Linux 3.12 compat: New shrinker API

torvalds/linux@24f7c6 introduced a new shrinker API while
torvalds/linux@a0b021 dropped support for the old shrinker API.
This patch adds support for the new shrinker API by wrapping
the old one with the new one.

This change also reorganizes the autotools checks on the shrinker
API such that the configure script will fail early if an unknown
API is encountered in the future.

Support for the set_shrinker() API which was used by Linux 2.6.22
and older has been dropped.  As a general rule compatibility is
only maintained back to Linux 2.6.26.

Signed-off-by: Richard Yao <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes zfsonlinux/zfs#1732
Closes zfsonlinux/zfs#1822
Closes #293
Closes #307

1 files changed, 143 insertions, 83 deletions

diff --git a/include/linux/mm_compat.h b/include/linux/mm_compat.h
index cb1bef9a4..37c9b0875 100644
--- a/include/linux/mm_compat.h
+++ b/include/linux/mm_compat.h
@@ -148,107 +148,167 @@ extern shrink_icache_memory_t shrink_icache_memory_fn;
 #endif /* HAVE_SHRINK_ICACHE_MEMORY */
 
 /*
- * Linux 2.6. - 2.6. Shrinker API Compatibility.
+ * Due to frequent changes in the shrinker API the following
+ * compatibility wrappers should be used.  They are as follows:
+ *
+ * SPL_SHRINKER_DECLARE is used to declare the shrinker which is
+ * passed to spl_register_shrinker()/spl_unregister_shrinker().  Use
+ * shrinker_name to set the shrinker variable name, shrinker_callback
+ * to set the callback function, and seek_cost to define the cost of
+ * reclaiming an object.
+ *
+ *   SPL_SHRINKER_DECLARE(shrinker_name, shrinker_callback, seek_cost);
+ *
+ * SPL_SHRINKER_CALLBACK_FWD_DECLARE is used when a forward declaration
+ * of the shrinker callback function is required.  Only the callback
+ * function needs to be passed.
+ *
+ *   SPL_SHRINKER_CALLBACK_FWD_DECLARE(shrinker_callback);
+ *
+ * SPL_SHRINKER_CALLBACK_WRAPPER is used to declare the callback function
+ * which is registered with the shrinker.  This function will call your
+ * custom shrinker which must use the following prototype.  Notice the
+ * leading __'s, these must be appended to the callback_function name.
+ *
+ *   int  __shrinker_callback(struct shrinker *, struct shrink_control *)
+ *   SPL_SHRINKER_CALLBACK_WRAPPER(shrinker_callback);a
+ *
+ *
+ * Example:
+ *
+ * SPL_SHRINKER_CALLBACK_FWD_DECLARE(my_shrinker_fn);
+ * SPL_SHRINKER_DECLARE(my_shrinker, my_shrinker_fn, 1);
+ *
+ * static int
+ * __my_shrinker_fn(struct shrinker *shrink, struct shrink_control *sc)
+ * {
+ *	if (sc->nr_to_scan) {
+ *		...scan objects in the cache and reclaim them...
+ *	}
+ *
+ *	...calculate number of objects in the cache...
+ *
+ *	return (number of objects in the cache);
+ * }
+ * SPL_SHRINKER_CALLBACK_WRAPPER(my_shrinker_fn);
  */
-#ifdef HAVE_SET_SHRINKER
-typedef struct spl_shrinker {
-	struct shrinker *shrinker;
-	shrinker_t fn;
-	int seeks;
-} spl_shrinker_t;
-
-static inline void
-spl_register_shrinker(spl_shrinker_t *ss)
-{
-	ss->shrinker = set_shrinker(ss->seeks, ss->fn);
-}
 
-static inline void
-spl_unregister_shrinker(spl_shrinker_t *ss)
-{
-	remove_shrinker(ss->shrinker);
-}
+#define	spl_register_shrinker(x)	register_shrinker(x)
+#define	spl_unregister_shrinker(x)	unregister_shrinker(x)
 
