Linux 5.17 compat: GENHD_FL_EXT_DEVT / GENHD_FL_NO_PART_SCAN

As of the 5.17 kernel the GENHD_FL_EXT_DEVT flag has been removed
and the GENHD_FL_NO_PART_SCAN flag renamed GENHD_FL_NO_PART. Update
zvol_alloc() to set GENHD_FL_NO_PART for the newer kernels which
is sufficient.  The behavior for prior kernels remains unchanged.

1ebe2e5f ("block: remove GENHD_FL_EXT_DEVT")
46e7eac6 ("block: rename GENHD_FL_NO_PART_SCAN to GENHD_FL_NO_PART")

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes openzfs#13294
Closes openzfs#13297

config/kernel-genhd-flags.m4

@@ -0,0 +1,58 @@
+dnl #
+dnl # 5.17 API change,
+dnl #
+dnl # GENHD_FL_EXT_DEVT flag removed
+dnl # GENHD_FL_NO_PART_SCAN renamed GENHD_FL_NO_PART
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_SRC_GENHD_FLAGS], [
+
+	ZFS_LINUX_TEST_SRC([genhd_fl_ext_devt], [
+		#include <linux/blkdev.h>
+	], [
+		int flags __attribute__ ((unused)) = GENHD_FL_EXT_DEVT;
+	])
+
+	ZFS_LINUX_TEST_SRC([genhd_fl_no_part], [
+		#include <linux/blkdev.h>
+	], [
+		int flags __attribute__ ((unused)) = GENHD_FL_NO_PART;
+	])
+
+	ZFS_LINUX_TEST_SRC([genhd_fl_no_part_scan], [
+		#include <linux/blkdev.h>
+	], [
+		int flags __attribute__ ((unused)) = GENHD_FL_NO_PART_SCAN;
+	])
+])
+
+AC_DEFUN([ZFS_AC_KERNEL_GENHD_FLAGS], [
+
+	AC_MSG_CHECKING([whether GENHD_FL_EXT_DEVT flag is available])
+	ZFS_LINUX_TEST_RESULT([genhd_fl_ext_devt], [
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(ZFS_GENHD_FL_EXT_DEVT, GENHD_FL_EXT_DEVT,
+		    [GENHD_FL_EXT_DEVT flag is available])
+	], [
+		AC_MSG_RESULT(no)
+		AC_DEFINE(ZFS_GENHD_FL_EXT_DEVT, 0,
+		    [GENHD_FL_EXT_DEVT flag is not available])
+	])
+
+	AC_MSG_CHECKING([whether GENHD_FL_NO_PART flag is available])
+	ZFS_LINUX_TEST_RESULT([genhd_fl_no_part], [
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(ZFS_GENHD_FL_NO_PART, GENHD_FL_NO_PART,
+		    [GENHD_FL_NO_PART flag is available])
+	], [
+		AC_MSG_RESULT(no)
+
+		AC_MSG_CHECKING([whether GENHD_FL_NO_PART_SCAN flag is available])
+		ZFS_LINUX_TEST_RESULT([genhd_fl_no_part_scan], [
+			AC_MSG_RESULT(yes)
+			AC_DEFINE(ZFS_GENHD_FL_NO_PART, GENHD_FL_NO_PART_SCAN,
+			    [GENHD_FL_NO_PART_SCAN flag is available])
+		], [
+			ZFS_LINUX_TEST_ERROR([GENHD_FL_NO_PART|GENHD_FL_NO_PART_SCAN])
+		])
+	])
+])

config/kernel.m4

@@ -61,6 +61,7 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_SRC], [
 	ZFS_AC_KERNEL_SRC_BIO
 	ZFS_AC_KERNEL_SRC_BLKDEV
 	ZFS_AC_KERNEL_SRC_BLK_QUEUE
+	ZFS_AC_KERNEL_SRC_GENHD_FLAGS
 	ZFS_AC_KERNEL_SRC_REVALIDATE_DISK
 	ZFS_AC_KERNEL_SRC_GET_DISK_RO
 	ZFS_AC_KERNEL_SRC_GENERIC_READLINK_GLOBAL
@@ -174,6 +175,7 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_RESULT], [
 	ZFS_AC_KERNEL_BIO
 	ZFS_AC_KERNEL_BLKDEV
 	ZFS_AC_KERNEL_BLK_QUEUE
+	ZFS_AC_KERNEL_GENHD_FLAGS
 	ZFS_AC_KERNEL_REVALIDATE_DISK
 	ZFS_AC_KERNEL_GET_DISK_RO
 	ZFS_AC_KERNEL_GENERIC_READLINK_GLOBAL

module/os/linux/zfs/zvol_os.c

@@ -906,22 +906,17 @@ zvol_alloc(dev_t dev, const char *name)
 	zso->zvo_disk->major = zvol_major;
 	zso->zvo_disk->events = DISK_EVENT_MEDIA_CHANGE;
 
+	/*
+	 * Setting ZFS_VOLMODE_DEV disables partitioning on ZVOL devices.
+	 * This is accomplished by limiting the number of minors for the
+	 * device to one and explicitly disabling partition scanning.
+	 */
 	if (volmode == ZFS_VOLMODE_DEV) {
-		/*
-		 * ZFS_VOLMODE_DEV disable partitioning on ZVOL devices: set
-		 * gendisk->minors = 1 as noted in include/linux/blkdev.h.
-		 * Also disable extended partition numbers (GENHD_FL_EXT_DEVT)
-		 * and suppresses partition scanning (GENHD_FL_NO_PART_SCAN)
-		 * setting gendisk->flags accordingly.
-		 */
 		zso->zvo_disk->minors = 1;
-#if defined(GENHD_FL_EXT_DEVT)
-		zso->zvo_disk->flags &= ~GENHD_FL_EXT_DEVT;
-#endif
-#if defined(GENHD_FL_NO_PART_SCAN)
-		zso->zvo_disk->flags |= GENHD_FL_NO_PART_SCAN;
-#endif
+		zso->zvo_disk->flags &= ~ZFS_GENHD_FL_EXT_DEVT;
+		zso->zvo_disk->flags |= ZFS_GENHD_FL_NO_PART;
 	}
+
 	zso->zvo_disk->first_minor = (dev & MINORMASK);
 	zso->zvo_disk->fops = &zvol_ops;
 	zso->zvo_disk->private_data = zv;