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.Dd March 30, 2020 29.Dt POSIX_FADVISE 2 30.Os 31.Sh NAME 32.Nm posix_fadvise 33.Nd give advice about use of file data 34.Sh LIBRARY 35.Lb libc 36.Sh SYNOPSIS 37.In fcntl.h 38.Ft int 39.Fn posix_fadvise "int fd" "off_t offset" "off_t len" "int advice" 40.Sh DESCRIPTION 41The 42.Fn posix_fadvise 43system call 44allows a process to describe to the system its data access behavior for an 45open file descriptor 46.Fa fd . 47The advice covers the data starting at offset 48.Fa offset 49and continuing for 50.Fa len 51bytes. 52If 53.Fa len 54is zero, 55all data from 56.Fa offset 57to the end of the file is covered. 58.Pp 59The behavior is specified by the 60.Fa advice 61parameter and may be one of: 62.Bl -tag -width POSIX_FADV_SEQUENTIAL 63.It Dv POSIX_FADV_NORMAL 64Tells the system to revert to the default data access behavior. 65.It Dv POSIX_FADV_RANDOM 66Is a hint that file data will be accessed randomly, 67and prefetching is likely not advantageous. 68.It Dv POSIX_FADV_SEQUENTIAL 69Tells the system that file data will be accessed sequentially. 70This currently does nothing as the default behavior uses heuristics to 71detect sequential behavior. 72.It Dv POSIX_FADV_WILLNEED 73Tells the system that the specified data will be accessed in the near future. 74The system may initiate an asynchronous read of the data if it is not already 75present in memory. 76.It Dv POSIX_FADV_DONTNEED 77Tells the system that the specified data will not be accessed in the near 78future. 79The system may decrease the in-memory priority of clean data within the 80specified range and future access to this data may require a read operation. 81.It Dv POSIX_FADV_NOREUSE 82Tells the system that the specified data will only be accessed once and 83then not reused. 84The system may decrease the in-memory priority of data once it has been 85read or written. 86Future access to this data may require a read operation. 87.El 88.Sh RETURN VALUES 89If successful, 90.Fn posix_fadvise 91returns zero. 92It returns an error on failure, without setting 93.Va errno . 94.Sh ERRORS 95Possible failure conditions: 96.Bl -tag -width Er 97.It Bq Er EBADF 98The 99.Fa fd 100argument is not a valid file descriptor. 101.It Bq Er EINVAL 102The 103.Fa advice 104argument is not valid. 105.It Bq Er EINVAL 106The 107.Fa offset 108or 109.Fa len 110arguments are negative, 111or 112.Fa offset 113+ 114.Fa len 115is greater than the maximum file size. 116.It Bq Er ENODEV 117The 118.Fa fd 119argument does not refer to a regular file. 120.It Bq Er ESPIPE 121The 122.Fa fd 123argument is associated with a pipe or FIFO. 124.It Bq Er EIO 125An I/O error occurred while reading from or writing to a file system. 126.It Bq Er EINTEGRITY 127Corrupted data was detected while reading from the file system. 128.El 129.Sh SEE ALSO 130.Xr madvise 2 131.Sh STANDARDS 132The 133.Fn posix_fadvise 134interface conforms to 135.St -p1003.1-2001 . 136.Sh HISTORY 137The 138.Fn posix_fadvise 139system call first appeared in 140.Fx 9.1 . 141