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 .