87 lines
2.6 KiB
Groff
87 lines
2.6 KiB
Groff
|
.\" SPDX-License-Identifier: BSD-2-Clause
|
||
|
|
.\"
|
||
|
|
.\" Copyright (c) 2021 The FreeBSD Foundation
|
||
|
|
.\"
|
||
|
|
.\" Redistribution and use in source and binary forms, with or without
|
||
|
|
.\" modification, are permitted provided that the following conditions
|
||
|
|
.\" are met:
|
||
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
||
|
|
.\" notice, this list of conditions and the following disclaimer.
|
||
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
||
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
||
|
|
.\" documentation and/or other materials provided with the distribution.
|
||
|
|
.\"
|
||
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
|
||
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
||
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
||
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
|
||
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
||
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
||
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
||
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
||
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
||
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
||
|
|
.\" SUCH DAMAGE.
|
||
|
|
.\"
|
||
|
|
.\" $FreeBSD$
|
||
|
|
.\"
|
||
|
|
.Dd March 2, 2021
|
||
|
|
.Dt ZERO_REGION 9
|
||
|
|
.Os
|
||
|
|
.Sh NAME
|
||
|
|
.Nm zero_region
|
||
|
|
.Nd Read-only region prefilled with zeroes
|
||
|
|
.Sh SYNOPSIS
|
||
|
|
.In sys/param.h
|
||
|
|
.In sys/systm.h
|
||
|
|
.In vm/vm_param.h
|
||
|
|
.Vt extern const void *zero_region ;
|
||
|
|
.Sh DESCRIPTION
|
||
|
|
The global variable
|
||
|
|
.Va zero_region
|
||
|
|
points to a read-only region prefilled with zeroes.
|
||
|
|
The size of the region is specified by the
|
||
|
|
.Dv ZERO_REGION_SIZE
|
||
|
|
macro.
|
||
|
|
.Sh IMPLEMENTATION NOTES
|
||
|
|
The region
|
||
|
|
.Va zero_region
|
||
|
|
points to is mapped to the same page multiple times.
|
||
|
|
.Sh EXAMPLES
|
||
|
|
.Bd -literal
|
||
|
|
/*
|
||
|
|
* This function writes zeroes to the vnode at offset 0
|
||
|
|
* with ZERO_REGION_SIZE length.
|
||
|
|
*/
|
||
|
|
static int
|
||
|
|
write_example(struct vnode *vp)
|
||
|
|
{
|
||
|
|
struct thread *td;
|
||
|
|
struct iovec aiov;
|
||
|
|
struct uio auio;
|
||
|
|
int error;
|
||
|
|
|
||
|
|
td = curthread;
|
||
|
|
|
||
|
|
aiov.iov_base = __DECONST(void *, zero_region);
|
||
|
|
aiov.iov_len = ZERO_REGION_SIZE;
|
||
|
|
auio.uio_iov = &aiov;
|
||
|
|
auio.uio_iovcnt = 1;
|
||
|
|
auio.uio_offset = 0;
|
||
|
|
auio.uio_resid = ZERO_REGION_SIZE;
|
||
|
|
auio.uio_segflg = UIO_SYSSPACE;
|
||
|
|
auio.uio_rw = UIO_WRITE;
|
||
|
|
auio.uio_td = td;
|
||
|
|
|
||
|
|
error = VOP_WRITE(vp, &auio, 0, td->td_ucred);
|
||
|
|
return (error);
|
||
|
|
}
|
||
|
|
.Ed
|
||
|
|
.Sh SEE ALSO
|
||
|
|
.Xr pmap 9 ,
|
||
|
|
.Xr vm_map 9
|
||
|
|
.Sh AUTHORS
|
||
|
|
This manual page was written by
|
||
|
|
.An Ka Ho Ng Aq Mt khng@FreeBSDFoundation.org
|
||
|
|
under sponsorship from the FreeBSD Foundation.
|