aio.5 (2010 09)

a
aio(5) aio(5)
NAME
aio - POSIX asynchronous I/O facility
SYNOPSIS
#include <aio.h>
DESCRIPTION
The POSIX Asynchronous I/O facility implements Section 6.7 of IEEE Standard 1003.1b-1993, Standard
for Information Technology, Portable Operating System Interface (POSIX), Part 1: System Application
Program Interface (API), Amendment 1: Realtime Extensions (C Language). It allows a process or
thread to start multiple simultaneous read and/or write operations to multiple files, to wait for or obtain
notification of completion of requested operations, and to retrieve the status of completed operations. The
purpose of the POSIX Asynchronous I/O facility is to allow a process or thread to overlap some elements
of computation and information processing with I/O processing.
Interface Functions
The POSIX Asynchronous I/O facility includes the following interface functions:
aio_read() Start an asynchronous read operation
aio_write() Start an asynchronous write operation
lio_listio() Start a list of asynchronous I/O operations
aio_suspend() Wait for completion of one or more asynchronous I/O operations
aio_error() Retrieve the error status of an asynchronous I/O operation
aio_return() Retrieve the return status of an asynchronous I/O operation and free any associated
system resources
aio_cancel() Request cancellation of a pending asynchronous I/O operation
aio_fsync() Request synchronization of the media image of a file to which asynchronous opera-
tions have been addressed
To use these functions, link in the realtime library by specifying
-lrt on the compiler or linker command
line.
Asynchronous I/O Control Block
The Asynchronous I/O Control Block (
aiocb) is used as a parameter to all of the asynchronous I/O func-
tions. The aiocb specifies parameters for an asynchronous I/O operation in a call to
aio_read(),
aio_write(),orlio_listio() and then may be used as a "handle" for the enqueued asynchronous
I/O operation in a subsequent call to aio_cancel(), aio_suspend()
, aio_fsync(),
aio_error(),oraio_return().
The
aiocb structure contains the following members:
int aio_fildes; /* file descriptor */
off_t aio_offset; /* file offset */
void *aio_buf; /* location of buffer */
size_t aio_nbytes; /* length of transfer */
int aio_reqprio; /* request priority offset */
struct sigevent aio_sigevent; /* signal number and value */
int aio_lio_opcode; /* operation to be performed */
The aiocb supplied to aio_read(), aio_write(),orlio_listio() must contain the parameters
that would be supplied in a normal synchronous read() or write() function call, where aio_fildes
corresponds to fildes, aio_nbytes corresponds to nbytes, and aio_offset corresponds to the
implicit file offset. The aiocb may also specify a request priority delta value (aio_reqprio), and sig-
naling information to satisfy unique realtime and asynchronous I/O requirements. For the
lio_listio() function, the aio_lio_opcode field specifies whether the operation is a read or
write.
Once an asynchronous I/O operation has been enqueued for a particular
aiocb, its address is used as a
handle for other asynchronous I/O functions and can only be used to refer to a single enqueued operation.
Other fields defined in the
aiocb structure are reserved for future use and extension. They are all
ignored by the asynchronous I/O facility.
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