SWAPCTL(2)

SWAPCTL(2) | 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 pathname 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 translating the pathname.
[`ENAMETOOLONG`]
  A component of a pathname exceeded {`NAME_MAX`} characters, or an entire path name exceeded {`PATH_MAX`} characters.
[`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>.

May 17, 2010 | NetBSD 8.3