写了个简单的Demo，使用内核提供的接口创建了一个红黑树。
API
// include/linux/rbtree_augmented.h
#define RB_RED 0
#define RB_BLACK 1
// linux-5.4/include/linux/rbtree.h
struct rb_root {
struct rb_node *rb_node;
};
struct rb_node {
unsigned long __rb_parent_color;
struct rb_node *rb_right;
struct rb_node *rb_left;
} __attribute__((aligned(sizeof(long))));
#define RB_ROOT (struct rb_root) { NULL, }
#define rb_parent(r) ((struct rb_node *)((r)->__rb_parent_color & ~3))
#define rb_color(rb) __rb_color((rb)->__rb_parent_color)
#define __rb_color(pc) ((pc) & 1)
#define rb_entry(ptr, type, member) container_of(ptr, type, member)
static inline void rb_link_node(struct rb_node * node, struct rb_node * parent, struct rb_node ** rb_link);
void rb_insert_color(struct rb_node *node, struct rb_root *root);
Demo
code
/*
* Linux kernel rb-tree test
*
* Tested on: Linux 5.4.0-58-generic #64-Ubuntu SMP Wed Dec 9 08:16:25 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
*
* */
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/rbtree.h>
#include <linux/rbtree_augmented.h>
#define BUFF_SIZE 24
struct planet {
char name[BUFF_SIZE];
int mass;
struct rb_node rb_node;
};
struct rb_root planet_rb_root = RB_ROOT;
void insert_planet( struct planet * planet);
void print_planet_tree(struct rb_node *n);
struct planet *create_planet(char * name, int mass);
// 创建一个节点(planet)
struct planet *create_planet(char * name, int mass){
struct planet *new_plt;
if(strlen(name) >= BUFF_SIZE){
pr_info("[-] name too long\n");
return NULL;
}
new_plt = vmalloc(sizeof(struct planet));
strcpy(new_plt->name, name);
new_plt->mass = mass;
pr_info("%s created: %px\n", name, new_plt);
return new_plt;
}
// 插入到红黑树(planet_rb_root)中
void insert_planet( struct planet * planet){
struct rb_node **p = &planet_rb_root.rb_node;
struct rb_node *parent = NULL;
while(*p){
struct planet *tmp_planet;
parent = *p;
tmp_planet = rb_entry(parent, struct planet, rb_node);
if(planet->mass < tmp_planet->mass){
p = &(*p)->rb_left;
}else{
p = &(*p)->rb_right;
}
}
rb_link_node(&planet->rb_node, parent, p);
rb_insert_color(&planet->rb_node, &planet_rb_root);
}
// 遍历红黑树并打印节点信息
void print_planet_tree(struct rb_node *n){
struct planet *planet;
char *p_buff = vmalloc(4096);
char *pos;
if(!n){
return;
}
planet = rb_entry(n, struct planet, rb_node);
pos = p_buff;
pos += sprintf(pos, "<%px> planet start ****************************************\n", planet);
pos += sprintf(pos, "<%px> planet->name: %s(%px)\n", &planet->name, planet->name, planet->name);
pos += sprintf(pos, "<%px> planet->mass: %d\n", &planet->mass, planet->mass);
pos += sprintf(pos, "<%px> planet->rb_node: \n", &planet->rb_node);
pos += sprintf(pos, "<%px> \tplanet->rb_node.__rb_parent_color %lx, rb_parent: %px, rb_color: %s\n",
&planet->rb_node.__rb_parent_color,
planet->rb_node.__rb_parent_color,
rb_parent(&planet->rb_node),
rb_color(&planet->rb_node)? "black": "red");
pos += sprintf(pos, "<%px> \tplanet->rb_node.rb_right %px\n", &planet->rb_node.rb_right, planet->rb_node.rb_right);
pos += sprintf(pos, "<%px> \tplanet->rb_node.rb_left %px\n", &planet->rb_node.rb_left, planet->rb_node.rb_left);
pos += sprintf(pos, "<%px> planet end *****************************************\n\n", planet+1);
pr_info("%s", p_buff);
vfree(p_buff);
if(n->rb_left){
print_planet_tree(n->rb_left);
}
if(n->rb_right){
print_planet_tree(n->rb_right);
}
return;
}
void rbt(void){
struct planet *earth, *mars, *saturn, *venus, *jupiter;
earth = create_planet("Earth", 0);
venus = create_planet("Venus", 1);
saturn = create_planet("Saturn", 3);
mars = create_planet("Mars", 4);
jupiter = create_planet("Jupiter", 7);
insert_planet(earth);
insert_planet(venus);
insert_planet(saturn);
insert_planet(mars);
insert_planet(jupiter);
pr_info("\n<%px> planet_rb_root.rb_node: %px\n\n", &planet_rb_root.rb_node, planet_rb_root.rb_node);
