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.\" Copyright (C) 2001 Andries Brouwer (aeb@cwi.nl)
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.\" Created Sun Jun 3 17:23:32 2001 by bert hubert <ahu@ds9a.nl>
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.TH MINCORE 2 "3 June 2001" "Linux 2.4.5" "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.

For
.B mincore
to return succesfully, 
.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 bytes.

.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 EINVAL
.i start
is not a multiple of PAGE_CACHE_SIZE (PAGE_SIZE) or 
.i len
has a non-positive value
.TP
.B EFAULT
.I vec
points to an illegal address
.TP
.B ENOMEM
.I address
to
.I address
+
.I length
contained unmapped memory, or memory not part of a file.

.SH "BUGS"
.B mincore
should return a bit vector and not a byte vector. As of Linux 2.4.5, it is not
possible to gain information on the core residency of pages which are not backed by a file. 
In other words, calling 
.B mincore
on an region returned by an anonymous
.B mmap(2)
does not work and sets errno to ENOMEM. Unless pages are locked in memory, the contents of
.I vec
may be stale by the time they reach userspace.

.SH "CONFORMING TO"
.B mincore
does not appear to be part of POSIX or the Single Unix Specification. 
.SH HISTORY
The mincore() function first appeared in 4.4BSD

.SH "SEE ALSO"
.BR getpagesize (2),
.BR mmap (2)