dm: do not forward ioctls from logical volumes to the underlying device

A logical volume can map to just part of underlying physical volume.
In this case, it must be treated like a partition.

Based on a patch from Alasdair G Kergon.

Cc: Alasdair G Kergon <agk@redhat.com>
Cc: dm-devel@redhat.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
static void __choose_pgpath(struct multipath *m, size_t nr_bytes)
{
	struct priority_group *pg;
	unsigned bypassed = 1;

	if (!m->nr_valid_paths)
		goto failed;

	/* Were we instructed to switch PG? */
	if (m->next_pg) {
		pg = m->next_pg;
		m->next_pg = NULL;
		if (!__choose_path_in_pg(m, pg, nr_bytes))
			return;
	}

	/* Don't change PG until it has no remaining paths */
	if (m->current_pg && !__choose_path_in_pg(m, m->current_pg, nr_bytes))
		return;

	/*
	 * Loop through priority groups until we find a valid path.
	 * First time we skip PGs marked 'bypassed'.
	 * Second time we only try the ones we skipped.
	 */
	do {
		list_for_each_entry(pg, &m->priority_groups, list) {
			if (pg->bypassed == bypassed)
				continue;
			if (!__choose_path_in_pg(m, pg, nr_bytes))
				return;
		}
	} while (bypassed--);

failed:
	m->current_pgpath = NULL;
	m->current_pg = NULL;
}

static void __choose_pgpath(struct multipath *m, size_t nr_bytes)
{
	struct priority_group *pg;
	unsigned bypassed = 1;

	if (!m->nr_valid_paths)
		goto failed;

	/* Were we instructed to switch PG? */
	if (m->next_pg) {
		pg = m->next_pg;
		m->next_pg = NULL;
		if (!__choose_path_in_pg(m, pg, nr_bytes))
			return;
	}

	/* Don't change PG until it has no remaining paths */
	if (m->current_pg && !__choose_path_in_pg(m, m->current_pg, nr_bytes))
		return;

	/*
	 * Loop through priority groups until we find a valid path.
	 * First time we skip PGs marked 'bypassed'.
	 * Second time we only try the ones we skipped.
	 */
	do {
		list_for_each_entry(pg, &m->priority_groups, list) {
			if (pg->bypassed == bypassed)
				continue;
			if (!__choose_path_in_pg(m, pg, nr_bytes))
				return;
		}
	} while (bypassed--);

failed:
	m->current_pgpath = NULL;
	m->current_pg = NULL;
}
