| Date | Sun, 11 Sep 2016 15:40:58 +0200 | From | Lukas Wunner <> | Subject | Re: [RFC/RFT][PATCH v2 2/7] driver core: Functional dependencies tracking support |
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On Thu, Sep 08, 2016 at 11:27:45PM +0200, Rafael J. Wysocki wrote: > +/** > + * device_is_dependent - Check if one device depends on another one > + * @dev: Device to check dependencies for. > + * @target: Device to check against. > + * > + * Check if @dev or any device dependent on it (its child or its consumer etc) > + * depends on @target. Return 1 if that is the case or 0 otherwise. > + */ > +static int device_is_dependent(struct device *dev, void *target) > +{ > + struct device_link *link; > + int ret; > + > + ret = device_for_each_child(dev, target, device_is_dependent); > + list_for_each_entry(link, &dev->links_to_consumers, s_node) { > + if (WARN_ON(link->consumer == target)) > + return 1; > + > + ret = ret || device_is_dependent(link->consumer, target); > + } > + return ret; > +}
What happens if someone tries to add a device link from a parent (as the consumer) to a child (as a supplier)? You're only checking if target is a consumer of dev, for full correctness you'd also have to check if target is a parent of dev. (Or grandparent, or great- grandparent, ... you need to walk the tree up to the root.)
The function can be sped up by returning immediately if a match is found instead of continuing searching and accumulating the result in ret, i.e.:
if (device_for_each_child(dev, target, device_is_dependent)) return 1;
and in the list_for_each_entry block:
if (device_is_dependent(link->consumer, target)) return 1;
Then at the end of the function "return 0".
I'd move the WARN_ON() to the single invocation of this function in device_link_add(), that way it's possible to use the function as a helper elsewhere should the need arise.
Thanks,
Lukas
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