AIO_READ(2) BSD System Calls Manual AIO_READ(2)NAMEaio_read — asynchronous read from a file (REALTIME)
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <time.h>
#include <aio.h>
int
aio_read(struct aiocb *iocb);
DESCRIPTION
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
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 iocb->aio_reqprio.
The iocb->aio_lio_opcode is ignored by the aio_read() call.
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 call 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.
RESTRICTIONS
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() 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 iocb->aio_offset is past the offset maximum for
iocb->aio_fildes, no I/O will occur.
RETURN VALUES
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
error.
DIAGNOSTICS
None.
ERRORS
The aio_read() function will fail if:
[EAGAIN] The request was not queued because of system resource
limitations.
[ENOSYS] The aio_read() call is not supported.
The following conditions may be synchronously detected when the
aio_read() call 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
aio_cancel().
[EINVAL] The offset iocb->aio_offset would be invalid.
STANDARDS
The aio_read() call is expected to conform to the IEEE Std 1003.2
(“POSIX.2”) standard.
HISTORY
The aio_read function first appeared in FreeBSD 3.0.
AUTHORS
This manual page was written by Terry Lambert ⟨terry@whistle.com⟩.
BUGS
The value of iocb->aio_offset is ignored. Invalid information in
iocb->_aiocb_private may confuse the kernel.
BSD November 17, 1998 BSD
