linux-kernel - Re: [PATCH v2 02/10] sysfs: introduce callback attribute_group::bin

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Message-ID: <da774e71-39f3-43ec-a366-c8c893132447@gmx.de>
Date: Wed, 6 Nov 2024 20:27:44 +0100
From: Armin Wolf <W_Armin@....de>
To: Thomas Weißschuh <linux@...ssschuh.net>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>, Bjorn Helgaas
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Subject: Re: [PATCH v2 02/10] sysfs: introduce callback
 attribute_group::bin_size

Am 03.11.24 um 18:03 schrieb Thomas Weißschuh:

> Several drivers need to dynamically calculate the size of an binary
> attribute. Currently this is done by assigning attr->size from the
> is_bin_visible() callback.

Hi,

i really like your idea of introducing this new callback, it will be very
useful for the wmi-bmof driver :).

Thanks,
Armin Wolf

>
> This has drawbacks:
> * It is not documented.
> * A single attribute can be instantiated multiple times, overwriting the
>    shared size field.
> * It prevents the structure to be moved to read-only memory.
>
> Introduce a new dedicated callback to calculate the size of the
> attribute.
>
> Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
> ---
>   fs/sysfs/group.c      | 2 ++
>   include/linux/sysfs.h | 8 ++++++++
>   2 files changed, 10 insertions(+)
>
> diff --git a/fs/sysfs/group.c b/fs/sysfs/group.c
> index 45b2e92941da1f49dcc71af3781317c61480c956..8b01a7eda5fb3239e138372417d01967c7a3f122 100644
> --- a/fs/sysfs/group.c
> +++ b/fs/sysfs/group.c
> @@ -98,6 +98,8 @@ static int create_files(struct kernfs_node *parent, struct kobject *kobj,
>   				if (!mode)
>   					continue;
>   			}
> +			if (grp->bin_size)
> +				size = grp->bin_size(kobj, *bin_attr, i);
>
>   			WARN(mode & ~(SYSFS_PREALLOC | 0664),
>   			     "Attribute %s: Invalid permissions 0%o\n",
> diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
> index c4e64dc112063f7cb89bf66059d0338716089e87..4746cccb95898b24df6f53de9421ea7649b5568f 100644
> --- a/include/linux/sysfs.h
> +++ b/include/linux/sysfs.h
> @@ -87,6 +87,11 @@ do {							\
>    *		SYSFS_GROUP_VISIBLE() when assigning this callback to
>    *		specify separate _group_visible() and _attr_visible()
>    *		handlers.
> + * @bin_size:
> + *		Optional: Function to return the size of a binary attribute
> + *		of the group. Will be called repeatedly for each binary
> + *		attribute in the group. Overwrites the size field embedded
> + *		inside the attribute itself.
>    * @attrs:	Pointer to NULL terminated list of attributes.
>    * @bin_attrs:	Pointer to NULL terminated list of binary attributes.
>    *		Either attrs or bin_attrs or both must be provided.
> @@ -97,6 +102,9 @@ struct attribute_group {
>   					      struct attribute *, int);
>   	umode_t			(*is_bin_visible)(struct kobject *,
>   						  struct bin_attribute *, int);
> +	size_t			(*bin_size)(struct kobject *,
> +					    const struct bin_attribute *,
> +					    int);
>   	struct attribute	**attrs;
>   	struct bin_attribute	**bin_attrs;
>   };
>