swapctl man page on NetBSD

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SWAPCTL(2)		    BSD System Calls Manual		    SWAPCTL(2)

NAME
     swapctl — modify swap configuration

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <unistd.h>
     #include <sys/swap.h>

     int
     swapctl(int cmd, void *arg, int misc);

DESCRIPTION
     The swapctl function is used to add and delete swap devices, and modify
     their configuration.

     The cmd parameter specifies the operation to be performed.	 The arg and
     misc parameters have different meanings, depending on the cmd parameter.

	   1.	If cmd is SWAP_NSWAP, the current number of swap devices in
		the system is returned.	 The arg and misc parameters are
		ignored.

	   2.	If cmd is SWAP_STATS, the current statistics for swap devices
		are returned in the arg parameter.  No more than misc swap
		devices are returned.  The arg parameter should point to an
		array of at least misc struct swapent structures:

		struct swapent {
			dev_t	se_dev;			/* device id */
			int	se_flags;		/* entry flags */
			int	se_nblks;		/* total blocks */
			int	se_inuse;		/* blocks in use */
			int	se_priority;		/* priority */
			char	se_path[PATH_MAX+1];	/* path to entry */
		};

		The flags are defined as

			SWF_INUSE	in use: we have swapped here
			SWF_ENABLE	enabled: we can swap here
			SWF_BUSY	busy: I/O happening here
			SWF_FAKE	fake: still being built

	   3.	If cmd is SWAP_ON, the arg parameter is used as a pathname of
		a file to enable swapping to.  The misc parameter is used to
		set the priority of this swap device.

	   4.	If cmd is SWAP_OFF, the arg parameter is used as the pathname
		of a file to disable swapping from.  The misc parameter is
		ignored.

	   5.	If cmd is SWAP_CTL, the arg and misc parameters have the same
		function as for the SWAP_ON case, except that they change the
		priority of a currently enabled swap device.

	   6.	If cmd is SWAP_DUMPDEV, the arg parameter is used as the path‐
		name of a device to use as the dump device, should the system
		panic.

	   7.	If cmd is SWAP_GETDUMPDEV, the arg parameter points to a
		dev_t, which is filled in by the current dump device.

     When swapping is enabled on a block device, the first portion of the disk
     is left unused to prevent any disklabel present from being overwritten.
     This space is allocated from the swap device when the SWAP_ON command is
     used.

     The priority of a swap device can be used to fill faster swap devices
     before slower ones.  A priority of 0 is the highest, with larger numbers
     having lower priority.  For a fuller discussion on swap priority, see the
     SWAP PRIORITY section in swapctl(8).

RETURN VALUES
     If the cmd parameter is SWAP_NSWAP or SWAP_STATS, swapctl() returns the
     number of swap devices, if successful.  The SWAP_NSWAP command is always
     successful.  Otherwise it returns 0 on success and -1 on failure, setting
     the global variable errno to indicate the error.

ERRORS
     swapctl() succeeds unless:

     [EACCES]		Search permission is denied for a component of the
			path prefix.

     [EBUSY]		The device specified by arg has already been made
			available for swapping.

     [EFAULT]		arg points outside the process' allocated address
			space.

     [EINVAL]		The device configured by arg has no associated size,
			or the cmd was unknown.

     [EIO]		An I/O error occurred while opening the swap device.

     [ELOOP]		Too many symbolic links were encountered in translat‐
			ing the pathname.

     [ENAMETOOLONG]	A component of a pathname exceeded {NAME_MAX} charac‐
			ters, or an entire path name exceeded {PATH_MAX} char‐
			acters.

     [ENOENT]		The named device does not exist.  For the SWAP_CTL
			command, the named device is not currently enabled for
			swapping.

     [ENOTDIR]		A component of the path prefix is not a directory.

     [ENXIO]		The major device number of arg is out of range (this
			indicates no device driver exists for the associated
			hardware); or the block device specified by arg is not
			marked as a swap partition in the disklabel.

     [EPERM]		The caller is not the super-user.

SEE ALSO
     swapctl(8)

HISTORY
     The swapctl() function call appeared in NetBSD 1.3.  The se_path member
     was added to struct swapent in NetBSD 1.4, when the header file was also
     moved from <vm/vm_swap.h> to its current location in <sys/swap.h>.

AUTHORS
     The current swap system was designed and implemented by Matthew Green
     ⟨mrg@eterna.com.au⟩, with help from Paul Kranenburg ⟨pk@NetBSD.org⟩ and
     Leo Weppelman ⟨leo@NetBSD.org⟩, and insights from Jason R. Thorpe
     ⟨thorpej@NetBSD.org⟩.

BSD				 May 17, 2010				   BSD
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