NetBSD/lib/libc/sys/mlockall.2

.\"	$NetBSD: mlockall.2,v 1.10 2003/01/18 11:33:08 thorpej Exp $
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Jason R. Thorpe of the Numerical Aerospace Simulation Facility,
.\" NASA Ames Research Center.
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.Dd June 12, 1999
.Dt MLOCKALL 2
.Os
.Sh NAME
.Nm mlockall ,
.Nm munlockall
.Nd lock (unlock) the address space of a process
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.Fd #include \*[Lt]sys/mman.h\*[Gt]
.Ft int
.Fn mlockall "int flags"
.Ft int
.Fn munlockall "void"
.Sh DESCRIPTION
The
.Nm mlockall
system call locks into memory the physical pages associated with the
address space of a process until the address space is unlocked, the
process exits, or execs another program image.
.Pp
The following flags affect the behavior of
.Nm mlockall :
.Bl -tag -width MCL_CURRENT
.It Dv MCL_CURRENT
Lock all pages currently mapped into the process's address space.
.It Dv MCL_FUTURE
Lock all pages mapped into the process's address space in the future,
at the time the mapping is established.
Note that this may cause future mappings to fail if those mappings
cause resource limits to be exceeded.
.El
.Pp
Since physical memory is a potentially scarce resource, processes are
limited in how much they can lock down.
A single process can lock the minimum of a system-wide
.Dq wired pages
limit and the per-process
.Li RLIMIT_MEMLOCK
resource limit.
.Pp
The
.Nm munlockall
call unlocks any locked memory regions in the process address space.
Any regions mapped after an
.Nm munlockall
call will not be locked.
.Sh RETURN VALUES
A return value of 0 indicates that the call
succeeded and all pages in the range have either been locked or unlocked.
A return value of -1 indicates an error occurred and the locked
status of all pages in the range remains unchanged.
In this case, the global location
.Va errno
is set to indicate the error.
.Sh ERRORS
.Fn mlockall
will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Ar flags
argument is zero, or includes unimplemented flags.
.It Bq Er ENOMEM
Locking the indicated range would exceed either the system or per-process
limit for locked memory.
.It Bq Er EAGAIN
Some or all of the memory mapped into the process's address space
could not be locked when the call was made.
.It Bq Er EPERM
The calling process does not have the appropriate privilege to perform
the requested operation.
.El
.Sh SEE ALSO
.Xr mincore 2 ,
.Xr mlock 2 ,
.Xr mmap 2 ,
.Xr munmap 2 ,
.Xr setrlimit 2
.Sh STANDARDS
The
.Fn mlockall
and
.Fn munlockall
functions conform to
.St -p1003.1b-93 .
.Sh HISTORY
The
.Fn mlockall
and
.Fn munlockall
functions first appeared in
.Nx 1.5 .
.Sh BUGS
The per-process resource limit is a limit on the amount of virtual
memory locked, while the system-wide limit is for the number of locked
physical pages.
Hence a process with two distinct locked mappings of the same physical page
counts as 2 pages against the per-process limit and as only a single page
in the system limit.