From 7d7d6068bee9d8004ea7cc8a2ebda2c99a57caec Mon Sep 17 00:00:00 2001
From: Yan <yanzheng@21cn.com>
Date: Fri, 14 Sep 2007 16:15:28 -0400
Subject: [PATCH] Btrfs: Fix cache_block_group to catch holes at the start of
 the group

Cache block group was overly complex and missed free blocks at the very start
of the group.  This patch simplifies things significantly.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
---
 fs/btrfs/extent-tree.c | 61 +++++++++++++++++++++++-------------------
 1 file changed, 33 insertions(+), 28 deletions(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index b074ad1416dd..9151850266b0 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -39,6 +39,7 @@ static int cache_block_group(struct btrfs_root *root,
 	u64 i;
 	u64 last = 0;
 	u64 hole_size;
+	u64 first_free;
 	int found = 0;
 
 	root = root->fs_info->extent_root;
@@ -51,16 +52,22 @@ static int cache_block_group(struct btrfs_root *root,
 	path = btrfs_alloc_path();
 	if (!path)
 		return -ENOMEM;
+
 	path->reada = 2;
+	first_free = block_group->key.objectid;
 	key.objectid = block_group->key.objectid;
 	key.flags = 0;
 	key.offset = 0;
+
 	btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
 	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+
 	if (ret < 0)
 		return ret;
+
 	if (ret && path->slots[0] > 0)
 		path->slots[0]--;
+
 	while(1) {
 		leaf = btrfs_buffer_leaf(path->nodes[0]);
 		slot = path->slots[0];
@@ -71,50 +78,48 @@ static int cache_block_group(struct btrfs_root *root,
 			if (ret == 0) {
 				continue;
 			} else {
-				if (found) {
-					hole_size = block_group->key.objectid +
-						block_group->key.offset - last;
-				} else {
-					last = block_group->key.objectid;
-					hole_size = block_group->key.offset;
-				}
-				for (i = 0; i < hole_size; i++) {
-					set_radix_bit(extent_radix,
-						      last + i);
-				}
 				break;
 			}
 		}
+
 		btrfs_disk_key_to_cpu(&key, &leaf->items[slot].key);
+		if (key.objectid < block_group->key.objectid) {
+			if (key.objectid + key.offset > first_free)
+				first_free = key.objectid + key.offset;
+			goto next;
+		}
+
 		if (key.objectid >= block_group->key.objectid +
 		    block_group->key.offset) {
-			if (found) {
-				hole_size = block_group->key.objectid +
-					block_group->key.offset - last;
-			} else {
-				last = block_group->key.objectid;
-				hole_size = block_group->key.offset;
-			}
-			for (i = 0; i < hole_size; i++) {
-				set_radix_bit(extent_radix, last + i);
-			}
 			break;
 		}
+
 		if (btrfs_key_type(&key) == BTRFS_EXTENT_ITEM_KEY) {
 			if (!found) {
-				last = key.objectid + key.offset;
+				last = first_free;
 				found = 1;
-			} else {
-				hole_size = key.objectid - last;
-				for (i = 0; i < hole_size; i++) {
-					set_radix_bit(extent_radix, last + i);
-				}
-				last = key.objectid + key.offset;
 			}
+			hole_size = key.objectid - last;
+			for (i = 0; i < hole_size; i++) {
+				set_radix_bit(extent_radix, last + i);
+			}
+			last = key.objectid + key.offset;
 		}
+next:
 		path->slots[0]++;
 	}
 
+	if (!found)
+		last = first_free;
+	if (block_group->key.objectid +
+	    block_group->key.offset > last) {
+		hole_size = block_group->key.objectid +
+			block_group->key.offset - last;
+		for (i = 0; i < hole_size; i++) {
+			set_radix_bit(extent_radix,
+					last + i);
+		}
+	}
 	block_group->cached = 1;
 err:
 	btrfs_free_path(path);
-- 
2.20.1