1.\" Copyright (c) 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)madvise.2 8.1 (Berkeley) 6/9/93 29.\" $FreeBSD: head/lib/libc/sys/posix_fadvise.2 314436 2017-02-28 23:42:47Z imp $ 30.\" 31.Dd May 4, 2019 32.Dt POSIX_FADVISE 3 33.Os 34.Sh NAME 35.Nm posix_fadvise 36.Nd give advice about use of file data 37.Sh LIBRARY 38.Lb libc 39.Sh SYNOPSIS 40.In fcntl.h 41.Ft int 42.Fn posix_fadvise "int fd" "off_t offset" "off_t len" "int advice" 43.Sh DESCRIPTION 44.Em Note 45that this implementation is a no-op. 46It only does some failure checks. 47Any 48.Fa advice 49has no effect on the system's data access behavior. 50.Pp 51The 52.Fn posix_fadvise 53function 54allows a process to describe to the system its data access behavior for an 55open file descriptor 56.Fa fd . 57The advice covers the data starting at offset 58.Fa offset 59and continuing for 60.Fa len 61bytes. 62If 63.Fa len 64is zero, 65all data from 66.Fa offset 67to the end of the file is covered. 68.Pp 69The behavior is specified by the 70.Fa advice 71parameter and may be one of: 72.Bl -tag -width POSIX_FADV_SEQUENTIAL 73.It Dv POSIX_FADV_NORMAL 74Tells the system to revert to the default data access behavior. 75.It Dv POSIX_FADV_RANDOM 76Is a hint that file data will be accessed randomly, 77and prefetching is likely not advantageous. 78.It Dv POSIX_FADV_SEQUENTIAL 79Tells the system that file data will be accessed sequentially. 80This currently does nothing as the default behavior uses heuristics to 81detect sequential behavior. 82.It Dv POSIX_FADV_WILLNEED 83Tells the system that the specified data will be accessed in the near future. 84The system may initiate an asynchronous read of the data if it is not already 85present in memory. 86.It Dv POSIX_FADV_DONTNEED 87Tells the system that the specified data will not be accessed in the near 88future. 89The system may decrease the in-memory priority of clean data within the 90specified range and future access to this data may require a read operation. 91.It Dv POSIX_FADV_NOREUSE 92Tells the system that the specified data will only be accessed once and 93then not reused. 94The system may decrease the in-memory priority of data once it has been 95read or written. 96Future access to this data may require a read operation. 97.El 98.Sh RETURN VALUES 99If successful, 100.Fn posix_fadvise 101returns zero. 102It returns an error on failure, without setting 103.Va errno . 104.Sh ERRORS 105Possible failure conditions: 106.Bl -tag -width Er 107.It Bq Er EBADF 108The 109.Fa fd 110argument is not a valid file descriptor. 111.It Bq Er EINVAL 112The 113.Fa advice 114argument is not valid. 115.It Bq Er EINVAL 116The 117.Fa offset 118or 119.Fa len 120arguments are negative, 121or 122.Fa offset 123+ 124.Fa len 125is greater than the maximum file size. 126.It Bq Er ENODEV 127The 128.Fa fd 129argument does not refer to a regular file. 130.It Bq Er ESPIPE 131The 132.Fa fd 133argument is associated with a pipe or FIFO. 134.El 135.Sh SEE ALSO 136.Xr madvise 2 137.Sh STANDARDS 138The 139.Fn posix_fadvise 140interface conforms to 141.St -p1003.1-2001 . 142.Sh HISTORY 143The 144.Fn posix_fadvise 145function first appeared in 146.Dx 5.5 . 147