相关的结构

• task_struct

定义了CONFIG_CGROUPS宏的话，task_struct和cgroup相关的变量有：

/* Control Group info protected by css_set_lock */    struct css_set __rcu *cgroups;//关联的css_set    /* cg_list protected by css_set_lock and tsk->alloc_lock */    struct list_head cg_list;//加入css_set中tasks链表，所有css_set相同的链表。

• CSS_SET

struct css_set {    /* Reference count */    atomic_t refcount;//引用计数    /*     * List running through all cgroup groups in the same hash     * slot. Protected by css_set_lock     */    struct hlist_node hlist;//具有hash的css_set 链表.    /*     * List running through all tasks using this cgroup     * group. Protected by css_set_lock     */    struct list_head tasks;//所有具有相同css_set的task_struct链表。    /*     * List of cg_cgroup_link objects on link chains from     * cgroups referenced from this css_set. Protected by     * css_set_lock     */    struct list_head cg_links;//由cg_cgroup_link组成的链表，链表上每一项cg_cgroup_link都指向和css_set关联的cgroup.    /*     * Set of subsystem states, one for each subsystem. This array     * is immutable after creation apart from the init_css_set     * during subsystem registration (at boot time) and modular subsystem     * loading/unloading.     */    /*     *css_set关联的css.每一个subsystem对应数组中相应id的项。     *subsys应当包括所有子系统的css.如果此css_set没有制定某个subsystem的css或者subsystem没有mount，则默认初始化为根css.     */    struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];    /* For RCU-protected deletion */    struct rcu_head rcu_head;    }

css_set是直接和task关联的结构，css_set用来关联一组cgroup_subsys_state对象，同时通过cg_cgroup_link和所有相关的cgroup建立关联。

• cgroup

struct cgroup {    unsigned long flags;        /* "unsigned long" so bitops work */    /*     * count users of this cgroup. >0 means busy, but doesn't     * necessarily indicate the number of tasks in the cgroup     */    atomic_t count;//cgroup引用计数    int id;                /* ida allocated in-hierarchy ID */    /*     * We link our 'sibling' struct into our parent's 'children'.     * Our children link their 'sibling' into our 'children'.     */    struct list_head sibling;    /* my parent's children */ //兄弟cgroup    struct list_head children;    /* my children */ //child cgroups    struct list_head files;        /* my files */    struct cgroup *parent;        /* my parent */   //parent cgroup    struct dentry *dentry;        /* cgroup fs entry, RCU protected */ //此cgroup对应的dentry    /*     * This is a copy of dentry->d_name, and it's needed because     * we can't use dentry->d_name in cgroup_path().     *     * You must acquire rcu_read_lock() to access cgrp->name, and     * the only place that can change it is rename(), which is     * protected by parent dir's i_mutex.     *     * Normally you should use cgroup_name() wrapper rather than     * access it directly.     */    struct cgroup_name __rcu *name; //cgroup的name,同dentry->d_name    /* Private pointers for each registered subsystem */    struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];//此cgroup关联subsystem的css结构，每个subsystem的css在数组中对应subsys[subsystem->subsys_id].    struct cgroupfs_root *root;//cgroup所处的cgroupfs_root,对应hirerarchy        /*     * List of cg_cgroup_links pointing at css_sets with     * tasks in this cgroup. Protected by css_set_lock     */    struct list_head css_sets; //通过cs_cgroup_link指向此cgroup关联的css_set    struct list_head allcg_node;    /* cgroupfs_root->allcg_list */    struct list_head cft_q_node;    /* used during cftype add/rm */    /*     * Linked list running through all cgroups that can     * potentially be reaped by the release agent. Protected by     * release_list_lock     */    struct list_head release_list;    /*     * list of pidlists, up to two for each namespace (one for procs, one     * for tasks); created on demand.     */    struct list_head pidlists;    struct mutex pidlist_mutex;    /* For RCU-protected deletion */    struct rcu_head rcu_head;    struct work_struct free_work;    /* List of events which userspace want to receive */    struct list_head event_list;    spinlock_t event_list_lock;    /* directory xattrs */    struct simple_xattrs xattrs;};

cgroup对应一个controll实例，需要和css_set关联，这样每个task_struct就可以通过task_struct->cgroups 继而和cgroup关联，达到控制和隔离资源的目的，那么css_set和cgroup具体是怎么关联的呢？

