aio_write

Date:: 10-20-2011

NAME

aio_write - Asynchronous I/O write

SYNOPSIS

#include <aio.h>

int aio_write(aiocb_t *aiocbp);

DESCRIPTION

The aio_write function allows the calling process to write aiocbp->aio_nbytes to the file associated with aiocbp->aio_fildes, at the file offset aiocbp->aio_offset, into the buffer pointed to by aiocbp->aio_buf (see the write man page). The function call returns when the write request has been initiated or, at a minimum, queued for the file or device.

The aiocb->aio_sigevent defines how the calling process will be notified upon I/O completion.

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), 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) 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.

All aio_write calls must supply a complete aiocb->aio_sigevent structure.

The aiocbp->aio_lio_opcode field is ignored by aio_write.

Prioritized I/O is not currently supported among asynchronous file operations. aiocbp->aio_reqprio will be ignored.

The I/O requests will be 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 were submitted.

After a call to aio_write the aiocbp may be used as an argument to aio_error and aio_return 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 queueing, the function call returns without having initiated or queued the request. After a successful call to enqueue an asynchronous I/O operation, the value of the file offset for the file is undefined.

If the buffer pointed to by aiocbp->aio_buf or the control block pointed to by aiocbp changes or 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.

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 asynchronous I/O is undefined.

RETURN VALUES

The aio_write returns the value 0 to the calling process if the I/O operation is successfully queued; otherwise, the function returns -1 and errno is set to indicate the error.

MESSAGES

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

EAGAIN: The requested asynchronous I/O operation was not queued due to library or system resource limitations. This is due to exceeding the maximum number of outstanding asynchronous I/O operations for the library or system. The library limit can be increased with aio_init. The system maximum can be checked with a call to sysconf with an argument of _SC_AIO_MAX.
EBADF: The aiocbp->aio_fildes argument is not a valid file descriptor open for writing.
EINVAL: The file offset value implied by aiocbp->aio_offset would be invalid, sigenv_notify is an invalid value, or aiocbp->aio_nbytes is an invalid value.

In the case that the aio_write successfully queues the I/O operation, the return status of the asynchronous operation shall be one of the values normally returned by the write function call. If the operation is successfully queued, but is subsequently canceled or encounters an error, the error status for the asynchronous operation will contain one of the values normally set by the write function call, or one of the following:

EBADF: The aiocbp->aio_fildes argument is not a valid file descriptor open for writing.
EINVAL: The file offset value implied by aiocbp->aio_offset would be invalid.
ECANCELED: The requested I/O was canceled before the I/O completed due to an explicit aio_cancel request.