+ * Active references for perag structures. This is for short term access to the
+ * per ag structures for walking trees or accessing state. If an AG is being
+ * shrunk or is offline, then this will fail to find that AG and return NULL
+ * instead.
+ */
+struct xfs_perag *
+xfs_perag_grab(
+ struct xfs_mount *mp,
+ xfs_agnumber_t agno)
+{
+ struct xfs_perag *pag;
+
+ rcu_read_lock();
+ pag = radix_tree_lookup(&mp->m_perag_tree, agno);
+ if (pag) {
+ trace_xfs_perag_grab(mp, pag->pag_agno,
+ atomic_read(&pag->pag_active_ref), _RET_IP_);
+ if (!atomic_inc_not_zero(&pag->pag_active_ref))
+ pag = NULL;
+ }
+ rcu_read_unlock();
+ return pag;
+}
+
+/*
+ * search from @first to find the next perag with the given tag set.
+ */
+struct xfs_perag *
+xfs_perag_grab_tag(
+ struct xfs_mount *mp,
+ xfs_agnumber_t first,
+ int tag)
+{
+ struct xfs_perag *pag;
+ int found;
+
+ rcu_read_lock();
+ found = radix_tree_gang_lookup_tag(&mp->m_perag_tree,
+ (void **)&pag, first, 1, tag);
+ if (found <= 0) {
+ rcu_read_unlock();
+ return NULL;
+ }
+ trace_xfs_perag_grab_tag(mp, pag->pag_agno,
+ atomic_read(&pag->pag_active_ref), _RET_IP_);
+ if (!atomic_inc_not_zero(&pag->pag_active_ref))
+ pag = NULL;
+ rcu_read_unlock();
+ return pag;
+}
+
+void
+xfs_perag_rele(
+ struct xfs_perag *pag)
+{
+ trace_xfs_perag_rele(pag->pag_mount, pag->pag_agno,
+ atomic_read(&pag->pag_active_ref), _RET_IP_);
+ if (atomic_dec_and_test(&pag->pag_active_ref))
+ wake_up(&pag->pag_active_wq);
+}
+
+/*