[autobuild] clock_gettime() -lrt with glibc < 2.17

clock_gettime() needs -lrt with glibc < 2.17,
and possibly other platforms

On systems without clock_gettime (-cough- Mac OSX -cough-),
use gettimeofday() (deprecated in POSIX.1-2008) which is slightly
lower precision, but reasonably fast in execution.  References:
http://stackoverflow.com/questions/5167269/clock-gettime-alternative-in-mac-os-x
http://stackoverflow.com/questions/11680461/monotonic-clock-on-osx
https://discussions.apple.com/thread/6023936?tstart=0

configure.ac

@@ -286,6 +286,9 @@ AC_SEARCH_LIBS(hstrerror,resolv)
 dnl On Haiku accept() and friends are in libnetwork
 AC_SEARCH_LIBS(accept,network)
 
+dnl clock_gettime() needs -lrt with glibc < 2.17, and possibly other platforms
+AC_SEARCH_LIBS([clock_gettime],[rt])
+
 save_LIBS=$LIBS
 AC_SEARCH_LIBS(dlopen,dl,[
   AC_CHECK_HEADERS([dlfcn.h],[
@@ -699,7 +702,7 @@ AC_CHECK_FUNCS([dup2 getcwd inet_ntoa inet_ntop inet_pton issetugid memset mmap
 		  gethostbyname poll epoll_ctl getrlimit chroot \
 		  getuid select signal pathconf madvise posix_fadvise posix_madvise \
 		  writev sigaction sendfile64 send_file kqueue port_create localtime_r gmtime_r \
-		  memset_s explicit_bzero])
+		  memset_s explicit_bzero clock_gettime])
 
 AC_MSG_CHECKING(if weak symbols are supported)
 AC_LINK_IFELSE([AC_LANG_PROGRAM([[

src/connections.c

@@ -692,7 +692,7 @@ static int connection_handle_read_state(server *srv, connection *con)  {
 	if (con->request_count > 1 && is_request_start) {
 		con->request_start = srv->cur_ts;
 		if (con->conf.high_precision_timestamps)
-			clock_gettime(CLOCK_REALTIME, &con->request_start_hp);
+			log_clock_gettime_realtime(&con->request_start_hp);
 	}
 
 		/* if there is a \r\n\r\n in the chunkqueue
@@ -1000,7 +1000,7 @@ int connection_state_machine(server *srv, connection *con) {
 			con->request_start = srv->cur_ts;
 			con->read_idle_ts = srv->cur_ts;
 			if (con->conf.high_precision_timestamps)
-				clock_gettime(CLOCK_REALTIME, &con->request_start_hp);
+				log_clock_gettime_realtime(&con->request_start_hp);
 
 			con->request_count++;
 			con->loops_per_request = 0;

src/log.c

@@ -28,6 +28,26 @@
 # define O_LARGEFILE 0
 #endif
 
+#ifndef HAVE_CLOCK_GETTIME
+#ifdef HAVE_SYS_TIME_H
+# include <sys/time.h>  /* gettimeofday() */
+#endif
+#endif
+
+int log_clock_gettime_realtime (struct timespec *ts) {
+      #ifdef HAVE_CLOCK_GETTIME
+	return clock_gettime(CLOCK_REALTIME, ts);
+      #else
+	/* Mac OSX does not provide clock_gettime()
+	 * e.g. defined(__APPLE__) && defined(__MACH__) */
+	struct timeval tv;
+	gettimeofday(&tv, NULL);
+	ts->tv_sec  = tv.tv_sec;
+	ts->tv_nsec = tv.tv_usec * 1000;
+	return 0;
+      #endif
+}
+
 /* retry write on EINTR or when not all data was written */
 ssize_t write_all(int fd, const void* buf, size_t count) {
 	ssize_t written = 0;

src/log.h

@@ -4,6 +4,9 @@
 
 #include "server.h"
 
+struct timespec; /* declaration */
+int log_clock_gettime_realtime (struct timespec *ts);
+
 ssize_t write_all(int fd, const void* buf, size_t count);
 
 /* Close fd and _try_ to get a /dev/null for it instead.

src/mod_accesslog.c

@@ -765,7 +765,7 @@ REQUESTDONE_FUNC(log_access_write) {
 						off_t t; /*(expected to be 64-bit since large file support enabled)*/
 						long ns;
 						if (!(f->opt & FORMAT_FLAG_TIME_BEGIN)) {
-							if (0 == ts.tv_sec) clock_gettime(CLOCK_REALTIME, &ts);
+							if (0 == ts.tv_sec) log_clock_gettime_realtime(&ts);
 							t = (off_t)ts.tv_sec;
 							ns = ts.tv_nsec;
 						} else {
@@ -787,7 +787,7 @@ REQUESTDONE_FUNC(log_access_write) {
 						long ns;
 						char *ptr;
 						if (!(f->opt & FORMAT_FLAG_TIME_BEGIN)) {
-							if (0 == ts.tv_sec) clock_gettime(CLOCK_REALTIME, &ts);
+							if (0 == ts.tv_sec) log_clock_gettime_realtime(&ts);
 							ns = ts.tv_nsec;
 						} else {
 							ns = con->request_start_hp.tv_nsec;
@@ -880,9 +880,13 @@ REQUESTDONE_FUNC(log_access_write) {
 				} else {
 					const struct timespec * const bs = &con->request_start_hp;
 					off_t tdiff; /*(expected to be 64-bit since large file support enabled)*/
-					if (0 == ts.tv_sec) clock_gettime(CLOCK_REALTIME, &ts);
+					if (0 == ts.tv_sec) log_clock_gettime_realtime(&ts);
 					tdiff = (off_t)(ts.tv_sec - bs->tv_sec)*1000000000 + (ts.tv_nsec - bs->tv_nsec);
-					if (f->opt & FORMAT_FLAG_TIME_MSEC) {
+					if (tdiff <= 0) {
+						/* sanity check for time moving backwards
+						 * (daylight savings adjustment or leap seconds or ?) */
+						tdiff  = -1;
+					} else if (f->opt & FORMAT_FLAG_TIME_MSEC) {
 						tdiff +=  999999; /* ceil */
 						tdiff /= 1000000;
 					} else if (f->opt & FORMAT_FLAG_TIME_USEC) {