In order to simplify implementation, this project will focus on implementing composite layouts that are grown by allocating objects in non-overlapping layout extents at the end of the file, and will not implement modification of already allocated layout extents containing data.

The client IO (CLIO) layer needs to be able to manage the growth of the file layout by reconfiguring its IO stack to add new OST objects into the layout. The client will request that the MDS instantiate OST objects based on the layout template before it begins writing to a file offset beyond the currently instantiated layout components. The layout generation stored in the composite layout and in each layout extent will allow CLIO to detect whether a specific layout extent has been modified when the lock is revoked. Since the existing components of the file layout will not be modified for PFL files, any in-flight IO operations and cached data do not need to be interrupted.