Re: [PATCH 2/8] cgroup: implement cgroup_from_id()

[Kamezawa Hiroyuki]

(2013/04/08 17:20), Li Zefan wrote:
> This will be used as a replacement for css_lookup().
> 
> Signed-off-by: Li Zefan <lizefan@xxxxxxxxxx>
> ---
>   include/linux/cgroup.h |  1 +
>   kernel/cgroup.c        | 31 +++++++++++++++++++++++++------
>   2 files changed, 26 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index 96072e4..6ae8ae1 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -732,6 +732,7 @@ unsigned short css_depth(struct cgroup_subsys_state *css);
>   struct cgroup_subsys_state *cgroup_css_from_dir(struct file *f, int id);
>   
>   bool cgroup_is_ancestor(struct cgroup *child, struct cgroup *root);
> +struct cgroup *cgroup_from_id(struct cgroup_subsys *ss, int id);
>   
>   #else /* !CONFIG_CGROUPS */
>   
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index e87872c..5ae1e87 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -139,7 +139,7 @@ struct cgroupfs_root {
>   	unsigned long flags;
>   
>   	/* IDs for cgroups in this hierarchy */
> -	struct ida cgroup_ida;
> +	struct idr cgroup_idr;
>   
>   	/* The path to use for release notifications. */
>   	char release_agent_path[PATH_MAX];
> @@ -908,7 +908,7 @@ static void cgroup_free_fn(struct work_struct *work)
>   
>   	simple_xattrs_free(&cgrp->xattrs);
>   
> -	ida_simple_remove(&cgrp->root->cgroup_ida, cgrp->id);
> +	idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
>   	kfree(rcu_dereference_raw(cgrp->name));
>   	kfree(cgrp);
>   }
> @@ -1512,7 +1512,8 @@ static struct cgroupfs_root *cgroup_root_from_opts(struct cgroup_sb_opts *opts)
>   
>   	root->subsys_mask = opts->subsys_mask;
>   	root->flags = opts->flags;
> -	ida_init(&root->cgroup_ida);
> +	idr_init(&root->cgroup_idr);
> +
>   	if (opts->release_agent)
>   		strcpy(root->release_agent_path, opts->release_agent);
>   	if (opts->name)
> @@ -1531,7 +1532,7 @@ static void cgroup_drop_root(struct cgroupfs_root *root)
>   	spin_lock(&hierarchy_id_lock);
>   	ida_remove(&hierarchy_ida, root->hierarchy_id);
>   	spin_unlock(&hierarchy_id_lock);
> -	ida_destroy(&root->cgroup_ida);
> +	idr_destroy(&root->cgroup_idr);
>   	kfree(root);
>   }
>   
> @@ -1645,6 +1646,11 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
>   		mutex_lock(&cgroup_mutex);
>   		mutex_lock(&cgroup_root_mutex);
>   
> +		root_cgrp->id = idr_alloc(&root->cgroup_idr, root_cgrp,
> +					  0, 0, GFP_KERNEL);
> +		if (root_cgrp->id < 0)
> +			goto unlock_drop;
> +
>   		/* Check for name clashes with existing mounts */
>   		ret = -EBUSY;
>   		if (strlen(root->name))
> @@ -4104,7 +4110,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
>   		goto err_free_cgrp;
>   	rcu_assign_pointer(cgrp->name, name);
>   
> -	cgrp->id = ida_simple_get(&root->cgroup_ida, 1, 0, GFP_KERNEL);
> +	cgrp->id = idr_alloc(&root->cgroup_idr, cgrp, 1, 0, GFP_KERNEL);
>   	if (cgrp->id < 0)
>   		goto err_free_name;
>   
> @@ -4215,7 +4221,7 @@ err_free_all:
>   	/* Release the reference count that we took on the superblock */
>   	deactivate_super(sb);
>   err_free_id:
> -	ida_simple_remove(&root->cgroup_ida, cgrp->id);
> +	idr_remove(&root->cgroup_idr, cgrp->id);
>   err_free_name:
>   	kfree(rcu_dereference_raw(cgrp->name));
>   err_free_cgrp:
> @@ -5320,6 +5326,19 @@ bool cgroup_is_ancestor(struct cgroup *child, struct cgroup *root)
>   	return (child == root);
>   }
>   
> +/**
> + * cgroup_from_id - lookup cgroup by id
> + * @ss: cgroup subsys to be looked into.
> + * @id: the id
> + *
> + * Returns pointer to cgroup if there is valid one with id.
> + * NULL if not. Should be called under rcu_read_lock()
> + */
> +struct cgroup *cgroup_from_id(struct cgroup_subsys *ss, int id)
> +{
> +	return idr_find(&ss->root->cgroup_idr, id);
> +}
> +

How about checking cgroup_populated_dir() have been called once ?
If not, returning NULL.

Thanks,
-Kame






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