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

int swapctl(int cmd, void *arg);

The swapctl() function adds, deletes, or returns information about swap resources. cmd specifies one of the following options contained in <sys/swap.h>:

SC_ADD /* add a resource for swapping */
SC_LIST /* list the resources for swapping */
SC_REMOVE /* remove a resource for swapping */
SC_GETNSWP /* return number of swap resources */

When SC_ADD or SC_REMOVE is specified, arg is a pointer to a swapres structure containing the following members:

char *sr_name; /* pathname of resource */
off_t sr_start; /* offset to start of swap area */
off_t sr_length; /* length of swap area */

The sr_start and sr_length members are specified in 512-byte blocks. A swap resource can only be removed by specifying the same values for the sr_start and sr_length members as were specified when it was added. Swap resources need not be removed in the order in which they were added.

When SC_LIST is specified, arg is a pointer to a swaptable structure containing the following members:

int swt_n; /* number of swapents following */
struct swapent swt_ent[]; /* array of swt_n swapents */

A swapent structure contains the following members:

char *ste_path; /* name of the swap file */
off_t ste_start; /* starting block for swapping */
off_t ste_length; /* length of swap area */
long ste_pages; /* number of pages for swapping */
long ste_free; /* number of ste_pages free */
long ste_flags; /* ST_INDEL bit set if swap file */
 /* is now being deleted */

The SC_LIST function causes swapctl() to return at most swt_n entries. The return value of swapctl() is the number actually returned. The ST_INDEL bit is turned on in ste_flags if the swap file is in the process of being deleted.

When SC_GETNSWP is specified, swapctl() returns as its value the number of swap resources in use. arg is ignored for this operation.

The SC_ADD and SC_REMOVE functions will fail if calling process does not have appropriate privileges.

Upon successful completion, the function swapctl() returns a value of 0 for SC_ADD or SC_REMOVE, the number of struct swapent entries actually returned for SC_LIST, or the number of swap resources in use for SC_GETNSWP. Upon failure, the function swapctl() returns a value of -1 and sets errno to indicate an error.

Under the following conditions, the function swapctl() fails and sets errno to:

EEXIST

EFAULT

EINVAL

EISDIR

ELOOP

ENAMETOOLONG

ENOENT

ENOMEM

ENOSYS

ENOTDIR

EPERM

EROFS

Additionally, the swapctl() function will fail for 32-bit interfaces if:

EOVERFLOW

Example 1 The usage of the SC_GETNSWP and SC_LIST commands.

The following example demonstrates the usage of the SC_GETNSWP and SC_LIST commands.

#include <sys/stat.h>
#include <sys/swap.h>
#include <stdio.h>

#define MAXSTRSIZE 80

main(argc, argv)
 int argc;
 char *argv[];
{
 swaptbl_t *s;
 int i, n, num;
 char *strtab; /* string table for path names */

again:
 if ((num = swapctl(SC_GETNSWP, 0)) == -1) {
 perror("swapctl: GETNSWP");
 exit(1);
 }
 if (num == 0) {
 fprintf(stderr, "No Swap Devices Configured\en");
 exit(2);
 }
 /* allocate swaptable for num+1 entries */
 if ((s = (swaptbl_t *)
 malloc(num * sizeof(swapent_t) + 
 sizeof(struct swaptable))) ==
 (void *) 0) {
 fprintf(stderr, "Malloc Failed\en");
 exit(3);
 }
 /* allocate num+1 string holders */
 if ((strtab = (char *)
 malloc((num + 1) * MAXSTRSIZE)) == (void *) 0) {
 fprintf(stderr, "Malloc Failed\en");
 exit(3);
 }
 /* initialize string pointers */
 for (i = 0; i < (num + 1); i++) {
 s->swt_ent[i].ste_path = strtab + (i * MAXSTRSIZE);
 }
 
 s->swt_n = num + 1;
 if ((n = swapctl(SC_LIST, s)) < 0) {
 perror("swapctl");
 exit(1);
 }
 if (n > num) { /* more were added */
 free(s);
 free(strtab);
 goto again;
 }
 for (i = 0; i < n; i++)
 printf("%s %ld\en",
 s->swt_ent[i].ste_path, s->swt_ent[i].ste_pages);
}

privileges(5)