a proposed patch for rsync v. 3.1.1 to fix faulty nanosecond mtimes -- ignoring 1 second overflow as well ( at least Linux futimens() wants that )

set_modtime.v.3.1.1-v3.patch

diff -r 27d7a363f071 rsync.c
--- a/rsync.c	Sat Apr 08 21:05:18 2017 +1000
+++ b/rsync.c	Sat Apr 08 23:04:43 2017 +1000
@@ -549,7 +549,29 @@
 		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) ;
+                /* check and complain */
+                if ( ns < 0 ) {
+                        rprintf(FWARNING, "warning: negative ns mtime (%ld) on %s\n",
+                                ns, full_fname(fname));
+                } else if ( ns >= NSEC_MAX ) {
+                        rprintf(FWARNING, "warning: ns mtime >= 1 sec (%ld) on %s\n",
+                                ns, full_fname(fname));
+                }
+                /* Ok, now let's fix it */
+                if ( NSEC_UNEXPECTED(ns) ) {
+                    if (DEBUG_GTE(TIME, 1)) {
+                            rprintf(FINFO, "! changing nsec time (%ld) to 0 on %s\n",
+                                    ns, full_fname(fname));
+                    }
+                    
+                    /* for negative values, that would also avoid implicit conversions */
+                    ns = 0 ;
+                }
+
+		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 27d7a363f071 rsync.h
--- a/rsync.h	Sat Apr 08 21:05:18 2017 +1000
+++ b/rsync.h	Sat Apr 08 23:04:43 2017 +1000
@@ -737,6 +737,11 @@
 #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 NSEC_MAX 1000000000 /* nb: fits in int32 */
+#define NSEC_UNEXPECTED(ns) (  ((ns) < 0) || (ns) >= NSEC_MAX  )
 
 /* If there is a symlink string, it is always right after the basename */
 #define F_SYMLINK(f) ((f)->basename + strlen((f)->basename) + 1)