首先需要明确的是cgroup和css_set是多对多的关系，既：一个css_set可以对应多个cgroup,同时一个cgroup也可以被多个css_set所包含。这种多对多的映射关系，是通过cg_cgroup_link这个中间结构来关联的。

/* Link structure for associating css_set objects with cgroups */struct cg_cgroup_link {    /*     * List running through cg_cgroup_links associated with a     * cgroup, anchored on cgroup->css_sets     */    struct list_head cgrp_link_list;    struct cgroup *cgrp;    /*     * List running through cg_cgroup_links pointing at a     * single css_set object, anchored on css_set->cg_links     */    struct list_head cg_link_list;    struct css_set *cg;};

一个cg_cgroup_link需要包含两类信息，即关联的cgroup和css_set信息，一个cg_cgroup_link可以让一个cgroup和一个css_set相关联。但是正如我们前面所说，css_set和cgroup是多对多的对应关系，所以，一个css_set需要保存多个cg_cgroup_link，一个cgroup也需要保存多个cg_cgroup_link信息。具体来说，css_set中的cg_links维护了一个链表，链表中的元素为cg_cgroup_link中的cg_link_list.cgroup中的css_set也维护了一个cg_cgroup_link链表，链表中元素为cgrp_link_list.结构如下图所示：

• cgroupfs_root

cgroup_root对应一个层级，从Linux 文件系统角度来讲，cgroupfs_root对应我们mount相应cgroup时创建的super_block.即，我们每进行一次mount操作，就对应一个cgroupfs_root的创建。

/* * A cgroupfs_root represents the root of a cgroup hierarchy, and may be * associated with a superblock to form an active hierarchy.  This is * internal to cgroup core.  Don't access directly from controllers. */struct cgroupfs_root {    //cgroupfs_root对应的super block    struct super_block *sb;    /*     * The bitmask of subsystems intended to be attached to this     * hierarchy     */    unsigned long subsys_mask;//此hierarchy层级中包含的子系统，以掩码表示    /* Unique id for this hierarchy. */    int hierarchy_id;//id    /* The bitmask of subsystems currently attached to this hierarchy */    unsigned long actual_subsys_mask;//TOBE DONE    /* A list running through the attached subsystems */    struct list_head subsys_list;//关联的cgroup_subsys list    /* The root cgroup for this hierarchy */    struct cgroup top_cgroup;// 此hierarchy的root cgroup    /* Tracks how many cgroups are currently defined in hierarchy.*/    int number_of_cgroups;//此hierarchy cgroup 数目    /* A list running through the active hierarchies */    struct list_head root_list; //系统中hierarchy链表     /* All cgroups on this root, cgroup_mutex protected */    struct list_head allcg_list;//此hierarchy包含的所有的cgroup    /* Hierarchy-specific flags */    unsigned long flags;    /* IDs for cgroups in this hierarchy */    struct ida cgroup_ida;    /* The path to use for release notifications. */    char release_agent_path[PATH_MAX];    /* The name for this hierarchy - may be empty */    char name[MAX_CGROUP_ROOT_NAMELEN];};

