The LSOM functionality should be integrated with lfs find so that it is possible to use this functionality directly on the client. The MDS can fill in the mbo_size and mbo_blocks fields from the LSOM xattr, if the actual size/blocks are not available, and then set new OBD_MD_FLLSIZE and OBD_MD_FLLBLOCKS flags in the reply so that the client knows these fields are valid.
The lfs find command can add a "--lazy" option (or maybe "--lsize" and "--lblocks"?) to allow the use of LSOM data from the MDS. We might consider to also use this for "--size" when it is specified in some large range, like "--size -1G" or "--blocks +1M" since we don't need accurate sizes to match those requests. That could probably be done as a separate patch after the initial functionality is implemented and we have some idea how well LSOM is keeping the size uptodate.
Please include updates to the command usage and man page.