Re: [PATCH 2/3] Fix Wunused-return warnings

When building with -D_FORTIFY_SOURCE=2 and -W-unused-return, there are a number of warnings caused by return values of functions marked with the warn_unused_result attribute being ignored. The audit codebase makes an attempt to suppress these warnings by casting the return value to void, but that does not work when D_FORITY_SOURCE is in use. Here's an explanation of how this patch fixes the warnings and how the potential error conditions are handled: Errors writing to the auditd pid file should be logged since errors opening the pid file are logged. These write() errors aren't treated as fatal. Problems adjusting auditd's out of memory score should be logged, if simply to catch a change to the kernel interface. These errors aren't treated as fatal. Auditd refuses to start when nice() fails during initialization, so it should take disk_error_action whenever nice() fails during a reconfigure.

Failure to chdir("/") while daemonizing should be logged and treated as fatal since errors while redirecting stdin, stdout, and stderr are logged and considered fatal. All nice() return values are handled sufficiently by relying on errno. However, they still throw warnings when D_FORTIFY_SOURCE is used. This patch quiets those warnings by capturing the return value and using it and errno to determine if nice() failed. Failure to adjust audit log file owner (fchown) and permissions (fchmod) are logged and considered fatal when opening the log file for the first time. They are not treated as fatal when the operations fail on during log rotation since we made sure that they file owner and permissions were correct when originally opening the log file.