function requests an asynchronous "n = read(fd, buf, count)"
with fd, buf, count given by
The return status n can be retrieved upon completion using
The data is read starting at the absolute file offset
regardless of the current file position.
After this request,
the value of the current file position is unspecified.
The "asynchronous" means that this call returns as soon as the
request has been enqueued; the read may or may not have completed
when the call returns.
One tests for completion using
is defined, and this file supports it,
then the asynchronous operation is submitted at a priority equal
to that of the calling process minus
No data is read from a regular file beyond its maximum offset.
On success, 0 is returned.
On error the request is not enqueued, -1
is returned, and
is set appropriately.
If an error is first detected later, it will
be reported via
(returns status -1) and
(error status whatever one would have gotten in
Out of resources.
is not a valid file descriptor open for reading.
One or more of
This function is not supported.
The file is a regular file, we start reading before end-of-file
and want at least one byte, but the starting position is past
the maximum offset for this file.
It is a good idea to zero out the control block before use.
This control block must not be changed while the read operation
is in progress.
The buffer area being read into
must not be accessed during the operation or undefined results may
The memory areas involved must remain valid.