posix_fadvise - file advisory information (ADVANCED REALTIME)
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:
- 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.
- Specifies that the application expects to access the specified data sequentially from lower offsets to higher offsets.
- Specifies that the application expects to access the specified data in a random order.
- Specifies that the application expects to access the specified data in the near future.
- Specifies that the application expects that it will not access the specified data in the near future.
- Specifies that the application expects to access the specified data once and then not reuse it thereafter.
These values are defined in <fcntl.h>.
Upon successful completion, posix_fadvise() shall return zero; otherwise, an error number shall be returned to indicate the error.
The posix_fadvise() function shall fail if:
- The fd argument is not a valid file descriptor.
- The value of advice is invalid.
- The fd argument is associated with a pipe or FIFO.
The posix_fadvise() function is part of the Advisory Information option and need not be provided on all implementations.
posix_madvise(), the Base Definitions volume of IEEE Std 1003.1-2001, <fcntl.h>
First released in Issue 6. Derived from IEEE Std 1003.1d-1999.
In the SYNOPSIS, the inclusion of <sys/types.h> is no longer required.
IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/68 is applied, changing the function prototype in the SYNOPSIS section. The previous prototype was not large file-aware, and the standard developers felt it acceptable to make this change before implementations of this function become widespread.