smbd: Don't always walk the share mode array in open_mode_check()

smbd: Don't always walk the share mode array in open_mode_check()

share_mode_data->flags contains the "most restrictive" share mode of
the whole array. This is maintained lazily: Whenever set_share_mode()
is called, d->flags is updated if the new share mode got more
restrictive. It is not updated when a file is closed, as this would
mean we would have to walk the whole array, making sure that the
closed handle was indeed the only most restrictive one. Instead, we
walk the share mode array only when a conflict happens: Then we need
to know "the truth" and recalculate it by walking the share mode
array.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Wed Sep 18 00:07:13 UTC 2019 on sn-devel-184