Re: [Emc-developers] Unifying error message reporting in LinuxCNC

[Matt S. <ma...@ma...>]

On Tue, 26 Feb 2013 21:19:53 +0100
Michael Haberler <ma...@ma...> wrote:

> I think we should have the option to log everything, and through a
> singel channel;

I don't usually comment on this kind of stuff, because I don't know
that much about it. Nevertheless, at the risk of exposing my naivete,
here's what I know and think:

1. Originally, messages ended up in the kernel log because real time
components had no access to user space things like file I/O. They did
have access to the shared memory buffer, and could printk into the log
(IIRC).

2. Otherwise (in user space), communications was supposed to be via
the NML channels, of command, status, and error. This is analogous to
the Unix stdin, stdout, and stderr. Both of these systems have a
dedicated channel for error communications.

3. I thought, and this is where I may misunderstand a lot of things,
that there were discussions about using a messaging system like
0MQ/crossroads.io/nano/??? to replace NML and be the "Grand Unified
Communications Mechanism". Or did I miss an important meeting...

4. If you're going to have a GUCM (see above), use it! If some errors
should go in the kernel log or a log file in the user's home directory,
(a) small program(s) can subscribe to the error socket and distribute
the messages as desired.

5. Does RTAI or Xenomai lessen or eliminate the restriction on real
time components ability to access user space? If so, then these
components can publish their error (and status) to the relevant GUCM
sockets/channels. If not, into the kernel log they go via printk.

Thanks,
Matt