[PATCH v5 2/3] sched/topology: Introduce for_each_numa_hop_mask()

[Valentin Schneider <vschneid@redhat.com>]

The recently introduced sched_numa_hop_mask() exposes cpumasks of CPUs
reachable within a given distance budget, wrap the logic for iterating over
all (distance, mask) values inside an iterator macro.

Signed-off-by: Valentin Schneider <vschneid@redhat.com>
---
 include/linux/topology.h | 30 +++++++++++++++++++++++++-----
 1 file changed, 25 insertions(+), 5 deletions(-)

diff --git a/include/linux/topology.h b/include/linux/topology.h
index 3e91ae6d0ad58..8185e12ec1ccc 100644
--- a/include/linux/topology.h
+++ b/include/linux/topology.h
@@ -246,16 +246,36 @@ static inline const struct cpumask *cpu_cpu_mask(int cpu)
 }
 
 #ifdef CONFIG_NUMA
-extern const struct cpumask *sched_numa_hop_mask(int node, int hops);
+extern const struct cpumask *sched_numa_hop_mask(unsigned int node, unsigned int hops);
 #else
-static inline const struct cpumask *sched_numa_hop_mask(int node, int hops)
+static inline const struct cpumask *
+sched_numa_hop_mask(unsigned int node, unsigned int hops)
 {
-	if (node == NUMA_NO_NODE && !hops)
-		return cpu_online_mask;
-
 	return ERR_PTR(-EOPNOTSUPP);
 }
 #endif	/* CONFIG_NUMA */
 
+/**
+ * for_each_numa_hop_mask - iterate over cpumasks of increasing NUMA distance
+ *                          from a given node.
+ * @mask: the iteration variable.
+ * @node: the NUMA node to start the search from.
+ *
+ * Requires rcu_lock to be held.
+ *
+ * Yields cpu_online_mask for @node == NUMA_NO_NODE.
+ */
+#define for_each_numa_hop_mask(mask, node)				     \
+	for (unsigned int __hops = 0;					     \
+	     /*								     \
+	      * Unsightly trickery required as we can't both initialize	     \
+	      * @mask and declare __hops in for()'s first clause	     \
+	      */							     \
+	     mask = __hops > 0 ? mask :					     \
+		    node == NUMA_NO_NODE ?				     \
+		    cpu_online_mask : sched_numa_hop_mask(node, 0),	     \
+	     !IS_ERR_OR_NULL(mask);					     \
+	     __hops++,							     \
+	     mask = sched_numa_hop_mask(node, __hops))
 
 #endif /* _LINUX_TOPOLOGY_H */
-- 
2.31.1