NAME

swapctl − manage swap space

SYNOPSIS

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

int swapctl(int cmd, void ∗arg);

DESCRIPTION

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_tsr_start;/∗ offset to start of swap area ∗/
off_tsr_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:

intswt_n;/∗ number of swapents following ∗/
structswapent swt_ent[];/∗ array of swt_n swapents ∗/

A swapent structure contains the following members:

char∗ste_path;/∗ name of the swap file ∗/
off_tste_start;/∗ starting block for swapping ∗/
off_tste_length;/∗ length of swap area ∗/
longste_pages;/∗ number of pages for swapping ∗/
longste_free;/∗ number of ste_pages free ∗/
longste_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. 

RETURN VALUES

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. 

ERRORS

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

EEXIST Part of the range specified by sr_start and sr_length is already being used for swapping on the specified resource (SC_ADD). 

EFAULT arg, sr_name, or ste_path points to an illegal address. 

EINVAL The specified function value is not valid, the path specified is not a swap resource (SC_REMOVE), part of the range specified by sr_start and sr_length lies outside the resource specified (SC_ADD), or the specified swap area is less than one page (SC_ADD). 

EISDIR The path specified for SC_ADD is a directory. 

ELOOP Too many symbolic links were encountered in translating the pathname provided to SC_ADD or SC_REMOVE . 

ENAMETOOLONG
The length of a component of the path specified for SC_ADD or SC_REMOVE exceeds {NAME_MAX} characters or the length of the path exceeds {PATH_MAX} characters and {_POSIX_NO_TRUNC} is in effect. 

ENOENT The pathname specified for SC_ADD or SC_REMOVE does not exist. 

ENOMEM An insufficient number of struct swapent structures were provided to SC_LIST, or there were insufficient system storage resources available during an SC_ADD or SC_REMOVE, or the system would not have enough swap space after an SC_REMOVE. 

ENOSYS The pathname specified for SC_ADD or SC_REMOVE is not a file or block special device. 

ENOTDIR Pathname provided to SC_ADD or SC_REMOVE contained a component in the path prefix that was not a directory. 

EPERM The effective user of the calling process is not super-user. 

EROFS The pathname specified for SC_ADD is a read-only file system. 

EXAMPLES

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\n");
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\n");
exit(3);
}
/∗ allocate num+1 string holders ∗/
if ((strtab = (char ∗)
    malloc((num + 1) ∗ MAXSTRSIZE)) == (void ∗) 0) {
fprintf(stderr, "Malloc Failed\n");
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\n",
    s->swt_ent[i].ste_path, s->swt_ent[i].ste_pages);
}

SunOS 5.6  —  Last change: 12 Mar 1997