理解kobeject

container_of 例子

#include<stdio.h>
#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
#define container_of(ptr, type, member) ({                    \
        const typeof(((type *)0)->member)*__mptr = (ptr);    \
        (type *)((char *)__mptr - offsetof(type, member)); })
struct Test{
      char i;
      int j;
      char k;
};

void main()
{
      struct Test test;
      test.i=7;
      test.j=10;
      test.k=12;
      char *p=&(test.k);//假设只知道test.k的地址
      struct Test *q=container_of(p,struct Test,k);
      printf("q->j=%d\n",q->j);                
 
}

运算结果

q->j=10

这下记忆就深刻了。

Documentation/kref.txt 有很好说明，当没有引用的时候就free.

obj-m := test.o

KERNEL := /lib/modules/`uname -r`/build

all:
        make -C $(KERNEL) M=`pwd` modules
install:
        make -C $(KERNEL) M=`pwd` modules_install
        depmod -A
clean:
        make -C $(KERNEL) M=`pwd` clean
        rm -f Module.*

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/kthread.h>
struct my_data{
        struct kref refcount;
};
void data_release(struct kref *ref)
{
        struct my_data *data = container_of(ref, struct my_data, refcount);
        printk(KERN_INFO "free my data\n");
        kfree(data);

}
int more_data_handling(void *cb_data)
{
        struct my_data *data = cb_data;
        printk(KERN_INFO "more_data_handling.\n");
        kref_put(&data->refcount, data_release);
        return 0;
}
int my_data_handler(void)
{
        int rv = 0;
        struct my_data *data;
        struct task_struct *task;
        data = kmalloc(sizeof(*data), GFP_KERNEL);
        if (!data)
                return -ENOMEM;
        kref_init(&data->refcount);

        kref_get(&data->refcount);
        task = kthread_run(more_data_handling, data, "more_data_handling");
        if (task == ERR_PTR(-ENOMEM)) {
                rv = -ENOMEM;
                    goto out;
        }
 out:
        kref_put(&data->refcount, data_release);
        return rv;
}
int  __init tst_start(void)
{
     int ret;
        printk(KERN_INFO "START\n");
       ret = my_data_handler();
        return 0;
}
static void __exit tst_end(void)
{
    printk(KERN_INFO "From tst module: Goodbye, Tony.\n");
}
module_init(tst_start);
module_exit(tst_end);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("xiayu");