posix_fadvise

POSIX_FADVISE(2)             BSD 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.

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.

BSD                              October 3, 2015                             BSD