七:创建子层cgroup

在目录下通过mkdir调用就可以创建一个子层cgroup.下面就分析这一过程:

经过上面的分析可以得知,cgroup中目录的操作集为:  cgroup_dir_inode_operations.结构如下:

static struct inode_operations cgroup_dir_inode_operations = {

    .lookup = simple_lookup,

    .mkdir = cgroup_mkdir,

    .rmdir = cgroup_rmdir,

    .rename = cgroup_rename,

};

从上面看到,对应mkdir的入口为cgroup_mkdir().代码如下:

static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, int mode)

{

    /*找到它的上一级cgroup*/

    struct cgroup *c_parent = dentry->d_parent->d_fsdata;

 

    /* the vfs holds inode->i_mutex already */

    /*调用cgroup_create创建cgroup*/

    return cgroup_create(c_parent, dentry, mode | S_IFDIR);

}

跟踪cgroup_create().代码如下:

static long cgroup_create(struct cgroup *parent, struct dentry *dentry,

                 int mode)

{

    struct cgroup *cgrp;

    struct cgroupfs_root *root = parent->root;

    int err = 0;

    struct cgroup_subsys *ss;

    struct super_block *sb = root->sb;

    /*分配并初始化一个cgroup*/

    cgrp = kzalloc(sizeof(*cgrp), GFP_KERNEL);

    if (!cgrp)

        return -ENOMEM;

 

    /* Grab a reference on the superblock so the hierarchy doesn't

     * get deleted on unmount if there are child cgroups.  This

     * can be done outside cgroup_mutex, since the sb can't

     * disappear while someone has an open control file on the

     * fs */

    atomic_inc(&sb->s_active);

 

    mutex_lock(&cgroup_mutex);

 

    init_cgroup_housekeeping(cgrp);

 

    /*设置cgrp的层次关系*/

    cgrp->parent = parent;

    cgrp->root = parent->root;

    cgrp->top_cgroup = parent->top_cgroup;

 

    /*如果上一级cgroup设置了CGRP_NOTIFY_ON_RELEASE.那cgrp也设置这个标志*/

    if (notify_on_release(parent))

        set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);

 

    /*调用subsys_create()生成cgroup_subsys_state.并与cgrp相关联*/

    for_each_subsys(root, ss) {

        struct cgroup_subsys_state *css = ss->create(ss, cgrp);

        if (IS_ERR(css)) {

            err = PTR_ERR(css);

            goto err_destroy;

        }

        init_cgroup_css(css, ss, cgrp);

    }

 

    /*将cgrp添加到上一层cgroup的children链表*/

    list_add(&cgrp->sibling, &cgrp->parent->children);

    /*增加root的cgroups数目计数*/

    root->number_of_cgroups++;

    /*在当前目录生成一个目录*/

    err = cgroup_create_dir(cgrp, dentry, mode);

    if (err < 0)

        goto err_remove;

 

    /* The cgroup directory was pre-locked for us */

    BUG_ON(!mutex_is_locked(&cgrp->dentry->d_inode->i_mutex));

    /*在cgrp下创建几个交互文件*/

    err = cgroup_populate_dir(cgrp);

    /* If err < 0, we have a half-filled directory - oh well ;) */

 

    mutex_unlock(&cgroup_mutex);

    mutex_unlock(&cgrp->dentry->d_inode->i_mutex);

 

    return 0;

 

 err_remove:

 

    list_del(&cgrp->sibling);

    root->number_of_cgroups--;

 

 err_destroy:

 

    for_each_subsys(root, ss) {

        if (cgrp->subsys[ss->subsys_id])

            ss->destroy(ss, cgrp);

    }

 

    mutex_unlock(&cgroup_mutex);

 

    /* Release the reference count that we took on the superblock */

    deactivate_super(sb);

 

    kfree(cgrp);

    return err;

}

在这个函数中,主要分配并初始化了一个cgroup结构.并且将它和它的上一层目录以及整个cgroupfs_root构成一个空间层次关系.然后,再调用subsys>create()操作函数.来让subsys知道已经创建了一个cgroup结构.

为了理顺这一部份.将前面分析的cgroup文件系统挂载和cgroup的创建.以及接下来要分析的attach_task()操作总结成一个图.如下示: