SWAPCTL(2)SWAPCTL(2)NAMEswapctl - 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_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.
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
Either 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 out‐
side 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 {PRIV_SYS_MOUNT} was not asserted in the effective
set of the calling process.
EROFS
The pathname specified for SC_ADD is a read-only file
system.
Additionally, the swapctl() function will fail for 32-bit interfaces
if:
EOVERFLOW
The amount of swap space configured on the machine is too
large to be represented by a 32-bit quantity.
EXAMPLES
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\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);
}
SEE ALSOprivileges(5)
Sep 25, 1997 SWAPCTL(2)
