From ffcd0c5434d652326723b6bc302090329d5704e4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hajo=20M=C3=B6ller?= <dasjoe@users.noreply.github.com>
Date: Wed, 26 Oct 2016 19:30:43 +0200
Subject: [PATCH] Fix lookup_bdev() on Ubuntu
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Ubuntu added support for checking inode permissions to lookup_bdev() in kernel
commit 193fb6a2c94fab8eb8ce70a5da4d21c7d4023bee (merged in 4.4.0-6.21).
Upstream bug: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1636517

This patch adds a test for Ubuntu's variant of lookup_bdev() to configure and
calls the function in the correct way.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Hajo Möller <dasjoe@gmail.com>
Closes #5336
---
 config/kernel-lookup-bdev.m4  | 22 +++++++++++++++++-----
 include/linux/blkdev_compat.h | 17 +++++++++++++----
 module/zfs/zvol.c             |  2 +-
 3 files changed, 31 insertions(+), 10 deletions(-)

diff --git a/config/kernel-lookup-bdev.m4 b/config/kernel-lookup-bdev.m4
index 245f95f041..abbf55d9bb 100644
--- a/config/kernel-lookup-bdev.m4
+++ b/config/kernel-lookup-bdev.m4
@@ -1,17 +1,29 @@
 dnl #
-dnl # 2.6.27 API change
-dnl # lookup_bdev() was exported.
+dnl # 2.6.27, lookup_bdev() was exported.
+dnl # 4.4.0-6.21 - x.y on Ubuntu, lookup_bdev() takes 2 arguments.
 dnl #
 AC_DEFUN([ZFS_AC_KERNEL_LOOKUP_BDEV],
-	[AC_MSG_CHECKING([whether lookup_bdev() is available])
+	[AC_MSG_CHECKING([whether lookup_bdev() wants 1 arg])
 	ZFS_LINUX_TRY_COMPILE_SYMBOL([
 		#include <linux/fs.h>
 	], [
 		lookup_bdev(NULL);
 	], [lookup_bdev], [fs/block_dev.c], [
 		AC_MSG_RESULT(yes)
-		AC_DEFINE(HAVE_LOOKUP_BDEV, 1, [lookup_bdev() is available])
+		AC_DEFINE(HAVE_1ARG_LOOKUP_BDEV, 1, [lookup_bdev() wants 1 arg])
 	], [
 		AC_MSG_RESULT(no)
+		AC_MSG_CHECKING([whether lookup_bdev() wants 2 args])
+		ZFS_LINUX_TRY_COMPILE_SYMBOL([
+			#include <linux/fs.h>
+		], [
+			lookup_bdev(NULL, FMODE_READ);
+		], [lookup_bdev], [fs/block_dev.c], [
+			AC_MSG_RESULT(yes)
+			AC_DEFINE(HAVE_2ARGS_LOOKUP_BDEV, 1,
+			    [lookup_bdev() wants 2 args])
+		], [
+			AC_MSG_RESULT(no)
+		])
 	])
-])
+])
\ No newline at end of file
diff --git a/include/linux/blkdev_compat.h b/include/linux/blkdev_compat.h
index d26d242954..286aadd1c6 100644
--- a/include/linux/blkdev_compat.h
+++ b/include/linux/blkdev_compat.h
@@ -261,12 +261,21 @@ bio_set_flags_failfast(struct block_device *bdev, int *flags)
 
 /*
  * 2.6.27 API change
- * The function was exported for use, prior to this it existed by the
+ * The function was exported for use, prior to this it existed but the
  * symbol was not exported.
+ *
+ * 4.4.0-6.21 API change for Ubuntu
+ * lookup_bdev() gained a second argument, FMODE_*, to check inode permissions.
  */
-#ifndef HAVE_LOOKUP_BDEV
-#define	lookup_bdev(path)		ERR_PTR(-ENOTSUP)
-#endif
+#ifdef HAVE_1ARG_LOOKUP_BDEV
+#define	vdev_lookup_bdev(path)	lookup_bdev(path)
+#else
+#ifdef HAVE_2ARGS_LOOKUP_BDEV
+#define	vdev_lookup_bdev(path)	lookup_bdev(path, 0)
+#else
+#define	vdev_lookup_bdev(path)	ERR_PTR(-ENOTSUP)
+#endif /* HAVE_2ARGS_LOOKUP_BDEV */
+#endif /* HAVE_1ARG_LOOKUP_BDEV */
 
 /*
  * 2.6.30 API change
diff --git a/module/zfs/zvol.c b/module/zfs/zvol.c
index 04f68b5f8b..0bb68f9b85 100644
--- a/module/zfs/zvol.c
+++ b/module/zfs/zvol.c
@@ -174,7 +174,7 @@ zvol_is_zvol(const char *device)
 	struct block_device *bdev;
 	unsigned int major;
 
-	bdev = lookup_bdev(device);
+	bdev = vdev_lookup_bdev(device);
 	if (IS_ERR(bdev))
 		return (B_FALSE);