aio_read(2) BSD 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 *aiocbp);
DESCRIPTION
The aio_read() 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 argu-
ments), 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.
RESTRICTIONS
The Asynchronous I/O Control Block structure pointed to by 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.
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] Because of system resource limitations, the request
was not queued.
[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. It will return -1; aio_error() must then be called to determine
the actual value that would have been returned in errno.
[EBADF] The aiocbp->aio_fildes argument is invalid.
[EINVAL] The offset aiocbp->aio_offset is not valid, the prior-
ity specified by aiocbp->aio_reqprio is not a valid
priority, or the number of bytes specified by
aiocbp->aio_nbytes is not valid.
[EOVERFLOW] The file is a regular file, 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] The aiocbp->aio_fildes argument is invalid for read-
ing.
[ECANCELED] The request was explicitly cancelled via a call to
aio_cancel().
[EINVAL] The offset aiocbp->aio_offset would be invalid.
SEE ALSO
aio_cancel(2), aio_error(2), aio_return(2), aio_suspend(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 <terry@whistle.com>.
BUGS
Invalid information in aiocbp->_aiocb_private may confuse the kernel.
BSD November 17, 1998 BSD
Mac OS X 10.9.1 - Generated Sun Jan 5 18:55:45 CST 2014