Linux 4.0 compat: bdi_setup_and_register()

The 'capabilities' argument which was passed to bdi_setup_and_register()
has been removed.  File systems should no longer pass BDI_CAP_MAP_COPY.
For our purposes this means there are now three different interfaces
which must be handled.  A zpl_bdi_setup_and_register() wrapper function
has been introduced to provide a single interface to the ZPL code.

* 2.6.32 - 2.6.33, bdi_setup_and_register() is not exported.
* 2.6.34 - 3.19, bdi_setup_and_register() takes 3 arguments.
* 4.0 - x.y, bdi_setup_and_register() takes 2 arguments.

I've also taken this opportunity to remove HAVE_BDI because kernels
older then 2.6.32 are no longer supported.  All kernels newer than
this will have one of the above interfaces.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Chunwei Chen <tuxoko@gmail.com>
Closes #3128

config/kernel-bdi-setup-and-register.m4

@@ -1,22 +1,36 @@
 dnl #
-dnl # 2.6.34 API change
+dnl # 2.6.32 - 2.6.33, bdi_setup_and_register() is not exported.
-dnl # The bdi_setup_and_register() helper function is avaliable and
+dnl # 2.6.34 - 3.19, bdi_setup_and_register() takes 3 arguments.
-dnl # exported by the kernel.  This is a trivial helper function but
+dnl # 4.0 - x.y, bdi_setup_and_register() takes 2 arguments.
-dnl # using it significantly simplifies the code surrounding setting
-dnl # up and tearing down the bdi structure.
 dnl #
-AC_DEFUN([ZFS_AC_KERNEL_BDI_SETUP_AND_REGISTER],
+AC_DEFUN([ZFS_AC_KERNEL_BDI_SETUP_AND_REGISTER], [
-	[AC_MSG_CHECKING([whether bdi_setup_and_register() is available])
+	AC_MSG_CHECKING([whether bdi_setup_and_register() wants 2 args])
 	ZFS_LINUX_TRY_COMPILE_SYMBOL([
 		#include <linux/backing-dev.h>
 	], [
-		int r = bdi_setup_and_register(NULL, NULL, 0);
+		struct backing_dev_info bdi;
-		r = *(&r);
+		char *name = "bdi";
+		(void) bdi_setup_and_register(&bdi, name);
 	], [bdi_setup_and_register], [mm/backing-dev.c], [
 		AC_MSG_RESULT(yes)
-		AC_DEFINE(HAVE_BDI_SETUP_AND_REGISTER, 1,
+		AC_DEFINE(HAVE_2ARGS_BDI_SETUP_AND_REGISTER, 1,
-		          [bdi_setup_and_register() is available])
+		    [bdi_setup_and_register() wants 2 args])
 	], [
 		AC_MSG_RESULT(no)
+		AC_MSG_CHECKING([whether bdi_setup_and_register() wants 3 args])
+		ZFS_LINUX_TRY_COMPILE_SYMBOL([
+			#include <linux/backing-dev.h>
+		], [
+			struct backing_dev_info bdi;
+			char *name = "bdi";
+			unsigned int cap = BDI_CAP_MAP_COPY;
+			(void) bdi_setup_and_register(&bdi, name, cap);
+		], [bdi_setup_and_register], [mm/backing-dev.c], [
+			AC_MSG_RESULT(yes)
+			AC_DEFINE(HAVE_3ARGS_BDI_SETUP_AND_REGISTER, 1,
+			    [bdi_setup_and_register() wants 3 args])
+		], [
+			AC_MSG_RESULT(no)
+		])
 	])
 ])

config/kernel-bdi.m4

@@ -1,21 +0,0 @@
-dnl #
-dnl # 2.6.32 API change
-dnl # Private backing_device_info interfaces available
-dnl #
-AC_DEFUN([ZFS_AC_KERNEL_BDI], [
-	AC_MSG_CHECKING([whether super_block has s_bdi])
-	ZFS_LINUX_TRY_COMPILE([
-		#include <linux/fs.h>
-
-		static const struct super_block
-		    sb __attribute__ ((unused)) = {
-			.s_bdi = NULL,
-		};
-	],[
-	],[
-		AC_MSG_RESULT(yes)
-		AC_DEFINE(HAVE_BDI, 1, [struct super_block has s_bdi])
-	],[
-		AC_MSG_RESULT(no)
-	])
-])

config/kernel.m4

@@ -90,7 +90,6 @@ AC_DEFUN([ZFS_AC_CONFIG_KERNEL], [
 	ZFS_AC_KERNEL_SHRINK
 	ZFS_AC_KERNEL_S_INSTANCES_LIST_HEAD
 	ZFS_AC_KERNEL_S_D_OP
-	ZFS_AC_KERNEL_BDI
 	ZFS_AC_KERNEL_BDI_SETUP_AND_REGISTER
 	ZFS_AC_KERNEL_SET_NLINK
 	ZFS_AC_KERNEL_ELEVATOR_CHANGE

include/linux/vfs_compat.h

@@ -65,25 +65,35 @@ truncate_setsize(struct inode *ip, loff_t new)
 }
 #endif /* HAVE_TRUNCATE_SETSIZE */
 
