Linux内核源码分析-基树处理- radix_tree

Linux内核源码分析-基树处理- radix_tree

本文主要参考《深入理解Linux内核》，结合2.6.11版的内核代码，分析内核文件子系统中的radix_tree处理函数。
注意：
1、 不描述内核同步、错误处理、参数合法性验证相关的内容
2、 源码摘自Linux内核2.6.11 stable版，获取命令:
git clone
git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git
cd ./linux-stable/
git checkout linux-2.6.11.y
3、 阅读本文请结合《深入理解Linux内核》第三版相关章节
4、 本文会不定时更新

函数调用结构

公共函数

1、radix_tree_init
源码：
在init/main.c:start_kernel函数中调用该函数

void __init radix_tree_init(void){    radix_tree_node_cachep = kmem_cache_create("radix_tree_node",            sizeof(struct radix_tree_node), 0,            SLAB_PANIC, radix_tree_node_ctor, NULL);    radix_tree_init_maxindex();    hotcpu_notifier(radix_tree_callback, 0);}

处理流出：
1、 调用函数kmem_cache_create分配类型为radix_tree_node、名称为radix_tree_node的slab高速缓存，存入全局变量radix_tree_node_cachep中
2、 调用函数radix_tree_init_maxindex初始化书中各层的最大索引数组height_to_maxindex（1-6层）
3、 调用函数hotcpu_notifier，设置热插拔cpu时的回调函数
2、radix_tree_insert
源码：

/** *  radix_tree_insert    -    insert into a radix tree *  @root:      radix tree root *  @index:     index key *  @item:      item to insert * *  Insert an item into the radix tree at position @index. */int radix_tree_insert(struct radix_tree_root *root,            unsigned long index, void *item){    struct radix_tree_node *node = NULL, *tmp, **slot;    unsigned int height, shift;    int offset;    int error;    /* Make sure the tree is high enough.  */    if ((!index && !root->rnode) ||            index > radix_tree_maxindex(root->height)) {        error = radix_tree_extend(root, index);        if (error)            return error;    }    slot = &root->rnode;    height = root->height;    shift = (height-1) * RADIX_TREE_MAP_SHIFT; //当前层偏移需要移动的位数    offset = 0;         /* uninitialised var warning */    while (height > 0) {        if (*slot == NULL) {            /* Have to add a child node.  */            if (!(tmp = radix_tree_node_alloc(root)))                return -ENOMEM;            *slot = tmp;            if (node)                node->count++;        }        /* Go a level down */        offset = (index >> shift) & RADIX_TREE_MAP_MASK;        node = *slot;        slot = (struct radix_tree_node **)(node->slots + offset);        shift -= RADIX_TREE_MAP_SHIFT;        height--;    }    if (*slot != NULL)        return -EEXIST;    if (node) {        node->count++;        BUG_ON(tag_get(node, 0, offset));        BUG_ON(tag_get(node, 1, offset));    }    *slot = item;    return 0;}

处理流程：
1、 调用函数radix_tree_extend扩展树的层数以满足index
2、 循环初始化各层的radix_tree_node对象
3、 初始化最终的页的指针
3、radix_tree_delete
源码：

/** *  radix_tree_delete    -    delete an item from a radix tree *  @root:      radix tree root *  @index:     index key * *  Remove the item at @index from the radix tree rooted at @root. * *  Returns the address of the deleted item, or NULL if it was not present. */void *radix_tree_delete(struct radix_tree_root *root, unsigned long index){    struct radix_tree_path path[RADIX_TREE_MAX_PATH], *pathp = path;    struct radix_tree_path *orig_pathp;    unsigned int height, shift;    void *ret = NULL;    char tags[RADIX_TREE_TAGS];    int nr_cleared_tags;    height = root->height;    if (index > radix_tree_maxindex(height))        goto out;    shift = (height - 1) * RADIX_TREE_MAP_SHIFT;    pathp->node = NULL;    pathp->slot = &root->rnode;    while (height > 0) {        int offset;        if (*pathp->slot == NULL)            goto out;        offset = (index >> shift) & RADIX_TREE_MAP_MASK;        pathp[1].offset = offset;        pathp[1].node = *pathp[0].slot;        pathp[1].slot = (struct radix_tree_node **)                (pathp[1].node->slots + offset);        pathp++;        shift -= RADIX_TREE_MAP_SHIFT;        height--;    }    ret = *pathp[0].slot;    if (ret == NULL)        goto out;    orig_pathp = pathp;    /*     * Clear all tags associated with the just-deleted item     */    memset(tags, 0, sizeof(tags));    do {        int tag;        nr_cleared_tags = RADIX_TREE_TAGS;        for (tag = 0; tag < RADIX_TREE_TAGS; tag++) {            int idx;            if (tags[tag])                continue;            tag_clear(pathp[0].node, tag, pathp[0].offset);            for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {                if (pathp[0].node->tags[tag][idx]) {                    tags[tag] = 1;                    nr_cleared_tags--;                    break;                }            }        }        pathp--;    } while (pathp[0].node && nr_cleared_tags);    pathp = orig_pathp;    *pathp[0].slot = NULL;    while (pathp[0].node && --pathp[0].node->count == 0) {        pathp--;        BUG_ON(*pathp[0].slot == NULL);        *pathp[0].slot = NULL;        radix_tree_node_free(pathp[1].node);    }    if (root->rnode == NULL)        root->height = 0;out:    return ret;}

