Linux 4.7 compat: replace blk_queue_flush with blk_queue_write_cache

Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue openzfs#4665

config/kernel-blk-queue-flush.m4

@@ -22,25 +22,64 @@ AC_DEFUN([ZFS_AC_KERNEL_BLK_QUEUE_FLUSH], [
 		AC_MSG_RESULT(yes)
 		AC_DEFINE(HAVE_BLK_QUEUE_FLUSH, 1,
 		          [blk_queue_flush() is available])
+
+		AC_MSG_CHECKING([whether blk_queue_flush() is GPL-only])
+		ZFS_LINUX_TRY_COMPILE([
+			#include <linux/module.h>
+			#include <linux/blkdev.h>
+
+			MODULE_LICENSE("$ZFS_META_LICENSE");
+		],[
+			struct request_queue *q = NULL;
+			(void) blk_queue_flush(q, REQ_FLUSH);
+		],[
+			AC_MSG_RESULT(no)
+		],[
+			AC_MSG_RESULT(yes)
+			AC_DEFINE(HAVE_BLK_QUEUE_FLUSH_GPL_ONLY, 1,
+				  [blk_queue_flush() is GPL-only])
+		])
 	],[
 		AC_MSG_RESULT(no)
 	])
 
-	AC_MSG_CHECKING([whether blk_queue_flush() is GPL-only])
+	dnl #
+	dnl # 4.7 API change
+	dnl # Replace blk_queue_flush with blk_queue_write_cache
+	dnl #
+	AC_MSG_CHECKING([whether blk_queue_write_cache() exists])
 	ZFS_LINUX_TRY_COMPILE([
-		#include <linux/module.h>
+		#include <linux/kernel.h>
 		#include <linux/blkdev.h>
 
-		MODULE_LICENSE("$ZFS_META_LICENSE");
 	],[
 		struct request_queue *q = NULL;
-		(void) blk_queue_flush(q, REQ_FLUSH);
-	],[
-		AC_MSG_RESULT(no)
+		blk_queue_write_cache(q, true, true);
 	],[
 		AC_MSG_RESULT(yes)
-		AC_DEFINE(HAVE_BLK_QUEUE_FLUSH_GPL_ONLY, 1,
-		          [blk_queue_flush() is GPL-only])
+		AC_DEFINE(HAVE_BLK_QUEUE_WRITE_CACHE, 1,
+			[blk_queue_write_cache() exists])
+
+		AC_MSG_CHECKING([whether blk_queue_write_cache() is GPL-only])
+		ZFS_LINUX_TRY_COMPILE([
+			#include <linux/kernel.h>
+			#include <linux/module.h>
+			#include <linux/blkdev.h>
+
+			MODULE_LICENSE("$ZFS_META_LICENSE");
+		],[
+			struct request_queue *q = NULL;
+			blk_queue_write_cache(q, true, true);
+		],[
+			AC_MSG_RESULT(no)
+		],[
+			AC_MSG_RESULT(yes)
+			AC_DEFINE(HAVE_BLK_QUEUE_WRITE_CACHE_GPL_ONLY, 1,
+				  [blk_queue_write_cache() is GPL-only])
+		])
+	],[
+		AC_MSG_RESULT(no)
 	])
+
 	EXTRA_KCFLAGS="$tmp_flags"
 ])

include/linux/blkdev_compat.h

@@ -52,6 +52,33 @@ __blk_queue_flush(struct request_queue *q, unsigned int flags)
 	q->flush_flags = flags & (REQ_FLUSH | REQ_FUA);
 }
 #endif /* HAVE_BLK_QUEUE_FLUSH && HAVE_BLK_QUEUE_FLUSH_GPL_ONLY */
+
+/*
+ * 4.7 API change,
+ * The blk_queue_write_cache() interface has replaced blk_queue_flush()
+ * interface.  However, while the new interface is GPL-only. Thus if the
+ * GPL-only version is detected we implement our own trivial helper
+ * compatibility funcion.
+ */
+#if defined(HAVE_BLK_QUEUE_WRITE_CACHE) && \
+	defined(HAVE_BLK_QUEUE_WRITE_CACHE_GPL_ONLY)
+#define	blk_queue_write_cache __blk_queue_write_cache
+static inline void
+__blk_queue_write_cache(struct request_queue *q, bool wc, bool fua)
+{
+	spin_lock_irq(q->queue_lock);
+	if (wc)
+		queue_flag_set(QUEUE_FLAG_WC, q);
+	else
+		queue_flag_clear(QUEUE_FLAG_WC, q);
+	if (fua)
+		queue_flag_set(QUEUE_FLAG_FUA, q);
+	else
+		queue_flag_clear(QUEUE_FLAG_FUA, q);
+	spin_unlock_irq(q->queue_lock);
+}
+#endif
+
 /*
  * Most of the blk_* macros were removed in 2.6.36.  Ostensibly this was
  * done to improve readability and allow easier grepping.  However, from

module/zfs/zvol.c

@@ -1291,7 +1291,9 @@ zvol_alloc(dev_t dev, const char *name)
 
 	blk_queue_make_request(zv->zv_queue, zvol_request);
 
-#ifdef HAVE_BLK_QUEUE_FLUSH
+#ifdef HAVE_BLK_QUEUE_WRITE_CACHE
+	blk_queue_write_cache(zv->zv_queue, B_TRUE, B_TRUE);
+#elif defined(HAVE_BLK_QUEUE_FLUSH)
 	blk_queue_flush(zv->zv_queue, VDEV_REQ_FLUSH | VDEV_REQ_FUA);
 #else
 	blk_queue_ordered(zv->zv_queue, QUEUE_ORDERED_DRAIN, NULL);