-#if defined(HAVE_BDI) && !defined(HAVE_BDI_SETUP_AND_REGISTER)
 /*
- * 2.6.34 API change,
+ * 2.6.32 - 2.6.33, bdi_setup_and_register() is not available.
- * Add bdi_setup_and_register() function if not yet provided by kernel.
+ * 2.6.34 - 3.19, bdi_setup_and_register() takes 3 arguments.
- * It is used to quickly initialize and register a BDI for the filesystem.
+ * 4.0 - x.y, bdi_setup_and_register() takes 2 arguments.
  */
+#if defined(HAVE_2ARGS_BDI_SETUP_AND_REGISTER)
+static inline int
+zpl_bdi_setup_and_register(struct backing_dev_info *bdi, char *name)
+{
+	return (bdi_setup_and_register(bdi, name));
+}
+#elif defined(HAVE_3ARGS_BDI_SETUP_AND_REGISTER)
+static inline int
+zpl_bdi_setup_and_register(struct backing_dev_info *bdi, char *name)
+{
+	return (bdi_setup_and_register(bdi, name, BDI_CAP_MAP_COPY));
+}
+#else
 extern atomic_long_t zfs_bdi_seq;
 
 static inline int
-bdi_setup_and_register(
+zpl_bdi_setup_and_register(struct backing_dev_info *bdi, char *name)
-	struct backing_dev_info *bdi,
-	char *name,
-	unsigned int cap)
 {
 	char tmp[32];
 	int error;
 
 	bdi->name = name;
-	bdi->capabilities = cap;
+	bdi->capabilities = BDI_CAP_MAP_COPY;
+
 	error = bdi_init(bdi);
 	if (error)
 		return (error);
@@ -98,7 +108,7 @@ bdi_setup_and_register(
 
 	return (error);
 }
-#endif /* HAVE_BDI && !HAVE_BDI_SETUP_AND_REGISTER */
+#endif
 
 /*
  * 2.6.38 API change,

module/zfs/zfs_vfsops.c

@@ -1198,9 +1198,10 @@ zfs_sb_teardown(zfs_sb_t *zsb, boolean_t unmounting)
 }
 EXPORT_SYMBOL(zfs_sb_teardown);
 
-#if defined(HAVE_BDI) && !defined(HAVE_BDI_SETUP_AND_REGISTER)
+#if !defined(HAVE_2ARGS_BDI_SETUP_AND_REGISTER) && \
+	!defined(HAVE_3ARGS_BDI_SETUP_AND_REGISTER)
 atomic_long_t zfs_bdi_seq = ATOMIC_LONG_INIT(0);
-#endif /* HAVE_BDI && !HAVE_BDI_SETUP_AND_REGISTER */
+#endif
 
 int
 zfs_domount(struct super_block *sb, void *data, int silent)
@@ -1227,23 +1228,12 @@ zfs_domount(struct super_block *sb, void *data, int silent)
 	sb->s_time_gran = 1;
 	sb->s_blocksize = recordsize;
 	sb->s_blocksize_bits = ilog2(recordsize);
-
-#ifdef HAVE_BDI
-	/*
-	 * 2.6.32 API change,
-	 * Added backing_device_info (BDI) per super block interfaces.  A BDI
-	 * must be configured when using a non-device backed filesystem for
-	 * proper writeback.  This is not required for older pdflush kernels.
-	 *
-	 * NOTE: Linux read-ahead is disabled in favor of zfs read-ahead.
-	 */
 	zsb->z_bdi.ra_pages = 0;
 	sb->s_bdi = &zsb->z_bdi;
 
-	error = -bdi_setup_and_register(&zsb->z_bdi, "zfs", BDI_CAP_MAP_COPY);
+	error = -zpl_bdi_setup_and_register(&zsb->z_bdi, "zfs");
 	if (error)
 		goto out;
-#endif /* HAVE_BDI */
 
 	/* Set callback operations for the file system. */
 	sb->s_op = &zpl_super_operations;
@@ -1336,10 +1326,7 @@ zfs_umount(struct super_block *sb)
 
 	VERIFY(zfs_sb_teardown(zsb, B_TRUE) == 0);
 	os = zsb->z_os;
-
-#ifdef HAVE_BDI
 	bdi_destroy(sb->s_bdi);
-#endif /* HAVE_BDI */
 
 	/*
 	 * z_os will be NULL if there was an error in