Write timestamps with exactly 9 digits after the period.

This ensures that the value written is both compatible with
older mtree versions (which expect the value after the period
to be an integer count of nanoseconds after the whole second)
and is a correct floating-point value.

Leave the parsing code unchanged so it will continue to read
older files.

usr.sbin/mtree/create.c

@@ -212,7 +212,7 @@ statf(int indent, FTSENT *p)
 		output(indent, &offset, "size=%jd",
 		    (intmax_t)p->fts_statp->st_size);
 	if (keys & F_TIME)
-		output(indent, &offset, "time=%ld.%ld",
+		output(indent, &offset, "time=%ld.%09ld",
 		    (long)p->fts_statp->st_mtimespec.tv_sec,
 		    p->fts_statp->st_mtimespec.tv_nsec);
 	if (keys & F_CKSUM && S_ISREG(p->fts_statp->st_mode)) {

usr.sbin/mtree/mtree.5

@@ -200,7 +200,9 @@ The size, in bytes, of the file.
 .It Cm link
 The file the symbolic link is expected to reference.
 .It Cm time
-The last modification time of the file.
+The last modification time of the file, in seconds and nanoseconds.
+The value should include a period character and exactly nine digits
+after the period.
 .It Cm type
 The type of the file; may be set to any one of the following:
 .Pp

usr.sbin/mtree/mtree.8

@@ -233,7 +233,9 @@ The size, in bytes, of the file.
 .It Cm link
 The file the symbolic link is expected to reference.
 .It Cm time
-The last modification time of the file.
+The last modification time of the file, in seconds and nanoseconds.
+The value should include a period character and exactly nine digits
+after the period.
 .It Cm type
 The type of the file; may be set to any one of the following:
 .Pp

usr.sbin/mtree/spec.c

@@ -255,6 +255,8 @@ set(char *t, NODE *ip)
 		case F_TIME:
 			ip->st_mtimespec.tv_sec = strtoul(val, &ep, 10);
 			if (*ep == '.') {
+				/* Note: we require exactly nine
+				 * digits after the decimal point. */
 				val = ep + 1;
 				ip->st_mtimespec.tv_nsec
 				    = strtoul(val, &ep, 10);