XkbAllocGeomOverlayKeys - Man Page
Allocate keys in an overlay row
Status XkbAllocGeomOverlayKeys (XkbOverlayRowPtr row, int num_needed);
section for which rows should be allocated
number of new rows required
Xkb provides a number of functions to allocate and free subcomponents of a keyboard geometry. Use these functions to create or modify keyboard geometries. Note that these functions merely allocate space for the new element(s), and it is up to you to fill in the values explicitly in your code. These allocation functions increase sz_* but never touch num_* (unless there is an allocation failure, in which case they reset both sz_* and num_* to zero). These functions return Success if they succeed, BadAlloc if they are not able to allocate space, or BadValue if a parameter is not as expected.
XkbAllocGeomOverlayKeys allocates num_needed keys and adds them to the row. No initialization of the keys is done.
Unable to allocate storage
An argument is out of range