idr机制-转载
一.结构体
1.idr结构体
struct idr {struct idr_layer __rcu *top; //idr_layer顶层,32叉树的根
struct idr_layer *id_free; //指向idr_layer的空闲链表
int layers; //idr_layer的层数量int id_free_cnt; //idr_layer空闲链表中剩余的idr_layer个数
spinlock_t lock;
};
2.idr_layer结构体
struct idr_layer {unsigned long bitmap; //标记位图,标记使用情况
struct idr_layer __rcu *ary[1<<IDR_BITS]; //子idr_layer数组ary[32]
int count; //ary数组使用情况
int layer; //层号
struct rcu_head rcu_head;
};
在32位系统中IDR_BITS的取值为5
#if BITS_PER_LONG == 32
# define IDR_BITS 5
# define IDR_FULL 0xfffffffful
# define TOP_LEVEL_FULL (IDR_FULL >> 30)
#elif BITS_PER_LONG == 64
# define IDR_BITS 6
# define IDR_FULL 0xfffffffffffffffful
# define TOP_LEVEL_FULL (IDR_FULL >> 62)
#else
# error "BITS_PER_LONG is not 32 or 64"
#endif
二.idr的初始化
#define IDR_INIT(name) \{ \
.top = NULL, \
.id_free = NULL, \
.layers = 0, \
.id_free_cnt = 0, \
.lock = __SPIN_LOCK_UNLOCKED(name.lock), \
}
#define DEFINE_IDR(name) struct idr name = IDR_INIT(name)
定义一个idr结构体并赋值
三.分配id
1.idr_pre_get
int idr_pre_get(struct idr *idp, gfp_t gfp_mask){
while (idp->id_free_cnt < IDR_FREE_MAX) { //IDR_FREE_MAX=14
struct idr_layer *new; //定义新的idr_layer结构体指针
new = kmem_cache_zalloc(idr_layer_cache, gfp_mask); //分配*new内存空间
if (new == NULL)
return (0);
move_to_free_list(idp, new); //-->move_to_free_list
}
return 1;
}
EXPORT_SYMBOL(idr_pre_get);
move_to_free_list
static void move_to_free_list(struct idr *idp, struct idr_layer *p)
{
unsigned long flags;
spin_lock_irqsave(&idp->lock, flags);
__move_to_free_list(idp, p); //-->__move_to_free_list
spin_unlock_irqrestore(&idp->lock, flags);
}
__move_to_free_list
static void __move_to_free_list(struct idr *idp, struct idr_layer *p)
{
p->ary[0] = idp->id_free;
idp->id_free = p;
idp->id_free_cnt++;
}
第一次循环结果
接着循环
再接着
一直这样下去直到循环结束(14次)
2.idr_get_new和idr_get_new_above
idr_get_newint idr_get_new(struct idr *idp, void *ptr, int *id)
{
int rv;
rv = idr_get_new_above_int(idp, ptr, 0);
if (rv < 0)
return _idr_rc_to_errno(rv);
*id = rv;
return 0;
}
EXPORT_SYMBOL(idr_get_new);
idr_get_new_above
int idr_get_new_above(struct idr *idp, void *ptr, int starting_id, int *id)
{
int rv;
rv = idr_get_new_above_int(idp, ptr, starting_id);
if (rv < 0)
return _idr_rc_to_errno(rv);
*id = rv;
return 0;
}
EXPORT_SYMBOL(idr_get_new_above);
两个函数都会调用idr_get_new_above_int函数,差别在于starting_id不同
下面分情况讨论,先以id为0走个过场
idr的top简称为根top,free简称为根free均为idr_layer指针类型,分别指向使用中和空闲idr_layer链表头
static int idr_get_new_above_int(struct idr *idp, void *ptr, int starting_id)
{
struct idr_layer *pa[MAX_LEVEL]; //MAX_LEVEL=7
int id;
id = idr_get_empty_slot(idp, starting_id, pa); //-->idr_get_empty_slot
if (id >= 0) {
rcu_assign_pointer(pa[0]->ary[id & IDR_MASK],(struct idr_layer *)ptr
//pa[0]->ary[0]=ptr 也就是idr_layer14->ary[0]=ptr
pa[0]->count++; //idr_layer14->count++
