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.\" Copyright (c) 1989, AT&T. All rights reserved.
.\" Copyright (c) 1997, 2023, Oracle and/or its affiliates.
.TH swapctl 2 "25 February 2023" "Oracle Solaris 11.4" "System Calls"
.SH NAME
swapctl \- manage swap space
.SH SYNOPSIS

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

\fBint\fR \fBswapctl\fR(\fBint\fR \fIcmd\fR, \fBvoid *\fR\fIarg\fR);
.fi
.SH DESCRIPTION
.sp
.LP
The \fBswapctl()\fR function adds, deletes, or returns information about swap resources. \fIcmd\fR specifies one of the following options contained in <\fBsys/swap.h\fR>:
.sp
.in +2
.nf
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 */
.fi
.in -2
.sp
.sp
.LP
When \fBSC_ADD\fR or \fBSC_REMOVE\fR are specified the \fBSC_PERSIST\fR flag can be added with a bitwise-OR with the command
.sp
.in +2
.nf
SC_PERSIST    /* Make the change permanent over reboots */
.fi
.in -2
.sp
.sp
.LP
When \fBSC_ADD\fR or \fBSC_REMOVE\fR is specified, \fIarg\fR is a pointer to a \fBswapres\fR structure containing the following members:
.sp
.in +2
.nf
char    *sr_name;    /* pathname of resource */
off_t   sr_start;    /* offset to start of swap area */
off_t   sr_length;   /* length of swap area */
.fi
.in -2
.sp
.sp
.LP
The \fBsr_start\fR and \fBsr_length\fR members are specified in 512-byte blocks. A swap resource can only be removed by specifying the same values for the \fBsr_start\fR and \fBsr_length\fR members as were specified when it was added. Swap resources need not be removed in the order in which they were added.
.sp
.LP
When adding or removing \fBZFS\fR volumes if \fBSC_PERSIST\fR is specified then update the \fBkvol_swap\fR property of the \fBZFS\fR volume so the change persists across reboots.
.sp
.LP
When \fBSC_LIST\fR is specified, \fIarg\fR is a pointer to a \fBswaptable\fR structure containing the following members:
.sp
.in +2
.nf

int             swt_n;       /* number of swapents following */
struct swapent  swt_ent[];   /* array of swt_n swapents */
.fi
.in -2
.sp
.sp
.LP
A \fBswapent\fR structure contains the following members:
.sp
.in +2
.nf

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 */
.fi
.in -2
.sp
.sp
.LP
The \fBSC_LIST\fR function causes \fBswapctl()\fR to return at most \fBswt_n\fR entries. The return value of \fBswapctl()\fR is the number actually returned. The \fBST_INDEL\fR bit is turned on in \fBste_flags\fR if the swap file is in the process of being deleted. The \fBST_ENCRYPTED\fR bit is turned on if data written to the swap device is reported being encrypted by the underlying device layer, eg \fBzfs\fR(8) or \fBlofi\fR(4d).
.sp
.LP
When \fBSC_GETNSWP\fR is specified, \fBswapctl()\fR returns as its value the number of swap resources in use. \fIarg\fR is ignored for this operation.
.sp
.LP
The \fBSC_ADD\fR and \fBSC_REMOVE\fR functions will fail if calling process does not have appropriate privileges.
.sp
.LP
The behaviour when \fBSC_PERSIST\fR is set and \fBSC_ADD\fR or \fBSC_REMOVE\fR is not set is undefined.
.sp
.LP
The behaviour when \fBSC_PERSIST\fR and the swap device is not a \fBZFS\fR volume is undefined.
.SH RETURN VALUES
.sp
.LP
Upon successful completion, the function \fBswapctl()\fR returns a value of \fB0\fR for \fBSC_ADD\fR or \fBSC_REMOVE\fR, the number of \fBstruct\fR  \fBswapent\fR entries actually returned for \fBSC_LIST\fR, or the number of swap resources in use for \fBSC_GETNSWP\fR. Upon failure, the function \fBswapctl()\fR returns a value of \fB\(mi1\fR and sets \fBerrno\fR to indicate an error.
.SH ERRORS
.sp
.LP
Under the following conditions, the function \fBswapctl()\fR fails and sets \fBerrno\fR to:
.sp
.ne 2
.mk
.na
\fB\fBEEXIST\fR\fR
.ad
.RS 16n
.rt
Part of the range specified by \fBsr_start\fR and \fBsr_length\fR is already being used for swapping on the specified resource (\fBSC_ADD\fR).
.RE

