livepatch: add sysfs entry "patched" for each klp_object

Add per klp_object sysfs entry "patched". It makes it easier to debug
typos in the module name.

Signed-off-by: Song Liu <song@kernel.org>
Reviewed-by: Joe Lawrence <joe.lawrence@redhat.com>
[pmladek@suse.com: Updated kernel version when the sysfs file will be introduced]
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220902205208.3117798-2-song@kernel.org

Documentation/ABI/testing/sysfs-kernel-livepatch

@@ -55,6 +55,14 @@ Description:
 		The object directory contains subdirectories for each function
 		that is patched within the object.
 
+What:		/sys/kernel/livepatch/<patch>/<object>/patched
+Date:		August 2022
+KernelVersion:	6.1.0
+Contact:	live-patching@vger.kernel.org
+Description:
+		An attribute which indicates whether the object is currently
+		patched.
+
 What:		/sys/kernel/livepatch/<patch>/<object>/<function,sympos>
 Date:		Nov 2014
 KernelVersion:	3.19.0

kernel/livepatch/core.c

@@ -325,6 +325,7 @@ int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
  * /sys/kernel/livepatch/<patch>/transition
  * /sys/kernel/livepatch/<patch>/force
  * /sys/kernel/livepatch/<patch>/<object>
+ * /sys/kernel/livepatch/<patch>/<object>/patched
  * /sys/kernel/livepatch/<patch>/<object>/<function,sympos>
  */
 static int __klp_disable_patch(struct klp_patch *patch);
@@ -431,6 +432,22 @@ static struct attribute *klp_patch_attrs[] = {
 };
 ATTRIBUTE_GROUPS(klp_patch);
 
+static ssize_t patched_show(struct kobject *kobj,
+			    struct kobj_attribute *attr, char *buf)
+{
+	struct klp_object *obj;
+
+	obj = container_of(kobj, struct klp_object, kobj);
+	return sysfs_emit(buf, "%d\n", obj->patched);
+}
+
+static struct kobj_attribute patched_kobj_attr = __ATTR_RO(patched);
+static struct attribute *klp_object_attrs[] = {
+	&patched_kobj_attr.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(klp_object);
+
 static void klp_free_object_dynamic(struct klp_object *obj)
 {
 	kfree(obj->name);
@@ -576,6 +593,7 @@ static void klp_kobj_release_object(struct kobject *kobj)
 static struct kobj_type klp_ktype_object = {
 	.release = klp_kobj_release_object,
 	.sysfs_ops = &kobj_sysfs_ops,
+	.default_groups = klp_object_groups,
 };
 
 static void klp_kobj_release_func(struct kobject *kobj)