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.TH AIO_READ 3 2017-09-15  "" "Linux Programmer's Manual"

.SH NAME

aio_read \- asynchronous read

.SH SYNOPSIS

.B "#include <aio.h>"

.PP

.BI "int aio_read(struct aiocb *" aiocbp );

.PP

Link with \fI\-lrt\fP.

.SH DESCRIPTION

The

.BR aio_read ()

function queues the I/O request described by the buffer pointed to by

.IR aiocbp .

This function is the asynchronous analog of

.BR read (2).

The arguments of the call

.PP

    read(fd, buf, count)

.PP

correspond (in order) to the fields

.IR aio_fildes ,

.IR aio_buf ,

and

.IR aio_nbytes

of the structure pointed to by

.IR aiocbp .

(See

.BR aio (7)

for a description of the

.I aiocb

structure.)

.PP

The data is read starting at the absolute position

.IR aiocbp\->aio_offset ,

regardless of the file offset.

After the call,

the value of the file offset is unspecified.

.PP

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).

The return status of a completed I/O operation can be obtained by

.BR aio_return (3).

Asynchronous notification of I/O completion can be obtained by setting

.IR aiocbp\->aio_sigevent

appropriately; see

.BR sigevent (7)

for details.

.PP

If

.B _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 .

.PP

The field

.I aiocbp\->aio_lio_opcode

is ignored.

.PP

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 detected only later, it will

be reported via

.BR aio_return (3)

(returns status \-1) and

.BR aio_error (3)

(error status\(emwhatever one would have gotten in

.IR errno ,

such as

.BR 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 ,

or

.I aio_nbytes

are invalid.

.TP

.B ENOSYS

.BR aio_read ()

is not implemented.

.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 VERSIONS

The

.BR aio_read ()

function is available since glibc 2.1.

.SH ATTRIBUTES

For an explanation of the terms used in this section, see

.BR attributes (7).

.TS

allbox;

lb lb lb

l l l.

Interface	Attribute	Value

T{

.BR aio_read ()

T}	Thread safety	MT-Safe

.TE

.SH CONFORMING TO

POSIX.1-2001, POSIX.1-2008.

.SH NOTES

It is a good idea to zero out the control block before use.

The 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.

.PP

Simultaneous I/O operations specifying the same

.I aiocb

structure produce undefined results.

.SH EXAMPLE

See

.BR aio (7).

.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),

.BR lio_listio (3),

.BR aio (7)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.