This is David Schultz's swapoff code which I am finally able to commit.

This should be considered highly experimental for the moment.

Submitted by:	David Schultz <dschultz@uclink.Berkeley.EDU>
MFC after:	3 weeks

3 files changed, 56 insertions, 26 deletions

diff --git a/sbin/swapon/Makefile b/sbin/swapon/Makefile
index be803b2..f052567 100644
--- a/sbin/swapon/Makefile
+++ b/sbin/swapon/Makefile
@@ -3,5 +3,7 @@
 
 PROG=	swapon
 MAN=	swapon.8
+LINKS=	${BINDIR}/swapon ${BINDIR}/swapoff
+MLINKS=	swapon.8 swapoff.8
 
 .include <bsd.prog.mk>
diff --git a/sbin/swapon/swapon.8 b/sbin/swapon/swapon.8
index ce23b38..edda998 100644
--- a/sbin/swapon/swapon.8
+++ b/sbin/swapon/swapon.8
@@ -36,39 +36,46 @@
 .Dt SWAPON 8
 .Os
 .Sh NAME
-.Nm swapon
-.Nd "specify additional device for paging and swapping"
+.Nm swapon , swapoff
+.Nd "specify devices for paging and swapping"
 .Sh SYNOPSIS
-.Nm
+.Nm swap[on|off]
 .Fl a
-.Nm
+.Nm swap[on|off]
 .Ar special_file ...
 .Sh DESCRIPTION
 The
-.Nm
+.Nm swapon
 utility is used to specify additional devices on which paging and swapping
 are to take place.
 The system begins by swapping and paging on only a single device
 so that only one disk is required at bootstrap time.
 Calls to
-.Nm
+.Nm swapon
 normally occur in the system multi-user initialization file
 .Pa /etc/rc
 making all swap devices available, so that the paging and swapping
 activity is interleaved across several devices.
 .Pp
+The
+.Nm swapoff
+utility disables paging and swapping on a device.
+Calls to
+.Nm swapoff
+succeed only if disabling the device would leave enough
+remaining virtual memory to accomodate all running programs.
+.Pp
 Normally, the first form is used:
 .Bl -tag -width indent
 .It Fl a
 All devices marked as ``sw''
 swap devices in
 .Pa /etc/fstab
-are made available unless their ``noauto'' option is also set.
+are added to or removed from the pool of available swap
+unless their ``noauto'' option is also set.
 .El
 .Pp
-The second form gives individual block devices as given
-in the system swap configuration table.  The call makes only this space
-available to the system for swap allocation.
+The second form is used to configure or disable individual devices.
 .Sh SEE ALSO
 .Xr swapon 2 ,
 .Xr fstab 5 ,
@@ -85,12 +92,12 @@ memory disk devices
 .It Pa /etc/fstab
 ASCII file system description table
 .El
-.Sh BUGS
-There is no way to stop paging and swapping on a device.
-It is therefore not possible to dismount swap devices which are
-mounted during system operation.
 .Sh HISTORY
 The
-.Nm
+.Nm swapon
 utility appeared in
 .Bx 4.0 .
+The
+.Nm swapoff
+utility appeared in
+.Fx 5.0 .
diff --git a/sbin/swapon/swapon.c b/sbin/swapon/swapon.c
index 69f4e73..51042bc 100644
--- a/sbin/swapon/swapon.c
+++ b/sbin/swapon/swapon.c
@@ -53,8 +53,9 @@ static const char rcsid[] =
 #include <string.h>
 #include <unistd.h>
 
-static void usage(void);
-int	add(char *name, int ignoreebusy);
+static void usage(const char *);
+static int is_swapoff(const char *);
+int	swap_on_off(char *name, int ignoreebusy, int do_swapoff);
 
 int
 main(int argc, char **argv)
@@ -62,6 +63,10 @@ main(int argc, char **argv)
 	struct fstab *fsp;
 	int stat;
 	int ch, doall;
+	int do_swapoff;
+	char *pname = argv[0];
+
+	do_swapoff = is_swapoff(pname);
 
 	doall = 0;
 	while ((ch = getopt(argc, argv, "a")) != -1)
@@ -71,7 +76,7 @@ main(int argc, char **argv)
 			break;
 		case '?':
 		default:
-			usage();
+			usage(pname);
 		}
 	argv += optind;
 
@@ -82,23 +87,24 @@ main(int argc, char **argv)
 				continue;
 			if (strstr(fsp->fs_mntops, "noauto"))
 				continue;
-			if (add(fsp->fs_spec, 1))
+			if (swap_on_off(fsp->fs_spec, 1, do_swapoff))
 				stat = 1;
 			else
-				printf("swapon: adding %s as swap device\n",
+				printf("%s: %sing %s as swap device\n",
+				    pname, do_swapoff ? "remov" : "add",
 				    fsp->fs_spec);
 		}
 	else if (!*argv)
-		usage();
+		usage(pname);
 	for (; *argv; ++argv)
-		stat |= add(*argv, 0);
+		stat |= swap_on_off(*argv, 0, do_swapoff);
 	exit(stat);
 }
 
 int
-add(char *name, int ignoreebusy)
+swap_on_off(char *name, int ignoreebusy, int do_swapoff)
 {
-	if (swapon(name) == -1) {
+	if ((do_swapoff ? swapoff(name) : swapon(name)) == -1) {
 		switch (errno) {
 		case EBUSY:
 			if (!ignoreebusy)
@@ -114,8 +120,23 @@ add(char *name, int ignoreebusy)
 }
 
 static void
-usage()
+usage(const char *pname)
 {
-	fprintf(stderr, "usage: swapon [-a] [special_file ...]\n");
+	fprintf(stderr, "usage: %s [-a] [special_file ...]\n", pname);
 	exit(1);
 }
+
+static int
+is_swapoff(const char *s)
+{
+	const char *u;
+
+	if ((u = strrchr(s, '/')) != NULL)
+		++u;
+	else
+		u = s;
+	if (strcmp(u, "swapoff") == 0)
+		return 1;
+	else
+		return 0;
+}