allow configuration file to override explicit configure-time log path

[carns]

At compile time, Darshan supports a configure option that causes Darshan to use an environment variable to determine where to place log files (see the --with-log-path-by-env option at https://darshan.readthedocs.io/en/latest/darshan-runtime/doc/darshan-runtime.html#compilation ).

This option takes precedent over the typical --with-log-path option. Unlike that option, however, --with-log-path-by-env does not use a year/month/day hierarchy; it is just a flat directory.

Also, once it has been set, I do not see any way to override it, at least if the env variable chosen is something that is always set, like $HOME. So even if you specify a Darshan configuration file, you cannot override this setting and place logs in a year/month/day hierarchy. This is particularly problematic for Spack installations that use this setting by default and redirect all logs to $HOME.

If DARSHAN_LOGPATH is set in the configuration file as documented in https://darshan.readthedocs.io/en/latest/darshan-runtime/doc/darshan-runtime.html#darshan-library-config-settings, then it should take precedence so that a default Spack-installed Darshan package can still be configured afterwards to work like a traditional installation. Or alternatively the configuration file can provide a means to disable the by-env option so that the normal logic falls through to the DARSHAN_LOGPATH.

[wkliao]

It appears that the while loop in subroutine darshan_parse_config_file() does not include a checking of option LOGPATH.

darshan/darshan-runtime/lib/darshan-config.c

Line 486 in 1074414

while(getline(&line, &len, fp) != -1)

[roblatham00]

from conversation:

which one takes highest priority? log-path-by-env
wrinkle: if built with log-path-by-env, and the choice was $HOME -- no way to un-set HOME (without breaking a bunch of stuff in the shell)

Our desired priority order:

1. DARSHAN_LOGPATH env var is top priority if set (a runtime check)
2. config file
3. compiled default (log-path-by-env or whatever was used)
4. if cannot find anything... error (at end of run)