AIO_READ(2) BSD System Calls Manual AIO_READ(2)NAMEaio_read — asynchronous read from a file (REALTIME)
Standard C Library (libc, -lc)
aio_read(struct aiocb *aiocbp);
The aio_read() system call allows the calling process to read
aiocbp->aio_nbytes from the descriptor aiocbp->aio_fildes, beginning at
the offset aiocbp->aio_offset, into the buffer pointed to by
aiocbp->aio_buf. The call returns immediately after the read request has
been enqueued to the descriptor; the read may or may not have completed
at the time the call returns.
If _POSIX_PRIORITIZED_IO is defined, and the descriptor supports it, then
the enqueued operation is submitted at a priority equal to that of the
calling process minus aiocbp->aio_reqprio.
The aiocbp->aio_lio_opcode argument is ignored by the aio_read() system
The aiocbp pointer may be subsequently used as an argument to
aio_return() and aio_error() in order to determine return or error status
for the enqueued operation while it is in progress.
If the request could not be enqueued (generally due to invalid argu‐
ments), then the call returns without having enqueued the request.
If the request is successfully enqueued, the value of aiocbp->aio_offset
can be modified during the request as context, so this value must not be
referenced after the request is enqueued.
The Asynchronous I/O Control Block structure pointed to by aiocbp and the
buffer that the aiocbp->aio_buf member of that structure references must
remain valid until the operation has completed. For this reason, use of
auto (stack) variables for these objects is discouraged.
The asynchronous I/O control buffer aiocbp should be zeroed before the
aio_read() call to avoid passing bogus context information to the kernel.
Modifications of the Asynchronous I/O Control Block structure or the buf‐
fer contents after the request has been enqueued, but before the request
has completed, are not allowed.
If the file offset in aiocbp->aio_offset is past the offset maximum for
aiocbp->aio_fildes, no I/O will occur.
The aio_read() function returns the value 0 if successful; otherwise the
value -1 is returned and the global variable errno is set to indicate the
The aio_read() system call will fail if:
[EAGAIN] Because of system resource limitations, the request
was not queued.
[ENOSYS] The aio_read() system call is not supported.
The following conditions may be synchronously detected when the
aio_read() system call is made, or asynchronously, at any time there‐
after. If they are detected at call time, aio_read() returns -1 and sets
errno appropriately. Otherwise, the aio_return() system call must be
called. It will return -1; aio_error() must then be called to determine
the actual value that would have been returned in errno.
[EBADF] The aiocbp->aio_fildes argument is invalid.
[EINVAL] The offset aiocbp->aio_offset is not valid, the prior‐
ity specified by aiocbp->aio_reqprio is not a valid
priority, or the number of bytes specified by
aiocbp->aio_nbytes is not valid.
[EOVERFLOW] The file is a regular file, aiocbp->aio_nbytes is
greater than zero, the starting offset in
aiocbp->aio_offset is before the end of the file, but
is at or beyond the aiocbp->aio_fildes offset maximum.
If the request is successfully enqueued, but subsequently cancelled or an
error occurs, the value returned by the aio_return() system call is per
the read(2) system call, and the value returned by the aio_error() system
call is either one of the error returns from the read(2) system call, or
[EBADF] The aiocbp->aio_fildes argument is invalid for read‐
[ECANCELED] The request was explicitly cancelled via a call to
[EINVAL] The offset aiocbp->aio_offset would be invalid.
SEE ALSOaio_cancel(2), aio_error(2), aio_return(2), aio_suspend(2), aio_write(2),
The aio_read() system call is expected to conform to the IEEE Std 1003.1
The aio_read() system call first appeared in FreeBSD 3.0.
This manual page was written by Terry Lambert ⟨email@example.com⟩.
Invalid information in aiocbp->_aiocb_private may confuse the kernel.
BSD November 17, 1998 BSD