MirOS Manual: swapctl(2)

SWAPCTL(2)                 BSD Programmer's Manual                  SWAPCTL(2)


     swapctl - modify swap configuration


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

     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[MAXPATHLEN];    /* 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 func-
           tion as for the SWAP_ON case, except that they change the priority
           of a currently enabled swap 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


     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.

                   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

     [ELOOP]       Too many symbolic links were encountered in translating the

     [EPERM]       The caller is not the superuser.

     [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 indi-
                   cates 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.


     config(8), 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>.


     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

MirOS BSD #10-current           June 20, 1997                                1

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