aio_read

AIO_READ(2) FreeBSD System Calls Manual AIO_READ(2)

NAME
aio_read -- asynchronous read from a file (REALTIME)

LIBRARY
Standard C Library (libc, -lc)

SYNOPSIS
#include <aio.h>

int
aio_read(struct aiocb *iocb);

DESCRIPTION
The aio_read() system call 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 argument is ignored by the aio_read() system
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
buffer 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() system call will fail if:

[EAGAIN] The request was not queued because of system resource
limitations.

[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 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 iocb->aio_fildes argument 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() 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] The iocb->aio_fildes argument 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.

SEE ALSO
aio_cancel(2), aio_error(2), aio_return(2), aio_suspend(2),
aio_waitcomplete(2), aio_write(2), aio(4)

STANDARDS
The aio_read() system call is expected to conform to the IEEE Std 1003.1
(``POSIX.1'') standard.

HISTORY
The aio_read() system call first appeared in FreeBSD 3.0.

AUTHORS
This manual page was written by Terry Lambert <terryATwhistle.com>.

BUGS
Invalid information in iocb->_aiocb_private may confuse the kernel.

FreeBSD 6.2 November 17, 1998 FreeBSD 6.2

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