Re: [PATCH] cgroup: support checking of subsystem dependencies

[KAMEZAWA Hiroyuki]

On Wed, 18 Jun 2008 16:01:49 +0800
Li Zefan <lizf@xxxxxxxxxxxxxx> wrote:

> This allows one subsystem to require that it only be mounted when some
> other subsystems are also present in the proposed hierarchy.
> 
> For example if subsystem foo depends on bar, the following will fail:
>  # mount -t cgroup -ofoo xxx /dev/cgroup
> 
> You should mount with both subsystems:
>  # mount -t cgroup -ofoo,bar xxx /dev/cgroup
> 
I'm just curious. May I ask "Is there such cgroup subsystem now ?"

Thanks,
-Kame



> Signed-off-by: Li Zefan <lizf@xxxxxxxxxxxxxx>
> ---
>  Documentation/cgroups.txt |    6 ++++++
>  include/linux/cgroup.h    |    2 ++
>  kernel/cgroup.c           |   30 ++++++++++++++++++++++++++++++
>  3 files changed, 38 insertions(+), 0 deletions(-)
> 
> diff --git a/Documentation/cgroups.txt b/Documentation/cgroups.txt
> index 824fc02..8252f5b 100644
> --- a/Documentation/cgroups.txt
> +++ b/Documentation/cgroups.txt
> @@ -530,6 +530,12 @@ and root cgroup. Currently this will only involve movement between
>  the default hierarchy (which never has sub-cgroups) and a hierarchy
>  that is being created/destroyed (and hence has no sub-cgroups).
>  
> +int subsys_depend(struct cgroup_subsys *ss, unsigned long subsys_bits)
> +
> +Called when a cgroup subsystem wants to check if some other subsystems
> +are also present in the proposed hierarchy. If this method returns error,
> +the mount of the cgroup filesystem will fail.
> +
>  4. Questions
>  ============
>  
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index e155aa7..fc99ba4 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -305,6 +305,8 @@ struct cgroup_subsys {
>  			struct cgroup *cgrp);
>  	void (*post_clone)(struct cgroup_subsys *ss, struct cgroup *cgrp);
>  	void (*bind)(struct cgroup_subsys *ss, struct cgroup *root);
> +	int (*subsys_depend)(struct cgroup_subsys *ss,
> +			      unsigned long subsys_bits);
>  	/*
>  	 * This routine is called with the task_lock of mm->owner held
>  	 */
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 15ac0e1..a4c8671 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -837,6 +837,25 @@ static int parse_cgroupfs_options(char *data,
>  	return 0;
>  }
>  
> +static int check_subsys_dependency(unsigned long subsys_bits)
> +{
> +	int i;
> +	int ret;
> +	struct cgroup_subsys *ss;
> +
> +	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
> +		ss = subsys[i];
> +
> +		if (test_bit(i, &subsys_bits) && ss->subsys_depend) {
> +			ret = ss->subsys_depend(ss, subsys_bits);
> +			if (ret)
> +				return ret;
> +		}
> +	}
> +
> +	return 0;
> +}
> +
>  static int cgroup_remount(struct super_block *sb, int *flags, char *data)
>  {
>  	int ret = 0;
> @@ -852,6 +871,10 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
>  	if (ret)
>  		goto out_unlock;
>  
> +	ret = check_subsys_dependency(opts.subsys_bits);
> +	if (ret)
> +		goto out_unlock;
> +
>  	/* Don't allow flags to change at remount */
>  	if (opts.flags != root->flags) {
>  		ret = -EINVAL;
> @@ -972,6 +995,13 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
>  		return ret;
>  	}
>  
> +	ret = check_subsys_dependency(opts.subsys_bits);
> +	if (ret) {
> +		if (opts.release_agent)
> +			kfree(opts.release_agent);
> +		return ret;
> +	}
> +
>  	root = kzalloc(sizeof(*root), GFP_KERNEL);
>  	if (!root) {
>  		if (opts.release_agent)
> -- 
> 1.5.4.rc3
> 
> 
> 

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