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AIO_READ(3) NetBSD Library Functions Manual AIO_READ(3)
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aio_read -- asynchronous read from a file (REALTIME)
POSIX Real-time Library (librt, -lrt)
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
buffer 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] The request was not queued because of system resource
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, and will return -1, and aio_error() must 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.
siginfo(2), aio_cancel(3), aio_error(3), aio_return(3), aio_suspend(3),
The aio_read() system call is expected to conform to the IEEE Std
1003.1-2001 (``POSIX.1'') standard.
The aio_read() system call first appeared in NetBSD 5.0.
NetBSD 5.0 May 4, 2007 NetBSD 5.0