[PATCH v4 v4 1/2] Union-Find: add a new module in kernel library

[Xavier <xavier_qy@163.com>]

This patch implements a union-find data structure in the kernel library,
which includes operations for allocating nodes, freeing nodes,
finding the root of a node, and merging two nodes.

Signed-off-by: Xavier <xavier_qy@163.com>
---
 MAINTAINERS                |  7 +++++++
 include/linux/union_find.h | 30 ++++++++++++++++++++++++++++++
 lib/Makefile               |  2 +-
 lib/union_find.c           | 38 ++++++++++++++++++++++++++++++++++++++
 4 files changed, 76 insertions(+), 1 deletion(-)
 create mode 100644 include/linux/union_find.h
 create mode 100644 lib/union_find.c

diff --git a/MAINTAINERS b/MAINTAINERS
index d6c90161c7..602d8c6f42 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -23054,6 +23054,13 @@ F:	drivers/cdrom/cdrom.c
 F:	include/linux/cdrom.h
 F:	include/uapi/linux/cdrom.h
 
+UNION-FIND
+M:	Xavier <xavier_qy@163.com>
+L:	linux-kernel@vger.kernel.org
+S:	Maintained
+F:	include/linux/union_find.h
+F:	lib/union_find.c
+
 UNIVERSAL FLASH STORAGE HOST CONTROLLER DRIVER
 R:	Alim Akhtar <alim.akhtar@samsung.com>
 R:	Avri Altman <avri.altman@wdc.com>
diff --git a/include/linux/union_find.h b/include/linux/union_find.h
new file mode 100644
index 0000000000..67e9f62bb3
--- /dev/null
+++ b/include/linux/union_find.h
@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_UNION_FIND_H
+#define __LINUX_UNION_FIND_H
+#include <linux/slab.h>
+
+/* Define a union-find node struct */
+struct uf_node {
+	struct uf_node *parent;
+	unsigned int rank;
+};
+
+/* Allocate nodes and initialize to 0 */
+static inline struct uf_node *uf_nodes_alloc(unsigned int node_num)
+{
+	return kzalloc(sizeof(struct uf_node) * node_num, GFP_KERNEL);
+}
+
+/* Free nodes*/
+static inline void uf_nodes_free(struct uf_node *nodes)
+{
+	kfree(nodes);
+}
+
+/* find the root of a node*/
+struct uf_node *uf_find(struct uf_node *node);
+
+/* Merge two intersecting nodes */
+void uf_union(struct uf_node *node1, struct uf_node *node2);
+
+#endif /*__LINUX_UNION_FIND_H*/
diff --git a/lib/Makefile b/lib/Makefile
index 3b17690456..e1769e6f03 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -34,7 +34,7 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
 	 is_single_threaded.o plist.o decompress.o kobject_uevent.o \
 	 earlycpio.o seq_buf.o siphash.o dec_and_lock.o \
 	 nmi_backtrace.o win_minmax.o memcat_p.o \
-	 buildid.o objpool.o
+	 buildid.o objpool.o union_find.o
 
 lib-$(CONFIG_PRINTK) += dump_stack.o
 lib-$(CONFIG_SMP) += cpumask.o
diff --git a/lib/union_find.c b/lib/union_find.c
new file mode 100644
index 0000000000..2f77bae1ca
--- /dev/null
+++ b/lib/union_find.c
@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/union_find.h>
+
+struct uf_node *uf_find(struct uf_node *node)
+{
+	struct uf_node *parent;
+
+	if (!node->parent) {
+		node->parent = node;
+		return node;
+	}
+
+	/*Find the root node and perform path compression at the same time*/
+	while (node->parent != node) {
+		parent = node->parent;
+		node->parent = parent->parent;
+		node = parent;
+	}
+	return node;
+}
+
+/*Function to merge two sets, using union by rank*/
+void uf_union(struct uf_node *node1, struct uf_node *node2)
+{
+	struct uf_node *root1 = uf_find(node1);
+	struct uf_node *root2 = uf_find(node2);
+
+	if (root1 != root2) {
+		if (root1->rank < root2->rank) {
+			root1->parent = root2;
+		} else if (root1->rank > root2->rank) {
+			root2->parent = root1;
+		} else {
+			root2->parent = root1;
+			root1->rank++;
+		}
+	}
+}
-- 
2.45.2