linux-kernel - Re: [PATCH v6 2/5] drivers: Add bus_for_each for iterating over the subsystems

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Message-ID: <8831b90c-4968-a618-a6ba-4bfcc97f74eb@csgroup.eu>
Date:   Sat, 3 Dec 2022 18:07:53 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Allen Webb <allenwebb@...gle.com>,
        "linux-modules@...r.kernel.org" <linux-modules@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Luis Chamberlain <mcgrof@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH v6 2/5] drivers: Add bus_for_each for iterating over the
 subsystems



Le 02/12/2022 à 23:47, Allen Webb a écrit :
> In order to print the match-id-based modaliases it must be possible to
> reach the match id tables of each driver. With this function it becomes
> possible to iterate over each subsystem which can be paired with
> iterating over each driver.
> 
> Signed-off-by: Allen Webb <allenwebb@...gle.com>
> ---
>   drivers/base/bus.c         | 42 ++++++++++++++++++++++++++++++++++++++
>   include/linux/device/bus.h |  1 +
>   2 files changed, 43 insertions(+)
> 
> diff --git a/drivers/base/bus.c b/drivers/base/bus.c
> index 7ca47e5b3c1f4..4e0c5925545e5 100644
> --- a/drivers/base/bus.c
> +++ b/drivers/base/bus.c
> @@ -178,6 +178,48 @@ static const struct kset_uevent_ops bus_uevent_ops = {
>   
>   static struct kset *bus_kset;
>   
> +/**
> + * bus_for_each - bus iterator.
> + * @start: bus to start iterating from.
> + * @data: data for the callback.
> + * @fn: function to be called for each device.
> + *
> + * Iterate over list of buses, and call @fn for each,
> + * passing it @data. If @start is not NULL, we use that bus to
> + * begin iterating from.
> + *
> + * We check the return of @fn each time. If it returns anything
> + * other than 0, we break out and return that value.
> + *
> + * NOTE: The bus that returns a non-zero value is not retained
> + * in any way, nor is its refcount incremented. If the caller needs
> + * to retain this data, it should do so, and increment the reference
> + * count in the supplied callback.
> + */
> +int bus_for_each(void *data, int (*fn)(struct bus_type *, void *))
> +{
> +	int error = 0;
> +	struct bus_type *bus;
> +	struct subsys_private *bus_prv;
> +	struct kset *subsys;
> +	struct kobject *k;

Those vars are not used outside of the list_for_each_entry() block, they 
should be declared inside the block.

> +
> +	spin_lock(&bus_kset->list_lock);
> +
> +	list_for_each_entry(k, &bus_kset->list, entry) {
> +		subsys = container_of(k, struct kset, kobj);
> +		bus_prv = container_of(subsys, struct subsys_private, subsys);
> +		bus = bus_prv->bus;
> +		error = fn(bus, data);
> +		if (error)
> +			break;
> +	}
> +
> +	spin_unlock(&bus_kset->list_lock);
> +	return error;
> +}
> +EXPORT_SYMBOL_GPL(bus_for_each);
> +
>   /* Manually detach a device from its associated driver. */
>   static ssize_t unbind_store(struct device_driver *drv, const char *buf,
>   			    size_t count)
> diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h
> index d8b29ccd07e56..82a5583437099 100644
> --- a/include/linux/device/bus.h
> +++ b/include/linux/device/bus.h
> @@ -161,6 +161,7 @@ void subsys_dev_iter_init(struct subsys_dev_iter *iter,
>   struct device *subsys_dev_iter_next(struct subsys_dev_iter *iter);
>   void subsys_dev_iter_exit(struct subsys_dev_iter *iter);
>   
> +int bus_for_each(void *data, int (*fn)(struct bus_type *, void *));
>   int bus_for_each_dev(struct bus_type *bus, struct device *start, void *data,
>   		     int (*fn)(struct device *dev, void *data));
>   struct device *bus_find_device(struct bus_type *bus, struct device *start,