaning
> > > description, so I'm not sure what exactly it does, e.g. what should
> > > cnmagic value look like for wskbd?
> > 
> > I've put an example in the updated man page for both a wskbd command
> > and regular text.
> > 
> | +sysctl variable must be prefixed by \\001 for normal characters and/or
> | +control codes.
> | +Alternatively it can be prefixed by \\002 for wskbd commands.
> 
> [...]
> 
> | +The default cnmagic is \\002\\040\\0364 which on most platforms is
> | +<Ctrl>-<Alt>-<Esc>
> | +the wskbd command for
> | +.Xr ddb 4 .
> 
> - How does \040\0364 (0x20 0xf4) correspond to <Ctrl><Alt><Esc>?
> 
> - Does the fact that KS_Cmd_Debugger is defined as 0xf420 have
>   anything to do with it?

Yes it does.

> 
> - If so, why the byte order is little endian?

Endianness could be an issue I'll test in a sparc emulator.

> 
> - KS_Cmd_Debugger becomes a meaningless placeholder - you will have it
>   mapped by default but you can set cnmagic to something else
> 
> > > But in general it's not even
> > > entirely clear to me what a semantic of cnmagic(9) for wskbd could be.
> > > Should it use individual key-presseses as the basic input stream it
> > > parses?  If yes, you will lose the ability to use, e.g., *both*
> > > C-A-Esc and A-C-Esc _chords_ to break into debuger, because with
> > > wskbd(4) keyboard mapping they are the same _chords_, but with
> > > cnmagic(9) they are different _sequences_.
> > 
> > That's why I have two different prefixes one for wskbd commands and
> > another for regular text.
> 
> - What if one wants to use a mixture of them?
> 

I can make it possibile to specify keycodes as well. So if a mixture was 
wanted one would have to use that.

> - What happens if you specify in cnmaigc the sequence of individual
>   keys that map (at wskbd level) to a KS_Cmd_*?
> 

It would jump into ddb and on return run the KS_Cmd_*.

> > > I'd also say that the very fact that the patch doesn't use
> > > cn_check_magic(9) indicates in some sense that it probably does not
> > > implement "cnmagic support for wscons". :)
> > 
> > Please see:
> > 
> > ftp://ftp.netbsd.org/pub/NetBSD/misc/nat/cnmagic.v2.diff
> > 
> > It now uses cn_check magic instead of the custom ws_check_magic which was
> > based on cn_check_magic.
> 
> I still intensly dislike the very idea behind this patch.  I don't
> think it's meaningful or useful to bolt cnmagic onto wskbd.  Yes, I
> can theoretically imagine the possibility that someone somewhere might
> need a wskbd sequence to break into the debugger that for some reason
> cannot be expressed with just mapping KS_Cmd_Debugger.  I'd estimate
> the probablity of that be to just slighly more than that someone
> somewhere will find it useful to be able to express morse code support
> in wskbd mappings :).
> 
> You PR states the motivation as:
> | wscons does not support cn_magic - setting hw.cnmagic has no effect.
> 
> So just drop hw.cnmagic sysctl node if the console doesn't support it.
> 
> -uwe

There are three specific cases I have experienced.

An Older hp microserver with remote access card - it was not possible to send 
ctrl-alt-esc.  It only has a vga remote console available.

A Newer gen8 hp microserver with lio4 graphical console - same senario as 
above.

Gen8 hp microserver with ilo4 textcons display - vga text send over ssh.  Once 
again it is not possible to send ctrl-alt-escape.

Textcons is preferable for me as as opposed to the inbuilt virtual serial port 
/ serial console on the gen8 machines as shift-pageup works in textcons so I 
can see things that were written to the console and not necessarily to 
/var/messages.

Best regards,

Nat