add slab test code

Makefile

@@ -40,3 +40,9 @@ vexpress_ca9x4:busybox vexpress_kernel
 samples:
 	make -C samples/compile-module
 	make -C samples/slab
+	-mkdir $(KBUILD_OUTPUT_BUSYBOX) -p
+	-rm -rf $(KBUILD_OUTPUT_BUSYBOX)/_install
+	make -C $(KBUILD_OUTPUT_BUSYBOX) install
+	find $(CURDIR)/build/samples -name "*.ko" | xargs cp -v -t $(KBUILD_OUTPUT_BUSYBOX)/_install
+	fakeroot ./make-rootfs.sh $(KBUILD_OUTPUT_BUSYBOX) $(CURDIR)/busybox-1.28.0
+

samples/slab/samples-slab.c

@@ -1,18 +1,57 @@
 #include <linux/init.h>
 #include <linux/module.h>
+#include <linux/slab.h>
+
 MODULE_LICENSE("Dual BSD/GPL");
-static int hello_init(void)
+
+struct kmem_cache *test_cache = NULL;
+#define TEST_CACHE_SIZE 128
+char *str[16] = {0};
+
+void slab_ctor(void *data)
+{
+	static int index = 0;
+	char *str = data;
+	memset(str, 0, TEST_CACHE_SIZE);
+	printk(KERN_ERR "slab actor, index=%d\n", index);
+	sprintf(str, "Hello, this is a cache entry, index = %d", index++);
+	return;
+}
+
+static __init int slab_init(void)
 {
-	printk(KERN_ALERT "Hello World enter\n");
+	test_cache = kmem_cache_create("test cache", TEST_CACHE_SIZE, 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, slab_ctor);
+	if (!test_cache)
+	{
+		printk(KERN_ERR "fail to create slab cache\n");
+		return 0;
+	}
+	printk (KERN_ERR "before kmem_cache_alloc\n");
+	str[0] = kmem_cache_alloc(test_cache, GFP_KERNEL); /* 首次分配时，会预分配出多个，目前测试的情况为21个 */
+	printk(KERN_ERR "after kmem_cache_alloc\n");
+	printk(KERN_ERR "str: %s\n", str[0]);
+
+	printk (KERN_ERR "before kmem_cache_alloc\n");
+	str[1] = kmem_cache_alloc(test_cache, GFP_KERNEL);
+	printk(KERN_ERR "after kmem_cache_alloc\n");
+	printk(KERN_ERR "str: %s\n", str[1]);
     return 0;
 }
-static void hello_exit(void)
+
+static __exit void slab_exit(void)
 {
-	printk(KERN_ALERT "Hello World exit\n");
+	/* kmem_cache_destroy can handle NULL pointer, no need to validate the param*/
+	kmem_cache_destroy(NULL);
+	/* before destroy kmem cache, the cache will be destroyed must has no allocated entries,
+     * or you will get a stack dump, and fail to destroy */
+	kmem_cache_free(test_cache, str[0]);
+	kmem_cache_free(test_cache, str[1]);
+	kmem_cache_destroy(test_cache);
+	printk(KERN_ERR "slab exit\n");
 }
 
-module_init(hello_init);
-module_exit(hello_exit);
+module_init(slab_init);
+module_exit(slab_exit);
 MODULE_AUTHOR("redstar");
-MODULE_DESCRIPTION("A Sample Hello World Module");
+MODULE_DESCRIPTION("Slab test module");
 MODULE_ALIAS("A Sample module");