处理流程：
1、 根据index把各层的节点对象和偏移值存入radix_tree_path对象的offset和node字段中
2、 运行一个三层循环，最外层处理各层节点，中间层循环标记数组，最内层循环各个子节点标记，如果子节点的所有标记都为0，则清楚本节点的标记
3、 从最底层节点开始，循环处理每一层节点，如果节点不为空且节点中的有效子节点个数为0，则调用函数radix_tree_node_free释放该节点
4、 如果树的根节点为空，这把树的高度设置为0（当删除一个最底层节点时，如果没有其他页子节点，树的高度为0；如果还有其他页子节点，树的高度不变）

4、radix_tree_lookup
函数功能：
在radix_tree_root中查找索引页，找到则返回页地址，未找到返回NULL
函数源码：

/** *  radix_tree_lookup    -    perform lookup operation on a radix tree *  @root:      radix tree root *  @index:     index key * *  Lookup the item at the position @index in the radix tree @root. */void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index){    unsigned int height, shift;    struct radix_tree_node **slot;    height = root->height;  //树的高度    if (index > radix_tree_maxindex(height))  //判断页索引是否超出树的最大索引        return NULL;    shift = (height-1) * RADIX_TREE_MAP_SHIFT; //树中各层页索引需要移动的位数    slot = &root->rnode; //树中的当前节点    while (height > 0) {        if (*slot == NULL)  //已结束            return NULL;        slot = (struct radix_tree_node **)            ((*slot)->slots +                ((index >> shift) & RADIX_TREE_MAP_MASK));//计算下一层树节点的指针        shift -= RADIX_TREE_MAP_SHIFT;        height--;    }    return *slot;}

5、radix_tree_tag_set
功能：
把index所对应的树的路径上的所有节点相应偏移的标志设置为tag
源码：

/** *  radix_tree_tag_set - set a tag on a radix tree node *  @root:      radix tree root *  @index:     index key *  @tag:       tag index * *  Set the search tag corresponging to @index in the radix tree.  From *  the root all the way down to the leaf node. * *  Returns the address of the tagged item.   Setting a tag on a not-present *  item is a bug. */void *radix_tree_tag_set(struct radix_tree_root *root,            unsigned long index, int tag){    unsigned int height, shift;    struct radix_tree_node **slot;    height = root->height;    if (index > radix_tree_maxindex(height))        return NULL;    shift = (height - 1) * RADIX_TREE_MAP_SHIFT;    slot = &root->rnode;    while (height > 0) {        int offset;        offset = (index >> shift) & RADIX_TREE_MAP_MASK;        tag_set(*slot, tag, offset);        slot = (struct radix_tree_node **)((*slot)->slots + offset);        BUG_ON(*slot == NULL);        shift -= RADIX_TREE_MAP_SHIFT;        height--;    }    return *slot;}

