Compatibility update for 5.14 for blk_alloc_disk()

In Linux 5.14, blk_alloc_queue is no longer exported, and its usage
has been superseded by blk_alloc_disk, which returns a gendisk struct
from which we can still retrieve the struct request_queue* that is
needed in the one place where it is used. This also replaces the call
to alloc_disk(minors), and minors is now set via struct member
assignment.

Signed-off-by: Coleman Kane <ckane@colemankane.org>

config/kernel-blk-alloc-disk.m4

@@ -0,0 +1,23 @@
+dnl #
+dnl # 5.14 API change
+dnl # blk_alloc_queue deprecated in favor of blk_alloc_disk
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_SRC_BLK_ALLOC_DISK], [
+	ZFS_LINUX_TEST_SRC([blk_alloc_disk], [
+		#include <linux/genhd.h>
+	], [
+		struct gendisk *disk = NULL;
+		disk = blk_alloc_disk(0);
+	])
+])
+
+AC_DEFUN([ZFS_AC_KERNEL_BLK_ALLOC_DISK], [
+	AC_MSG_CHECKING([whether blk_alloc_disk() is available])
+	ZFS_LINUX_TEST_RESULT([blk_alloc_disk], [
+		    AC_MSG_RESULT(yes)
+		    AC_DEFINE(HAVE_BLK_ALLOC_DISK, 1,
+			    [blk_alloc_disk() is available])
+		], [
+			AC_MSG_RESULT(no)
+	])
+])

config/kernel.m4

@@ -132,6 +132,7 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_SRC], [
 	ZFS_AC_KERNEL_SRC_SIGNAL_STOP
 	ZFS_AC_KERNEL_SRC_SIGINFO
 	ZFS_AC_KERNEL_SRC_SET_SPECIAL_STATE
+	ZFS_AC_KERNEL_SRC_BLK_ALLOC_DISK
 
 	AC_MSG_CHECKING([for available kernel interfaces])
 	ZFS_LINUX_TEST_COMPILE_ALL([kabi])
@@ -237,6 +238,7 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_RESULT], [
 	ZFS_AC_KERNEL_SIGNAL_STOP
 	ZFS_AC_KERNEL_SIGINFO
 	ZFS_AC_KERNEL_SET_SPECIAL_STATE
+	ZFS_AC_KERNEL_BLK_ALLOC_DISK
 ])
 
 dnl #

module/os/linux/zfs/zvol_os.c

@@ -794,10 +794,19 @@ zvol_alloc(dev_t dev, const char *name)
 	list_link_init(&zv->zv_next);
 	mutex_init(&zv->zv_state_lock, NULL, MUTEX_DEFAULT, NULL);
 
+#ifdef HAVE_BLK_ALLOC_DISK
+	zso->zvo_disk = blk_alloc_disk(NUMA_NO_NODE);
+	if (zso->zvo_disk == NULL)
+		goto out_kmem;
+
+	zso->zvo_queue = zso->zvo_disk->queue;
+	zso->zvo_disk->minors = ZVOL_MINORS;
+#else
 #ifdef HAVE_SUBMIT_BIO_IN_BLOCK_DEVICE_OPERATIONS
 	zso->zvo_queue = blk_alloc_queue(NUMA_NO_NODE);
 #else
 	zso->zvo_queue = blk_generic_alloc_queue(zvol_request, NUMA_NO_NODE);
+#endif
 #endif
 	if (zso->zvo_queue == NULL)
 		goto out_kmem;
@@ -810,9 +819,11 @@ zvol_alloc(dev_t dev, const char *name)
 	/* Disable write merging in favor of the ZIO pipeline. */
 	blk_queue_flag_set(QUEUE_FLAG_NOMERGES, zso->zvo_queue);
 
+#ifndef HAVE_BLK_ALLOC_DISK
 	zso->zvo_disk = alloc_disk(ZVOL_MINORS);
 	if (zso->zvo_disk == NULL)
 		goto out_queue;
+#endif
 
 	zso->zvo_queue->queuedata = zv;
 	zso->zvo_dev = dev;
@@ -851,7 +862,11 @@ zvol_alloc(dev_t dev, const char *name)
 	return (zv);
 
 out_queue:
+#ifdef HAVE_BLK_ALLOC_DISK
+	blk_cleanup_disk(zso->zvo_disk);
+#else
 	blk_cleanup_queue(zso->zvo_queue);
+#endif
 out_kmem:
 	kmem_free(zso, sizeof (struct zvol_state_os));
 	kmem_free(zv, sizeof (zvol_state_t));