man-pages/man2/mincore.2

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.\" Copyright (C) 2001 Bert Hubert <ahu@ds9a.nl>
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.\" Created Sun Jun 3 17:23:32 2001 by bert hubert <ahu@ds9a.nl>
.\" Slightly adapted, following comments by Hugh Dickins, aeb, 2001-06-04.
.\" Modified, 20 May 2003, Michael Kerrisk <mtk-manpages@gmx.net>
.\" Modified, 30 Apr 2004, Michael Kerrisk <mtk-manpages@gmx.net>
.\" 2005-04-05 mtk, Fixed error descriptions
.\" 	after message from <gordon.jin@intel.com>
.\"
.TH MINCORE 2 2004-04-30 "Linux 2.6.5" "Linux Programmer's Manual"
.SH NAME
mincore \- get information on whether pages are in core
.SH SYNOPSIS
.B #include <unistd.h>
.br
.B #include <sys/mman.h>
.sp
.BI "int mincore(void *" start ", size_t " length ", unsigned char *" vec );
.SH DESCRIPTION
The
.B mincore
function requests a vector describing which pages of a file are in core and
can be read without disk access. The kernel will supply data for
.I length
bytes following the 
.I start
address. On return, the kernel will have filled
.I vec
with bytes, of which the least significant bit indicates if a page is 
core resident. (The other bits are undefined, reserved for possible
later use.)
Of course this is only a snapshot: pages that are not
locked in core can come and go any moment, and the contents of
.I vec
may be stale already when this call returns.

For
.B mincore
to return successfully, 
.I start
must lie on a page boundary. It is the caller's responsibility to
round up to the nearest page. The
.I length
parameter need not be a multiple of the page size. The vector
.I vec
must be large enough to contain (length+PAGE_SIZE-1) / PAGE_SIZE bytes.
One may obtain the page size from
.BR getpagesize (2).

.SH "RETURN VALUE"
On success,
.B mincore
returns zero.
On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.B EAGAIN
kernel is temporarily out of resources
.TP
.B EFAULT
.I vec
points to an invalid address
.TP
.B EINVAL
.I start
is not a multiple of the page size.
.TP
.B ENOMEM
.I len
is greater than
.RI ( TASK_SIZE " \- " start ).
(This could occur if a negative value is specified for
.IR len ,
since that value will be interpreted as a large
unsigned integer.)
In Linux 2.6.11 and earlier, the error
.B EINVAL
was returned for this condition.
.TP
.B ENOMEM
.I address
to
.I address
+
.I length
contained unmapped memory, or memory not part of a file.
.SH BUGS
Up to now (Linux 2.6.5),
.B mincore
does not return correct information for MAP_PRIVATE mappings.

.\" Linux (up to now, 2.6.5),
.\" .B mincore
.\" does not return correct information for MAP_PRIVATE mappings:
.\" for a MAP_PRIVATE file mapping,
.\" .B mincore
.\" returns the residency of the file pages, rather than any
.\" modified process-private pages that have been copied on write;
.\" for a MAP_PRIVATE mapping of
.\" .IR /dev/zero ,
.\" .B mincore
.\" always reports pages as non-resident;
.\" and for a MAP_PRIVATE, MAP_ANONYMOUS mapping,
.\" .B mincore
.\" always fails with the error
.\" .BR ENOMEM .
.SH "CONFORMING TO"
.B mincore
is not specified in POSIX.1-2001,
and it is not available on all Unix implementations. 
.SH HISTORY
The mincore() function first appeared in 4.4BSD.
.SH AVAILABILITY
Since Linux 2.3.99pre1 and glibc 2.2.
.SH "SEE ALSO"
.BR getpagesize (2),
.BR mlock (2),
.BR mmap (2)