idr_mark_full(pa, id); //设置其位图-->走完0过场的效果见图c
}
return id;
}
idr_get_empty_slot
static int idr_get_empty_slot(struct idr *idp, int starting_id,struct idr_layer **pa)
{
struct idr_layer *p, *new;
int layers, v, id;
unsigned long flags;
id = starting_id; //按常规出牌吧,假设这个为0
build_up:
p = idp->top; //根top指向的idr_layer NULL
layers = idp->layers; //获取layers层数量(0)
if (unlikely(!p)) { //第一次运行idp->top=NULL,所以if条件为真,执行if分支的结果参考 图A
if (!(p = get_from_free_list(idp))) //>>>1-->get_from_free_list 从根free中获取一个idr_layer14
return -1;
p->layer = 0; //指定idr_layer14的层号为0
layers = 1; //layers层数量设为1
}
//layers<6 && id>=2^(layers*5) 看需不需要增加层数 见图B
while ((layers < (MAX_LEVEL - 1)) && (id >= (1 << (layers*IDR_BITS)))) {
layers++;
if (!p->count) {
p->layer++;
continue;
}
if (!(new = get_from_free_list(idp))) {
spin_lock_irqsave(&idp->lock, flags);
for (new = p; p && p != idp->top; new = p) {
p = p->ary[0];
new->ary[0] = NULL;
new->bitmap = new->count = 0;
__move_to_free_list(idp, new);
}
spin_unlock_irqrestore(&idp->lock, flags);
return -1;
}
new->ary[0] = p;
new->count = 1;
new->layer = layers-1;
if (p->bitmap == IDR_FULL)
__set_bit(0, &new->bitmap);
p = new;
}
rcu_assign_pointer(idp->top, p); //根top指向idr_layer14
idp->layers = layers; //设置更新idr->layers层数量
//----------------------------------------------分割线----------------------------------------------
//以上部分主要处理layer相关,以下部分主要处理id相关
v = sub_alloc(idp, &id, pa); //>>>2-->sub_alloc
if (v == IDR_NEED_TO_GROW) //IDR_NEED_TO_GROW=-2需要扩大
goto build_up;
return(v);
}
图A：
图B
>>>get_from_free_list 从idr空闲idr_layer链表中获取第一个idr_layer
static struct idr_layer *get_from_free_list(struct idr *idp)
{
struct idr_layer *p; //定义一个idr_layer指针
unsigned long flags;
spin_lock_irqsave(&idp->lock, flags);
if ((p = idp->id_free)) { //根free获取一个空闲idr_layer
idp->id_free = p->ary[0]; //idr空闲链表指针指向第二个idr_layer
idp->id_free_cnt--; //idr的空闲idr_layer个数减1(14-1)
p->ary[0] = NULL; //断开第一个idr_layer和第二个idr_layer的联系
}
spin_unlock_irqrestore(&idp->lock, flags);
return(p);
}
这里先穿插一下32进制的计算,上面图B中2^0,2^5,2^10,2^15,2^20,2^25可以(32=2^5)理解成32^0,32^1,32^2,32^3,32^3,32^4,32^5
那么用32进制表达一个十进制数id可以套用一下公式
a的值属于[0,31]
an的值如何获得id/(32^n)即可,等同于id/(2^5^n)等同于id/((1<<5)^n)
an-1的值如何获得id>>(5*(n-1))即可
>>>sub_alloc
static int sub_alloc(struct idr *idp, int *starting_id, struct idr_layer **pa)
{int n, m, sh;
struct idr_layer *p, *new;
int l, id, oid;
unsigned long bm;
id = *starting_id;
restart:
p = idp->top; //根top
l = idp->layers; //l=1
pa[l--] = NULL; //p[1]=NULL;l=0
while (1) {
n = (id >> (IDR_BITS*l)) & IDR_MASK; //计算对应的n值,属于[0,31]
bm = ~p->bitmap; //取反位图
m = find_next_bit(&bm, IDR_SIZE, n); //>>>1 find_next_bit 位图中偏移量为n处查找'1'
if (m == IDR_SIZE) { //位图满了
l++;
oid = id;
id = (id | ((1 << (IDR_BITS * l)) - 1)) + 1;
if (id >= 1 << (idp->layers * IDR_BITS)) {
