Where is the fsync_fd() function defined?

[nagalenoj]

Dear monks,

I've downloaded File::Sync from CPAN. I found the below line of code in Sync.pm and I don't understand, how this function is working

# Interface from Perl filehandle to POSIX file descriptor.
sub fsync(*) {
    @_ == 1 or croak "usage: fsync FILEHANDLE";

    fsync_fd(fileno(qualify_to_ref($_[0], caller())));
}

# Make fsync a method of IO::Handle and FileHandle.
*IO::Handle::fsync = *FileHandle::fsync = \&fsync;

I don't know where the fsync_fd function is defined? Can someone clarify me.

[marto]

The docs state:

"The fsync_fd() function is used internally by fsync(); it takes a file descriptor as its only argument."

If you'd like to look at fsync_fd() see Sync.xs.

Update: Fixed typo: s/fsync_df/fsync_fd/ Thanks kennethk for pointing this out.