int ntfs_rl_truncate_nolock (const ntfs_volume * vol, runlist *const runlist, const s64 new_length);
Truncate the runlist described by runlist as well as the memory buffer holding the runlist elements to a length of new_length VCNs.
If new_length lies within the runlist, the runlist elements with VCNs of new_length and above are discarded.
If new_length lies beyond the runlist, a sparse runlist element is added to the end of the runlist runlist or if the last runlist element is a sparse one already, this is extended.
Return 0 on success and -errno on error.
The caller must hold runlist->lock for writing.