posix_fadvise Subroutine

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Purpose

Provides advisory information to the system about the future behavior of the application with respect to a given file.

Syntax

 #include <fcntl.h>
int posix_fadvise (int fd, off_t offset, size_t len, int advice);

Description

This function advises the system on the expected future behavior of the application with regards to a given file. The system can take this advice into account when performing operations on file data specified by this function. The advice is given over the range covered by the offset parameter and continuing for the number of bytes specified by the len parameter. If the value of the len parameter is 0, then all data following the offset parameter is covered.

To use the posix_fadvise subroutine, you must first open the file, and then call the posix_fadvise subroutine. The advisory information of a file is not reset when the file is closed. The client application must call the posix_fadvise subroutine along with the POSIX_FADV_NORMAL flag to reset all advisory information.

The advice parameter must have one of the following values:
POSIX_FADV_NORMAL
Resets all advisory information of a file to its default values.
POSIX_FADV_SEQUENTIAL
Valid option, but this value does not perform any action.
POSIX_FADV_RANDOM
Valid option, but this value does not perform any action.
POSIX_FADV_WILLNEED
Valid option, but this value does not perform any action.
POSIX_FADV_DONTNEED
Valid option, but this value does not perform any action.
POSIX_FADV_NOREUSE
Valid option, but this value does not perform any action.
POSIX_FADV_NOWRITEBEHIND
Instructs a file to ignore the normal write-behind functionality. You can run a system call, such as the sync system call, to explicitly write-back the information present in the file to the disk. This parameter value can be used only for regular files in enhanced Journaled File System (JFS2).

Parameters

Item Description
fd File descriptor of the file to be advised.
offset Represents the beginning of the address range.
len Determines the length of the address range.
advice Defines the advice to be provided.

Return Values

Upon successful completion, the posix_fadvise subroutine returns 0. Otherwise, one of the following error codes will be returned.

Error Codes

Item Description
EBADF The fd parameter is not a valid file descriptor.
EINVAL The value of the advice parameter is invalid.
ESPIPE The fd parameter is associated with a pipe of FIFO.