6、radix_tree_tag_clear
源码：

/** *  radix_tree_tag_clear - clear a tag on a radix tree node *  @root:      radix tree root *  @index:     index key *  @tag:       tag index * *  Clear the search tag corresponging to @index in the radix tree.  If *  this causes the leaf node to have no tags set then clear the tag in the *  next-to-leaf node, etc. * *  Returns the address of the tagged item on success, else NULL.  ie: *  has the same return value and semantics as radix_tree_lookup(). */void *radix_tree_tag_clear(struct radix_tree_root *root,            unsigned long index, int tag){    struct radix_tree_path path[RADIX_TREE_MAX_PATH], *pathp = path;    unsigned int height, shift;    void *ret = NULL;    height = root->height;    if (index > radix_tree_maxindex(height))        goto out;    shift = (height - 1) * RADIX_TREE_MAP_SHIFT;    pathp->node = NULL;    pathp->slot = &root->rnode;    while (height > 0) {        int offset;        if (*pathp->slot == NULL)            goto out;        offset = (index >> shift) & RADIX_TREE_MAP_MASK;        pathp[1].offset = offset;        pathp[1].node = *pathp[0].slot;        pathp[1].slot = (struct radix_tree_node **)                (pathp[1].node->slots + offset);        pathp++;        shift -= RADIX_TREE_MAP_SHIFT;        height--;    }    ret = *pathp[0].slot;    if (ret == NULL)        goto out;    do {        int idx;        tag_clear(pathp[0].node, tag, pathp[0].offset);        for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {            if (pathp[0].node->tags[tag][idx])                goto out;        }        pathp--;    } while (pathp[0].node);out:    return ret;}

处理流程：
1、 根据index在树中查找，把各层节点信息存入radix_tree_path类型的数组中
2、 从底层开始循环处理各层所找到的节点，把当前偏移处的标记清除，如果子节点标记中有设置的则退出，没有则继续循环下一个节点
7、radix_tree_tag_get
功能：
返回index对应的最底层节点对应的标记
源码：

/** *  radix_tree_tag_get - get a tag on a radix tree node *  @root:      radix tree root *  @index:     index key *  @tag:       tag index * *  Return the search tag corresponging to @index in the radix tree. * *  Returns zero if the tag is unset, or if there is no corresponding item *  in the tree. */int radix_tree_tag_get(struct radix_tree_root *root,            unsigned long index, int tag){    unsigned int height, shift;    struct radix_tree_node **slot;    int saw_unset_tag = 0;    height = root->height;    if (index > radix_tree_maxindex(height))        return 0;    shift = (height - 1) * RADIX_TREE_MAP_SHIFT;    slot = &root->rnode;    for ( ; ; ) {        int offset;        if (*slot == NULL)            return 0;        offset = (index >> shift) & RADIX_TREE_MAP_MASK;        /*         * This is just a debug check.  Later, we can bale as soon as         * we see an unset tag.         */        if (!tag_get(*slot, tag, offset))            saw_unset_tag = 1;        if (height == 1) {            int ret = tag_get(*slot, tag, offset);            BUG_ON(ret && saw_unset_tag);            return ret;        }        slot = (struct radix_tree_node **)((*slot)->slots + offset);        shift -= RADIX_TREE_MAP_SHIFT;        height--;    }}

8、radix_tree_gang_lookup
功能：
循环调用函数__lookup，查找radix_tree_root中最底层的非空页
源码：

/** *  radix_tree_gang_lookup - perform multiple lookup on a radix tree *  @root:      radix tree root *  @results:   where the results of the lookup are placed *  @first_index:   start the lookup from this key *  @max_items: place up to this many items at *results * *  Performs an index-ascending scan of the tree for present items.  Places *  them at *@results and returns the number of items which were placed at *  *@results. * *  The implementation is naive. */unsigned intradix_tree_gang_lookup(struct radix_tree_root *root, void **results,            unsigned long first_index, unsigned int max_items){    const unsigned long max_index = radix_tree_maxindex(root->height);    unsigned long cur_index = first_index;    unsigned int ret = 0;    while (ret < max_items) {        unsigned int nr_found;        unsigned long next_index;   /* Index of next search */        if (cur_index > max_index)            break;        nr_found = __lookup(root, results + ret, cur_index,                    max_items - ret, &next_index);        ret += nr_found;        if (next_index == 0)            break;        cur_index = next_index;    }    return ret;}

9、radix_tree_gang_lookup_tag
功能：
循环调用函数__lookup_tag，查找radix_tree_root中最底层的设置了tag标记的页
源码：

