swapctl - modify swap configuration
Standard C Library (libc, -lc)
#include <unistd.h>
#include <sys/swap.h>
int
swapctl(int cmd, const void *arg, int misc);
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.
If cmd is SWAP_NSWAP, the current number of swap devices in the
system is returned. The arg and misc parameters are ignored.
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
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.
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.
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.
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.
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).
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.
swapctl() succeeds unless:
[ENOTDIR] A component of the path prefix is not a directory.
[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.
[EACCES] Search permission is denied for a component of the
path prefix.
[ELOOP] Too many symbolic links were encountered in translating
the pathname.
[EPERM] The caller is not the super-user.
[EBUSY] The device specified by arg has already been made
available for swapping.
[EINVAL] The device configured by arg has no associated size,
or the cmd was unknown.
[ENXIO] The major device number of arg is out of range (this
indicates no device driver exists for the associated
hardware).
[EIO] An I/O error occurred while opening the swap device.
[EFAULT] arg points outside the process' allocated address
space.
swapctl(8)
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>.
The current swap system was designed and implemented by Matthew Green
<[email protected]>, with help from Paul Kranenburg <[email protected]> and
Leo Weppelman <[email protected]>, and insights from Jason R. Thorpe <[email protected]>.
BSD June 20, 1997 BSD
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