btrfs: add support for multiple global roots

With extent tree v2 you will be able to create multiple csum, extent,
and free space trees.  They will be used based on the block group, which
will now use the block_group_item->chunk_objectid to point to the set of
global roots that it will use.  When allocating new block groups we'll
simply mod the gigabyte offset of the block group against the number of
global roots we have and that will be the block groups global id.

>From there we can take the bytenr that we're modifying in the respective
tree, look up the block group and get that block groups corresponding
global root id.  From there we can get to the appropriate global root
for that bytenr.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 26 insertions, 2 deletions

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index 8202ad6aa131..3113f6d7f335 100644
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -2006,6 +2006,7 @@ static int read_one_block_group(struct btrfs_fs_info *info,
 	cache->length = key->offset;
 	cache->used = btrfs_stack_block_group_used(bgi);
 	cache->flags = btrfs_stack_block_group_flags(bgi);
+	cache->global_root_id = btrfs_stack_block_group_chunk_objectid(bgi);
 
 	set_free_space_tree_thresholds(cache);
 
@@ -2288,7 +2289,7 @@ static int insert_block_group_item(struct btrfs_trans_handle *trans,
 	spin_lock(&block_group->lock);
 	btrfs_set_stack_block_group_used(&bgi, block_group->used);
 	btrfs_set_stack_block_group_chunk_objectid(&bgi,
-				BTRFS_FIRST_CHUNK_TREE_OBJECTID);
+						   block_group->global_root_id);
 	btrfs_set_stack_block_group_flags(&bgi, block_group->flags);
 	key.objectid = block_group->start;
 	key.type = BTRFS_BLOCK_GROUP_ITEM_KEY;
@@ -2444,6 +2445,27 @@ next:
 	btrfs_trans_release_chunk_metadata(trans);
 }
 
+/*
+ * For extent tree v2 we use the block_group_item->chunk_offset to point at our
+ * global root id.  For v1 it's always set to BTRFS_FIRST_CHUNK_TREE_OBJECTID.
+ */
+static u64 calculate_global_root_id(struct btrfs_fs_info *fs_info, u64 offset)
+{
+	u64 div = SZ_1G;
+	u64 index;
+
+	if (!btrfs_fs_incompat(fs_info, EXTENT_TREE_V2))
+		return BTRFS_FIRST_CHUNK_TREE_OBJECTID;
+
+	/* If we have a smaller fs index based on 128MiB. */
+	if (btrfs_super_total_bytes(fs_info->super_copy) <= (SZ_1G * 10ULL))
+		div = SZ_128M;
+
+	offset = div64_u64(offset, div);
+	div64_u64_rem(offset, fs_info->nr_global_roots, &index);
+	return index;
+}
+
 struct btrfs_block_group *btrfs_make_block_group(struct btrfs_trans_handle *trans,
 						 u64 bytes_used, u64 type,
 						 u64 chunk_offset, u64 size)
@@ -2464,6 +2486,8 @@ struct btrfs_block_group *btrfs_make_block_group(struct btrfs_trans_handle *tran
 	cache->flags = type;
 	cache->last_byte_to_unpin = (u64)-1;
 	cache->cached = BTRFS_CACHE_FINISHED;
+	cache->global_root_id = calculate_global_root_id(fs_info, cache->start);
+
 	if (btrfs_fs_compat_ro(fs_info, FREE_SPACE_TREE))
 		cache->needs_free_space = 1;
 
@@ -2693,7 +2717,7 @@ static int update_block_group_item(struct btrfs_trans_handle *trans,
 	bi = btrfs_item_ptr_offset(leaf, path->slots[0]);
 	btrfs_set_stack_block_group_used(&bgi, cache->used);
 	btrfs_set_stack_block_group_chunk_objectid(&bgi,
-			BTRFS_FIRST_CHUNK_TREE_OBJECTID);
+						   cache->global_root_id);
 	btrfs_set_stack_block_group_flags(&bgi, cache->flags);
 	write_extent_buffer(leaf, &bgi, bi, sizeof(bgi));
 	btrfs_mark_buffer_dirty(leaf);