int
aio_read(
struct aiocb *aiocbp
)
)
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 call.
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 arguments), 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.
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.
)
system call will fail if:
EAGAIN
]
The following conditions may be synchronously detected when the
aio_read()
system 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(
)
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
]
aiocbp->aio_fildes
argument
is invalid.
EINVAL
]
aiocbp->aio_offset
is not valid, the priority specified by
aiocbp->aio_reqprio
is not a valid priority, or the number of bytes specified by
aiocbp->aio_nbytes
is not valid.
EOVERFLOW
]
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 one of:
EBADF
]
aiocbp->aio_fildes
argument
is invalid for reading.
ECANCELED
]
).
EINVAL
]
aiocbp->aio_offset
would be invalid.
)
system call is expected to conform to the
IEEE Std 1003.1-2001 (``POSIX.1'')
standard.
)
system call first appeared in
NetBSD5.0.