*starting_id = id;
return IDR_NEED_TO_GROW;
}
p = pa[l];
BUG_ON(!p);
sh = IDR_BITS * (l + 1);
if (oid >> sh == id >> sh)
continue;
else
goto restart;
}
if (m != n) { //期望的n值被占用,但可找到可用的m值
sh = IDR_BITS*l;
id = ((id >> sh) ^ n ^ m) << sh; //>>>2 重新计算id值
}
if ((id >= MAX_ID_BIT) || (id < 0))
return IDR_NOMORE_SPACE;
if (l == 0) //l==0跳出while循环
break;
if (!p->ary[m]) {
new = get_from_free_list(idp);
if (!new)
return -1;
new->layer = l-1;
rcu_assign_pointer(p->ary[m], new);
p->count++;
}
pa[l--] = p;
p = p->ary[m];
}
pa[l] = p; //pa[0]=p 也就是idr_layer14
return id;
}
>>>find_next_bit
#define find_next_bit(p,sz,off) _find_next_bit_le(p,sz,off) //>>_find_next_bit_le
该宏的意思是在p指向的(大小为sz的)位图表中的第off个位置开始找寻可用(为"1")的格子,找到返回该位
_find_next_bit_le是汇编代码实现的定义在/arch/arm/lib/findbit.S
ENTRY(_find_next_bit_le)
teq r1, #0
beq 3b
ands ip, r2, #7
beq 1b @ If new byte, goto old routine
ARM( ldrb r3, [r0, r2, lsr #3] )
THUMB( lsr r3, r2, #3 )
THUMB( ldrb r3, [r0, r3] )
movs r3, r3, lsr ip @ shift off unused bits
bne .L_found
orr r2, r2, #7 @ if zero, then no bits here
add r2, r2, #1 @ align bit pointer
b 2b @ loop for next bit
ENDPROC(_find_next_bit_le)
.L_found找到合适的跳转
.L_found:
#if __LINUX_ARM_ARCH__ >= 5
rsb r0, r3, #0
and r3, r3, r0
clz r3, r3
rsb r3, r3, #31
add r0, r2, r3
#else
tst r3, #0x0f
addeq r2, r2, #4
movne r3, r3, lsl #4
tst r3, #0x30
addeq r2, r2, #2
movne r3, r3, lsl #2
tst r3, #0x40
addeq r2, r2, #1
mov r0, r2
#endif
cmp r1, r0 @ Clamp to maxbit
movlo r0, r1
mov pc, lr
>>>id值的计算的补充说明
首先前面n的取值n = (id >> (IDR_BITS*l)) & IDR_MASK;
IDR_MASK的定义#define IDR_MASK ((1 << IDR_BITS)-1)也就是说IDR_MASK=31等于2进制的1,1111b
所以&IDR_MASK只是框定n值落在0~31之间,掩码作用
那么不出意外的话n = (id >> (IDR_BITS*l))
接着
sh = IDR_BITS*l;
id = ((id >> sh) ^ n ^ m) << sh;
带入表达式中
id=((id >> IDR_BITS*l) ^ (id >> (IDR_BITS*l)) ^ m) << IDR_BITS*l;
异或的操作是相同为1,不同为0,结合起来化简得
id = ((1 ^ m) << sh=m<<sh
图C
^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_^_
已经借用id0走了过场,下面分析下其他情况
static int idr_get_new_above_int(struct idr *idp, void *ptr, int starting_id)
{
struct idr_layer *pa[MAX_LEVEL]; //定义父idr_layer数组
int id;
id = idr_get_empty_slot(idp, starting_id, pa); //获取id
if (id >= 0) {
rcu_assign_pointer(pa[0]->ary[id & IDR_MASK],(struct idr_layer *)ptr);
//pa[0]->ary[id]=ptr
pa[0]->count++; //idr_layer->count++
idr_mark_full(pa, id); //标记id位图
}
return id;
}
static int idr_get_empty_slot(struct idr *idp, int starting_id,struct idr_layer **pa)
{
struct idr_layer *p, *new;
int layers, v, id;
unsigned long flags;
id = starting_id;
build_up:
p = idp->top; //获取根top
layers = idp->layers; //获取层数量 layers=1
if (unlikely(!p)) { //FALSE
if (!(p = get_from_free_list(idp)))
return -1;
p->layer = 0;
layers = 1;
}
while ((layers < 6) && (id >= (1 << (layers*5)))) { //参考图B,如果id值超过或等于对应层所能容纳的最大数,则进入循环
