.\"	$OpenBSD: mquery.2,v 1.10 2013/04/08 19:35:00 guenther Exp $
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.\" Copyright (c) 2003 Artur Grabowski <art@openbsd.org>
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.Dd $Mdocdate: April 8 2013 $
.Dt MQUERY 2
.Os
.Sh NAME
.Nm mquery
.Nd provide mapping hints to applications
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/mman.h>
.Ft void *
.Fn mquery "void *addr" "size_t len" "int prot" "int flags" "int fd" "off_t offset"
.Sh DESCRIPTION
The
.Nm mquery
system call checks the existing memory mappings of a process and returns
hints to the caller about where to put a memory mapping.
This hint can be later used when performing memory mappings with the
.Fn mmap
system call with
.Dv MAP_FIXED
in the flags.
The
.Fa addr
argument should be a memory location that which the caller specifies the
preferred address.
The
.Fa size
argument specifies the requested size of the memory area the caller
is looking for.
The
.Fa fd
and
.Fa off
arguments specify the file that will be mapped and the offset in it,
this is the same as the corresponding arguments to
.Fn mmap .
.Pp
The behavior of the function depends on the
.Fa flags
argument.
If set to
.Dv MAP_FIXED
the pointer
.Fa addr
is used as a fixed hint and
.Fn mquery
will return
.Dv MAP_FAILED
and set
.Va errno
to
.Er ENOMEM
if there is not
.Fa size
bytes free after that address.
Otherwise it will return the hint addr.
If no flags are set
.Fn mquery
will use
.Fa addr
as a starting point in memory and will search forward to find
a memory area with
.Fa size
bytes free and that will be suitable for creating a mapping for the
file and offset specified in the
.Fa fd
and
.Fa off
arguments.
When no such area can be found
.Fn mquery
will return
and set
.Va errno
to indicate the error.
.Sh RETURN VALUES
When a memory range satisfying the request is found
.Fn mquery
returns the available address.
Otherwise,
.Dv MAP_FAILED
is returned and
.Va errno
is set to indicate the error.
.Sh ERRORS
.Fn mquery
will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
.Dv MAP_FIXED
was specified and the requested memory area is unavailable.
.It Bq Er ENOMEM
There was not enough memory left after the hint specified.
.It Bq Er EBADF
.Fa fd
is not a valid open file descriptor.
.El
.Sh SEE ALSO
.Xr mmap 2
.Sh STANDARDS
The
.Fn mquery
function should not be used in portable applications.
.Sh HISTORY
The
.Fn mquery
function first appeared in
.Ox 3.4 .