linux-kernel - Re: [PATCH 1/2] driver core: bus.h: document bus notifiers better

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Message-ID: <CAJZ5v0g63jNzqsnvg_UC7aBhX9_aNT=s=K9JpU9x8UpfoJ=dXQ@mail.gmail.com>
Date:   Tue, 10 Jan 2023 13:52:24 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH 1/2] driver core: bus.h: document bus notifiers better

On Tue, Jan 10, 2023 at 1:43 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> The bus notifier values are not documented all that well, so clean this
> up and make a real enumerated type for them and document them much
> better.
>
> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
>  include/linux/device/bus.h | 43 +++++++++++++++++++++++++-------------
>  1 file changed, 29 insertions(+), 14 deletions(-)
>
> diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h
> index d529f644e92b..1e1a593348bc 100644
> --- a/include/linux/device/bus.h
> +++ b/include/linux/device/bus.h
> @@ -257,21 +257,36 @@ extern int bus_register_notifier(struct bus_type *bus,
>  extern int bus_unregister_notifier(struct bus_type *bus,
>                                    struct notifier_block *nb);
>
> -/* All 4 notifers below get called with the target struct device *
> - * as an argument. Note that those functions are likely to be called
> - * with the device lock held in the core, so be careful.
> +/**
> + * enum bus_notifier_event: Bus Notifier events that have happened
> + *
> + * These are the value passed to a bus notifier when a specific event happens.
> + *
> + * Note that bus notifiers are likely to be called with the device lock already
> + * held by the driver core, so be careful in any notifier callback as to what
> + * you do with the device structure.
> + *
> + * All bus notifiers are called with the target struct device * as an argument.
> + *
> + * BUS_NOTIFY_ADD_DEVICE: device is added to this bus
> + * BUS_NOTIFY_DEL_DEVICE: device is about to be removed from this bus
> + * BUS_NOTIFY_REMOVED_DEVICE: device is successfully removed from this bus
> + * BUS_NOTIFY_BIND_DRIVER: a driver is about to be bound to this device on this bus
> + * BUS_NOTIFY_BOUND_DRIVER: a driver is successfully bound to this device on this bus
> + * BUS_NOTIFY_UNBIND_DRIVER: a driver is about to be unbound from this device on this bus
> + * BUS_NOTIFY_UNBOUND_DRIVER: a driver is successfully unbound from this device on this bus
> + * BUS_NOTIFY_DRIVER_NOT_BOUND: a driver failed to be bound to this device on this bus
>   */
> -#define BUS_NOTIFY_ADD_DEVICE          0x00000001 /* device added */
> -#define BUS_NOTIFY_DEL_DEVICE          0x00000002 /* device to be removed */
> -#define BUS_NOTIFY_REMOVED_DEVICE      0x00000003 /* device removed */
> -#define BUS_NOTIFY_BIND_DRIVER         0x00000004 /* driver about to be
> -                                                     bound */
> -#define BUS_NOTIFY_BOUND_DRIVER                0x00000005 /* driver bound to device */
> -#define BUS_NOTIFY_UNBIND_DRIVER       0x00000006 /* driver about to be
> -                                                     unbound */
> -#define BUS_NOTIFY_UNBOUND_DRIVER      0x00000007 /* driver is unbound
> -                                                     from the device */
> -#define BUS_NOTIFY_DRIVER_NOT_BOUND    0x00000008 /* driver fails to be bound */
> +enum bus_notifier_event {
> +       BUS_NOTIFY_ADD_DEVICE =         0x00000001,
> +       BUS_NOTIFY_DEL_DEVICE =         0x00000002,
> +       BUS_NOTIFY_REMOVED_DEVICE =     0x00000003,
> +       BUS_NOTIFY_BIND_DRIVER =        0x00000004,
> +       BUS_NOTIFY_BOUND_DRIVER =       0x00000005,
> +       BUS_NOTIFY_UNBIND_DRIVER =      0x00000006,
> +       BUS_NOTIFY_UNBOUND_DRIVER =     0x00000007,
> +       BUS_NOTIFY_DRIVER_NOT_BOUND =   0x00000008,

I'm wondering why the values are in hex (the 0x prefix doesn't matter
for these numbers AFAICS) and what the initial zeros are for (AFAICS
they don't matter either).

> +};
>
>  extern struct kset *bus_get_kset(struct bus_type *bus);
>
> --