NAME

fdatasync — synchronize the data of a file (REALTIME)

SYNOPSIS

[SIO] #include <unistd.h>

int fdatasync(int fildes);

DESCRIPTION

The fdatasync() function shall force all currently queued I/O operations associated with the file indicated by file descriptor fildes to the synchronized I/O completion state.

The functionality shall be equivalent to fsync() with the symbol _POSIX_SYNCHRONIZED_IO defined, with the exception that all I/O operations shall be completed as defined for synchronized I/O data integrity completion.

RETURN VALUE

If successful, the fdatasync() function shall return the value 0; otherwise, the function shall return the value -1 and set errno to indicate the error. If the fdatasync() function fails, outstanding I/O operations are not guaranteed to have been completed.

ERRORS

The fdatasync() function shall fail if:

[EBADF]

The fildes argument is not a valid file descriptor.

[EINVAL]

This implementation does not support synchronized I/O for this file.

In the event that any of the queued I/O operations fail, fdatasync() shall return the error conditions defined for read() and write().

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 fdatasync().

An application that modifies a directory, for example, by creating a file in the directory, can invoke fdatasync() on the directory to ensure that the directory's entries are synchronized, although for most applications this should not be necessary (see XBD 4.11 File System Cache).

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

aio_fsync, fcntl, fsync, open, read, write

XBD <unistd.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 Synchronized Input and Output option.

The fdatasync() function is marked as part of the Synchronized Input and Output option.

Issue 7

POSIX.1-2008, Technical Corrigendum 2, XSH/TC2-2008/0110 [501] is applied.

Issue 8

Austin Group Defect 672 is applied, changing the APPLICATION USAGE section.