freebsd-dev/share/man/man9/vslock.9

.\"	$NetBSD: vslock.9,v 1.1 1996/06/15 20:47:29 pk Exp $
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.Dd June 15, 1996
.Dt VSLOCK 9
.Os
.Sh NAME
.Nm vslock ,
.Nm vsunlock
.Nd lock/unlock user space addresses in memory
.Sh SYNOPSIS
.In sys/param.h
.In sys/proc.h
.In vm/vm.h
.In vm/vm_extern.h
.Ft int
.Fn vslock "void *addr" "size_t len"
.Ft void
.Fn vsunlock "void *addr" "size_t len"
.Sh DESCRIPTION
The
.Fn vslock
and
.Fn vsunlock
functions respectively lock and unlock a range of
addresses belonging to the currently running process into memory.
The actual amount of memory locked is a multiple of the machine's page size.
The starting page number is computed by truncating
.Fa addr
to the nearest preceding page boundary, and by rounding up
.Fa addr +
.Fa len
to the next page boundary.
The process context to use for this operation is taken from the
global variable
.Va curproc .
.Sh RETURN VALUES
The
.Fn vslock
function will return 0 on success, otherwise it will return
one of the errors listed below.
.Sh ERRORS
The
.Fn vslock
function will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa addr
and
.Fa len
parameters specify a memory range that wraps around the end of the
machine address space.
.It Bq Er ENOMEM
The size of the specified address range exceeds the system
limit on locked memory.
.It Bq Er ENOMEM
Locking the requested address range would cause the process to exceed
its per-process locked memory limit.
.It Bq Er EFAULT
Some portion of the indicated address range is not allocated.
There was an error faulting/mapping a page.
.El
.Sh BUGS
The
.Fn vslock
function does not prevent memory from being unmapped out from underneath.
This can lead to system instability and blocking conditions where they
are required not to occur when accessing the locked memory.