The current API for byte-range locks [glfs_posix_lock()] doesn't allow applications to specify whether it is advisory or mandatory type locks. This particular change is to introduce an extended byte-range lock API with an additional argument for including the byte-range lock mode to be one among advisory(default) or mandatory. Patch also includes a gfapi test case which make use of this new api to acquire mandatory locks. Ref: https://github.com/gluster/glusterfs-specs/blob/master/done/GlusterFS%203.8/Mandatory%20Locks.md Change-Id: Ia09042c755d891895d96da857321abc4ce03e20c Updates #393 Signed-off-by: Anoop C S <anoopcs@redhat.com>