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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 $
36 .Nd give advice about use of file data
42 .Fn posix_fadvise "int fd" "off_t offset" "off_t len" "int advice"
45 that this implementation is a no-op.
46 It only does some failure checks.
49 has no effect on the system's data access behavior.
54 allows a process to describe to the system its data access behavior for an
57 The advice covers the data starting at offset
67 to the end of the file is covered.
69 The behavior is specified by the
71 parameter and may be one of:
72 .Bl -tag -width POSIX_FADV_SEQUENTIAL
73 .It Dv POSIX_FADV_NORMAL
74 Tells the system to revert to the default data access behavior.
75 .It Dv POSIX_FADV_RANDOM
76 Is a hint that file data will be accessed randomly,
77 and prefetching is likely not advantageous.
78 .It Dv POSIX_FADV_SEQUENTIAL
79 Tells the system that file data will be accessed sequentially.
80 This currently does nothing as the default behavior uses heuristics to
81 detect sequential behavior.
82 .It Dv POSIX_FADV_WILLNEED
83 Tells the system that the specified data will be accessed in the near future.
84 The system may initiate an asynchronous read of the data if it is not already
86 .It Dv POSIX_FADV_DONTNEED
87 Tells the system that the specified data will not be accessed in the near
89 The system may decrease the in-memory priority of clean data within the
90 specified range and future access to this data may require a read operation.
91 .It Dv POSIX_FADV_NOREUSE
92 Tells the system that the specified data will only be accessed once and
94 The system may decrease the in-memory priority of data once it has been
96 Future access to this data may require a read operation.
102 It returns an error on failure, without setting
105 Possible failure conditions:
110 argument is not a valid file descriptor.
114 argument is not valid.
120 arguments are negative,
125 is greater than the maximum file size.
129 argument does not refer to a regular file.
133 argument is associated with a pipe or FIFO.
140 interface conforms to
145 function first appeared in