jammy (2) posix_fadvise.2freebsd.gz

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.