.TH io_cancel 2 2002-09-03 "Linux 2.4" "Linux AIO"
.SH NAME
io_cancel \- Cancel io requests
.SH SYNOPSIS
.nf
.B #include <errno.h>
.sp
.br
.B #include <libaio.h>
.sp
.br
.BI "int io_cancel(io_context_t ctx, struct iocb *iocb)"
.br
.sp
struct iocb {
	void		*data; /* Return in the io completion event */
	unsigned	key;	/* For use in identifying io requests */
	short		aio_lio_opcode;
	short		aio_reqprio; 	/* Not used */
	int		aio_fildes;
};
.fi
.SH DESCRIPTION
Attempts to cancel an iocb previously passed to io_submit.  If
the operation is successfully cancelled, the resulting event is
copied into the memory pointed to by result without being placed
into the completion queue.
.PP
When one or more requests are asynchronously processed, it might be
useful in some situations to cancel a selected operation, e.g., if it
becomes obvious that the written data is no longer accurate and would
have to be overwritten soon.  As an example, assume an application, which
writes data in files in a situation where new incoming data would have
to be written in a file which will be updated by an enqueued request.
.SH "RETURN VALUES"
0 is returned on success , otherwise returns Errno.
.SH ERRORS
.TP
.B EFAULT 
If any of the data structures pointed to are invalid.
.TP
.B EINVAL 
If aio_context specified by ctx_id is
invalid.  
.TP
.B EAGAIN
If the iocb specified was not
cancelled.  
.TP
.B ENOSYS 
if not implemented.
.SH "SEE ALSO"
.BR io(3),
.BR io_fsync(3),
.BR io_getevents(3),
.BR io_prep_fsync(3),
.BR io_prep_pread(3),
.BR io_prep_pwrite(3),
.BR io_queue_init(3),
.BR io_queue_release(3),
.BR io_queue_run(3),
.BR io_queue_wait(3),
.BR io_set_callback(3),
.BR io_submit(3),
.BR errno(3)