Code review comment for ~epics-core/epics-base/+git/Com:errlog2syslog

iocLogPrefix() can only be called once, and if you're using it that's presumably because you want to be able to identify which IOC generated each log message, so you should be running it before any messages will be logged anyway. Thus I see no problem with that new restriction.

However with this change applied any supported IOC that sets iocLogPrefix() would always pass its log messages to syslog; I don't see any way to set a prefix for logging to an external log-server without also enabling errlogToSyslog(). An IOC currently has to run iocLogInit to connect to an external log-server, so maybe errlogToSyslog should become a similar command that must appear in st.cmd (iocBuild is too late anyway, dbLoadRecords calls errlogPrintf() and its output should be logged). It would probably need protection against being run twice, and maybe emit an error message if the prefix isn't set.

I'm not convinced we have the prefix logic right — sorry! Wouldn't the following be more intuitive: If the _PREFIX environment variable is set (and not blank) it should be used automatically without needing to call iocLogPrefix(). The user can set the variable in the st.cmd file, so the command isn't really necessary anyway. There should be one or more commands in the st.cmd file to enable the desired log mechanisms. The enable commands can check any necessary preconditions (such as requiring _PREFIX to be set, and saving its value) and report errors then.