[PATCH 0/1] ns: introduce proc_get_ns_by_fd()

[Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On 09/25, Konstantin Khlebnikov wrote:
>
> +struct ns_common *proc_ns_fdget(int fd, int nstype, struct fd *fd_ref)
>  {
> -	struct file *file;
> +	struct ns_common *ns;
> +	struct fd f;
>  
> -	file = fget(fd);
> -	if (!file)
> +	f = fdget(fd);
> +	if (!f.file)
>  		return ERR_PTR(-EBADF);
>  
> -	if (file->f_op != &ns_file_operations)
> +	if (f.file->f_op != &ns_file_operations)
> +		goto out_invalid;
> +
> +	ns = get_proc_ns(file_inode(f.file));
> +	if (nstype && (ns->ops->type != nstype))
>  		goto out_invalid;
>  
> -	return file;
> +	*fd_ref = f;
> +	return ns;
>  
>  out_invalid:
> -	fput(file);
> +	fdput(f);
>  	return ERR_PTR(-EINVAL);
>  }

Well yes, fdget() makes sense but this is minor.

Honestly, I do not really like the new helper... I understand this
is subjective, so I won't insist. But how about 1/1? We do not need
fd/file at all. With this patch your sys_getvpid() can just use
proc_get_ns_by_fd(fd, CLONE_NEWPID) and put_pid_ns().

Eric, what do you think?

See also "TODO" in the changelog.

Oleg.