lio_listio

Date:: 10-20-2011

NAME

lio_listio - Linked asynchronous I/O operations

SYNOPSIS

#include <aio.h>

int lio_listio(int mode, aiocb_t * const list[], int nent, sigevent_t *sig);

IMPLEMENTATION

Cray Linux Environment (CLE)

DESCRIPTION

The lio_listio function allows the calling process to initiate a list of I/O requests with a single function call.

The mode argument takes a value of either LIO_WAIT or LIO_NOWAIT 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 waits until all I/O is complete and the sig argument is ignored.

If the mode argument is LIO_NOWAIT, the function returns immediately, and signal delivery shall occur, according to the sig argument, when all the I/O operations complete. If sig is NULL, then no signal delivery occurs at the completion of all the items in the list, however notifications for each item in the list will happen according to their aiocb->aio_sigevent structures. If sig is not NULL then notification will happen according to sig->sigev_notify when all items in the list have completed their I/O operations.

If sigev_notify is SIGEV_NONE, then no notification will be posted to the calling application.

If sigev_notify is SIGEV_SIGNAL, then the signal specified in sigev_signo will be sent to the calling process. If SA_SIGINFO is set for the signal (see sigaction(2)) and the signal is in the range of SIGRTMIN and SIGRTMAX then the signal will be queued to the process and the value in sigev_value will be the si_value in the generated signal.

(Deferred implementation) If sigev_notify is SIGEV_CALLBACK then the function sigev_func will be called with sigev_value as the argument. Only one callback will be called at a time, however programs should be careful to note that a callback may be run in parallel with the calling process.

(Deferred implementation) If sigev_notify is SIGEV_THREAD then the function sigev_notify_function will be called by a new thread (see pthreads(3p)) with sigev_value as the argument. This thread is created when the event arrives with the attributes specified in sigev_notify_attributes except that it is automatically detached. The calling process should ensure there are sufficient resources to create the thread.

The list argument is a pointer to an array of pointers to aiocb structures. The array contains nent elements.

The I/O requests enumerated by list are submitted in an unspecified order unless the file was opened with the O_APPEND in which case the write operations will happen in the order that they appear in the list.

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. The LIO_NOP operation causes that 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.

RETURN VALUES

If the mode argument has the value LIO_NOWAIT, the lio_listio() function returns the value 0 to the calling process 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 returns the value 0 to the calling process when all the indicated I/O has completed successfully. Otherwise, lio_listio() returns -1 to the calling process, and sets 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 returned are identical to those returned as the result of an aio_read(3) or aio_write() function.

MESSAGES

If any of the following conditions occur, the lio_listio() function returns -1 and sets errno to the corresponding value:

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. 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 a 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. It is not possible to receive this error return when the mode argument to the lio_listio() request was LIO_NOWAIT.

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 ERIO, then some of the I/O operations specified by the list may 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 which can be set are the same as would be set by a read(2) or write(2) function, with the following error codes possible:

EAGAIN: The requested asynchronous I/O operation was not queued due to system resource limitations.
ECANCELED: The requested I/O was canceled before the I/O completed due to an explicit aio_cancel()request.
EINPROGRESS: The requested I/O is in progress.