layers++; //增加层数量
if (!p->count) { //0~31没使用,直接使用32就属于这种情况
p->layer++; //由于32需要添加1层的,所以之前的层的层号需要+1
continue; //层数量也需要加1
}
if (!(new = get_from_free_list(idp))) { //空闲链表中获取新的idr_layer
spin_lock_irqsave(&idp->lock, flags); //分配失败,--空闲idr_layer链表缺货
for (new = p; p && p != idp->top; new = p) { //p指针还原
p = p->ary[0];
new->ary[0] = NULL;
new->bitmap = new->count = 0;
__move_to_free_list(idp, new); //分配更多空闲链表
}
spin_unlock_irqrestore(&idp->lock, flags);
return -1;
}
new->ary[0] = p; //新的idr_layer->ary[0]指向旧的idr_layer
new->count = 1; //新的idr_layer计数加1
new->layer = layers-1; //设置新的idr_layer的层号
if (p->bitmap == IDR_FULL) //若旧的(叶子)idr_layer的id全用过了
__set_bit(0, &new->bitmap); //那么标记下新(父)idr_layer位图的第0位
p = new; //根top指向新的idr_layer
}
rcu_assign_pointer(idp->top, p); //设置根top
idp->layers = layers; //更新层数量
v = sub_alloc(idp, &id, pa); //获取id
if (v == IDR_NEED_TO_GROW) //该层id号全用完了,必须扩大idr_layer层数量
goto build_up;
return(v);
}
static int sub_alloc(struct idr *idp, int *starting_id, struct idr_layer **pa)
{
int n, m, sh;
struct idr_layer *p, *new;
int l, id, oid;
unsigned long bm;
id = *starting_id;
restart:
p = idp->top; //获取根top
l = idp->layers; //获取层数量l=1
pa[l--] = NULL; //pa[1]=NULL,l=0
while (1) {
n = (id >> (5*l)) & IDR_MASK; //n做处理 属于[0,31]
bm = ~p->bitmap; //位图取反
m = find_next_bit(&bm, IDR_SIZE, n); //查找n开始能用的位
if (m == IDR_SIZE) { //id表满了
l++; 层数+1
oid = id;
id = (id | ((1 << (5 * l)) - 1)) + 1; //id或上掩码再+1
if (id >= 1 << (idp->layers * 5)) { //需要添加层
*starting_id = id;
return IDR_NEED_TO_GROW;
}
p = pa[l];
BUG_ON(!p);
sh = 5 * (l + 1);
if (oid >> sh == id >> sh)
continue;
else
goto restart;
}
if (m != n) { //期望id给用但有可用id
sh = 5*l;
id = ((id >> sh) ^ n ^ m) << sh; //id设置为可用id
}
if ((id >= MAX_ID_BIT) || (id < 0))
return IDR_NOMORE_SPACE;
if (l == 0) //一层层循环计算直到到达叶子处l才为0
break;
if (!p->ary[m]) { //叶子m为空
new = get_from_free_list(idp); //从空闲链表拿一个idr_layer
if (!new)
return -1;
new->layer = l-1; //设置新链表层数
rcu_assign_pointer(p->ary[m], new); //叶子m指向新链表
p->count++; //使用计数加1
}
pa[l--] = p; //pa[大]=节点
p = p->ary[m]; //p=节点->叶子m
}
pa[l] = p; //pa[小]=叶子
return id;
}
来个效果图id=4吧
id=32情况(idr_layer13的位图1标记错了)
1024情况
四.查找id
1.idr_find
void *idr_find(struct idr *idp, int id){
int n;
struct idr_layer *p;
p = rcu_dereference_raw(idp->top); //获取根top
if (!p)
return NULL;
n = (p->layer+1) * IDR_BITS; //计算最外层的n值
id &= MAX_ID_MASK;
if (id >= (1 << n))
return NULL;
BUG_ON(n == 0);
while (n > 0 && p) { //循环一层层查找
n -= IDR_BITS;
BUG_ON(n != p->layer*IDR_BITS);
p = rcu_dereference_raw(p->ary[(id >> n) & IDR_MASK]); //一次获取an ... a0
}
return((void *)p);
}
EXPORT_SYMBOL(idr_find);
前面讲过32进制的id值算法
当构建完idr机制之后
id=top->ary[an]->ary[a(n-1)]->....->ary[a0]来获得
借助图片分析下(idr_layer13的位图标记有错)
五.idr操作
1. idr_remove idr_remove_all 移除
