From b6ef899ded3848f44e637802cf348e26af57fcc2 Mon Sep 17 00:00:00 2001
From: Thomas Schoebel-Theuer <tst@1und1.de>
Date: Sun, 23 Oct 2016 11:54:01 +0200
Subject: [PATCH] Revert "if: remove obsolete merge_bvec_fn()"

This reverts commit d96b6e3fbf23a1428629cd38942eef55d94925d4.

Altough newer kernels don't have this anymore, old kernels
need it.

Make it dependend from the kernel version.
---
 kernel/mars_if.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/kernel/mars_if.c b/kernel/mars_if.c
index ae854716..6fbf4a48 100644
--- a/kernel/mars_if.c
+++ b/kernel/mars_if.c
@@ -46,7 +46,7 @@
 #define USE_SEGMENT_BOUNDARY    (PAGE_SIZE-1)
 
 #define USE_CONGESTED_FN
-//      end_remove_this
+#define USE_MERGE_BVEC
 //#define DENY_READA
 
 #include <linux/kernel.h>
@@ -853,6 +853,16 @@ int mars_congested(void *data, int bdi_bits)
 	return ret;
 }
 
+static
+int mars_merge_bvec(struct request_queue *q, struct bvec_merge_data *bvm, struct bio_vec *bvec)
+{
+	unsigned int bio_size = bvm->bi_size;
+	if (!bio_size) {
+		return bvec->bv_len;
+	}
+	return 128;
+}
+
 static
 loff_t if_get_capacity(struct if_brick *brick)
 {
@@ -1010,6 +1020,10 @@ static int if_switch(struct if_brick *brick)
 		q->backing_dev_info.congested_fn = mars_congested;
 		q->backing_dev_info.congested_data = input;
 #endif
+#ifdef USE_MERGE_BVEC
+		MARS_DBG("blk_queue_merge_bvec()\n");
+		blk_queue_merge_bvec(q, mars_merge_bvec);
+#endif
 
 		// point of no return
 		MARS_DBG("add_disk()\n");