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(5).

ATTRIBUTES


See attributes(5) for descriptions of the following attributes:


+--------------------+-------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|Interface Stability | Committed |
+--------------------+-------------------+
|MT-Level | MT-Safe |
+--------------------+-------------------+
|Standard | See standards(5). |
+--------------------+-------------------+

SEE ALSO


close(2), exec(2), exit(2), fork(2), lseek(2), read(2), write(2),
aio_cancel(3C), aio_return(3C), aio.h(3HEAD), lio_listio(3C),
siginfo.h(3HEAD), signal.h(3HEAD), attributes(5), lf64(5), standards(5)


February 5, 2008 AIO_READ(3C)