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.

Debian                                           March 30, 2020                                 POSIX_FADVISE(2)