int ntfs_sync_mft_mirror_umount (ntfs_volume * vol, const unsigned long mft_no, MFT_RECORD * m);
Write the mapped, mst protected (extent) mft record m with mft record number mft_no to the mft mirror ($MFTMirr) of the ntfs volume vol, bypassing the page cache and the $MFTMirr inode itself.
This function is only for use at umount time when the mft mirror inode has already been disposed off. We BUG if we are called while the mft mirror inode is still attached to the volume.
On success return 0. On error return -errno.
This function is not implemented yet as I am not convinced it can actually be triggered considering the sequence of commits we do in super.c:: ntfs_put_super. But just in case we provide this place holder as the alternative would be either to BUG or to get a NULL pointer dereference and Oops.