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NAME
lio_listio - list directed I/O (REALTIME)
SYNOPSIS
#include <aio.h>
int lio_listio(int mode, struct aiocb *restrict const list[restrict],
int nent, struct sigevent *restrict sig);
DESCRIPTION
The lio_listio() function shall initiate a list of I/O requests with a single function
call.
The mode argument takes one of the values LIO_WAIT or LIO_NOWAIT declared in <aio.h> and
determines whether the function returns when the I/O operations have been completed, or as
soon as the operations have been queued. If the mode argument is LIO_WAIT, the function
shall wait until all I/O is complete and the sig argument shall be ignored.
If the mode argument is LIO_NOWAIT, the function shall return immediately, and
asynchronous notification shall occur, according to the sig argument, when all the I/O
operations complete. If sig is NULL, then no asynchronous notification shall occur. If
sig is not NULL, asynchronous notification occurs as specified in Signal Generation and
Delivery when all the requests in list have completed.
The I/O requests enumerated by list are submitted in an unspecified order.
The list argument is an array of pointers to aiocb structures. The array contains nent
elements. The array may contain NULL elements, which shall be ignored.
The aio_lio_opcode field of each aiocb structure specifies the operation to be performed.
The supported operations are LIO_READ, LIO_WRITE, and LIO_NOP; these symbols are defined
in <aio.h>. The LIO_NOP operation causes the list entry to be ignored. If the
aio_lio_opcode element is equal to LIO_READ, then an I/O operation is submitted as if by a
call to aio_read() with the aiocbp equal to the address of the aiocb structure. If the
aio_lio_opcode element is equal to LIO_WRITE, then an I/O operation is submitted as if by
a call to aio_write() with the aiocbp equal to the address of the aiocb structure.
The aio_fildes member specifies the file descriptor on which the operation is to be
performed.
The aio_buf member specifies the address of the buffer to or from which the data is
transferred.
The aio_nbytes member specifies the number of bytes of data to be transferred.
The members of the aiocb structure further describe the I/O operation to be performed, in
a manner identical to that of the corresponding aiocb structure when used by the
aio_read() and aio_write() functions.
The nent argument specifies how many elements are members of the list; that is, the length
of the array.
The behavior of this function is altered according to the definitions of synchronized I/O
data integrity completion and synchronized I/O file integrity completion if synchronized
I/O is enabled on the file associated with aio_fildes.
For regular files, no data transfer shall occur past the offset maximum established in the
open file description associated with aiocbp->aio_fildes.
RETURN VALUE
If the mode argument has the value LIO_NOWAIT, the lio_listio() function shall return the
value zero if the I/O operations are successfully queued; otherwise, the function shall
return the value -1 and set errno to indicate the error.
If the mode argument has the value LIO_WAIT, the lio_listio() function shall return the
value zero when all the indicated I/O has completed successfully. Otherwise, lio_listio()
shall return a value of -1 and set errno to indicate the error.
In either case, the return value only indicates the success or failure of the lio_listio()
call itself, not the status of the individual I/O requests. In some cases one or more of
the I/O requests contained in the list may fail. Failure of an individual request does not
prevent completion of any other individual request. To determine the outcome of each I/O
request, the application shall examine the error status associated with each aiocb control
block. The error statuses so returned are identical to those returned as the result of an
aio_read() or aio_write() function.
ERRORS
The lio_listio() function shall fail if:
EAGAIN The resources necessary to queue all the I/O requests were not available. The
application may check the error status for each aiocb to determine the individual
request(s) that failed.
EAGAIN The number of entries indicated by nent would cause the system-wide limit {AIO_MAX}
to be exceeded.
EINVAL The mode argument is not a proper value, or the value of nent was greater than
{AIO_LISTIO_MAX}.
EINTR A signal was delivered while waiting for all I/O requests to complete during an
LIO_WAIT operation. Note that, since each I/O operation invoked by lio_listio() may
possibly provoke a signal when it completes, this error return may be caused by the
completion of one (or more) of the very I/O operations being awaited. Outstanding
I/O requests are not canceled, and the application shall examine each list element
to determine whether the request was initiated, canceled, or completed.
EIO One or more of the individual I/O operations failed. The application may check the
error status for each aiocb structure to determine the individual request(s) that
failed.
In addition to the errors returned by the lio_listio() function, if the lio_listio()
function succeeds or fails with errors of [EAGAIN], [EINTR], or [EIO], then some of the
I/O specified by the list may have been initiated. If the lio_listio() function fails with
an error code other than [EAGAIN], [EINTR], or [EIO], no operations from the list shall
have been initiated. The I/O operation indicated by each list element can encounter errors
specific to the individual read or write function being performed. In this event, the
error status for each aiocb control block contains the associated error code. The error
codes that can be set are the same as would be set by a read() or write() function, with
the following additional error codes possible:
EAGAIN The requested I/O operation was not queued due to resource limitations.
ECANCELED
The requested I/O was canceled before the I/O completed due to an explicit
aio_cancel() request.
EFBIG The aiocbp->aio_lio_opcode is LIO_WRITE, the file is a regular file,
aiocbp->aio_nbytes is greater than 0, and the aiocbp->aio_offset is greater than or
equal to the offset maximum in the open file description associated with
aiocbp->aio_fildes.
EINPROGRESS
The requested I/O is in progress.
EOVERFLOW
The aiocbp->aio_lio_opcode is LIO_READ, the file is a regular file,
aiocbp->aio_nbytes is greater than 0, and the aiocbp->aio_offset is before the end-
of-file and is greater than or equal to the offset maximum in the open file
description associated with aiocbp->aio_fildes.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
Although it may appear that there are inconsistencies in the specified circumstances for
error codes, the [EIO] error condition applies when any circumstance relating to an
individual operation makes that operation fail. This might be due to a badly formulated
request (for example, the aio_lio_opcode field is invalid, and aio_error() returns
[EINVAL]) or might arise from application behavior (for example, the file descriptor is
closed before the operation is initiated, and aio_error() returns [EBADF]).
The limitation on the set of error codes returned when operations from the list shall have
been initiated enables applications to know when operations have been started and whether
aio_error() is valid for a specific operation.
FUTURE DIRECTIONS
None.
SEE ALSO
aio_read() , aio_write() , aio_error() , aio_return() , aio_cancel() , close() , exec() ,
exit() , fork() , lseek() , read() , the Base Definitions volume of IEEE Std 1003.1-2001,
<aio.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and The Open Group
Standard, the original IEEE and The Open Group Standard is the referee document. The
original Standard can be obtained online at http://www.opengroup.org/unix/online.html .