a proposed patch for rsync v. 3.1.1 to fix faulty nanosecond mtimes

set_modtime.v.3.1.1.patch

diff -r 534ce1d4fb97 rsync.c
--- a/rsync.c	Sat Apr 08 20:56:59 2017 +1000
+++ b/rsync.c	Sat Apr 08 21:02:00 2017 +1000
@@ -549,7 +549,21 @@
 		flags |= ATTRS_SKIP_MTIME;
 	if (!(flags & ATTRS_SKIP_MTIME)
 	    && cmp_time(sxp->st.st_mtime, file->modtime) != 0) {
-		int ret = set_modtime(fname, file->modtime, F_MOD_NSEC(file), sxp->st.st_mode);
+                /* tv_nsec is a long type */
+                long ns = F_MOD_NSEC(file) ;
+                /* warnings / debug */
+                if ( ns < 0 ) {
+                        rprintf(FWARNING, "negative ns mtime (%ld) on %s\n",
+                                ns, full_fname(fname));
+                } else if ( ns >= NS_MAX ) {
+                        if (DEBUG_GTE(TIME, 1)) {
+                                rprintf(FWARNING, "ns mtime >= 1 sec (%ld) on %s\n",
+                                        ns, full_fname(fname));
+                        }
+                }
+                /* do an explicit conversion before set_modtime() does an implicit one */
+                ns = ZERO_IF_NEG(ns);
+		int ret = set_modtime(fname, file->modtime, ns, sxp->st.st_mode);
 		if (ret < 0) {
 			rsyserr(FERROR_XFER, errno, "failed to set times on %s",
 				full_fname(fname));
diff -r 534ce1d4fb97 rsync.h
--- a/rsync.h	Sat Apr 08 20:56:59 2017 +1000
+++ b/rsync.h	Sat Apr 08 21:02:00 2017 +1000
@@ -737,6 +737,10 @@
 #endif
 
 #define F_MOD_NSEC(f) ((f)->flags & FLAG_MOD_NSEC ? OPT_EXTRA(f, 0)->unum : 0)
+/* since we use unsigned ns, and since they are not supposed to be negative: */
+#define ZERO_IF_NEG(ns) (  ((ns) < 0) ? 0 : (ns)  )
+/* ns tail is expected to be < 10^9 */
+#define NS_MAX 1000000000 /* nb: fits in int32 */
 
 /* If there is a symlink string, it is always right after the basename */
 #define F_SYMLINK(f) ((f)->basename + strlen((f)->basename) + 1)