Tribblix: manual page: aio

AIO_READ(3C) Standard C Library Functions AIO_READ(3C)

NAME

aio_read - asynchronous read from a file

SYNOPSIS

#include <aio.h>

int aio_read(struct aiocb *aiocbp);

DESCRIPTION

The aio_read() function allows the calling process to read
aiocbp->aio_nbytes from the file associated with aiocbp->aio_fildes
into the buffer pointed to by aiocbp->aio_buf. 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 _POSIX_PRIORITIZED_IO 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
aiocbp->aio_reqprio. The aiocbp value may be used as an argument to
aio_error(3C) and aio_return(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 aio_offset, as if lseek(2) were
called immediately prior to the operation with an offset equal to
aio_offset and a whence equal to SEEK_SET. After a successful call to
enqueue an asynchronous I/O operation, the value of the file offset
for the file is unspecified.

The aiocbp->aio_sigevent structure defines what asynchronous
notification is to occur when the asynchronous operation completes,
as specified in signal.h(3HEAD).

The aiocbp->aio_lio_opcode field is ignored by aio_read().

The aiocbp argument points to an aiocb structure. If the buffer
pointed to by aiocbp->aio_buf or the control block pointed to by
aiocbp becomes an illegal address prior to asynchronous I/O
completion, then the behavior is undefined.

Simultaneous asynchronous operations using the same aiocbp produce
undefined results.

If _POSIX_SYNCHRONIZED_IO is defined and synchronized I/O is enabled
on the file associated with aiocbp->aio_fildes, the behavior of this
function is according to the definitions of synchronized I/O data
integrity completion and synchronized I/O file integrity completion.

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.

For regular files, no data transfer will occur past the offset
maximum established in the open file description associated with
aiocbp->aio_fildes.

RETURN VALUES

The aio_read() function returns 0 to the calling process if the I/O
operation is successfully queued; otherwise, the function returns -1
and sets errno to indicate the error.

ERRORS

The aio_read() function will fail if:

EAGAIN
The requested asynchronous I/O operation was not queued due
to system resource limitations.

Each of the following conditions may be detected synchronously at the
time of the call to aio_read(), or asynchronously. If any of the
conditions below are detected synchronously, the aio_read() function
returns -1 and sets errno to the corresponding value. If any of the
conditions below are detected asynchronously, the return status of
the asynchronous operation is set to -1, and the error status of the
asynchronous operation will be set to the corresponding value.

EBADF
The aiocbp->aio_fildes argument is not a valid file
descriptor open for reading.

EINVAL
The file offset value implied by aiocbp->aio_offset would
be invalid, aiocbp->aio_reqprio is not a valid value, or
aiocbp->aio_nbytes is an invalid value.

In the case that the aio_read() 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 read(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 read() function call, or one of
the following values:

EBADF
The aiocbp->aio_fildes argument is not a valid file
descriptor open for reading.

ECANCELED
The requested I/O was canceled before the I/O completed
due to an explicit aio_cancel(3C) request.

EINVAL
The file offset value implied by aiocbp->aio_offset
would be invalid.

The following condition may be detected synchronously or
asynchronously:

EOVERFLOW
The file is a regular file, aiobcp->aio_nbytes is
greater than 0 and the starting offset in
aiobcp->aio_offset is before the end-of-file and is at
or beyond the offset maximum in the open file
description associated with aiocbp->aio_fildes.

USAGE

For portability, the application should set aiocb->aio_reqprio to 0.

The aio_read() function has a transitional interface for 64-bit file
offsets. See lf64(7).

ATTRIBUTES