Index: swapon.c
===================================================================
--- swapon.c
+++ swapon.c
@@ -77,7 +77,7 @@
 
 static enum { SWAPON, SWAPOFF, SWAPCTL } orig_prog, which_prog = SWAPCTL;
 
-static int qflag;
+static int Eflag, qflag;
 
 int
 main(int argc, char **argv)
@@ -100,7 +100,7 @@
 	
 	doall = 0;
 	etc_fstab = NULL;
-	while ((ch = getopt(argc, argv, "AadghklLmqsUF:")) != -1) {
+	while ((ch = getopt(argc, argv, "AadEghklLmqsUF:")) != -1) {
 		switch(ch) {
 		case 'A':
 			if (which_prog == SWAPCTL) {
@@ -121,6 +121,12 @@
 			else
 				usage();
 			break;
+		case 'E':
+			if (which_prog == SWAPON)
+				Eflag = 1;
+			else
+				usage();
+			break;
 		case 'g':
 			hflag = 'G';
 			break;
@@ -182,6 +188,8 @@
 				    strstr(fsp->fs_mntops, "late") == NULL &&
 				    late != 0)
 					continue;
+				if (strstr(fsp->fs_mntops, "trimonce") != NULL)
+					Eflag = 1;
 				swfile = swap_on_off(fsp->fs_spec, 1,
 				    fsp->fs_mntops);
 				if (swfile == NULL) {
@@ -378,12 +386,19 @@
 					return (NULL);
 				}
 			} else if (strcmp(token, "notrim") == 0) {
+				if (Eflag) {
+					warn("Options \"notrim\" and "
+					    "\"trimonce\" conflict");
+					free(ops);
+					return (NULL);
+				}
 				Tflag = " -T ";
 			} else if (strcmp(token, "late") == 0) {
 				/* ignore known option */
 			} else if (strcmp(token, "noauto") == 0) {
 				/* ignore known option */
-			} else if (strcmp(token, "sw") != 0) {
+			} else if (strcmp(token, "sw") != 0 &&
+			    strcmp(token, "trimonce") != 0) {
 				warnx("Invalid option: %s", token);
 				free(ops);
 				return (NULL);
@@ -721,14 +736,46 @@
 	return (WEXITSTATUS(status));
 }
 
+static void
+swap_trim(const char *name)
+{
+
+	struct stat sb;
+	off_t ioarg[2], sz;
+	int fd;
+
+	fd = open(name, O_WRONLY);
+	if (fd < 0)
+		return;
+	if (fstat(fd, &sb) >= 0) {
+		if (S_ISREG(sb.st_mode)) {
+			sz = sb.st_size;
+		} else if (S_ISCHR(sb.st_mode) || S_ISBLK(sb.st_mode)) {
+			if (ioctl(fd, DIOCGMEDIASIZE, &sz) != 0)
+				err(1, "ioctl(DIOCGMEDIASIZE)");
+		} else {
+			errx(1, "%s has an invalid file type", name);
+		}
+
+		ioarg[0] = 0;
+		ioarg[1] = sz;
+		if (ioctl(fd, DIOCGDELETE, ioarg) != 0)
+			warn(1, "ioctl(DIOCGDELETE)");
+	}
+	close(fd);
+}
+
 static const char *
 swap_on_off_sfile(const char *name, int doingall)
 {
+
 	int error;
 
-	if (which_prog == SWAPON)
+	if (which_prog == SWAPON) {
+		if (Eflag)
+			swap_trim(name);
 		error = swapon(name);
-	else /* SWAPOFF */
+	} else /* SWAPOFF */
 		error = swapoff(name);
 
 	if (error == -1) {
@@ -759,6 +806,8 @@
 	fprintf(stderr, "usage: %s ", getprogname());
 	switch(orig_prog) {
 	case SWAPON:
+	    fprintf(stderr, "[-F fstab] -aLq | [-E] file ...\n");
+	    break;
 	case SWAPOFF:
 	    fprintf(stderr, "[-F fstab] -aLq | file ...\n");
 	    break;