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.\" -*- nroff -*-
.\"
.\" Copyright (c) 2013 Hudson River Trading LLC
.\" Written by: John H. Baldwin <jhb@FreeBSD.org>
.\" All rights reserved.
.\"
.\" 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 October 3, 2013
.Dt VOP_ADVISE 9
.Os
.Sh NAME
.Nm VOP_ADVISE
.Nd apply advice about use of file data
.Sh SYNOPSIS
.In sys/param.h
.In sys/vnode.h
.Ft int
.Fn VOP_ADVISE "struct vnode *vp" "off_t start" "off_t end" "int advice"
.Sh DESCRIPTION
This call applies advice for a range of a file's data.
It is used to implement the
.Xr posix_fadvise
system call.
.Pp
Its arguments are:
.Bl -tag -width offset
.It Fa vp
The vnode of the file.
.It Fa start
The start of the range of file data.
.It Fa end
The end of the range of file data.
.It Fa advice
The type of operation to apply to the file data.
Possible values are:
.Bl -tag -width POSIX_FADV_WILLNEED
.It Dv POSIX_FADV_WILLNEED
Initiate an asynchronous read of the file data if it is not already resident.
.It Dv POSIX_FADV_DONTNEED
Decrease the in-memory priority of clean file data or discard clean file data.
.El
.El
.Pp
If the
.Fa start
and
.Fa end
offsets are both zero,
then the operation should be applied to the entire file.
Note that this call is advisory only and may perform the requested
operation on a subset of the requested range
.Pq including not performing it at all
and still return success.
.Sh LOCKS
The file should be unlocked on entry.
.Sh RETURN VALUES
Zero is returned if the call is successful, otherwise an appropriate
error code is returned.
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EINVAL
An invalid value was given for
.Fa advice .
.El
.Sh SEE ALSO
.Xr vnode 9
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