-# define SPL_SHRINKER_DECLARE(s, x, y)                                 \
-	static spl_shrinker_t s = {                                    \
-		.shrinker = NULL,                                      \
-		.fn = x,                                               \
-		.seeks = y                                             \
-	}
-
-# define SPL_SHRINKER_CALLBACK_FWD_DECLARE(fn)                         \
-	static int fn(int, unsigned int)
-# define SPL_SHRINKER_CALLBACK_WRAPPER(fn)                             \
-static int                                                             \
-fn(int nr_to_scan, unsigned int gfp_mask)                              \
-{                                                                      \
-	struct shrink_control sc;                                      \
-                                                                       \
-        sc.nr_to_scan = nr_to_scan;                                    \
-        sc.gfp_mask = gfp_mask;                                        \
-                                                                       \
-	return __ ## fn(NULL, &sc);                                    \
+/*
+ * Linux 2.6.23 - 2.6.34 Shrinker API Compatibility.
+ */
+#if defined(HAVE_2ARGS_OLD_SHRINKER_CALLBACK)
+#define	SPL_SHRINKER_DECLARE(s, x, y)					\
+static struct shrinker s = {						\
+	.shrink = x,							\
+	.seeks = y							\
 }
 
-#else
+#define	SPL_SHRINKER_CALLBACK_FWD_DECLARE(fn)				\
+static int fn(int nr_to_scan, unsigned int gfp_mask)
 
-# define spl_register_shrinker(x)	register_shrinker(x)
-# define spl_unregister_shrinker(x)	unregister_shrinker(x)
-# define SPL_SHRINKER_DECLARE(s, x, y)                                 \
-	static struct shrinker s = {                                   \
-		.shrink = x,                                           \
-		.seeks = y                                             \
-	}
+#define	SPL_SHRINKER_CALLBACK_WRAPPER(fn)				\
+static int								\
+fn(int nr_to_scan, unsigned int gfp_mask)				\
+{									\
+	struct shrink_control sc;					\
+									\
+	sc.nr_to_scan = nr_to_scan;					\
+	sc.gfp_mask = gfp_mask;						\
+									\
+	return (__ ## fn(NULL, &sc));					\
+}
 
 /*
- * Linux 2.6. - 2.6. Shrinker API Compatibility.
+ * Linux 2.6.35 to 2.6.39 Shrinker API Compatibility.
  */
-# if defined(HAVE_SHRINK_CONTROL_STRUCT)
-#  define SPL_SHRINKER_CALLBACK_FWD_DECLARE(fn)                        \
-	static int fn(struct shrinker *, struct shrink_control *)
-#  define SPL_SHRINKER_CALLBACK_WRAPPER(fn)                            \
-static int                                                             \
-fn(struct shrinker *shrink, struct shrink_control *sc) {               \
-	return __ ## fn(shrink, sc);                                   \
+#elif defined(HAVE_3ARGS_SHRINKER_CALLBACK)
+#define	SPL_SHRINKER_DECLARE(s, x, y)					\
+static struct shrinker s = {						\
+	.shrink = x,							\
+	.seeks = y							\
+}
+
+#define	SPL_SHRINKER_CALLBACK_FWD_DECLARE(fn)				\
+static int fn(struct shrinker *, int, unsigned int)
+
+#define	SPL_SHRINKER_CALLBACK_WRAPPER(fn)				\
+static int								\
+fn(struct shrinker *shrink, int nr_to_scan, unsigned int gfp_mask)	\
+{									\
+	struct shrink_control sc;					\
+									\
+	sc.nr_to_scan = nr_to_scan;					\
+	sc.gfp_mask = gfp_mask;						\
+									\
+	return (__ ## fn(shrink, &sc));					\
 }
 
