.\" Copyright (c) 2003 Andries Brouwer (aeb@cwi.nl)
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.TH AIO_READ 3 2003-11-14  "" "Linux Programmer's Manual"
.SH NAME
aio_read \- asynchronous read
.SH SYNOPSIS
.sp
.B "#include <aio.h>"
.sp
.BI "int aio_read(struct aiocb *" aiocbp );
.SH DESCRIPTION
The
.BR aio_read ()
function requests an asynchronous "n = read(fd, buf, count)"
with fd, buf, count given by
.IR aiocbp->aio_fildes ,
.IR aiocbp->aio_buf ,
.IR aiocbp->aio_nbytes ,
respectively.
The return status n can be retrieved upon completion using
.BR aio_return (3).
.LP
The data is read starting at the absolute file offset
.IR aiocbp->aio_offset ,
regardless of the current file position.
After this request,
the value of the current file position is unspecified.
.LP
The "asynchronous" means that this call returns as soon as the
request has been enqueued; the read may or may not have completed
when the call returns.
One tests for completion using
.BR aio_error (3).
.LP
If _POSIX_PRIORITIZED_IO is defined, and this file supports it,
then the asynchronous operation is submitted at a priority equal
to that of the calling process minus
.IR aiocbp->aio_reqprio .
.LP
The field
.I aiocbp->aio_lio_opcode
is ignored.
.LP
No data is read from a regular file beyond its maximum offset.
.SH "RETURN VALUE"
On success, 0 is returned.
On error the request is not enqueued, \-1
is returned, and
.I errno
is set appropriately.
If an error is first detected later, it will
be reported via
.BR aio_return (3)
(returns status \-1) and
.BR aio_error (3)
(error status whatever one would have gotten in
.IR errno ,
such as EBADF).
.SH ERRORS
.TP
.B EAGAIN
Out of resources.
.TP
.B EBADF
.I aio_fildes
is not a valid file descriptor open for reading.
.TP
.B EINVAL
One or more of
.IR aio_offset ,
.IR aio_reqprio ,
.IR aio_nbytes
are invalid.
.TP
.B ENOSYS
This function is not supported.
.TP
.B EOVERFLOW
The file is a regular file, we start reading before end-of-file
and want at least one byte, but the starting position is past
the maximum offset for this file.
.SH "CONFORMING TO"
POSIX.1-2001
.SH NOTES
It is a good idea to zero out the control block before use.
This control block must not be changed while the read operation
is in progress.
The buffer area being read into
.\" or the control block of the operation
must not be accessed during the operation or undefined results may
occur.
The memory areas involved must remain valid.
.SH "SEE ALSO"
.BR aio_cancel (3),
.BR aio_error (3),
.BR aio_fsync (3),
.BR aio_return (3),
.BR aio_suspend (3),
.BR aio_write (3)