Update dumpon(8) to include sysctl variable information

[felix.the.red_gmail.com]

Summary

Document debug.minidump, machdep.dump_retry_count, and kern.bootfile sysctl variables.

[gbe]

LGTM

[markj]

sbin/dumpon/dumpon.8

379

kern.bootfile really has nothing to do with dumpon, it is just mentioned in dumpon.8 as part of an example. Several debugging tools, such as kgdb and dtrace use it to find the kernel executable. I think dumpon.8 is not the right place to document it.

kern.bootfile is effectively set by loader(8), together with kern.module_path. I'm not sure where exactly they would best be documented, but IMO it should be grouped with boot loader documentation. We could certainly use better documentation of the handoff between loader and the kernel, I spent a lot of time last weekend trying to figure out how exactly loader(8) picks the kernel to boot (loader.conf variables which control this include kernel, kernel_path, module_path, bootfile, currdev, loaddev, and some are not meant to be set by users), and it's really not clear from our man pages.