aio_read
- asynchronous read from a file (REALTIME)
LIBRARY
Lb libc
SYNOPSIS
#include <aio.h> int
aio_read (struct aiocb *iocb);
DESCRIPTION
The
aio_read ();
system call allows the calling process to read
Fa iocb->aio_nbytes
from the descriptor
Fa iocb->aio_fildes
beginning at the offset
Fa iocb->aio_offset
into the buffer pointed to by
Fa 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
Fa iocb->aio_reqprio .
The
Fa iocb->aio_lio_opcode
argument
is ignored by the
aio_read ();
system call.
The
Fa 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 arguments),
then the call returns without having enqueued the request.
If the request is successfully enqueued, the value of
Fa 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
Fa iocb
and the buffer that the
Fa 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
Fa 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
buffer contents after the request has been enqueued, but before the
request has completed, are not allowed.
If the file offset in
Fa iocb->aio_offset
is past the offset maximum for
Fa iocb->aio_fildes ,
no I/O will occur.
RETURN VALUES
Rv -std aio_read
DIAGNOSTICS
None.
ERRORS
The
aio_read ();
system call will fail if:
Bq Er EAGAIN
The request was not queued because of system resource limitations.
Bq Er 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 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
Bq Er EBADF
The
Fa iocb->aio_fildes
argument
is invalid.
Bq Er EINVAL
The offset
Fa iocb->aio_offset
is not valid, the priority specified by
Fa iocb->aio_reqprio
is not a valid priority, or the number of bytes specified by
Fa iocb->aio_nbytes
is not valid.
Bq Er EOVERFLOW
The file is a regular file,
Fa iocb->aio_nbytes
is greater than zero, the starting offset in
Fa iocb->aio_offset
is before the end of the file, but is at or beyond the
Fa 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 ();
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:
Bq Er EBADF
The
Fa iocb->aio_fildes
argument
is invalid for reading.
Bq Er ECANCELED
The request was explicitly cancelled via a call to
aio_cancel (.);
