stand: Add support for `print_delay` environment variable in loader

[obiwac]

Summary

This adds support for a new print_delay environment variable, which inserts a delay (in microseconds, maybe this should be in millis instead?) when putchar encounters a newline character. This can be useful when debugging.

Sponsored by: The FreeBSD Foundation

Test Plan

Just tested in loader.efi, on my machine & in VM.

[markj]

Let me know if it's not desirable to add new error codes to libsa.

For my taste it's a bit gratuitous--EINVAL should be fine. I'd think that we want to avoid adding new error strings in memory-constrained loader, but Warner has better intuition there.

stand/common/misc.c

216 ↗

(On Diff #156965)

222 ↗

(On Diff #156965)

Why not have this function in console.c? Then you don't need to export print_delay_usec.

[imp]

I tend to think the new error values are a bit gratuitous as well... strtonum is approximately what we're doing and it return ERANGE or EINVAL.

stand/common/misc.c

222 ↗

(On Diff #156965)

and the print_delay_usec variable...

[obiwac]

Move setprint_delay to console.c

[obiwac]

Replace ENAN and ENUMNEG errors with existing EINVAL

[markj]

stand/common/console.c

47

[obiwac]

Fix suggestions by ziaee@

[obiwac]

fix markj comment & ziaee

[ziaee]

Doc LGTM!

[ziaee]

Rene and John Grafton helped with the doc also in the hacker lounge.

[mckusick]

Review process is complete with all the right folks signing off.