On Mon, Mar 29, 2021 at 11:44:25AM +0300, Heikki Krogerus wrote:
> Introducing usb_for_each_port(). It works the same way as
> usb_for_each_dev(), but instead of going through every USB
> device in the system, it walks through the USB ports in the
> system.
>
> Signed-off-by: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
> ---
> drivers/usb/core/usb.c | 46 ++++++++++++++++++++++++++++++++++++++++++
> include/linux/usb.h | 1 +
> 2 files changed, 47 insertions(+)
>
> diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
> index 2ce3667ec6fae..62368c4ed37af 100644
> --- a/drivers/usb/core/usb.c
> +++ b/drivers/usb/core/usb.c
> @@ -398,6 +398,52 @@ int usb_for_each_dev(void *data, int (*fn)(struct usb_device *, void *))
> }
> EXPORT_SYMBOL_GPL(usb_for_each_dev);
>
> +struct each_hub_arg {
> + void *data;
> + int (*fn)(struct device *, void *);
> +};
> +
> +static int __each_hub(struct usb_device *hdev, void *data)
> +{
> + struct each_hub_arg *arg = (struct each_hub_arg *)data;
> + struct usb_hub *hub;
> + int ret = 0;
> + int i;
> +
> + hub = usb_hub_to_struct_hub(hdev);
> + if (!hub)
> + return 0;
What happens if the hub is removed exactly now? Although hdev is
reference-counted (and the loop iterator does take a reference to it),
usb_hub_to_struct_hub doesn't take a reference to hub. And hub->ports
isn't refcounted at all.
> +
> + mutex_lock(&usb_port_peer_mutex);
> +
> + for (i = 0; i < hdev->maxchild; i++) {
> + ret = arg->fn(&hub->ports[i]->dev, arg->data);
> + if (ret)
> + break;
> + }
> +
> + mutex_unlock(&usb_port_peer_mutex);
I have a feeling that it would be better to take and release this mutex
in usb_for_each_port (or its caller), so that it is held over the whole
loop.
Alan Stern
> +
> + return ret;
> +}
> +
> +/**
> + * usb_for_each_port - interate over all USB ports in the system
> + * @data: data pointer that will be handed to the callback function
> + * @fn: callback function to be called for each USB port
> + *
> + * Iterate over all USB ports and call @fn for each, passing it @data. If it
> + * returns anything other than 0, we break the iteration prematurely and return
> + * that value.
> + */
> +int usb_for_each_port(void *data, int (*fn)(struct device *, void *))
> +{
> + struct each_hub_arg arg = {data, fn};
> +
> + return usb_for_each_dev(&arg, __each_hub);
> +}
> +EXPORT_SYMBOL_GPL(usb_for_each_port);
> +
> /**
> * usb_release_dev - free a usb device structure when all users of it are finished.
> * @dev: device that's been disconnected
> diff --git a/include/linux/usb.h b/include/linux/usb.h
> index ddd2f5b2a2827..e4d2eb703cf89 100644
> --- a/include/linux/usb.h
> +++ b/include/linux/usb.h
> @@ -871,6 +871,7 @@ extern int usb_match_one_id(struct usb_interface *interface,
> const struct usb_device_id *id);
>
> extern int usb_for_each_dev(void *data, int (*fn)(struct usb_device *, void *));
> +int usb_for_each_port(void *data, int (*fn)(struct device *, void *));
> extern struct usb_interface *usb_find_interface(struct usb_driver *drv,
> int minor);
> extern struct usb_interface *usb_ifnum_to_if(const struct usb_device *dev,
> --
> 2.30.2
>
