PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

NAME

       posix_fadvise — file advisory information (ADVANCED REALTIME)

SYNOPSIS

       #include <fcntl.h>

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

DESCRIPTION

       The  posix_fadvise() function shall advise the implementation on the expected behavior of the application
       with respect to the data in the file associated with the open file descriptor, fd, starting at offset and
       continuing for len bytes. The specified range need not currently exist in the file. If len is  zero,  all
       data  following  offset is specified. The implementation may use this information to optimize handling of
       the specified data. The posix_fadvise()  function  shall  have  no  effect  on  the  semantics  of  other
       operations on the specified data, although it may affect the performance of other operations.

       The advice to be applied to the data is specified by the advice parameter and may be one of the following
       values:

       POSIX_FADV_NORMAL
             Specifies  that the application has no advice to give on its behavior with respect to the specified
             data. It is the default characteristic if no advice is given for an open file.

       POSIX_FADV_SEQUENTIAL
             Specifies that the application expects to access the specified data sequentially from lower offsets
             to higher offsets.

       POSIX_FADV_RANDOM
             Specifies that the application expects to access the specified data in a random order.

       POSIX_FADV_WILLNEED
             Specifies that the application expects to access the specified data in the near future.

       POSIX_FADV_DONTNEED
             Specifies that the application expects that it will not access  the  specified  data  in  the  near
             future.

       POSIX_FADV_NOREUSE
             Specifies  that  the  application  expects  to access the specified data once and then not reuse it
             thereafter.

       These values are defined in <fcntl.h>.

RETURN VALUE

       Upon successful completion, posix_fadvise() shall return  zero;  otherwise,  an  error  number  shall  be
       returned to indicate the error.

ERRORS

       The posix_fadvise() function shall fail if:

       EBADF  The fd argument is not a valid file descriptor.

       EINVAL The value of advice is invalid, or the value of len is less than zero.

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

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       The  posix_fadvise()  function is part of the Advisory Information option and need not be provided on all
       implementations.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       posix_madvise()

       The Base Definitions volume of POSIX.1‐2017, <fcntl.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any discrepancy between this version and the original
       IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee  document.
       The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any  typographical  or formatting errors that appear in this page are most likely to have been introduced
       during  the  conversion  of  the  source  files  to  man  page  format.  To  report  such   errors,   see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                 POSIX_FADVISE(3POSIX)