Re: Cnmagic support for wscons

[Valery Ushakov <uwe%stderr.spb.ru@localhost>]

On Tue, Jan 17, 2017 at 11:55:52 +1100, Nathanial Sloss wrote:

> 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 would expect the proposal to actually describe and document all of
that and more.  Do we really need to play the game where I have to ask
very specific direct questions that you try to answer as literally as
possible?


> > > > 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.
> 
> 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.

And again the only bit of information you provide is that you cannot
send Ctrl-Alt-Esc to those remote access cards.  What keys those cards
do support?  Why can't you man KS_Cmd_Debugger to something else?
What cnmagic setting you can use for them with your patch?  Etc, etc.


> 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.

I'd naively expect remote serial port to be accessible via network
with ssh or telnet.  I'd naively expect your favorite terminal
emulator to support scrolling.  I have to guess here b/c again you
provide no useful information besides implying (not even saying
explicitely) that it doesn't work.

-uwe