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

     The posix_fadvise() function returns the value 0 if successful; otherwise the value -1 is
     returned and the global variable errno is set to indicate the error.

ERRORS

     The posix_fadvise() system call will fail if:

     [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.

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.