Re: [PATCH v2 12/17] xen/hypfs: add new enter() and exit() per node callbacks

[Jan Beulich <jbeulich@xxxxxxxx>]

On 01.12.2020 09:21, Juergen Gross wrote:
> @@ -100,11 +112,58 @@ static void hypfs_unlock(void)
>      }
>  }
>  
> +const struct hypfs_entry *hypfs_node_enter(const struct hypfs_entry *entry)
> +{
> +    return entry;
> +}
> +
> +void hypfs_node_exit(const struct hypfs_entry *entry)
> +{
> +}
> +
> +static int node_enter(const struct hypfs_entry *entry)
> +{
> +    const struct hypfs_entry **last = &this_cpu(hypfs_last_node_entered);
> +
> +    entry = entry->funcs->enter(entry);
> +    if ( IS_ERR(entry) )
> +        return PTR_ERR(entry);
> +
> +    ASSERT(!*last || *last == entry->parent);
> +
> +    *last = entry;

In such a callback case I wonder whether you wouldn't want to also
guard against NULL coming back, perhaps simply by mistake, but of
course once handling it here such could even become permissible
behavior.

Jan