Linux 5.11 compat: lookup_bdev()

The lookup_bdev() function has been updated to require a dev_t
be passed as the second argument. This is actually pretty nice
since the major number stored in the dev_t was the only part we
were interested in. This allows to us avoid handling the bdev
entirely.  The vdev_lookup_bdev() wrapper was updated to emulate
the behavior of the new lookup_bdev() for all supported kernels.

Reviewed-by: Rafael Kitover <rkitover@gmail.com>
Reviewed-by: Coleman Kane <ckane@colemankane.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #11387
Closes #11390

config/kernel-blkdev.m4

@@ -154,25 +154,51 @@ AC_DEFUN([ZFS_AC_KERNEL_BLKDEV_INVALIDATE_BDEV], [
 ])
 
 dnl #
-dnl # 2.6.27, lookup_bdev() was exported.
-dnl # 4.4.0-6.21 - lookup_bdev() takes 2 arguments.
+dnl # 5.11 API, lookup_bdev() takes dev_t argument.
+dnl # 2.6.27 API, lookup_bdev() was first exported.
+dnl # 4.4.0-6.21 API, lookup_bdev() on Ubuntu takes mode argument.
 dnl #
 AC_DEFUN([ZFS_AC_KERNEL_SRC_BLKDEV_LOOKUP_BDEV], [
+	ZFS_LINUX_TEST_SRC([lookup_bdev_devt], [
+		#include <linux/blkdev.h>
+	], [
+		int error __attribute__ ((unused));
+		const char path[] = "/example/path";
+		dev_t dev;
+
+		error = lookup_bdev(path, &dev);
+	])
+
 	ZFS_LINUX_TEST_SRC([lookup_bdev_1arg], [
 		#include <linux/fs.h>
 		#include <linux/blkdev.h>
 	], [
-		lookup_bdev(NULL);
+		struct block_device *bdev __attribute__ ((unused));
+		const char path[] = "/example/path";
+
+		bdev = lookup_bdev(path);
 	])
 
-	ZFS_LINUX_TEST_SRC([lookup_bdev_2args], [
+	ZFS_LINUX_TEST_SRC([lookup_bdev_mode], [
 		#include <linux/fs.h>
 	], [
-		lookup_bdev(NULL, FMODE_READ);
+		struct block_device *bdev __attribute__ ((unused));
+		const char path[] = "/example/path";
+
+		bdev = lookup_bdev(path, FMODE_READ);
 	])
 ])
 
 AC_DEFUN([ZFS_AC_KERNEL_BLKDEV_LOOKUP_BDEV], [
+	AC_MSG_CHECKING([whether lookup_bdev() wants dev_t arg])
+	ZFS_LINUX_TEST_RESULT_SYMBOL([lookup_bdev_devt],
+	    [lookup_bdev], [fs/block_dev.c], [
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_DEVT_LOOKUP_BDEV, 1,
+		    [lookup_bdev() wants dev_t arg])
+	], [
+		AC_MSG_RESULT(no)
+
 		AC_MSG_CHECKING([whether lookup_bdev() wants 1 arg])
 		ZFS_LINUX_TEST_RESULT_SYMBOL([lookup_bdev_1arg],
 		    [lookup_bdev], [fs/block_dev.c], [
@@ -182,16 +208,17 @@ AC_DEFUN([ZFS_AC_KERNEL_BLKDEV_LOOKUP_BDEV], [
 		], [
 			AC_MSG_RESULT(no)
 
-		AC_MSG_CHECKING([whether lookup_bdev() wants 2 args])
-		ZFS_LINUX_TEST_RESULT_SYMBOL([lookup_bdev_2args],
+			AC_MSG_CHECKING([whether lookup_bdev() wants mode arg])
+			ZFS_LINUX_TEST_RESULT_SYMBOL([lookup_bdev_mode],
 			    [lookup_bdev], [fs/block_dev.c], [
 				AC_MSG_RESULT(yes)
-			AC_DEFINE(HAVE_2ARGS_LOOKUP_BDEV, 1,
-			    [lookup_bdev() wants 2 args])
+				AC_DEFINE(HAVE_MODE_LOOKUP_BDEV, 1,
+				    [lookup_bdev() wants mode arg])
 			], [
 				ZFS_LINUX_TEST_ERROR([lookup_bdev()])
 			])
 		])
+	])
 ])
 
 dnl #

include/os/linux/kernel/linux/blkdev_compat.h

@@ -318,16 +318,38 @@ zfs_check_media_change(struct block_device *bdev)
  *
  * 4.4.0-6.21 API change for Ubuntu
  * lookup_bdev() gained a second argument, FMODE_*, to check inode permissions.
+ *
+ * 5.11 API change
+ * Changed to take a dev_t argument which is set on success and return a
+ * non-zero error code on failure.
  */
-#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)
+static inline int
+vdev_lookup_bdev(const char *path, dev_t *dev)
+{
+#if defined(HAVE_DEVT_LOOKUP_BDEV)
+	return (lookup_bdev(path, dev));
+#elif defined(HAVE_1ARG_LOOKUP_BDEV)
+	struct block_device *bdev = lookup_bdev(path);
+	if (IS_ERR(bdev))
+		return (PTR_ERR(bdev));
+
+	*dev = bdev->bd_dev;
+	bdput(bdev);
+
+	return (0);
+#elif defined(HAVE_MODE_LOOKUP_BDEV)
+	struct block_device *bdev = lookup_bdev(path, FMODE_READ);
+	if (IS_ERR(bdev))
+		return (PTR_ERR(bdev));
+
+	*dev = bdev->bd_dev;
+	bdput(bdev);
+
+	return (0);
 #else
 #error "Unsupported kernel"
-#endif /* HAVE_2ARGS_LOOKUP_BDEV */
-#endif /* HAVE_1ARG_LOOKUP_BDEV */
+#endif
+}
 
 /*
  * Kernels without bio_set_op_attrs use bi_rw for the bio flags.

module/os/linux/zfs/zvol_os.c

@@ -66,19 +66,14 @@ typedef struct zv_request {
  * Given a path, return TRUE if path is a ZVOL.
  */
 static boolean_t
-zvol_is_zvol_impl(const char *device)
+zvol_is_zvol_impl(const char *path)
 {
-	struct block_device *bdev;
-	unsigned int major;
+	dev_t dev = 0;
 
-	bdev = vdev_lookup_bdev(device);
-	if (IS_ERR(bdev))
+	if (vdev_lookup_bdev(path, &dev) != 0)
 		return (B_FALSE);
 
-	major = MAJOR(bdev->bd_dev);
-	bdput(bdev);
-
-	if (major == zvol_major)
+	if (MAJOR(dev) == zvol_major)
 		return (B_TRUE);
 
 	return (B_FALSE);