Man page 9 : ida_simple_get

ida_simple_get - get a new id.

int ida_simple_get(struct ida *  ida , unsigned int  start , unsigned int  end , gfp_t  gfp_mask );

ida
    the (initialized) ida.

start
    the minimum id (inclusive, < 0x8000000)

end
    the maximum id (exclusive, < 0x8000000 or 0)

gfp_mask
    memory allocation flags

Allocates an id in the range start <= id < end, or returns -ENOSPC. On memory allocation failure, returns -ENOMEM.

Use ida_simple_remove to get rid of an id.