savecore(8) reporting when insufficient disk space

[farhan_farhan.codes]

Summary

Spent 2-3 days trying to figure out why savecore(8) was not writing /var/crash dumps. It was due to insufficient disk space. However, this was not reported as the reason from savecore(8). This patch prints out an error message.

Test Plan

Fill up disk beyond what minfree requires, trigger a kernel panic and dump the core, observe error message from savecore.

[farhan_farhan.codes]

Raising Warning to Err

[rlibby]

I don't have an objection to changing the LOG_WARNING to LOG_ERR, but I'm confused about what this actually changes. I looked at man 3 syslog and vsyslog1() to see if we printed to stderr by default for LOG_ERR but I'm not seeing that. So, what does this actually do?

[farhan_farhan.codes]

In D34484#781354, @rlibby wrote:

I don't have an objection to changing the LOG_WARNING to LOG_ERR, but I'm confused about what this actually changes. I looked at man 3 syslog and vsyslog1() to see if we printed to stderr by default for LOG_ERR but I'm not seeing that. So, what does this actually do?

I am willing to acknowledge that this is a mistake on my end, but running savecore with verbosity did not seem to print out the warning when disk space was full.
The objective is to print out a warning/error message. If this can be done through another means then my commit is a moot point.

[glebius]

Were you uncompressing a compressed kernel dump?