aio_read - asynchronous read
#include <aio.h>
int aio_read(struct aiocb *aiocbp);
Link with
-lrt.
The
aio_read() function queues the I/O request described by the buffer
pointed to by
aiocbp. This function is the asynchronous analog of
read(2). The arguments of the call
read(fd, buf, count)
correspond (in order) to the fields
aio_fildes,
aio_buf, and
aio_nbytes of the structure pointed to by
aiocbp. (See
aio(7) for a description of the
aiocb structure.)
The data is read starting at the absolute position
aiocbp->aio_offset,
regardless of the file offset. After the call, the value of the file offset 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
aio_error(3). The return status
of a completed I/O operation can be obtained by
aio_return(3).
Asynchronous notification of I/O completion can be obtained by setting
aiocbp->aio_sigevent appropriately; see
sigevent(7) for
details.
If
_POSIX_PRIORITIZED_IO is defined, and this file supports it, then the
asynchronous operation is submitted at a priority equal to that of the calling
process minus
aiocbp->aio_reqprio.
The field
aiocbp->aio_lio_opcode is ignored.
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
errno is set appropriately. If an error is detected only
later, it will be reported via
aio_return(3) (returns status -1) and
aio_error(3) (error status—whatever one would have gotten in
errno, such as
EBADF).
- EAGAIN
- Out of resources.
- EBADF
- aio_fildes is not a valid file descriptor open for reading.
- EINVAL
- One or more of aio_offset, aio_reqprio, or aio_nbytes
are invalid.
- ENOSYS
- aio_read() is not implemented.
- EOVERFLOW
- 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.
The
aio_read() function is available since glibc 2.1.
For an explanation of the terms used in this section, see
attributes(7).
| Interface |
Attribute |
Value |
| aio_read () |
Thread safety |
MT-Safe |
POSIX.1-2001, POSIX.1-2008.
It is a good idea to zero out the control block before use. The 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 occur. The memory areas involved must remain valid.
Simultaneous I/O operations specifying the same
aiocb structure produce
undefined results.
See
aio(7).
aio_cancel(3),
aio_error(3),
aio_fsync(3),
aio_return(3),
aio_suspend(3),
aio_write(3),
lio_listio(3),
aio(7)