[PATCH v2] xen/blkfront: remove redundant flush_op

[Vitaly Kuznetsov <vkuznets@redhat.com>]

flush_op is unambiguously defined by feature_flush:
    REQ_FUA | REQ_FLUSH -> BLKIF_OP_WRITE_BARRIER
    REQ_FLUSH -> BLKIF_OP_FLUSH_DISKCACHE
    0 -> 0
and thus can be removed. This is just a cleanup.

The patch was suggested by Boris Ostrovsky.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
Changes from v1:
   Future-proof feature_flush against new flags [Boris Ostrovsky].

The patch is supposed to be applied after "xen/blkfront: improve protection
against issuing unsupported REQ_FUA".
---
 drivers/block/xen-blkfront.c | 51 +++++++++++++++++++++++++++-----------------
 1 file changed, 31 insertions(+), 20 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 2e6c103..2236c6f 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -126,7 +126,6 @@ struct blkfront_info
 	unsigned int persistent_gnts_c;
 	unsigned long shadow_free;
 	unsigned int feature_flush;
-	unsigned int flush_op;
 	unsigned int feature_discard:1;
 	unsigned int feature_secdiscard:1;
 	unsigned int discard_granularity;
@@ -479,7 +478,19 @@ static int blkif_queue_request(struct request *req)
 				 * way.  (It's also a FLUSH+FUA, since it is
 				 * guaranteed ordered WRT previous writes.)
 				 */
-				ring_req->operation = info->flush_op;
+				switch (info->feature_flush &
+					((REQ_FLUSH|REQ_FUA))) {
+				case REQ_FLUSH|REQ_FUA:
+					ring_req->operation =
+						BLKIF_OP_WRITE_BARRIER;
+					break;
+				case REQ_FLUSH:
+					ring_req->operation =
+						BLKIF_OP_FLUSH_DISKCACHE;
+					break;
+				default:
+					ring_req->operation = 0;
+				}
 			}
 			ring_req->u.rw.nr_segments = nseg;
 		}
@@ -685,20 +696,26 @@ static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size,
 	return 0;
 }
 
+static const char *flush_info(unsigned int feature_flush)
+{
+	switch (feature_flush & ((REQ_FLUSH | REQ_FUA))) {
+	case REQ_FLUSH|REQ_FUA:
+		return "barrier: enabled;";
+	case REQ_FLUSH:
+		return "flush diskcache: enabled;";
+	default:
+		return "barrier or flush: disabled;";
+	}
+}
 
 static void xlvbd_flush(struct blkfront_info *info)
 {
 	blk_queue_flush(info->rq, info->feature_flush);
-	printk(KERN_INFO "blkfront: %s: %s: %s %s %s %s %s\n",
-	       info->gd->disk_name,
-	       info->flush_op == BLKIF_OP_WRITE_BARRIER ?
-		"barrier" : (info->flush_op == BLKIF_OP_FLUSH_DISKCACHE ?
-		"flush diskcache" : "barrier or flush"),
-	       info->feature_flush ? "enabled;" : "disabled;",
-	       "persistent grants:",
-	       info->feature_persistent ? "enabled;" : "disabled;",
-	       "indirect descriptors:",
-	       info->max_indirect_segments ? "enabled;" : "disabled;");
+	pr_info("blkfront: %s: %s %s %s %s %s\n",
+		info->gd->disk_name, flush_info(info->feature_flush),
+		"persistent grants:", info->feature_persistent ?
+		"enabled;" : "disabled;", "indirect descriptors:",
+		info->max_indirect_segments ? "enabled;" : "disabled;");
 }
 
 static int xen_translate_vdev(int vdevice, int *minor, unsigned int *offset)
@@ -1190,7 +1207,6 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
 				if (error == -EOPNOTSUPP)
 					error = 0;
 				info->feature_flush = 0;
-				info->flush_op = 0;
 				xlvbd_flush(info);
 			}
 			/* fall through */
@@ -1810,7 +1826,6 @@ static void blkfront_connect(struct blkfront_info *info)
 		physical_sector_size = sector_size;
 
 	info->feature_flush = 0;
-	info->flush_op = 0;
 
 	err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
 			    "feature-barrier", "%d", &barrier,
@@ -1823,10 +1838,8 @@ static void blkfront_connect(struct blkfront_info *info)
 	 *
 	 * If there are barriers, then we use flush.
 	 */
-	if (!err && barrier) {
+	if (!err && barrier)
 		info->feature_flush = REQ_FLUSH | REQ_FUA;
-		info->flush_op = BLKIF_OP_WRITE_BARRIER;
-	}
 	/*
 	 * And if there is "feature-flush-cache" use that above
 	 * barriers.
@@ -1835,10 +1848,8 @@ static void blkfront_connect(struct blkfront_info *info)
 			    "feature-flush-cache", "%d", &flush,
 			    NULL);
 
-	if (!err && flush) {
+	if (!err && flush)
 		info->feature_flush = REQ_FLUSH;
-		info->flush_op = BLKIF_OP_FLUSH_DISKCACHE;
-	}
 
 	err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
 			    "feature-discard", "%d", &discard,
-- 
1.9.3