Lesson 4: Add dynamic memory allocation to ”xxx” driver

lesson-04-memory-management/mm/Makefile

@@ -8,7 +8,16 @@ obj-m += xxx.o
 
 else
 
-KERNELDIR := $(BUILD_KERNEL)
+ifeq ($(KERNELDIR),)
+ifeq ($(BBB_KERNEL),)
+	$(error Path to kernel tree - KERNELDIR or BBB_KERNEL variable is not defined!)
+endif
+endif
+
+KERNELDIR ?= $(BBB_KERNEL)
+
+export ARCH ?= arm
+export CROSS_COMPILE ?= arm-linux-gnueabihf-
 
 .PHONY: all clean
 all:

lesson-04-memory-management/mm/xxx.c

@@ -5,25 +5,136 @@
 #include <linux/pci.h>
 #include <linux/version.h>
 #include <linux/init.h>
+#include <linux/slab.h>
 
-#define LEN_MSG 160
-static char buf_msg[LEN_MSG + 1] = "Hello from module!\n";
+#define MEM_TYPE_KMALLOC	0
+#define MEM_TYPE_KCACHE 	1
+#define MEM_TYPE_KVMALLOC	2
+
+#define BUFFER_SIZE			160
+
+static size_t	buf_size = 0;
+static char 	*pbuf_msg = 0;
+static int  	mem_type = MEM_TYPE_KMALLOC;
+struct KCACHE_STRUCT {
+	char buf[BUFFER_SIZE];
+};
+
+static struct kmem_cache* pmem_cache = NULL;
+
+const char* get_mem_type(int type)
+{
+	switch (type) {
+		case MEM_TYPE_KMALLOC:
+			return "MEM_TYPE_KMALLOC";
+		case MEM_TYPE_KCACHE:
+			return "MEM_TYPE_KCACHE";
+		case MEM_TYPE_KVMALLOC:
+			return "MEM_TYPE_KVMALLOC";
+	}
+	return "UNKNOWN";
+}
+
+static void* mem_alloc(int type, size_t size)
+{
+	void* buf = NULL;
+	switch (type) {
+		case MEM_TYPE_KMALLOC:
+			buf = kmalloc(size, GFP_KERNEL);
+			break;
+		case MEM_TYPE_KCACHE:
+			buf = kmem_cache_alloc( pmem_cache, GFP_KERNEL );
+			break;
+		case MEM_TYPE_KVMALLOC:
+			buf = vmalloc(size);
+			break;
+	}
+
+	if (buf) buf_size = size;
+
+	pr_info("[%s:%s] {%s} %zu bytes --> %p\n", THIS_MODULE->name, __FUNCTION__, get_mem_type(type), size, buf);
+	return buf;
+}
+
+static void mem_free(int type, void* buf)
+{
+	if (!buf) {
+		pr_warning("[%s:%s] Wrong parameter %p\n", THIS_MODULE->name, __FUNCTION__, buf);
+		return;
+	}
+	switch (type) {
+		case MEM_TYPE_KMALLOC:
+			kfree(buf);
+			break;
+		case MEM_TYPE_KCACHE:
+			kmem_cache_free( pmem_cache, buf );
+			buf = kmem_cache_alloc( pmem_cache, GFP_KERNEL );
+			break;
+		case MEM_TYPE_KVMALLOC:
+			vfree(buf);
+			break;
+	}
+	pr_info("[%s:%s] {%s} bytes --> %p\n", THIS_MODULE->name, __FUNCTION__, get_mem_type(type), buf);
+}
+
+void init_kcache(void) 
+{
+	if (mem_type != MEM_TYPE_KCACHE) return;
+/*
+ * 140 * Please use this macro to create slab caches. Simply specify the
+ * 141 * name of the structure and maybe some flags that are listed above.
+ * 142 *
+ * 143 * The alignment of the struct determines object alignment. If you
+ * 144 * f.e. add ____cacheline_aligned_in_smp to the struct declaration
+ * 145 * then the objects will be properly aligned in SMP configurations.
+ * 146
+ * #define KMEM_CACHE(__struct, __flags) kmem_cache_create(#__struct,\
+ * 148  sizeof(struct __struct), __alignof__(struct __struct),\
+ * 149  (__flags), NULL)
+ */
+	pmem_cache = KMEM_CACHE(KCACHE_STRUCT, 0);
+	pr_info("[%s:%s] pmem_cache: %p\n", THIS_MODULE->name, __FUNCTION__, pmem_cache);
+}
+
+void deinit_kcache(void)
+{
+	if (mem_type != MEM_TYPE_KCACHE) {
+		mem_free(mem_type, pbuf_msg);
+		return;
+	}
+	kmem_cache_destroy( pmem_cache );
+}
 