/** *  radix_tree_gang_lookup_tag - perform multiple lookup on a radix tree *                               based on a tag *  @root:      radix tree root *  @results:   where the results of the lookup are placed *  @first_index:   start the lookup from this key *  @max_items: place up to this many items at *results *  @tag:       the tag index * *  Performs an index-ascending scan of the tree for present items which *  have the tag indexed by @tag set.  Places the items at *@results and *  returns the number of items which were placed at *@results. */unsigned intradix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,        unsigned long first_index, unsigned int max_items, int tag){    const unsigned long max_index = radix_tree_maxindex(root->height);    unsigned long cur_index = first_index;    unsigned int ret = 0;    while (ret < max_items) {        unsigned int nr_found;        unsigned long next_index;   /* Index of next search */        if (cur_index > max_index)            break;        nr_found = __lookup_tag(root, results + ret, cur_index,                    max_items - ret, &next_index, tag);        ret += nr_found;        if (next_index == 0)            break;        cur_index = next_index;    }    return ret;}

10、radix_tree_tagged
功能：
判断radix_tree_root中是否有设置了tag标记的页，有则返回1，没有则返回0
源码：

/** *  radix_tree_tagged - test whether any items in the tree are tagged *  @root:      radix tree root *  @tag:       tag to test */int radix_tree_tagged(struct radix_tree_root *root, int tag){    int idx;    if (!root->rnode)        return 0;    for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {        if (root->rnode->tags[tag][idx])            return 1;    }    return 0;}

11、radix_tree_preload
功能：
补充每cpu变量radix_tree_preloads中的radix_tree_node对象，在把页加入高速缓存中时调用（add_to_page_cache）
源码：

/* * Load up this CPU's radix_tree_node buffer with sufficient objects to * ensure that the addition of a single element in the tree cannot fail.  On * success, return zero, with preemption disabled.  On error, return -ENOMEM * with preemption not disabled. */int radix_tree_preload(int gfp_mask){    struct radix_tree_preload *rtp;    struct radix_tree_node *node;    int ret = -ENOMEM;    preempt_disable();    rtp = &__get_cpu_var(radix_tree_preloads);    while (rtp->nr < ARRAY_SIZE(rtp->nodes)) {        preempt_enable();        node = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);        if (node == NULL)            goto out;        preempt_disable();        rtp = &__get_cpu_var(radix_tree_preloads);        if (rtp->nr < ARRAY_SIZE(rtp->nodes))            rtp->nodes[rtp->nr++] = node;        else            kmem_cache_free(radix_tree_node_cachep, node);    }    ret = 0;out:    return ret;}

文件私有函数

1、radix_tree_maxindex
功能：
该函数隐藏树高度对应的最大索引号的具体实现
源码：

/* *  Return the maximum key which can be store into a *  radix tree with height HEIGHT. */static inline unsigned long radix_tree_maxindex(unsigned int height){    return height_to_maxindex[height];}

2、radix_tree_extend
功能：
根据index需要扩展树的深度
源码：

/* *  Extend a radix tree so it can store key @index. */static int radix_tree_extend(struct radix_tree_root *root, unsigned long index){    struct radix_tree_node *node;    unsigned int height;    char tags[RADIX_TREE_TAGS];    int tag;    /* Figure out what the height should be.  */    height = root->height + 1;    while (index > radix_tree_maxindex(height))        height++;    if (root->rnode == NULL) {        root->height = height;        goto out;    }    /*     * Prepare the tag status of the top-level node for propagation     * into the newly-pushed top-level node(s)     */    for (tag = 0; tag < RADIX_TREE_TAGS; tag++) {        int idx;        tags[tag] = 0;        for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {            if (root->rnode->tags[tag][idx]) {                tags[tag] = 1;                break;            }        }    }    do {        if (!(node = radix_tree_node_alloc(root)))            return -ENOMEM;        /* Increase the height.  */        node->slots[0] = root->rnode;        /* Propagate the aggregated tag info into the new root */        for (tag = 0; tag < RADIX_TREE_TAGS; tag++) {            if (tags[tag])                tag_set(node, tag, 0);        }        node->count = 1;        root->rnode = node;        root->height++;    } while (height > root->height);out:    return 0;}

3、radix_tree_node_alloc
源码：

/* * This assumes that the caller has performed appropriate preallocation, and * that the caller has pinned this thread of control to the current CPU. */static struct radix_tree_node *radix_tree_node_alloc(struct radix_tree_root *root){    struct radix_tree_node *ret;    ret = kmem_cache_alloc(radix_tree_node_cachep, root->gfp_mask);    if (ret == NULL && !(root->gfp_mask & __GFP_WAIT)) {        struct radix_tree_preload *rtp;        rtp = &__get_cpu_var(radix_tree_preloads);        if (rtp->nr) {            ret = rtp->nodes[rtp->nr - 1];            rtp->nodes[rtp->nr - 1] = NULL;            rtp->nr--;        }    }    return ret;}

