fadvise(2) System Calls Manual fadvise(2)
NAME
fadvise() - file advisory information
SYNOPSIS
Parameters
fad_fd The open file descriptor to which the fadvise operation applies.
fad_offset The beginning of the specified range as a positive, byte offset.
fad_len The length of the specified range in bytes.
fad_advice Specifies advice to be applied to range (see fadvise(5)).
fad_extparms Pointer to an array of (see fadvise(5)).
DESCRIPTION
The function is used to advise the system about the expected behavior of the application with respect to the data in the file associated
with the open file descriptor, fad_fd, starting at fad_offset and continuing for fad_len bytes. The specified range need not currently
exist in the file. If fad_len is zero, all data following fad_offset is specified.
The interpretation of the fad_offset and fad_len parameters are conditional in that they are ignored in the case of a non-null fad_extparms
argument. If non-null, the fad_extparms argument is used as a pointer to an extended parameter list of type (see fadvise(5)).
The extended parameter list allows an application to batch hints over multiple ranges in one call. The fad_count items are processed in
list order where, in the case of overlapping ranges, entries lower on the list of hints take precedence.
It should be noted that the effect of all hints is cumulative for a given file object. All hints will be removed on processing the last
close of the file object.
The fad_advice parameter is used to convey the hint to be applied to the data and may be one of the following values:
The cc-numa related policies are to be used by VM for physical memory locality when allocating memory for file I/O. This attribute applies
to the entire file only.
Either one of the following policies can be combined with the command (for further reference see fadvise(5):
Policy specifying that memory for the file will be allocated
from interleaved memory. Interleaved memory is memory allocated from several locality domains and then striped together. It
should be used if equal-cost allocations are needed.
Policy specifying that memory for the file will be allocated
from the locality of the calling CPU. Fast when memory is available from the closest locality otherwise search by distance
for available memory to allocate.
Specifies that the application will expect that it will not
access the specified range of data in the near future.
The application prefers that large pages be used
by VM in allocating memory for file I/O. The preferred page size is passed in the fad_pgsize alias (see fadvise(5)). The page size
specified in the fad_pgsize alias will be rounded down to the supported large page size in the system. If no hint is specified,
then the page size specified in the tunable will be used.
Specifies that the application will expect to access the specified range
of data once and then not reuse it thereafter.
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 will expect to access the specified
specified range of data in a random order.
Specifies that the application expects to access the specified range of data
sequentially from the lower offsets to higher offsets.
No pages associated with given
fd should be sync'd by VM.
Sets paging policies used by the VM syncer for a
fd when selecting pages for page out. This policy indicates that pages associated with file i/o should be sync'd in a time interval
designated by the fad_synctime alias (see fadvise(5)). This is default behavior with time interval set by VM.
Specifies that the application will expect to access the specified
range of data in the near future.
These values will be defined in
RETURN VALUE
Successful completion.
Failure.
is set to indicate the error.
ERRORS
If the service fails, is set to one of the following values:
The fd argument is not a valid file descriptor.
The value of fad_advice or one of the other input values has been found to be invalid.
A designated hint is not supported by the underlying file object.
The fadvise operation is not supported by the underlying file system.
The fd argument is associated with a pipe or FIFO.
If an error is detected while processing a given fad_advice hint, an error number will be returned indicating the related error (see The
error number value, therefore, is independent of the error numbers listed above.
EXAMPLES
AUTHOR
was derived by HP from the IEEE POSIX 1003.1-2001 Standard.
SEE ALSO
fcntl(2), posix_fadvise(2), fadvise(5), fcntl(5).
STANDARDS CONFORMANCE
fadvise(2)