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