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.TH AIO_READ 3C "Feb 5, 2008"
.SH NAME
aio_read \- asynchronous read from a file
.SH SYNOPSIS
.LP
.nf
#include <aio.h>

\fBint\fR \fBaio_read\fR(\fBstruct aiocb *\fR\fIaiocbp\fR);
.fi

.SH DESCRIPTION
.sp
.LP
The \fBaio_read()\fR function allows the calling process to read
\fIaiocbp\fR->\fBaio_nbytes\fR from the file associated with
\fIaiocbp\fR->\fBaio_fildes\fR into the buffer pointed to by
\fIaiocbp\fR->\fBaio_buf\fR. The function call returns when the read request
has been initiated or queued to the file or device (even when the data cannot
be delivered immediately). If \fB_POSIX_PRIORITIZED_IO\fR is defined and
prioritized I/O is supported for this file, then the asynchronous operation is
submitted at a priority equal to the scheduling priority of the process minus
\fIaiocbp\fR->\fBaio_reqprio\fR. The \fIaiocbp\fR value may be used as an
argument to \fBaio_error\fR(3C) and \fBaio_return\fR(3C) in order to determine
the error status and return status, respectively, of the asynchronous operation
while it is proceeding. If an error condition is encountered during queuing,
the function call returns without having initiated or queued the request. The
requested operation takes place at the absolute position in the file as given
by \fIaio_offset\fR, as if \fBlseek\fR(2) were called immediately prior to the
operation with an \fIoffset\fR equal to \fIaio_offset\fR and a \fBwhence\fR
equal to \fBSEEK_SET\fR. After a successful call to enqueue an asynchronous I/O
operation, the value of the file offset for the file is unspecified.
.sp
.LP
The \fIaiocbp\fR->\fBaio_sigevent\fR structure defines what asynchronous
notification is to occur when the asynchronous operation completes, as
specified in \fBsignal.h\fR(3HEAD).
.sp
.LP
The \fIaiocbp\fR->\fBaio_lio_opcode\fR field is ignored by \fBaio_read()\fR.
.sp
.LP
The \fIaiocbp\fR argument points to an \fBaiocb\fR structure. If the buffer
pointed to by \fIaiocbp\fR->\fBaio_buf\fR or the control block pointed to by
\fIaiocbp\fR becomes an illegal address prior to asynchronous I/O completion,
then the behavior is undefined.
.sp
.LP
Simultaneous asynchronous operations using the same \fIaiocbp\fR produce
undefined results.
.sp
.LP
If \fB_POSIX_SYNCHRONIZED_IO\fR is defined and synchronized I/O is enabled on
the file associated with \fIaiocbp\fR->\fBaio_fildes,\fR the behavior of this
function is according to the definitions of synchronized I/O data integrity
completion and synchronized I/O file integrity completion.
.sp
.LP
For any system action that changes the process memory space while an
asynchronous I/O is outstanding to the address range being changed, the result
of that action is undefined.
.sp
.LP
For regular files, no data transfer will occur past the offset maximum
established in the open file description associated with
\fIaiocbp\fR->\fBaio_fildes\fR.
.SH RETURN VALUES
.sp
.LP
The \fBaio_read()\fR function returns \fB0\fR to the calling process if the I/O
operation is successfully queued; otherwise, the function returns \fB\(mi1\fR
and sets \fBerrno\fR to indicate the error.
.SH ERRORS
.sp
.LP
The \fBaio_read()\fR function will fail if:
.sp
.ne 2
.na
\fB\fBEAGAIN\fR\fR
.ad
.RS 10n
The requested asynchronous I/O operation was not queued due to system resource
limitations.
.RE

.sp
.LP
Each of the following conditions may be detected synchronously at the time of
the call to \fBaio_read()\fR, or asynchronously. If any of the conditions below
are detected synchronously, the \fBaio_read()\fR function returns \fB-1\fR and
sets \fBerrno\fR to the corresponding value. If any of the conditions below are
detected asynchronously, the return status of the asynchronous operation is set
to \(mi1, and the error status of the asynchronous operation will be set to the
corresponding value.
.sp
.ne 2
.na
\fB\fBEBADF\fR\fR
.ad
.RS 10n
The \fIaiocbp\fR->\fBaio_fildes\fR argument is not a valid file descriptor open
for reading.
.RE

.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 10n
The file offset value implied by \fIaiocbp\fR->\fBaio_offset\fR would be
invalid, \fIaiocbp->\fR\fBaio_reqprio\fR is not a valid value, or
\fIaiocbp\fR->\fBaio_nbytes\fR is an invalid value.
.RE

.sp
.LP
In the case that the \fBaio_read()\fR successfully queues the I/O operation but
the operation is subsequently canceled or encounters an error, the return
status of the asynchronous operation is one of the values normally returned by
the \fBread\fR(2) function call. In addition, the error status of the
asynchronous operation will be set to one of the error statuses normally set by
the \fBread()\fR function call, or one of the following values:
.sp
.ne 2
.na
\fB\fBEBADF\fR\fR
.ad
.RS 13n
The \fIaiocbp\fR->\fBaio_fildes\fR argument is not a valid file descriptor open
for reading.
.RE

.sp
.ne 2
.na
\fB\fBECANCELED\fR\fR
.ad
.RS 13n
The requested I/O was canceled before the I/O completed due to an explicit
\fBaio_cancel\fR(3C) request.
.RE

.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 13n
The file offset value implied by \fIaiocbp\fR->\fBaio_offset\fR would be
invalid.
.RE

.sp
.LP
The following condition may be detected synchronously or asynchronously:
.sp
.ne 2
.na
\fB\fBEOVERFLOW\fR\fR
.ad
.RS 13n
The file is a regular file, \fIaiobcp\fR->\fBaio_nbytes\fR is greater than 0
and the starting offset in \fIaiobcp\fR->\fBaio_offset\fR is before the
end-of-file and is at or beyond the offset maximum in the open file description
associated with \fIaiocbp\fR->\fBaio_fildes\fR.
.RE

.SH USAGE
.sp
.LP
For portability, the application should set \fIaiocb->\fR\fBaio_reqprio\fR to
\fB0\fR.
.sp
.LP
The \fBaio_read()\fR function has a transitional interface for 64-bit file
offsets.  See \fBlf64\fR(5).
.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(5) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Committed
_
MT-Level	MT-Safe
_
Standard	See \fBstandards\fR(5).
.TE

.SH SEE ALSO
.sp
.LP
\fBclose\fR(2), \fBexec\fR(2), \fBexit\fR(2), \fBfork\fR(2), \fBlseek\fR(2),
\fBread\fR(2), \fBwrite\fR(2), \fBaio_cancel\fR(3C), \fBaio_return\fR(3C),
\fBaio.h\fR(3HEAD), \fBlio_listio\fR(3C), \fBsiginfo.h\fR(3HEAD),
\fBsignal.h\fR(3HEAD), \fBattributes\fR(5), \fBlf64\fR(5), \fBstandards\fR(5)