A file named 
cxgb3.driver must exist in the directory 
/etc/libibverbs.d,
which enables you to use the driver for the Chelsio T3 Ethernet adapter
10 GB iWARP, by default. The 
cxgb3.driver file must
contain the following code:
# cat /etc/libibverbs.d/cxgb3.driver
driver cxgb3
 
Use the environment variable IBV_CONFIG_DIR to use another
directory than the /etc/libibverbs.d/ directory.