man pages section 3: Basic Library Functions

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Updated: July 2014
 
 

aio_write(3C)

Name

aio_write - asynchronous write to a file

Synopsis

#include <aio.h>

int aio_write(struct aiocb *aiocbp);

Description

The aio_write() function allows the calling process to write aiocbp→aio_nbytes to the file associated with aiocbp→aio_fildes from the buffer pointed to by aiocbp→ aio_buf. The function call returns when the write request has been initiated or, at a minimum, queued to the file or device. 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 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.

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.

If O_APPEND is not set for the file descriptor aio_fildes, then 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. If O_APPEND is set for the file descriptor, write operations append to the file in the same order as the calls were made. 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).

If SIGEV_MEM sigevent type is specified, the error and return values are updated in the aiocb_t structure when I/O is completed. Applications can get the error value using aio_error(3C) and the return value using aio_return(3C). For SIGEV_MEM sigevent type requests, aio_error(3C) and aio_return(3C) simply return the error and return values from the structure, no system calls are involved. While the I/O is in progress an EINPROGRESS error is returned. I/O completion can be detected by monitoring the error value returned by aio_error(3C).

The aiocbp→aio_lio_opcode field is ignored by aio_write().

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 shall be 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_write() 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_write() 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_write(), or asynchronously. If any of the conditions below are detected synchronously, the aio_write() 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 writing.

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_write() successfully queues the I/O operation, the return status of the asynchronous operation will be one of the values normally returned by the write (2) function call. If the operation is successfully queued but is subsequently canceled or encounters an error, the error status for the asynchronous operation contains 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(3C) request.

The following condition may be detected synchronously or asynchronously:

EFBIG

The file is a regular file, aiobcp→aio_nbytes is greater than 0 and the starting offset in aiobcp→aio_offset is at or beyond the offset maximum in the open file description associated with aiocbp→aio_fildes.

Usage

The aio_write() 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 Also

aio_cancel(3C), aio_error(3C), aio_read(3C), aio_return(3C), lio_listio(3C), close(2) , _Exit(2), fork(2) , lseek(2), write(2) , aio.h(3HEAD), signal.h(3HEAD) , attributes(5), lf64(5) , standards(5)