void idr_remove(struct idr *idp, int id){
struct idr_layer *p;
struct idr_layer *to_free;
id &= MAX_ID_MASK;
sub_remove(idp, (idp->layers - 1) * IDR_BITS, id);
if (idp->top && idp->top->count == 1 && (idp->layers > 1) &&
idp->top->ary[0]) {
to_free = idp->top;
p = idp->top->ary[0];
rcu_assign_pointer(idp->top, p);
--idp->layers;
to_free->bitmap = to_free->count = 0;
free_layer(to_free);
}
while (idp->id_free_cnt >= IDR_FREE_MAX) {
p = get_from_free_list(idp);
kmem_cache_free(idr_layer_cache, p);
}
return;
}
EXPORT_SYMBOL(idr_remove);
移除全部
void idr_remove_all(struct idr *idp)
{
int n, id, max;
int bt_mask;
struct idr_layer *p;
struct idr_layer *pa[MAX_LEVEL];
struct idr_layer **paa = &pa[0];
n = idp->layers * IDR_BITS;
p = idp->top;
rcu_assign_pointer(idp->top, NULL);
max = 1 << n;
id = 0;
while (id < max) {
while (n > IDR_BITS && p) {
n -= IDR_BITS;
*paa++ = p;
p = p->ary[(id >> n) & IDR_MASK];
}
bt_mask = id;
id += 1 << n;
/* Get the highest bit that the above add changed from 0->1. */
while (n < fls(id ^ bt_mask)) {
if (p)
free_layer(p);
n += IDR_BITS;
p = *--paa;
}
}
idp->layers = 0;
}
EXPORT_SYMBOL(idr_remove_all);
2.idr_replace 替换
void *idr_replace(struct idr *idp, void *ptr, int id){
int n;
struct idr_layer *p, *old_p;
p = idp->top;
if (!p)
return ERR_PTR(-EINVAL);
n = (p->layer+1) * IDR_BITS;
id &= MAX_ID_MASK;
if (id >= (1 << n))
return ERR_PTR(-EINVAL);
n -= IDR_BITS;
while ((n > 0) && p) {
p = p->ary[(id >> n) & IDR_MASK];
n -= IDR_BITS;
}
n = id & IDR_MASK;
if (unlikely(p == NULL || !test_bit(n, &p->bitmap)))
return ERR_PTR(-ENOENT);
old_p = p->ary[n];
rcu_assign_pointer(p->ary[n], ptr);
return old_p;
}
EXPORT_SYMBOL(idr_replace);
六.idr空闲链表的销毁
idr_destroyvoid idr_destroy(struct idr *idp)
{
while (idp->id_free_cnt) {
struct idr_layer *p = get_from_free_list(idp);
kmem_cache_free(idr_layer_cache, p);
}
}
EXPORT_SYMBOL(idr_destroy);
七.用法
1.api函数
void *idr_find(struct idr *idp, int id); //查找id对应的指针int idr_pre_get(struct idr *idp, gfp_t gfp_mask); //分配idr_layer空闲链表
int idr_get_new(struct idr *idp, void *ptr, int *id); //获取id,捆绑指针ptr
int idr_get_new_above(struct idr *idp, void *ptr, int starting_id, int *id); //起始数值获取id,捆绑指针ptr
int idr_for_each(struct idr *idp,int (*fn)(int id, void *p, void *data), void *data);
void *idr_get_next(struct idr *idp, int *nextid);
void *idr_replace(struct idr *idp, void *ptr, int id); //替换id捆绑的指针
void idr_remove(struct idr *idp, int id); //移除id
void idr_remove_all(struct idr *idp); //移除所有id
void idr_destroy(struct idr *idp); //销毁idr_layer空闲链表
void idr_init(struct idr *idp); //初始化idr
2.大致用法
1.idr_init声明设置idr2.idr_pre_get分配空闲idr_layer链表
3.id_get_new/idr_get_new_above分配id并将id与指针ptr捆绑
4.利用idr_find根据id获取指针ptr
5.idr_remove/idr_remove_all移除分配的id
6.idr_destroy销毁空闲idr_layer链表
7.idr_replace替换id