[PATCH] Btrfs: fix compile warning from __btrfs_map_block

[liubo <liubo2009@cn.fujitsu.com>]

While compile btrfs modules on 32bit box, I encounter the following:

WARNING: "__umoddi3" [fs/btrfs/btrfs.ko] undefined!

The WARNING comes from that __btrfs_map_block does not use do_div() for
relative operations, this will cause problems on 32bit box, for values
with "u64" type should use do_div() instead of a direct "%".

Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
---
 fs/btrfs/volumes.c |   23 +++++++++++++++--------
 1 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 41afd50..7b23d0f 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3076,16 +3076,19 @@ again:
 			multi->stripes[i].dev = map->stripes[stripe_index].dev;
 
 			if (map->type & BTRFS_BLOCK_GROUP_RAID0) {
-				u64 stripes;
-				int last_stripe = (stripe_nr_end - 1) %
-					map->num_stripes;
+				u64 stripes = stripe_nr_end - 1;
+				int last_stripe = do_div(stripes,
+					map->num_stripes);
 				int j;
 
 				for (j = 0; j < map->num_stripes; j++) {
-					if ((stripe_nr_end - 1 - j) %
-					      map->num_stripes == stripe_index)
+					stripes = stripe_nr_end - 1 - j;
+
+					if (do_div(stripes, map->num_stripes) ==
+					    stripe_index)
 						break;
 				}
+
 				stripes = stripe_nr_end - 1 - j;
 				do_div(stripes, map->num_stripes);
 				multi->stripes[i].length = map->stripe_len *
@@ -3100,18 +3103,22 @@ again:
 					multi->stripes[i].length -=
 						stripe_end_offset;
 			} else if (map->type & BTRFS_BLOCK_GROUP_RAID10) {
-				u64 stripes;
+				u64 stripes = stripe_nr_end - 1;
 				int j;
 				int factor = map->num_stripes /
 					     map->sub_stripes;
-				int last_stripe = (stripe_nr_end - 1) % factor;
+				int last_stripe = do_div(stripes, factor);
+
 				last_stripe *= map->sub_stripes;
 
 				for (j = 0; j < factor; j++) {
-					if ((stripe_nr_end - 1 - j) % factor ==
+					stripes = stripe_nr_end - 1 - j;
+
+					if (do_div(stripes, factor) ==
 					    stripe_index / map->sub_stripes)
 						break;
 				}
+
 				stripes = stripe_nr_end - 1 - j;
 				do_div(stripes, factor);
 				multi->stripes[i].length = map->stripe_len *
-- 
1.6.5.2