• cgroup_subsys

对应特定的子系统。

/* * Control Group subsystem type. * See Documentation/cgroups/cgroups.txt for details */struct cgroup_subsys {    struct cgroup_subsys_state *(*css_alloc)(struct cgroup *cgrp);    int (*css_online)(struct cgroup *cgrp);    void (*css_offline)(struct cgroup *cgrp);    void (*css_free)(struct cgroup *cgrp);    int (*can_attach)(struct cgroup *cgrp, struct cgroup_taskset *tset);    void (*cancel_attach)(struct cgroup *cgrp, struct cgroup_taskset *tset);    void (*attach)(struct cgroup *cgrp, struct cgroup_taskset *tset);    void (*fork)(struct task_struct *task);    void (*exit)(struct cgroup *cgrp, struct cgroup *old_cgrp,             struct task_struct *task);    void (*bind)(struct cgroup *root);    /*上面的针对不同的子系统指向不同的函数指针*/        int subsys_id;// subsystem id    int disabled;    int early_init;//是否early_init    /*     * True if this subsys uses ID. ID is not available before cgroup_init()     * (not available in early_init time.)     */    bool use_id;    /*     * If %false, this subsystem is properly hierarchical -     * configuration, resource accounting and restriction on a parent     * cgroup cover those of its children.  If %true, hierarchy support     * is broken in some ways - some subsystems ignore hierarchy     * completely while others are only implemented half-way.     *     * It's now disallowed to create nested cgroups if the subsystem is     * broken and cgroup core will emit a warning message on such     * cases.  Eventually, all subsystems will be made properly     * hierarchical and this will go away.     */    bool broken_hierarchy;    bool warned_broken_hierarchy;#define MAX_CGROUP_TYPE_NAMELEN 32    const char *name;    /*     * Link to parent, and list entry in parent's children.     * Protected by cgroup_lock()     */    struct cgroupfs_root *root;//指向所属的hierarchy    struct list_head sibling;    /* used when use_id == true */    struct idr idr;    spinlock_t id_lock;    /* list of cftype_sets */    struct list_head cftsets;    /* base cftypes, automatically [de]registered with subsys itself */    struct cftype *base_cftypes;    struct cftype_set base_cftset;    /* should be defined only by modular subsystems */    struct module *module;    }

• cgroup_subsys_state

/* Per-subsystem/per-cgroup state maintained by the system. */struct cgroup_subsys_state {/* * The cgroup that this subsystem is attached to. Useful * for subsystems that want to know about the cgroup * hierarchy structure */struct cgroup *cgroup;//此css关联的cgroup. 1个cgroup可对应多个css/* * State maintained by the cgroup system to allow subsystems * to be "busy". Should be accessed via css_get(), * css_tryget() and css_put(). */atomic_t refcnt;unsigned long flags;/* ID for this css, if possible */struct css_id __rcu *id;/* Used to put @cgroup->dentry on the last css_put() */struct work_struct dput_work;};

此外，还有几个cgroup相关的全局变量

/* * The "rootnode" hierarchy is the "dummy hierarchy", reserved for the * subsystems that are otherwise unattached - it never has more than a * single cgroup, and all tasks are part of that cgroup. * 初始化默认cgroupfs_root. 系统初始化时所有的subsystem都关联到此hierarchy. 不可以在默认 * hierarchy上创建cgroup，因此其只有一个默认的root cgroup. */static struct cgroupfs_root rootnode;/* The default css_set - used by init and its children prior to any * hierarchies being mounted. It contains a pointer to the root state * for each subsystem. Also used to anchor the list of css_sets. Not * reference-counted, to improve performance when child cgroups * haven't been created. * 初始化默认的css_set. 在没有hierarchy被mount之前，系统初始化时init及其子进程关联此css_set。 * init_css_set->subsys指向每个subsys的root css. */static struct css_set init_css_set;/* * hash table for cgroup groups. This improves the performance to find * an existing css_set. This hash doesn't (currently) take into * account cgroups in empty hierarchies. * css_set的hash table.将task关联到指定css，就是将task->cgroup指针指向一个 * css_set. css_set_table以css[]为key,相同的css集合，即为同一个css_set. 当有task需要关联到到一 * 组css时，以css[]为key在hash table中查找是否存在,存在直接引用此key的css_set，否则创建css_set * 并添加到hash table. * #define CSS_SET_HASH_BITS    7static DEFINE_HASHTABLE(css_set_table, CSS_SET_HASH_BITS);