'\" te
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.\" Copyright 1989 AT&T
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.TH aio_read 3C "28 Jan 2014" "SunOS 5.11" "Standard C Library Functions"
.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
If \fBSIGEV_MEM\fR sigevent type is specified, the error and return values are updated in the \fBaiocb_t\fR structure when I/O is completed. Applications can get the error value using \fBaio_error\fR(3C) and the return value using \fBaio_return\fR(3C). For \fBSIGEV_MEM\fR sigevent type requests, \fBaio_error\fR(3C) and \fBaio_return\fR(3C) simply return the error and return values from the structure, no system calls are involved. While the I/O is in progress an \fBEINPROGRESS\fR error is returned. I/O completion can be detected by monitoring the error value returned by \fBaio_error\fR(3C).
.sp
.LP
I/O completion notifications of SIGEV_MEM sigevent type requests cannot be collected using aio_waitn(3C) or aio_suspend(3C) calls.
.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
.mk
.na
\fB\fBEAGAIN\fR\fR
.ad
.RS 10n
.rt  
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
.mk
.na
\fB\fBEBADF\fR\fR
.ad
.RS 10n
.rt  
The \fIaiocbp\fR->\fBaio_fildes\fR argument is not a valid file descriptor open for reading.
.RE

.sp
.ne 2
.mk
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 10n
.rt  
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
.mk
.na
\fB\fBEBADF\fR\fR
.ad
.RS 13n
.rt  
The \fIaiocbp\fR->\fBaio_fildes\fR argument is not a valid file descriptor open for reading.
.RE

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

.sp
.ne 2
.mk
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 13n
.rt  
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
.mk
.na
\fB\fBEOVERFLOW\fR\fR
.ad
.RS 13n
.rt  
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
tab() box;
cw(2.75i) |cw(2.75i) 
lw(2.75i) |lw(2.75i) 
.
ATTRIBUTE TYPEATTRIBUTE VALUE
_
Interface StabilityCommitted
_
MT-LevelMT-Safe
_
StandardSee \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)