Re: cpuset: return -EINVAL for legacy non-subset child creation attempt

[Zefan Li]

On 2015/12/1 23:22, Mike Galbraith wrote:
> A legacy hierarchy child set that is not a subset of its parent is not
> a permissions issue, it's an invalid configuration.  Return -EINVAL.

It's sometimes arguable which errno should be used. In this case I don't
see why we can't use EACCES. It's even documented in man page.

       EACCES Attempted to add, using write(2), a CPU  or  memory  node  to  a
              cpuset, when that CPU or memory node was not already in its par-
              ent.

Let's see another example. In mmap manual:

	EACCES A  file descriptor refers to a non-regular file.

We can argue fd of a non-regular file is an invalid configuration, but
here we return EACCES.

> Signed-off-by: Mike Galbraith <efault@xxxxxx>
> ---
>   kernel/cpuset.c |    3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
>
> --- a/kernel/cpuset.c
> +++ b/kernel/cpuset.c
> @@ -472,7 +472,7 @@ static int validate_change(struct cpuset
>   	par = parent_cs(cur);
>
>   	/* On legacy hiearchy, we must be a subset of our parent cpuset. */
> -	ret = -EACCES;
> +	ret = -EINVAL;
>   	if (!cgroup_subsys_on_dfl(cpuset_cgrp_subsys) &&
>   	    !is_cpuset_subset(trial, par))
>   		goto out;
> @@ -481,7 +481,6 @@ static int validate_change(struct cpuset
>   	 * If either I or some sibling (!= me) is exclusive, we can't
>   	 * overlap
>   	 */
> -	ret = -EINVAL;
>   	cpuset_for_each_child(c, css, par) {
>   		if ((is_cpu_exclusive(trial) || is_cpu_exclusive(c)) &&
>   		    c != cur &&

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