The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group

#### NAME

> aio_fsync - asynchronous file synchronization

#### SYNOPSIS

> ``[FSC|SIO] #include <aio.h>
> int aio_fsync(int` op`, struct aiocb *`aiocbp`);``
> `
> `

#### DESCRIPTION

> The aio_fsync() function shall asynchronously perform a file synchronization operation, as specified by the op argument, for I/O operations associated with the file indicated by the file descriptor aio_fildes member of the aiocb structure referenced by the aiocbp argument and queued at the time of the call to aio_fsync(). The function call shall return when the synchronization request has been initiated or queued to the file or device (even when the data cannot be synchronized immediately).

> [SIO] If op is O_DSYNC, all currently queued I/O operations shall be completed as if by a call to fdatasync(); that is, as defined for synchronized I/O data integrity completion.

> [FSC] If op is O_SYNC, all currently queued I/O operations shall be completed as if by a call to fsync(); [FSC SIO] that is, as defined for synchronized I/O file integrity completion. If the aio_fsync() function fails, or if the operation queued by aio_fsync() fails, then outstanding I/O operations are not guaranteed to have been completed.

> If aio_fsync() succeeds, then it is only the I/O that was queued at the time of the call to aio_fsync() that is guaranteed to be forced to the relevant completion state. The completion of subsequent I/O on the file descriptor is not guaranteed to be completed in a synchronized fashion.

> The aiocbp argument refers to an asynchronous I/O control block. The aiocbp value 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. When the request is queued, the error status for the operation is [EINPROGRESS]. When all data has been successfully transferred, the error status shall be reset to reflect the success or failure of the operation. If the operation does not complete successfully, the error status for the operation shall be set to indicate the error. The aio_sigevent member determines the asynchronous notification to occur as specified in Signal Generation and Delivery when all operations have achieved synchronized I/O completion. All other members of the structure referenced by aiocbp are ignored. If the control block referenced by aiocbp becomes an illegal address prior to asynchronous I/O completion, then the behavior is undefined.

> If the aio_fsync() function fails or aiocbp indicates an error condition, data is not guaranteed to have been successfully transferred.

#### RETURN VALUE

> The aio_fsync() function shall return the value 0 if the I/O operation is successfully queued; otherwise, the function shall return the value -1 and set errno to indicate the error.

#### ERRORS

> The aio_fsync() function shall fail if:

> [EAGAIN]
>   The requested asynchronous operation was not queued due to temporary resource limitations.
> [EBADF]
>   The aio_fildes member of the aiocb structure referenced by the aiocbp argument is not a valid file descriptor.
> [EINVAL]
>   [SIO] This implementation does not support synchronized I/O for this file.
> [EINVAL]
>   [FSC] The aio_fildes member of the aiocb structure refers to a file on which an fsync() operation is not possible.
> [EINVAL]
>   A value of op other than O_DSYNC or O_SYNC was specified, or O_DSYNC was specified and the implementation does not provide runtime support for the Synchronized Input and Output option, or O_SYNC was specified and the implementation does not provide runtime support for the File Synchronization option.

> In the event that any of the queued I/O operations fail, aio_fsync() shall return the error condition defined for read() and write(). The error is returned in the error status for the asynchronous operation, which can be retrieved using aio_error().

The following sections are informative.

#### EXAMPLES

> None.

#### APPLICATION USAGE

> Note that even if the file descriptor is not open for writing, if there are any pending write requests on the underlying file, then that I/O will be completed prior to the return of a call to aio_error() or aio_return() indicating that the operation has completed.

#### RATIONALE

> None.

#### FUTURE DIRECTIONS

> None.

#### SEE ALSO

> aio_error, aio_return, fcntl, fdatasync, fsync, open, read, write

> XBD <aio.h>

#### CHANGE HISTORY

> First released in Issue 5. Included for alignment with the POSIX Realtime Extension.

#### Issue 6

> The [ENOSYS] error condition has been removed as stubs need not be provided if an implementation does not support the Asynchronous Input and Output option.

> The APPLICATION USAGE section is added.

> IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/11 is applied, removing the words ``to the calling process'' in the RETURN VALUE section. The term was unnecessary and precluded threads.

#### Issue 7

> The aio_fsync() function is moved from the Asynchronous Input and Output option to the Base.

> POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0026 [98] and XSH/TC1-2008/0027 [98] are applied.

> POSIX.1-2008, Technical Corrigendum 2, XSH/TC2-2008/0045 [671] is applied.

End of informative text.

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