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AIO_READ(3) DragonFly Library Functions Manual AIO_READ(3)
aio_read -- asynchronous read from a file (REALTIME)
POSIX Real-time Library (librt, -lrt)
aio_read(struct aiocb *iocb);
The aio_read() function allows the calling process to read
iocb->aio_nbytes from the descriptor iocb->aio_fildes beginning at the
offset iocb->aio_offset into the buffer pointed to by iocb->aio_buf. The
function returns immediately after the read request has been enqueued to
the descriptor; the read may or may not have completed at the time the
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 iocb->aio_reqprio.
The iocb->aio_lio_opcode is ignored by the aio_read() function.
The iocb 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 function returns without having enqueued the request.
If the request is successfully enqueued, the value of iocb->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 iocb and the
buffer that the iocb->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 iocb should be zeroed before the
aio_read() function .
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 iocb->aio_offset is past the offset maximum for
iocb->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() function will fail if:
[EAGAIN] The request was not queued because of system resource
[ENOSYS] The aio_read() function is not supported.
The following conditions may be synchronously detected when the
aio_read() function is made, or asynchronously, at any time thereafter.
If they are detected at call time, aio_read() returns -1 and sets errno
appropriately; otherwise the aio_return() function 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] iocb->aio_fildes is invalid.
[EINVAL] The offset iocb->aio_offset is not valid, the priority
specified by iocb->aio_reqprio is not a valid prior-
ity, or the number of bytes specified by
iocb->aio_nbytes is not valid.
[EOVERFLOW] The file is a regular file, iocb->aio_nbytes is
greater than zero, the starting offset in
iocb->aio_offset is before the end of the file, but is
at or beyond the iocb->aio_fildes offset maximum.
If the request is successfully enqueued, but subsequently cancelled or an
error occurs, the value returned by the aio_return() function is per the
read(2) call, and the value returned by the aio_error() function is
either one of the error returns from the read(2) call, or one of:
[EBADF] iocb->aio_fildes is invalid for reading.
[ECANCELED] The request was explicitly cancelled via a call to
[EINVAL] The offset iocb->aio_offset would be invalid.
The aio_read() function is expected to conform to the IEEE Std 1003.2
The aio_read function first appeared in FreeBSD 3.0.
This manual page was written by Terry Lambert <email@example.com>.
DragonFly 3.5 November 17, 1998 DragonFly 3.5