Re: [PATCH -next 1/4] cgroup: Add cgroup_get_from_fd

[Tejun Heo <tj@kernel.org>]

Hello, Martin.

On Tue, Jun 21, 2016 at 05:23:19PM -0700, Martin KaFai Lau wrote:
> @@ -6205,6 +6206,31 @@ struct cgroup *cgroup_get_from_path(const char *path)
>  }
>  EXPORT_SYMBOL_GPL(cgroup_get_from_path);

Proper function comment would be nice.

> +struct cgroup *cgroup_get_from_fd(int fd)
> +{
> +	struct cgroup_subsys_state *css;
> +	struct cgroup *cgrp;
> +	struct file *f;
> +
> +	f = fget_raw(fd);
> +	if (!f)
> +		return NULL;

It returns NULL here.

> +	css = css_tryget_online_from_dir(f->f_path.dentry, NULL);
> +	fput(f);
> +	if (IS_ERR(css))
> +		return ERR_CAST(css);
> +
> +	cgrp = css->cgroup;
> +	if (!cgroup_on_dfl(cgrp)) {
> +		cgroup_put(cgrp);
> +		return ERR_PTR(-EINVAL);

But an ERR_PTR value here.  Is this intentional?  Also, wouldn't it
make more sense to return -EBADF here, given that that's what
css_tryget_online_from_dir() would return if the filesystem type is
wrong?

Thanks!

-- 
tejun