monitor size of /tmp

OpenBMC application use /tmp for a variety of reasons. If /tmp becomes
full, then certain applications will start to fail (in very undefined
ways).

/tmp uses a tmpfs filesystem that is backed by BMC memory. Just
monitoring BMC memory is not enough though because by default, only 50%
of memory is allowed to be used by /tmp.

This commit adds in a default to monitor /tmp and log to the journal if
it sees /tmp exceed 85% usage. This will at least offer a clue to users
when debugging issues.

Tested:
- Tested as a part of the following commit:
  https://gerrit.openbmc.org/c/openbmc/openbmc/+/56065

Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
Change-Id: I1355f0d29a0b7a0840075561069d4ec7d3b27672
1 file changed