I will focus on the code implementation to give a detail description. If you like, enjoy it.
#include <linux/module.h>
#include <linux/list.h>
#include <linux/err.h>
#include <linux/slab.h>
/* Create a link list head, its name is container_measurement */
LIST_HEAD(container_measurement);
/* The main data structure that you define to construct a link list */
struct container_entry{
int container_id;
int status;
struct list_head later;
};
/*Create the link list node and add it to the previous link list by "LIST_HEAD()"*/
static struct container_entry *container_entry_create(int container_id, int status)
{
struct container_entry *entry;
entry = kmalloc(sizeof(*entry),GFP_KERNEL);
if(entry == NULL){
pr_err("OUT OF MEMORY ERROR creating container_entry\n");
return -ENOMEM;
}
entry->container_id = container_id;
entry->status = status;
INIT_LIST_HEAD(&entry->later);
list_add(&entry->later,&container_measurement);
return entry;
}
/*Lookup every link list node and find the node you want*/
static struct container_entry *container_entry_lookup(int container_id)
{
struct container_entry *entry_p;
#if 0
list_for_each(p, &container_measurement){
entry_p = list_entry(p, struct container_entry,later);
printk("Current: container_id:%d,status:%d\n", entry_p->container_id, entry_p->status);
}
#endif
list_for_each_entry(entry_p, &container_measurement,later){
printk("Current: container_id:%d,status:%d\n", entry_p->container_id, entry_p->status);
if( entry_p->container_id == container_id ){
printk("Success: %d:status:%d\n", entry_p->container_id, entry_p->status);
return entry_p;
}
}
return NULL;
}
/*Remove the node by its single value*/
int container_entry_del(int container_id)
{
struct container_entry *entry_p;
entry_p = container_entry_lookup(container_id);
if(entry_p == NULL){
printk("There is no container_id: %d\n", container_id);
return -1;
}
list_del(&entry_p->later);
kfree(entry_p);
return 0;
}
/*kernel module init*/
static int __init hello_init(void)
{
struct container_entry *entry;
int id;
id = 200;
entry = container_entry_create(100,0);
entry = container_entry_create(200,1);
container_entry_del(200);
if ( container_entry_lookup(200) == NULL){
printk("Sorry, container:%d does exist\n", id);
}
pr_info("hello\n");
return 0;
}
/*kernel module exit*/
static void __exit hello_exit(void)
{
printk("hello,I am leaving\n");
}
module_init(hello_init);
module_exit(hello_exit);
MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("sam");
