.\"	$NetBSD: swapctl.2,v 1.24 2002/10/01 18:10:45 wiz Exp $
.\"
.\" Copyright (c) 1997 Matthew R. Green
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.Dd June 20, 1997
.Dt SWAPCTL 2
.Os
.Sh NAME
.Nm swapctl
.Nd modify swap configuration
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.Fd #include \*[Lt]unistd.h\*[Gt]
.Fd #include \*[Lt]sys/swap.h\*[Gt]
.Ft int
.Fn swapctl "int cmd" "const void *arg" "int misc"
.Sh DESCRIPTION
The
.Nm
function is used to add and delete swap devices, and modify their
configuration.
.Pp
The
.Fa cmd
parameter specifies the operation to be performed.
The
.Fa arg
and
.Fa misc
parameters have different meanings, depending on the
.Fa cmd
parameter.
.Bl -item -offset indent
.It
If
.Fa cmd
is
.Dv SWAP_NSWAP ,
the current number of swap devices in the system is returned.
The
.Fa arg
and
.Fa misc
parameters are ignored.
.It
If
.Fa cmd
is
.Dv SWAP_STATS ,
the current statistics for swap devices are returned in the
.Fa arg
parameter.
No more than
.Fa misc
swap devices are returned.
The
.Fa arg
parameter should point to an array of at least
.Fa misc
struct swapent structures:
.Bd -literal
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 */
};
.Ed
.Pp
The flags are defined as
.Bd -literal
	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
.Ed
.It
If
.Fa cmd
is
.Dv SWAP_ON ,
the
.Fa arg
parameter is used as a pathname of a file to enable swapping to.
The
.Fa misc
parameter is used to set the priority of this swap device.
.It
If
.Fa cmd
is
.Dv SWAP_OFF ,
the
.Fa arg
parameter is used as the pathname of a file to disable swapping from.
The
.Fa misc
parameter is ignored.
.It
If
.Fa cmd
is
.Dv SWAP_CTL ,
the
.Fa arg
and
.Fa misc
parameters have the same function as for the
.Dv SWAP_ON
case, except that they change the priority of a currently enabled swap device.
.It
If
.Fa cmd
is
.Dv SWAP_DUMPDEV ,
the
.Fa arg
parameter is used as the pathname of a device to use as the dump device,
should the system panic.
.It
If
.Fa cmd
is
.Dv SWAP_GETDUMPDEV ,
the
.Fa arg
parameter points to a dev_t, which is filled in by the current dump device.
.El
.Pp
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
.Dv SWAP_ON
command is used.
.Pp
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
.Sx SWAP PRIORITY
section in
.Xr swapctl 8 .
.Sh RETURN VALUES
If the
.Fa cmd
parameter is
.Dv SWAP_NSWAP
or
.Dv SWAP_STATS ,
.Fn swapctl
returns the number of swap devices, if successful.
The
.Dv SWAP_NSWAP
command is always successful.
Otherwise it returns 0 on success and -1
on failure, setting the global variable
.Va errno
to indicate the error.
.Sh ERRORS
.Fn swapctl
succeeds unless:
.Bl -tag -width Er
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded
.Dv NAME_MAX
characters, or an entire path name exceeded
.Dv PATH_MAX
characters.
.It Bq Er ENOENT
The named device does not exist.
For the
.Dv SWAP_CTL
command, the named device is not currently enabled for swapping.
.It Bq Er EACCES
Search permission is denied for a component of the path prefix.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.It Bq Er EPERM
The caller is not the super-user.
.It Bq Er EBUSY
The device specified by
.Fa arg
has already been made available for swapping.
.It Bq Er EINVAL
The device configured by
.Fa arg
has no associated size, or the
.Fa cmd
was unknown.
.It Bq Er ENXIO
The major device number of
.Fa arg
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 arg
points outside the process' allocated address space.
.El
.Sh SEE ALSO
.Xr swapctl 8
.Sh HISTORY
The
.Fn swapctl
function call appeared in
.Nx 1.3 .
The
.Fa se_path
member was added to
.Va struct swapent
in
.Nx 1.4 ,
when the header file was also moved from
.Pa \*[Lt]vm/vm_swap.h\*[Gt] ,
to its current location in
.Pa \*[Lt]sys/swap.h\*[Gt] .
.Sh AUTHORS
The current swap system was designed and implemented by
Matthew Green \*[Lt]mrg@eterna.com.au\*[Gt],
with help from Paul Kranenburg \*[Lt]pk@NetBSD.ORG\*[Gt]
and Leo Weppelman \*[Lt]leo@NetBSD.ORG\*[Gt],
and insights from Jason R. Thorpe \*[Lt]thorpej@NetBSD.ORG\*[Gt].