module: show version information for built-in modules in sysfs

Currently only drivers that are built as modules have their versions
shown in /sys/module/<module_name>/version, but this information might
also be useful for built-in drivers as well. This especially important
for drivers that do not define any parameters - such drivers, if
built-in, are completely invisible from userspace.

This patch changes MODULE_VERSION() macro so that in case when we are
compiling built-in module, version information is stored in a separate
section. Kernel then uses this data to create 'version' sysfs attribute
in the same fashion it creates attributes for module parameters.

Signed-off-by: Dmitry Torokhov <dtor@vmware.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

3 files changed, 88 insertions, 11 deletions

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 68649336c4ad..6ebb81030d2d 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -364,6 +364,13 @@
                 VMLINUX_SYMBOL(__start___param) = .;                    \
                 *(__param)                                              \
                 VMLINUX_SYMBOL(__stop___param) = .;                     \
+        }                                                               \
+                                                                        \
+        /* Built-in module versions. */                                 \
+        __modver : AT(ADDR(__modver) - LOAD_OFFSET) {                   \
+                VMLINUX_SYMBOL(__start___modver) = .;                   \
+                *(__modver)                                             \
+                VMLINUX_SYMBOL(__stop___modver) = .;                    \
                 . = ALIGN((align));                                     \
                 VMLINUX_SYMBOL(__end_rodata) = .;                       \
         }                                                               \
diff --git a/include/linux/module.h b/include/linux/module.h
index 8b17fd8c790d..50efcd3ae850 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -58,6 +58,12 @@ struct module_attribute {
         void (*free)(struct module *);
 };
 
+struct module_version_attribute {
+        struct module_attribute mattr;
+        const char *module_name;
+        const char *version;
+};
+
 struct module_kobject
 {
         struct kobject kobj;
@@ -161,7 +167,28 @@ extern struct module __this_module;
   Using this automatically adds a checksum of the .c files and the
   local headers in "srcversion".
 */
+
+#ifdef MODULE
 #define MODULE_VERSION(_version) MODULE_INFO(version, _version)
+#else
+#define MODULE_VERSION(_version)                                        \
+        extern ssize_t __modver_version_show(struct module_attribute *, \
+                                             struct module *, char *);  \
+        static struct module_version_attribute __modver_version_attr    \
+        __used                                                          \
+    __attribute__ ((__section__ ("__modver"),aligned(sizeof(void *)))) \
+        = {                                                             \
+                .mattr  = {                                             \
+                        .attr   = {                                     \
+                                .name   = "version",                    \
+                                .mode   = S_IRUGO,                      \
+                        },                                              \
+                        .show   = __modver_version_show,                \
+                },                                                      \
+                .module_name    = KBUILD_MODNAME,                       \
+                .version        = _version,                             \
+        }
+#endif
 
 /* Optional firmware file (or files) needed by the module
  * format is simply firmware file name.  Multiple firmware
diff --git a/kernel/params.c b/kernel/params.c
index 08107d181758..0da1411222b9 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -719,9 +719,7 @@ void destroy_params(const struct kernel_param *params, unsigned num)
                         params[i].ops->free(params[i].arg);
 }
 
-static void __init kernel_add_sysfs_param(const char *name,
-                                          struct kernel_param *kparam,
-                                          unsigned int name_skip)
+static struct module_kobject * __init locate_module_kobject(const char *name)
 {
         struct module_kobject *mk;
         struct kobject *kobj;
@@ -729,10 +727,7 @@ static void __init kernel_add_sysfs_param(const char *name,
 
         kobj = kset_find_obj(module_kset, name);
         if (kobj) {
-                /* We already have one.  Remove params so we can add more. */
                 mk = to_module_kobject(kobj);
-                /* We need to remove it before adding parameters. */
-                sysfs_remove_group(&mk->kobj, &mk->mp->grp);
         } else {
                 mk = kzalloc(sizeof(struct module_kobject), GFP_KERNEL);
                 BUG_ON(!mk);
@@ -743,15 +738,36 @@ static void __init kernel_add_sysfs_param(const char *name,
                                            "%s", name);
                 if (err) {
                         kobject_put(&mk->kobj);
-                        printk(KERN_ERR "Module '%s' failed add to sysfs, "
-                               "error number %d\n", name, err);
-                        printk(KERN_ERR "The system will be unstable now.\n");
-                        return;
+                        printk(KERN_ERR
+                                "Module '%s' failed add to sysfs, error number %d\n",
+                                name, err);
+                        printk(KERN_ERR
+                                "The system will be unstable now.\n");
+                        return NULL;
                 }
-                /* So that exit path is even. */
+
+                /* So that we hold reference in both cases. */
                 kobject_get(&mk->kobj);
         }
 
+        return mk;
+}
+
+static void __init kernel_add_sysfs_param(const char *name,
+                                          struct kernel_param *kparam,
+                                          unsigned int name_skip)
+{
+        struct module_kobject *mk;
+        int err;
+
+        mk = locate_module_kobject(name);
+        if (!mk)
+                return;
+
+        /* We need to remove old parameters before adding more. */
+        if (mk->mp)
+                sysfs_remove_group(&mk->kobj, &mk->mp->grp);
+
         /* These should not fail at boot. */
         err = add_sysfs_param(mk, kparam, kparam->name + name_skip);
         BUG_ON(err);
@@ -796,6 +812,32 @@ static void __init param_sysfs_builtin(void)
         }
 }
 
+ssize_t __modver_version_show(struct module_attribute *mattr,
+                              struct module *mod, char *buf)
+{
+        struct module_version_attribute *vattr =
+                container_of(mattr, struct module_version_attribute, mattr);
+
+        return sprintf(buf, "%s\n", vattr->version);
+}
+
+extern struct module_version_attribute __start___modver[], __stop___modver[];
+
+static void __init version_sysfs_builtin(void)
+{
+        const struct module_version_attribute *vattr;
+        struct module_kobject *mk;
+        int err;
+
+        for (vattr = __start___modver; vattr < __stop___modver; vattr++) {
+                mk = locate_module_kobject(vattr->module_name);
+                if (mk) {
+                        err = sysfs_create_file(&mk->kobj, &vattr->mattr.attr);
+                        kobject_uevent(&mk->kobj, KOBJ_ADD);
+                        kobject_put(&mk->kobj);
+                }
+        }
+}
 
 /* module-related sysfs stuff */
 
@@ -875,6 +917,7 @@ static int __init param_sysfs_init(void)
         }
         module_sysfs_initialized = 1;
 
+        version_sysfs_builtin();
         param_sysfs_builtin();
 
         return 0;