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

2 files changed, 46 insertions, 18 deletions

diff --git a/lib/libc/sys/Makefile.inc b/lib/libc/sys/Makefile.inc
index 4fe3d7e..257ef7a 100644
--- a/lib/libc/sys/Makefile.inc
+++ b/lib/libc/sys/Makefile.inc
@@ -131,6 +131,7 @@ MLINKS+=shmat.2 shmdt.2
 MLINKS+=stat.2 fstat.2 stat.2 lstat.2
 MLINKS+=statfs.2 fstatfs.2
 MLINKS+=syscall.2 __syscall.2
+MLINKS+=swapon.2 swapoff.2
 MLINKS+=truncate.2 ftruncate.2
 MLINKS+=utimes.2 futimes.2 utimes.2 lutimes.2
 MLINKS+=wait.2 wait3.2 wait.2 wait4.2 wait.2 waitpid.2
diff --git a/lib/libc/sys/swapon.2 b/lib/libc/sys/swapon.2
index a852ba0..f4f9092 100644
--- a/lib/libc/sys/swapon.2
+++ b/lib/libc/sys/swapon.2
@@ -36,14 +36,16 @@
 .Dt SWAPON 2
 .Os
 .Sh NAME
-.Nm swapon
-.Nd add a swap device for interleaved paging/swapping
+.Nm swapon , swapoff
+.Nd control devices for interleaved paging/swapping
 .Sh LIBRARY
 .Lb libc
 .Sh SYNOPSIS
 .In unistd.h
 .Ft int
 .Fn swapon "const char *special"
+.Ft int
+.Fn swapoff "const char *special"
 .Sh DESCRIPTION
 .Fn Swapon
 makes the block device
@@ -55,13 +57,22 @@ configuration time.  The size of the swap area on
 .Fa special
 is calculated at the time the device is first made available
 for swapping.
+.Pp
+The
+.Fn swapoff
+system call disables paging and swapping on the given device.
+All associated swap metadata are deallocated, and the device
+is made available for other purposes.
 .Sh RETURN VALUES
 If an error has occurred, a value of -1 is returned and
 .Va errno
 is set to indicate the error.
 .Sh ERRORS
-.Fn Swapon
-succeeds unless:
+Both
+.Fn swapon
+and
+.Fn swapoff
+can fail if:
 .Bl -tag -width Er
 .It Bq Er ENOTDIR
 A component of the path prefix is not a directory.
@@ -76,6 +87,19 @@ Search permission is denied for a component of the path prefix.
 Too many symbolic links were encountered in translating the pathname.
 .It Bq Er EPERM
 The caller is not the super-user.
+.It Bq Er EFAULT
+.Fa Special
+points outside the process's allocated address space.
+.El
+.Pp
+Additionally,
+.Fn swapon
+can fail for the following reasons:
+.Bl -tag -width Er
+.It Bq Er EINVAL
+The system has reached the boot-time limit on the number of
+swap devices,
+.Va vm.nswapdev .
 .It Bq Er ENOTBLK
 .Fa Special
 is not a block device.
@@ -84,11 +108,6 @@ The device specified by
 .Fa special
 has already
 been made available for swapping
-.It Bq Er EINVAL
-The device configured by
-.Fa special
-was not
-configured into the system as a swap device.
 .It Bq Er ENXIO
 The major device number of
 .Fa special
@@ -96,20 +115,28 @@ is out of range (this indicates no device driver exists
 for the associated hardware).
 .It Bq Er EIO
 An I/O error occurred while opening the swap device.
-.It Bq Er EFAULT
-.Fa Special
-points outside the process's allocated address space.
+.El
+.Pp
+Lastly,
+.Fn swapoff
+can fail if:
+.Bl -tag -width Er
+.It Bq Er EINVAL
+The system is not currently swapping to
+.Fa special .
+.It Bq Er ENOMEM
+Not enough virtual memory is available to safely disable
+paging and swapping to the given device.
 .El
 .Sh SEE ALSO
 .Xr config 8 ,
-.Xr swapon 8
-.Sh BUGS
-There is no way to stop swapping on a disk so that the pack may be
-dismounted.
-.Pp
-This call will be upgraded in future versions of the system.
+.Xr swapon 8 ,
+.Xr sysctl 8
 .Sh HISTORY
 The
 .Fn swapon
 function call appeared in
 .Bx 4.0 .
+.Fn Swapoff
+appeared in
+.Fx 5.0 .