re: setting DDB_COMMANDONENTER="bt" by default

[matthew green <mrg%eterna.com.au@localhost>]

Christos Zoulas writes:
> In article <c842f063-4d5a-4713-7a1e-350c174b9e7e%geeklan.co.uk@localhost>,
> Sevan Janiyan  <venture37%geeklan.co.uk@localhost> wrote:
> >Hello,
> >Is there any reason good reason why we should not opt for
> >DDB_COMMANDONENTER="bt" by default across the board??
> >We have it set or a variation of, on some ports (amd64, some evbarm and
> >evbmips configs, i386, macppc). Would be useful to have it there by
> >default, especially on the slower ports which require a little more time
> >to get going. Cuts out one it
> >Happy to make the change to the configs.
> 
> You can just do the same with sysctl ddb.onpanic=2...

more importantly, this method also has checks to make sure it
doesn't recurse if the backtrace happens to fault.  the 
enter command method doesn't..

we used to do this:

- if entering ddb, just enter it (onpanic = 1)
- otherwise, dump a trace and reboot (onpanic = 0)

the later, we added support for doing both via onpanic = 2,
but left the default as-is.

i think we should actually make ddb default to this with a
new sysctl, and remove interpretting onpanic = 2 differently.
eg, make it look like, with new "dumpstack" sysctl, defaults
to value of 1:

   if (dumpstack > 0)
      do current dumpstack method
   if (onpanic > 0)
      enter ddb
   reboot

(this idea came from jmcneill@.)


.mrg.