Lustre has a 'squash credentials' concept similar to the "anon_uid"
for nfsd. When accessing a file with squashed credentials, we
need to also drop capabilities.
Linux has cap_drop_fs_set() and cap_drop_nfsd_set(). Rather than
taking a completely different approach, this patch changes lustre
to use this same cap_drop_*_set() approach.
With this change we also drop CAP_MKNOD and CAP_MAC_OVERRIDE
which are probably appropriate, and don't drop
CAP_SYS_ADMIN or CAP_SYS_BOOT which should be irrelevant for
file permission checking
Calling both cap_drop_*_set() seems a bit clumsy, but gets
the job done.