POSIX_FADVISE(2)          FreeBSD System Calls Manual         POSIX_FADVISE(2)

NAME
     posix_fadvise - give advice about use of file data

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <fcntl.h>

     int
     posix_fadvise(int fd, off_t offset, off_t len, int advice);

DESCRIPTION
     The posix_fadvise() system call allows a process to describe to the
     system its data access behavior for an open file descriptor fd.  The
     advice covers the data starting at offset offset and continuing for len
     bytes.  If len is zero, all data from offset to the end of the file is
     covered.

     The behavior is specified by the advice parameter and may be one of:

     POSIX_FADV_NORMAL      Tells the system to revert to the default data
                            access behavior.

     POSIX_FADV_RANDOM      Is a hint that file data will be accessed
                            randomly, and prefetching is likely not
                            advantageous.

     POSIX_FADV_SEQUENTIAL  Tells the system that file data will be accessed
                            sequentially.  This currently does nothing as the
                            default behavior uses heuristics to detect
                            sequential behavior.

     POSIX_FADV_WILLNEED    Tells the system that the specified data will be
                            accessed in the near future.  The system may
                            initiate an asynchronous read of the data if it is
                            not already present in memory.

     POSIX_FADV_DONTNEED    Tells the system that the specified data will not
                            be accessed in the near future.  The system may
                            decrease the in-memory priority of clean data
                            within the specified range and future access to
                            this data may require a read operation.

     POSIX_FADV_NOREUSE     Tells the system that the specified data will only
                            be accessed once and then not reused.  The system
                            may decrease the in-memory priority of data once
                            it has been read or written.  Future access to
                            this data may require a read operation.

RETURN VALUES
     If successful, posix_fadvise() returns zero.  It returns an error on
     failure, without setting errno.

ERRORS
     Possible failure conditions:

     [EBADF]            The fd argument is not a valid file descriptor.

     [EINVAL]           The advice argument is not valid.

     [EINVAL]           The offset or len arguments are negative, or offset +
                        len is greater than the maximum file size.

     [ENODEV]           The fd argument does not refer to a regular file.

     [ESPIPE]           The fd argument is associated with a pipe or FIFO.

     [EIO]              An I/O error occurred while reading from or writing to
                        a file system.

     [EINTEGRITY]       Corrupted data was detected while reading from the
                        file system.

SEE ALSO
     madvise(2)

STANDARDS
     The posix_fadvise() interface conforms to IEEE Std 1003.1-2001
     ("POSIX.1").

HISTORY
     The posix_fadvise() system call first appeared in FreeBSD 9.1.

FreeBSD 13.1-RELEASE-p6         March 30, 2020         FreeBSD 13.1-RELEASE-p6