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driver core: Add device_show_string() helper for sysfs attributes

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For drivers wishing to expose an unsigned long, int or bool at a static
memory location in sysfs, the driver core provides ready-made helpers
such as device_show_ulong() to be used as ->show() callback.

Some drivers need to expose a string and so far they all provide their
own ->show() implementation.  arch/powerpc/perf/hv-24x7.c went so far
as to create a device_show_string() helper but kept it private.

Make it public for reuse by other drivers.  The pattern seems to be
sufficiently frequent to merit a public helper.

Add a DEVICE_STRING_ATTR_RO() macro in line with the existing
DEVICE_ULONG_ATTR() and similar macros to ease declaration of string
attributes.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/2e3eaaf2600bb55c0415c23ba301e809403a7aa2.1713608122.git.lukas@wunner.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Lukas Wunner 2024-04-20 22:00:01 +02:00 committed by Greg Kroah-Hartman
parent e5019b1423
commit 3cc50d07be
3 changed files with 24 additions and 10 deletions
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10
arch/powerpc/perf/hv-24x7.c
View file

@ -425,16 +425,6 @@ static char *memdup_to_str(char *maybe_str, int max_len, gfp_t gfp)
return kasprintf(gfp, "%.*s", max_len, maybe_str);
}
static ssize_t device_show_string(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct dev_ext_attribute *d;
d = container_of(attr, struct dev_ext_attribute, attr);
return sprintf(buf, "%s\n", (char *)d->var);
}
static ssize_t cpumask_show(struct device *dev,
struct device_attribute *attr, char *buf)
{

9
drivers/base/core.c
View file

@ -2538,6 +2538,15 @@ ssize_t device_show_bool(struct device *dev, struct device_attribute *attr,
}
EXPORT_SYMBOL_GPL(device_show_bool);
ssize_t device_show_string(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct dev_ext_attribute *ea = to_ext_attr(attr);
return sysfs_emit(buf, "%s\n", (char *)ea->var);
}
EXPORT_SYMBOL_GPL(device_show_string);
/**
* device_release - free device structure.
* @kobj: device's kobject.

15
include/linux/device.h
View file

@ -132,6 +132,8 @@ ssize_t device_show_bool(struct device *dev, struct device_attribute *attr,
char *buf);
ssize_t device_store_bool(struct device *dev, struct device_attribute *attr,
const char *buf, size_t count);
ssize_t device_show_string(struct device *dev, struct device_attribute *attr,
char *buf);
/**
* DEVICE_ATTR - Define a device attribute.
@ -251,6 +253,19 @@ ssize_t device_store_bool(struct device *dev, struct device_attribute *attr,
struct dev_ext_attribute dev_attr_##_name = \
{ __ATTR(_name, _mode, device_show_bool, device_store_bool), &(_var) }
/**
* DEVICE_STRING_ATTR_RO - Define a device attribute backed by a r/o string.
* @_name: Attribute name.
* @_mode: File mode.
* @_var: Identifier of string.
*
* Like DEVICE_ULONG_ATTR(), but @_var is a string. Because the length of the
* string allocation is unknown, the attribute must be read-only.
*/
#define DEVICE_STRING_ATTR_RO(_name, _mode, _var) \
struct dev_ext_attribute dev_attr_##_name = \
{ __ATTR(_name, (_mode) & ~0222, device_show_string, NULL), (_var) }
#define DEVICE_ATTR_IGNORE_LOCKDEP(_name, _mode, _show, _store) \
struct device_attribute dev_attr_##_name = \
__ATTR_IGNORE_LOCKDEP(_name, _mode, _show, _store)