#include <fcntl.h> int posix_fadvise(int fd, off_t offset, off_t len, int advice);
The posix_fadvise() function advises the system 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 system may use this information to optimize handling of the specified data. The posix_fadvise() function has 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() returns zero. Otherwise, an error number is returned to indicate the error.
The posix_fadvise() function will fail if:
The fd argument is not a valid file descriptor.
The value of advice is invalid, or the value of len is less than zero.
The fd argument is associated with a pipe or FIFO.
The posix_fadvise() function has a transitional interface for 64-bit file offsets. See lf64(5).
See attributes(5) for descriptions of the following attributes: