[PATCH v6 1/5] module: Add empty modalias sysfs attribute

[Allen Webb <allenwebb@xxxxxxxxxx>]

This adds the modalias sysfs attribute in preparation for its
implementation.

Signed-off-by: Allen Webb <allenwebb@xxxxxxxxxx>
---
 include/linux/module.h   |  1 +
 kernel/module/internal.h |  2 ++
 kernel/module/sysfs.c    | 33 +++++++++++++++++++++++++++++++++
 kernel/params.c          |  7 +++++++
 4 files changed, 43 insertions(+)

diff --git a/include/linux/module.h b/include/linux/module.h
index ec61fb53979a9..0bfa859a21566 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -47,6 +47,7 @@ struct module_kobject {
 	struct kobject *drivers_dir;
 	struct module_param_attrs *mp;
 	struct completion *kobj_completion;
+	struct bin_attribute modalias_attr;
 } __randomize_layout;
 
 struct module_attribute {
diff --git a/kernel/module/internal.h b/kernel/module/internal.h
index 2e2bf236f5582..8d7ae37584868 100644
--- a/kernel/module/internal.h
+++ b/kernel/module/internal.h
@@ -259,11 +259,13 @@ static inline void add_kallsyms(struct module *mod, const struct load_info *info
 #endif /* CONFIG_KALLSYMS */
 
 #ifdef CONFIG_SYSFS
+void add_modalias_attr(struct module_kobject *mk);
 int mod_sysfs_setup(struct module *mod, const struct load_info *info,
 		    struct kernel_param *kparam, unsigned int num_params);
 void mod_sysfs_teardown(struct module *mod);
 void init_param_lock(struct module *mod);
 #else /* !CONFIG_SYSFS */
+static inline void add_modalias_attr(struct module_kobject *mk) {}
 static inline int mod_sysfs_setup(struct module *mod,
 			   	  const struct load_info *info,
 			   	  struct kernel_param *kparam,
diff --git a/kernel/module/sysfs.c b/kernel/module/sysfs.c
index ce68f821dcd12..8dafec7455fbe 100644
--- a/kernel/module/sysfs.c
+++ b/kernel/module/sysfs.c
@@ -240,6 +240,37 @@ static inline void add_notes_attrs(struct module *mod, const struct load_info *i
 static inline void remove_notes_attrs(struct module *mod) { }
 #endif /* CONFIG_KALLSYMS */
 
+static ssize_t module_modalias_read(struct file *filp, struct kobject *kobj,
+				    struct bin_attribute *bin_attr,
+				    char *buf, loff_t pos, size_t count)
+{
+	return 0;
+}
+
+/* Used in kernel/params.c for builtin modules.
+ *
+ * `struct module_kobject` is used instead of `struct module` because for
+ * builtin modules, the `struct module` is not available when this is called.
+ */
+void add_modalias_attr(struct module_kobject *mk)
+{
+	sysfs_bin_attr_init(&mk->modalias_attr);
+	mk->modalias_attr.attr.name = "modalias";
+	mk->modalias_attr.attr.mode = 0444;
+	mk->modalias_attr.read = module_modalias_read;
+	if (sysfs_create_bin_file(&mk->kobj, &mk->modalias_attr)) {
+		/* We shouldn't ignore the return type, but there is nothing to
+		 * do.
+		 */
+		return;
+	}
+}
+
+static void remove_modalias_attr(struct module_kobject *mk)
+{
+	sysfs_remove_bin_file(&mk->kobj, &mk->modalias_attr);
+}
+
 static void del_usage_links(struct module *mod)
 {
 #ifdef CONFIG_MODULE_UNLOAD
@@ -398,6 +429,7 @@ int mod_sysfs_setup(struct module *mod,
 
 	add_sect_attrs(mod, info);
 	add_notes_attrs(mod, info);
+	add_modalias_attr(&mod->mkobj);
 
 	return 0;
 
@@ -415,6 +447,7 @@ int mod_sysfs_setup(struct module *mod,
 
 static void mod_sysfs_fini(struct module *mod)
 {
+	remove_modalias_attr(&mod->mkobj);
 	remove_notes_attrs(mod);
 	remove_sect_attrs(mod);
 	mod_kobject_put(mod);
diff --git a/kernel/params.c b/kernel/params.c
index 5b92310425c50..b7fd5313a3118 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -14,6 +14,12 @@
 #include <linux/ctype.h>
 #include <linux/security.h>
 
+#ifdef CONFIG_MODULES
+#include "module/internal.h"
+#else
+static inline void add_modalias_attr(struct module_kobject *mk) {}
+#endif /* !CONFIG_MODULES */
+
 #ifdef CONFIG_SYSFS
 /* Protects all built-in parameters, modules use their own param_lock */
 static DEFINE_MUTEX(param_lock);
@@ -815,6 +821,7 @@ static void __init kernel_add_sysfs_param(const char *name,
 	BUG_ON(err);
 	kobject_uevent(&mk->kobj, KOBJ_ADD);
 	kobject_put(&mk->kobj);
+	add_modalias_attr(mk);
 }
 
 /*
-- 
2.37.3