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28 .\" @(#)madvise.2 8.1 (Berkeley) 6/9/93
36 .Nd give advice about use of file data
42 .Fn posix_fadvise "int fd" "off_t offset" "off_t len" "int advice"
47 allows a process to describe to the system its data access behavior for an
50 The advice covers the data starting at offset
60 to the end of the file is covered.
62 The behavior is specified by the
64 parameter and may be one of:
65 .Bl -tag -width POSIX_FADV_SEQUENTIAL
66 .It Dv POSIX_FADV_NORMAL
67 Tells the system to revert to the default data access behavior.
68 .It Dv POSIX_FADV_RANDOM
69 Is a hint that file data will be accessed randomly,
70 and prefetching is likely not advantageous.
71 .It Dv POSIX_FADV_SEQUENTIAL
72 Tells the system that file data will be accessed sequentially.
73 This currently does nothing as the default behavior uses heuristics to
74 detect sequential behavior.
75 .It Dv POSIX_FADV_WILLNEED
76 Tells the system that the specified data will be accessed in the near future.
77 The system may initiate an asynchronous read of the data if it is not already
79 .It Dv POSIX_FADV_DONTNEED
80 Tells the system that the specified data will not be accessed in the near
82 The system may decrease the in-memory priority of clean data within the
83 specified range and future access to this data may require a read operation.
84 .It Dv POSIX_FADV_NOREUSE
85 Tells the system that the specified data will only be accessed once and
87 The system may decrease the in-memory priority of data once it has been
89 Future access to this data may require a read operation.
92 .Rv -std posix_fadvise
96 system call will fail if:
101 argument is not a valid file descriptor.
105 argument is not valid.
111 arguments are negative,
116 is greater than the maximum file size.
120 argument does not refer to a regular file.
124 argument is associated with a pipe or FIFO.
131 interface conforms to
136 system call first appeared in