print_planet_tree(planet_rb_root.rb_node);
}
static int __init rbt_init(void)
{
printk(KERN_INFO "Hello rbt\n");
rbt();
return 0;
}
static void __exit rbt_exit(void)
{
printk(KERN_INFO "Goodbye rbt\n");
}
module_init(rbt_init);
module_exit(rbt_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("X++D");
MODULE_DESCRIPTION("Kernel xxx Module.");
MODULE_VERSION("0.1");
output
$ insmod rbt-t.ko
$ rmmod rbt-t.ko
$ dmesg
[1954676.388309] Earth created: ffff9d49c00b5000
[1954676.388311] Venus created: ffff9d49c0213000
[1954676.388314] Saturn created: ffff9d49c0247000
[1954676.388316] Mars created: ffff9d49c0277000
[1954676.388318] Jupiter created: ffff9d49c0279000
[1954676.388319]
<ffffffffc0ed5380> planet_rb_root.rb_node: ffff9d49c0213020
[1954676.388325] <ffff9d49c0213000> planet start ****************************************
<ffff9d49c0213000> planet->name: Venus(ffff9d49c0213000)
<ffff9d49c0213018> planet->mass: 1
<ffff9d49c0213020> planet->rb_node:
<ffff9d49c0213020> planet->rb_node.__rb_parent_color 1, rb_parent: 0000000000000000, rb_color: black
<ffff9d49c0213028> planet->rb_node.rb_right ffff9d49c0277020
<ffff9d49c0213030> planet->rb_node.rb_left ffff9d49c00b5020
<ffff9d49c0213038> planet end *****************************************
[1954676.388330] <ffff9d49c00b5000> planet start ****************************************
<ffff9d49c00b5000> planet->name: Earth(ffff9d49c00b5000)
<ffff9d49c00b5018> planet->mass: 0
<ffff9d49c00b5020> planet->rb_node:
<ffff9d49c00b5020> planet->rb_node.__rb_parent_color ffff9d49c0213021, rb_parent: ffff9d49c0213020, rb_color: black
<ffff9d49c00b5028> planet->rb_node.rb_right 0000000000000000
<ffff9d49c00b5030> planet->rb_node.rb_left 0000000000000000
<ffff9d49c00b5038> planet end *****************************************
[1954676.388335] <ffff9d49c0277000> planet start ****************************************
<ffff9d49c0277000> planet->name: Mars(ffff9d49c0277000)
<ffff9d49c0277018> planet->mass: 4
<ffff9d49c0277020> planet->rb_node:
<ffff9d49c0277020> planet->rb_node.__rb_parent_color ffff9d49c0213021, rb_parent: ffff9d49c0213020, rb_color: black
<ffff9d49c0277028> planet->rb_node.rb_right ffff9d49c0279020
<ffff9d49c0277030> planet->rb_node.rb_left ffff9d49c0247020
<ffff9d49c0277038> planet end *****************************************
[1954676.388340] <ffff9d49c0247000> planet start ****************************************
<ffff9d49c0247000> planet->name: Saturn(ffff9d49c0247000)
<ffff9d49c0247018> planet->mass: 3
<ffff9d49c0247020> planet->rb_node:
<ffff9d49c0247020> planet->rb_node.__rb_parent_color ffff9d49c0277020, rb_parent: ffff9d49c0277020, rb_color: red
<ffff9d49c0247028> planet->rb_node.rb_right 0000000000000000
<ffff9d49c0247030> planet->rb_node.rb_left 0000000000000000
<ffff9d49c0247038> planet end *****************************************
[1954676.388344] <ffff9d49c0279000> planet start ****************************************
<ffff9d49c0279000> planet->name: Jupiter(ffff9d49c0279000)
<ffff9d49c0279018> planet->mass: 7
<ffff9d49c0279020> planet->rb_node:
<ffff9d49c0279020> planet->rb_node.__rb_parent_color ffff9d49c0277020, rb_parent: ffff9d49c0277020, rb_color: red
<ffff9d49c0279028> planet->rb_node.rb_right 0000000000000000
<ffff9d49c0279030> planet->rb_node.rb_left 0000000000000000
<ffff9d49c0279038> planet end *****************************************
visualization
rbt-demo.png
画图工具：https://www.cs.usfca.edu/~galles/visualization/RedBlack.html
说明
比较迷惑的是__rb_parent_color这个点，它是unsigned long类型，同时包含了parent的指针和当前节点的color。
由于struct rb_node是long长度对齐的，也就是说在64位机器上rb_node的内存起始地址都是8的倍数，所以地址的最低4个bit要么是0000要么是 1000，最低3bit是用不上的，而color只有0(red)和1(black) 刚好用parent地址的最低1个bit来保存就行了。
这样就能理解rb_parent和rb_parent这两个宏了。
至于为什么rb_parent用的 __rb_parent_color & ~3而不是~7应该是为了兼容32位系统。但是为什么不是~1呢？
还有，为什么8字节对齐，内存起始地址就是8的倍数，🤔？
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