job-manager: history plugin fails for root

[grondo]

Kind of a corner case, but I was testing in a container and was running as root and saw these errors:

# flux run hostname
2023-03-10T16:04:11.546543Z job-manager.err[0]: jobtap: job.new: callback returned error
b93e807bb66e
2023-03-10T16:04:11.606407Z job-manager.err[0]: jobtap: job.inactive-add: callback returned error

With some printf debugging, I tracked the error down to EINVAL returned from hola_list_insert() in the history plugin since int2ptr(0) returns NULL.

I'm not exactly sure what to do about it (maybe use a special value for root), and it does not seem like a critical issue, but thought I'd report it in case another container user runs across the error.

[garlick]

Doh! Good catch. Maybe mapping root to "nobody" would be the least surprising thing to do? According to this wikipedia article, 65534 is usually the uid assigned to nobody these days.

[grondo]

Would it work instead to use int2ptr ((uid_t) -1)?

[garlick]

Oh I read right past this in the wikipedia article:

−1: The value (uid_t) -1 is reserved by POSIX to identify an omitted argument

Yeah, good idea!