Linux 6.0 compat: register_shrinker() now var-arg

The 6.0 kernel added a printf-style var-arg for args > 0 to the
register_shrinker function, in order to add names to shrinkers, in
commit e33c267ab70de4249d22d7eab1cc7d68a889bac2. This enables the
shrinkers to have friendly names exposed in /sys/kernel/debug/shrinker/.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Coleman Kane <ckane@colemankane.org>
Closes #13748

config/kernel-shrink.m4

@@ -54,6 +54,21 @@ AC_DEFUN([ZFS_AC_KERNEL_SHRINK_CONTROL_HAS_NID], [
 	])
 ])
 
+AC_DEFUN([ZFS_AC_KERNEL_SRC_REGISTER_SHRINKER_VARARG], [
+	ZFS_LINUX_TEST_SRC([register_shrinker_vararg], [
+		#include <linux/mm.h>
+		unsigned long shrinker_cb(struct shrinker *shrink,
+		    struct shrink_control *sc) { return 0; }
+	],[
+		struct shrinker cache_shrinker = {
+			.count_objects = shrinker_cb,
+			.scan_objects = shrinker_cb,
+			.seeks = DEFAULT_SEEKS,
+		};
+		register_shrinker(&cache_shrinker, "vararg-reg-shrink-test");
+	])
+])
+
 AC_DEFUN([ZFS_AC_KERNEL_SRC_SHRINKER_CALLBACK], [
 	ZFS_LINUX_TEST_SRC([shrinker_cb_shrink_control], [
 		#include <linux/mm.h>
@@ -82,6 +97,25 @@ AC_DEFUN([ZFS_AC_KERNEL_SRC_SHRINKER_CALLBACK], [
 ])
 
 AC_DEFUN([ZFS_AC_KERNEL_SHRINKER_CALLBACK],[
+	dnl #
+	dnl # 6.0 API change
+	dnl # register_shrinker() becomes a var-arg function that takes
+	dnl # a printf-style format string as args > 0
+	dnl #
+	AC_MSG_CHECKING([whether new var-arg register_shrinker() exists])
+	ZFS_LINUX_TEST_RESULT([register_shrinker_vararg], [
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_REGISTER_SHRINKER_VARARG, 1,
+		    [register_shrinker is vararg])
+
+		dnl # We assume that the split shrinker callback exists if the
+		dnl # vararg register_shrinker() exists, because the latter is
+		dnl # a much more recent addition, and the macro test for the
+		dnl # var-arg version only works if the callback is split
+		AC_DEFINE(HAVE_SPLIT_SHRINKER_CALLBACK, 1,
+			[cs->count_objects exists])
+	],[
+		AC_MSG_RESULT(no)
 		dnl #
 		dnl # 3.0 - 3.11 API change
 		dnl # cs->shrink(struct shrinker *, struct shrink_control *sc)
@@ -99,8 +133,9 @@ AC_DEFUN([ZFS_AC_KERNEL_SHRINKER_CALLBACK],[
 			dnl # cs->shrink() is logically split in to
 			dnl # cs->count_objects() and cs->scan_objects()
 			dnl #
-		AC_MSG_CHECKING([whether cs->count_objects callback exists])
+			AC_MSG_CHECKING([if cs->count_objects callback exists])
-		ZFS_LINUX_TEST_RESULT([shrinker_cb_shrink_control_split], [
+			ZFS_LINUX_TEST_RESULT(
+				[shrinker_cb_shrink_control_split],[
 					AC_MSG_RESULT(yes)
 					AC_DEFINE(HAVE_SPLIT_SHRINKER_CALLBACK, 1,
 						[cs->count_objects exists])
@@ -108,6 +143,7 @@ AC_DEFUN([ZFS_AC_KERNEL_SHRINKER_CALLBACK],[
 					ZFS_LINUX_TEST_ERROR([shrinker])
 			])
 		])
+	])
 ])
 
 dnl #
@@ -141,6 +177,7 @@ AC_DEFUN([ZFS_AC_KERNEL_SRC_SHRINKER], [
 	ZFS_AC_KERNEL_SRC_SHRINK_CONTROL_HAS_NID
 	ZFS_AC_KERNEL_SRC_SHRINKER_CALLBACK
 	ZFS_AC_KERNEL_SRC_SHRINK_CONTROL_STRUCT
+	ZFS_AC_KERNEL_SRC_REGISTER_SHRINKER_VARARG
 ])
 
 AC_DEFUN([ZFS_AC_KERNEL_SHRINKER], [

include/os/linux/spl/sys/shrinker.h

@@ -64,7 +64,11 @@
  * }
  */
 
+#ifdef HAVE_REGISTER_SHRINKER_VARARG
+#define	spl_register_shrinker(x)	register_shrinker(x, "zfs-arc-shrinker")
+#else
 #define	spl_register_shrinker(x)	register_shrinker(x)
+#endif
 #define	spl_unregister_shrinker(x)	unregister_shrinker(x)
 
 /*