btrfs: only call inode_sub_bytes in truncate paths that care

We currently have a bunch of awkward checks to make sure we only update
the inode i_bytes if we're truncating the real inode.  Instead keep
track of the number of bytes we need to sub in the
btrfs_truncate_control, and then do the appropriate adjustment in the
truncate paths that care.
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/free-space-cache.c

@@ -339,6 +339,7 @@ int btrfs_truncate_free_space_cache(struct btrfs_trans_handle *trans,
 	 */
 	ret = btrfs_truncate_inode_items(trans, root, inode, &control);
 
+	inode_sub_bytes(&inode->vfs_inode, control.sub_bytes);
 	btrfs_inode_safe_disk_i_size_write(inode, control.last_size);
 
 	unlock_extent_cached(&inode->io_tree, 0, (u64)-1, &cached_state);

fs/btrfs/inode-item.c

@@ -466,6 +466,7 @@ int btrfs_truncate_inode_items(struct btrfs_trans_handle *trans,
 	BUG_ON(new_size > 0 && control->min_type != BTRFS_EXTENT_DATA_KEY);
 
 	control->last_size = new_size;
+	control->sub_bytes = 0;
 
 	/*
 	 * For shareable roots we want to back off from time to time, this turns
@@ -574,10 +575,8 @@ int btrfs_truncate_inode_items(struct btrfs_trans_handle *trans,
 				btrfs_set_file_extent_num_bytes(leaf, fi,
 							 extent_num_bytes);
 				num_dec = (orig_num_bytes - extent_num_bytes);
-				if (test_bit(BTRFS_ROOT_SHAREABLE, &root->state) &&
-				    extent_start != 0)
-					inode_sub_bytes(&inode->vfs_inode,
-							num_dec);
+				if (extent_start != 0)
+					control->sub_bytes += num_dec;
 				btrfs_mark_buffer_dirty(leaf);
 			} else {
 				extent_num_bytes =
@@ -587,12 +586,8 @@ int btrfs_truncate_inode_items(struct btrfs_trans_handle *trans,
 
 				/* FIXME blocksize != 4096 */
 				num_dec = btrfs_file_extent_num_bytes(leaf, fi);
-				if (extent_start != 0) {
-					if (test_bit(BTRFS_ROOT_SHAREABLE,
-						     &root->state))
-						inode_sub_bytes(&inode->vfs_inode,
-								num_dec);
-				}
+				if (extent_start != 0)
+					control->sub_bytes += num_dec;
 			}
 			clear_len = num_dec;
 		} else if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
@@ -625,9 +620,7 @@ int btrfs_truncate_inode_items(struct btrfs_trans_handle *trans,
 				clear_len = fs_info->sectorsize;
 			}
 
-			if (test_bit(BTRFS_ROOT_SHAREABLE, &root->state))
-				inode_sub_bytes(&inode->vfs_inode,
-						item_end + 1 - new_size);
+			control->sub_bytes += item_end + 1 - new_size;
 		}
 delete:
 		/*

fs/btrfs/inode-item.h

@@ -29,6 +29,9 @@ struct btrfs_truncate_control {
 	/* OUT: the last size we truncated this inode to. */
 	u64 last_size;
 
+	/* OUT: the number of bytes to sub from this inode. */
+	u64 sub_bytes;
+
 	/*
 	 * IN: minimum key type to remove.  All key types with this type are
 	 * removed only if their offset >= new_size.

fs/btrfs/inode.c

@@ -8621,6 +8621,7 @@ static int btrfs_truncate(struct inode *inode, bool skip_writeback)
 		ret = btrfs_truncate_inode_items(trans, root, BTRFS_I(inode),
 						 &control);
 
+		inode_sub_bytes(inode, control.sub_bytes);
 		btrfs_inode_safe_disk_i_size_write(BTRFS_I(inode), control.last_size);
 
 		unlock_extent_cached(&BTRFS_I(inode)->io_tree, lock_start,