 /*
- * Linux 2.6. - 2.6. Shrinker API Compatibility.
+ * Linux 3.0 to 3.11 Shrinker API Compatibility.
  */
-# elif defined(HAVE_3ARGS_SHRINKER_CALLBACK)
-#  define SPL_SHRINKER_CALLBACK_FWD_DECLARE(fn)                       \
-	static int fn(struct shrinker *, int, unsigned int)
-#  define SPL_SHRINKER_CALLBACK_WRAPPER(fn)                           \
-static int                                                            \
-fn(struct shrinker *shrink, int nr_to_scan, unsigned int gfp_mask)    \
-{                                                                     \
-	struct shrink_control sc;                                     \
-                                                                      \
-        sc.nr_to_scan = nr_to_scan;                                   \
-        sc.gfp_mask = gfp_mask;                                       \
-                                                                      \
-	return __ ## fn(shrink, &sc);                                 \
+#elif defined(HAVE_2ARGS_NEW_SHRINKER_CALLBACK)
+#define	SPL_SHRINKER_DECLARE(s, x, y)					\
+static struct shrinker s = {						\
+	.shrink = x,							\
+	.seeks = y							\
+}
+
+#define	SPL_SHRINKER_CALLBACK_FWD_DECLARE(fn)				\
+static int fn(struct shrinker *, struct shrink_control *)
+
+#define	SPL_SHRINKER_CALLBACK_WRAPPER(fn)				\
+static int								\
+fn(struct shrinker *shrink, struct shrink_control *sc)			\
+{									\
+	return (__ ## fn(shrink, sc));					\
 }
 
 /*
- * Linux 2.6. - 2.6. Shrinker API Compatibility.
+ * Linux 3.12 and later Shrinker API Compatibility.
  */
-# else
-#  define SPL_SHRINKER_CALLBACK_FWD_DECLARE(fn)                       \
-	static int fn(int, unsigned int)
-#  define SPL_SHRINKER_CALLBACK_WRAPPER(fn)                           \
-static int                                                            \
-fn(int nr_to_scan, unsigned int gfp_mask)                             \
-{                                                                     \
-	struct shrink_control sc;                                     \
-                                                                      \
-        sc.nr_to_scan = nr_to_scan;                                   \
-        sc.gfp_mask = gfp_mask;                                       \
-                                                                      \
-	return __ ## fn(NULL, &sc);                                   \
+#elif defined(HAVE_SPLIT_SHRINKER_CALLBACK)
+#define	SPL_SHRINKER_DECLARE(s, x, y)					\
+static struct shrinker s = {						\
+	.count_objects = x ## _count_objects,				\
+	.scan_objects = x ## _scan_objects,				\
+	.seeks = y							\
 }
 
-# endif
-#endif /* HAVE_SET_SHRINKER */
+#define	SPL_SHRINKER_CALLBACK_FWD_DECLARE(fn)				\
+static unsigned long fn ## _count_objects(struct shrinker *,		\
+    struct shrink_control *);						\
+static unsigned long fn ## _scan_objects(struct shrinker *,		\
+    struct shrink_control *)
+
+#define	SPL_SHRINKER_CALLBACK_WRAPPER(fn)				\
+static unsigned long							\
+fn ## _count_objects(struct shrinker *shrink, struct shrink_control *sc)\
+{									\
+	int __ret__;							\
+									\
+	sc->nr_to_scan = 0;						\
+	__ret__ = __ ## fn(NULL, sc);					\
+									\
+	/* Errors may not be returned and must be converted to zeros */	\
+	return ((__ret__ < 0) ? 0 : __ret__);				\
+}									\
+									\
+static unsigned long							\
+fn ## _scan_objects(struct shrinker *shrink, struct shrink_control *sc)	\
+{									\
+	int __ret__;							\
+									\
+	__ret__ = __ ## fn(NULL, sc);					\
+	return ((__ret__ < 0) ? SHRINK_STOP : __ret__);			\
+}
+#else
+/*
+ * Linux 2.x to 2.6.22, or a newer shrinker API has been introduced.
+ */
+#error "Unknown shrinker callback"
+#endif
 
 #endif /* SPL_MM_COMPAT_H */