In lov_io_slice_mirror_init, the client code assumes that a RDONLY flag in the layout implies SOM and skips glimpse if so.  This is something like a layering violation - SOM is communicated from the MDS when it is valid, and the client already skips glimpse in that case.

Prior to "LU-14526 flr: mirror split downgrade SOM"/https://review.whamcloud.com/43168/, this was incorrect but not a problem, because LCM_FL_RDONLY always implied valid SOM.    That patch made that assumption invalid.

Fix is for client not to assume LCM_FL_RDONLY means SOM.