处理流程：
1、 调用函数kmem_cache_alloc在slab高速缓存radix_tree_node_cachep中分配radix_tree_node对象，地址存入局部变量ret中并返回
2、 如果分配失败，在本地cpu变量radix_tree_preloads中分配radix_tree_node对象，地址存入局部变量ret中并返回
4、tag_set
功能：
设置节点子节点0的相应标志值
源码：

static inline void tag_set(struct radix_tree_node *node, int tag, int offset){    if (!test_bit(offset, &node->tags[tag][0]))        __set_bit(offset, &node->tags[tag][0]);}

5、radix_tree_node_free
功能：
释放radix_tree_node对象给slab高速缓存
源码：

static inline voidradix_tree_node_free(struct radix_tree_node *node){    kmem_cache_free(radix_tree_node_cachep, node);}

6、__lookup
功能：
搜索radix_tree_root中最底层节点中的所有非空页返回
源码：

static unsigned int__lookup(struct radix_tree_root *root, void **results, unsigned long index,    unsigned int max_items, unsigned long *next_index){    unsigned int nr_found = 0;    unsigned int shift;    unsigned int height = root->height;    struct radix_tree_node *slot;    shift = (height-1) * RADIX_TREE_MAP_SHIFT;    slot = root->rnode;    while (height > 0) {  //循环处理树中的每一层        unsigned long i = (index >> shift) & RADIX_TREE_MAP_MASK;//当前层开始索引        for ( ; i < RADIX_TREE_MAP_SIZE; i++) {//在当前层中查找第一个不为空的子树索引，存入i中            if (slot->slots[i] != NULL)                break;            index &= ~((1UL << shift) - 1);            index += 1UL << shift;            if (index == 0)                goto out;   /* 32-bit wraparound */        }        if (i == RADIX_TREE_MAP_SIZE) //如果当前层为空            goto out;        height--;        if (height == 0) {  /* Bottom level: grab some items */            unsigned long j = index & RADIX_TREE_MAP_MASK; //最后一层的开始索引            for ( ; j < RADIX_TREE_MAP_SIZE; j++) {//搜索最后一层中的所有非空页返回                index++;                if (slot->slots[j]) {                    results[nr_found++] = slot->slots[j];                    if (nr_found == max_items)                        goto out;                }            }        }        shift -= RADIX_TREE_MAP_SHIFT;        slot = slot->slots[i];    }out:    *next_index = index;    return nr_found;}

7、__lookup_tag
功能：
搜索radix_tree_root中最底层节点中的所有设置了tag标记的页并返回
源码：

/* * FIXME: the two tag_get()s here should use find_next_bit() instead of * open-coding the search. */static unsigned int__lookup_tag(struct radix_tree_root *root, void **results, unsigned long index,    unsigned int max_items, unsigned long *next_index, int tag){    unsigned int nr_found = 0;    unsigned int shift;    unsigned int height = root->height;    struct radix_tree_node *slot;    shift = (height - 1) * RADIX_TREE_MAP_SHIFT;    slot = root->rnode;    while (height > 0) {        unsigned long i = (index >> shift) & RADIX_TREE_MAP_MASK;        for ( ; i < RADIX_TREE_MAP_SIZE; i++) { //查找第一个设置了tag标记的节点            if (tag_get(slot, tag, i)) {                BUG_ON(slot->slots[i] == NULL);                break;            }            index &= ~((1UL << shift) - 1);            index += 1UL << shift;            if (index == 0)                goto out;   /* 32-bit wraparound */        }        if (i == RADIX_TREE_MAP_SIZE)             goto out;        height--;        if (height == 0) {  /* Bottom level: grab some items */            unsigned long j = index & RADIX_TREE_MAP_MASK;            for ( ; j < RADIX_TREE_MAP_SIZE; j++) {//查找最后一层中设置了tag标记的节点并返回                index++;                if (tag_get(slot, tag, j)) {                     BUG_ON(slot->slots[j] == NULL);                    results[nr_found++] = slot->slots[j];                    if (nr_found == max_items)                        goto out;                }            }        }        shift -= RADIX_TREE_MAP_SHIFT;        slot = slot->slots[i];    }out:    *next_index = index;    return nr_found;}