Btrfs: do not mark ems as prealloc if we are writing to them

We are going to use EM's to log extents in the future, so we need to not
mark them as prealloc if they aren't actually prealloc extents.  Instead
mark them with FILLING so we know to ammend mod_start/mod_len and that way
we don't confuse the extent logging code.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

fs/btrfs/extent_map.c

@@ -266,9 +266,9 @@ int unpin_extent_cache(struct extent_map_tree *tree, u64 start, u64 len,
 	em->mod_start = em->start;
 	em->mod_len = em->len;
 
-	if (test_bit(EXTENT_FLAG_PREALLOC, &em->flags)) {
+	if (test_bit(EXTENT_FLAG_FILLING, &em->flags)) {
 		prealloc = true;
-		clear_bit(EXTENT_FLAG_PREALLOC, &em->flags);
+		clear_bit(EXTENT_FLAG_FILLING, &em->flags);
 	}
 
 	try_merge_map(tree, em);

fs/btrfs/extent_map.h

@@ -14,6 +14,7 @@
 #define EXTENT_FLAG_VACANCY 2 /* no file extent item found */
 #define EXTENT_FLAG_PREALLOC 3 /* pre-allocated extent */
 #define EXTENT_FLAG_LOGGING 4 /* Logging this extent */
+#define EXTENT_FLAG_FILLING 5 /* Filling in a preallocated extent */
 
 struct extent_map {
 	struct rb_node rb_node;

fs/btrfs/inode.c

@@ -1327,7 +1327,7 @@ static noinline int run_delalloc_nocow(struct inode *inode,
 			em->orig_block_len = disk_num_bytes;
 			em->bdev = root->fs_info->fs_devices->latest_bdev;
 			set_bit(EXTENT_FLAG_PINNED, &em->flags);
-			set_bit(EXTENT_FLAG_PREALLOC, &em->flags);
+			set_bit(EXTENT_FLAG_FILLING, &em->flags);
 			while (1) {
 				write_lock(&em_tree->lock);
 				ret = add_extent_mapping(em_tree, em);
@@ -5945,7 +5945,7 @@ static struct extent_map *create_pinned_em(struct inode *inode, u64 start,
 	em->orig_block_len = orig_block_len;
 	set_bit(EXTENT_FLAG_PINNED, &em->flags);
 	if (type == BTRFS_ORDERED_PREALLOC)
-		set_bit(EXTENT_FLAG_PREALLOC, &em->flags);
+		set_bit(EXTENT_FLAG_FILLING, &em->flags);
 
 	do {
 		btrfs_drop_extent_cache(inode, em->start,