.sp
.ne 2
.mk
.na
\fB\fBEFAULT\fR\fR
.ad
.RS 16n
.rt
Either \fIarg\fR, \fBsr_name\fR, or \fBste_path\fR points to an illegal address.
.RE

.sp
.ne 2
.mk
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 16n
.rt
The specified function value is not valid, the path specified is not a swap resource (\fBSC_REMOVE\fR), part of the range specified by \fBsr_start\fR and \fBsr_length\fR lies outside the resource specified (\fBSC_ADD\fR), or the specified swap area is less than one page (\fBSC_ADD\fR).
.RE

.sp
.ne 2
.mk
.na
\fB\fBEISDIR\fR\fR
.ad
.RS 16n
.rt
The path specified for \fBSC_ADD\fR is a directory.
.RE

.sp
.ne 2
.mk
.na
\fB\fBELOOP\fR\fR
.ad
.RS 16n
.rt
Too many symbolic links were encountered in translating the pathname provided to \fBSC_ADD\fR or \fBSC_REMOVE\fR.
.RE

.sp
.ne 2
.mk
.na
\fB\fBENAMETOOLONG\fR\fR
.ad
.RS 16n
.rt
The length of a component of the path specified for \fBSC_ADD\fR or \fBSC_REMOVE\fR exceeds \fBNAME_MAX\fR characters or the length of the path exceeds \fBPATH_MAX\fR characters and \fB_POSIX_NO_TRUNC\fR is in effect.
.RE

.sp
.ne 2
.mk
.na
\fB\fBENOENT\fR\fR
.ad
.RS 16n
.rt
The pathname specified for \fBSC_ADD\fR or \fBSC_REMOVE\fR does not exist.
.RE

.sp
.ne 2
.mk
.na
\fB\fBENOMEM\fR\fR
.ad
.RS 16n
.rt
An insufficient number of \fBstruct\fR  \fBswapent\fR structures were provided to \fBSC_LIST\fR, or there were insufficient system storage resources available during an \fBSC_ADD\fR or \fBSC_REMOVE\fR, or the system would not have enough swap space after an \fBSC_REMOVE\fR.
.RE

.sp
.ne 2
.mk
.na
\fB\fBENOSYS\fR\fR
.ad
.RS 16n
.rt
The pathname specified for \fBSC_ADD\fR or \fBSC_REMOVE\fR is not a file or block special device.
.RE

.sp
.ne 2
.mk
.na
\fB\fBENOTDIR\fR\fR
.ad
.RS 16n
.rt
Pathname provided to \fBSC_ADD\fR or \fBSC_REMOVE\fR contained a component in the path prefix that was not a directory.
.RE

.sp
.ne 2
.mk
.na
\fB\fBEPERM\fR\fR
.ad
.RS 16n
.rt
The {\fBPRIV_SYS_MOUNT\fR} was not asserted in the effective set of the calling process.
.RE

.sp
.ne 2
.mk
.na
\fB\fBEROFS\fR\fR
.ad
.RS 16n
.rt
The pathname specified for \fBSC_ADD\fR is a read-only file system.
.RE

.sp
.LP
Additionally, the \fBswapctl()\fR function will fail for 32-bit interfaces if:
.sp
.ne 2
.mk
.na
\fB\fBEOVERFLOW\fR\fR
.ad
.RS 13n
.rt
The amount of swap space configured on the machine is too large to be represented by a 32-bit quantity.
.RE

.SH EXAMPLES
.LP
\fBExample 1\fR The usage of the \fBSC_GETNSWP\fR and \fBSC_LIST\fR commands.

.sp
.LP
The following example demonstrates the usage of the \fBSC_GETNSWP\fR and \fBSC_LIST\fR commands.

.sp
.in +2
.nf
#include <sys/stat.h>
#include <sys/swap.h>
#include <stdio.h>
#include <limits.h>

#define MAXSTRSIZE PATH_MAX

int
main(int argc, char **argv)
{
    swaptbl_t      *s;
    int            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 (int 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 (int i = 0; i < n; i++) {
        printf("%s %ld%s\en",
            s->swt_ent[i].ste_path, s->swt_ent[i].ste_pages,
            s->swt_ent[i].ste_flags & ST_ENCRYPTED ? " Encrypted" : "");
    }
    exit(0);
}
.fi
.in -2
.sp
.SH SEE ALSO
.sp
.LP
\fBlofi\fR(4d), \fBprivileges\fR(7), \fBzfs\fR(8)