param: locking for kernel parameters

There may be cases (most obviously, sysfs-writable charp parameters) where
a module needs to prevent sysfs access to parameters.

Rather than express this in terms of a big lock, the functions are
expressed in terms of what they protect against.  This is clearer, esp.
if the implementation changes to a module-level or even param-level lock.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Tested-by: Phil Carmody <ext-phil.2.carmody@nokia.com>

1 files changed, 56 insertions, 0 deletions

diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index 6d48831fe7d2..ca74a3402d63 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -130,6 +130,62 @@ __check_old_set_param(int (*oldset)(const char *, struct kernel_param *))
 #define module_param(name, type, perm)                          \
         module_param_named(name, name, type, perm)
 
+/**
+ * kparam_block_sysfs_write - make sure a parameter isn't written via sysfs.
+ * @name: the name of the parameter
+ *
+ * There's no point blocking write on a paramter that isn't writable via sysfs!
+ */
+#define kparam_block_sysfs_write(name)                  \
+        do {                                            \
+                BUG_ON(!(__param_##name.perm & 0222));  \
+                __kernel_param_lock();                  \
+        } while (0)
+
+/**
+ * kparam_unblock_sysfs_write - allows sysfs to write to a parameter again.
+ * @name: the name of the parameter
+ */
+#define kparam_unblock_sysfs_write(name)                \
+        do {                                            \
+                BUG_ON(!(__param_##name.perm & 0222));  \
+                __kernel_param_unlock();                \
+        } while (0)
+
+/**
+ * kparam_block_sysfs_read - make sure a parameter isn't read via sysfs.
+ * @name: the name of the parameter
+ *
+ * This also blocks sysfs writes.
+ */
+#define kparam_block_sysfs_read(name)                   \
+        do {                                            \
+                BUG_ON(!(__param_##name.perm & 0444));  \
+                __kernel_param_lock();                  \
+        } while (0)
+
+/**
+ * kparam_unblock_sysfs_read - allows sysfs to read a parameter again.
+ * @name: the name of the parameter
+ */
+#define kparam_unblock_sysfs_read(name)                 \
+        do {                                            \
+                BUG_ON(!(__param_##name.perm & 0444));  \
+                __kernel_param_unlock();                \
+        } while (0)
+
+#ifdef CONFIG_SYSFS
+extern void __kernel_param_lock(void);
+extern void __kernel_param_unlock(void);
+#else
+static inline void __kernel_param_lock(void)
+{
+}
+static inline void __kernel_param_unlock(void)
+{
+}
+#endif
+
 #ifndef MODULE
 /**
  * core_param - define a historical core kernel parameter.