git: 43afeee2fbf9 - main - share/man/man9: document zero_region(9)

[Philip Paeps]

The branch main has been updated by philip:

URL: https://cgit.FreeBSD.org/src/commit/?id=43afeee2fbf99e51ffd0006e6bb4adcbbd80a6f4

commit 43afeee2fbf99e51ffd0006e6bb4adcbbd80a6f4
Author:     Ka Ho Ng <khng300 at gmail.com>
AuthorDate: 2021-03-02 09:14:05 +0000
Commit:     Philip Paeps <philip at FreeBSD.org>
CommitDate: 2021-03-02 09:14:06 +0000

    share/man/man9: document zero_region(9)
    
    The zero_region() kernel interface was previously undocumented.
    Add a new zero_region(9) manual page to document it.
    
    Submitted by:   Ka Ho Ng <khng at freebsdfoundation.org>
    Sponsored by:   The FreeBSD Foundation
    Differential Revision:  https://reviews.freebsd.org/D28914
---
 share/man/man9/Makefile      |  1 +
 share/man/man9/zero_region.9 | 86 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 87 insertions(+)

diff --git a/share/man/man9/Makefile b/share/man/man9/Makefile
index 50e760d3e047..64e234c3d696 100644
--- a/share/man/man9/Makefile
+++ b/share/man/man9/Makefile
@@ -442,6 +442,7 @@ MAN=	accept_filter.9 \
 	vrele.9 \
 	vslock.9 \
 	watchdog.9 \
+	zero_region.9 \
 	zone.9
 
 MLINKS=	unr.9 alloc_unr.9 \
diff --git a/share/man/man9/zero_region.9 b/share/man/man9/zero_region.9
new file mode 100644
index 000000000000..27b1b50be14d
--- /dev/null
+++ b/share/man/man9/zero_region.9
@@ -0,0 +1,86 @@
+.\" 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 at FreeBSDFoundation.org
+under sponsorship from the FreeBSD Foundation.