 
 static ssize_t xxx_show(struct class *class, struct class_attribute *attr,
 						char *buf)
 {
-	strcpy(buf, buf_msg);
-	pr_info("read %ld\n", (long)strlen(buf));
-	return strlen(buf);
+	if (!pbuf_msg) {
+		printk( "[%s:%s] nothing to read\n", THIS_MODULE->name, __FUNCTION__);
+		return 0; 
+	}
+	strcpy( buf, pbuf_msg );
+	pr_info( "[%s:%s] read %ld\n", THIS_MODULE->name, __FUNCTION__, (long)strlen( buf ) );
+	return strlen( buf );
 }
 
 static ssize_t xxx_store(struct class *class, struct class_attribute *attr,
 						 const char *buf, size_t count)
 {
-	pr_info("write %ld\n", (long)count);
-	strncpy(buf_msg, buf, count);
-	buf_msg[count] = '\0';
+	if (!pbuf_msg) {
+		pbuf_msg = mem_alloc(mem_type, BUFFER_SIZE);
+		if (!pbuf_msg) {
+		   pr_err( "[%s:%s] Wrong alloc buffer! \n", THIS_MODULE->name, __FUNCTION__);
+		   return 0;
+		}
+	}
+	if (count >= BUFFER_SIZE) {
+		pr_err( "[%s:%s]  Wrong buffer size %lu\n", THIS_MODULE->name, __FUNCTION__, (long)count );
+		return 0;
+	}
+	pr_info( "[%s:%s] write %ld\n", THIS_MODULE->name, __FUNCTION__, (long)count );
+	strncpy( pbuf_msg, buf, count );
+	pbuf_msg[ count ] = '\0';
 	return count;
 }
 
@@ -35,20 +146,37 @@ int __init x_init(void)
 {
 	int res;
 
+   pr_info("mem_type is %d\n", mem_type);
 	x_class = class_create(THIS_MODULE, "x-class");
 	if (IS_ERR(x_class))
 		pr_info("bad class create\n");
 	res = class_create_file(x_class, &class_attr_xxx);
 	pr_info("'xxx' module initialized\n");
+	init_kcache();
 	return res;
 }
 
 void x_cleanup(void)
 {
 	class_remove_file(x_class, &class_attr_xxx);
 	class_destroy(x_class);
+	deinit_kcache();
 }
 
+/**
+ * 137 * module_param_named - typesafe helper for a renamed module/cmdline parameter
+ * 138 * @name: a valid C identifier which is the parameter name.
+ * 139 * @value: the actual lvalue to alter.
+ * 140 * @type: the type of the parameter
+ * 141 * @perm: visibility in sysfs.
+ * 142 *
+ * 143 * Usually it's a good idea to have variable names and user-exposed names the
+ * 144 * same, but that's harder if the variable must be non-static or is inside a
+ * 145 * structure.  This allows exposure under a different name.
+ * 146 */
+module_param( mem_type, int, 0444 );
+MODULE_PARM_DESC(mem_type, "Type of memory allocation: 0 - kmalloc; 1 - cache; 2 - vmalloc");
+
 module_init(x_init);
 module_exit(x_cleanup);