swapctl - Manages the system swap space
#include <sys/stat.h> #include <sys/swap.h>
int swapctl(
int cmd,
void *arg );
Specifies the operation to be performed. Options include
adding a resource, deleting a resource, removing a
resource, or returning the number of swap resources.
Specifies a pointer to a structure. See the DESCRIPTION
section for information on this structure.
The swapctl function manages the system swap space by
adding, deleting, or returning information about swap
resources. The cmd parameter that you select determines
the value of the arg parameter. The following sections
discuss the available commands and command arguments.
Available Commands [Toc] [Back]
The swapctl function adds, removes, or returns information
on the system swap space using the following values for
the cmd parameter: Includes a new resource in the swap
list. Provides a list of the resources available for
swapping. Removes a resource from the swap list. Counts
and returns the number of swap resources
Use this command to determine how many swapent
structures will be needed for a SC_LIST command
request
With the exception of the SC_GETSNSWP command, each of
these commands returns information in a structure pointed
to by the arg parameter. The next sections discusses the
information that is contained in these structures after a
successful return.
Command Arguments [Toc] [Back]
The value of the arg parameter is specific to the type of
command specified by the cmd parameter. This section
highlights the value for the arg parameter as it pertains
to the commands.
If either the SC_ADD or SC_REMOVE command is specified,
the arg parameter is a pointer to the following swapres
structure:
typdef struct swapres {
char sr_name;
off_t sr_start;
off_t sr_length; } swapres_t;
The fields are defined as follows: Provides the pathname
of the resource that is being added or removed. Specifies
in 512-byte blocks, the offset of the resource area from
the start. Specifies in 512-byte blocks, the length of
the swap area.
When using the SC_ADD and SC_REMOVE commands, the calling
process fails if the appropriate privileges do not exist
for the operation.
If the SC_LIST command is specified, the arg parameter is
a pointer to the following swaptable structure:
int swt_n; struct swapent swt_ent [];
In this structure, the field swt_n specifies the maximum
entries that will be returned by the swapctl function. The
swt_ent field is an array of swt_n swapents. The swapent
structure is as follows:
typdef struct swapwent {
char *ste_path;
off_t ste_start;
off_t ste_length;
long ste_pages;
long ste_free;
long ste_flags; } swapwent_t;
Before the swapctl(2) is issued, allocate memory to all of
the ste_path pointers. Ensure that each of the areas
allocated is at least MAXPATHLEN bytes long. MAXPATHLEN
is defined in <sys/param.h>.
The fields are defined as follows: Specifies the name of
the swap file. Specifies the starting block to begin
swapping. Specifies in 512-byte blocks, the length of the
swap area. Specifies the number of pages available for
swapping. Specifies the number of pages that are free.
Sets the ST_INDEL bit if the swap file is being deleted.
On success, the swapctl function returns zero (0) when
used with the SC_ADD or SC_REMOVE commands. For the
SC_LIST command, the number of struct swapent entries
actually returned indicates success, and for SC_GETNSWP,
the number of swap resources in use is returned upon success.
On error, the swapctl function returns a value of -1 and
sets errno to indicate the error.
If the swapctl function fails, errno is set to one of the
following: Indicates that the range specified by the
sr_start and sr_length fields for the SC_ADD command is
already in use for swapping. Specifies that the structure
pointed to by the arg parameter, or one of the fields
sr_name or ste_path is outside the allocated address
space. Specifies one of the following: The command value
is not valid. The path used with the SC_REMOVE command is
not a swap resource. The range indicated by the sr_start
and sr_length fields for the SC_ADD command is outside the
resource specified. The indicated swap area is less than
one page for the SC_ADD command. Indicates that the path
used with the SC_ADD command is not a directory. Indicates
that the pathname used with the SC_ADD or SC_REMOVE
commands has too many symbolic links to correctly translate
the pathname. Indicates that the length or path used
with the SC_ADD or SC_REMOVE command exceeds the maximum
allowed with {_POSIX_NO_TRUNC} in effect. Indicates that
a nonexisting pathname was specified with either the
SC_ADD or SC_REMOVE commands. Specifies one of the following:
Not enough struct swapent structures exist for the
SC_LIST command. Sufficient system storage resources were
not available during an SC_ADD or SC_REMOVE operation.
Not enough swap space would exists after an SC_REMOVE
operation. Indicates that the pathname specified for a
SC_ADD or SC_REMOVE operation is not a filename or special
block device. Specifies that the pathname used with the
SC_ADD or SC_REMOVE commands contained a component in the
path that was not a directory. Indicates that insufficient
privileges do not exist for the operation. Indicates
that a read-only file system was specified by the
path for the SC_ADD command.
swapctl(2)
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