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sysfs: introduce callback attribute_group::bin_size

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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.

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@weissschuh.net>
Acked-by: Krzysztof Wilczyński <kw@linux.com>
Link: https://lore.kernel.org/r/20241103-sysfs-const-bin_attr-v2-2-71110628844c@weissschuh.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Thomas Weißschuh 2024-11-03 17:03:31 +00:00 committed by Greg Kroah-Hartman
parent 0afcee132b
commit bebf29b18f
2 changed files with 10 additions and 0 deletions
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2
fs/sysfs/group.c
View File

@ -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",

8
include/linux/sysfs.h
View File

@ -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;
};