Libibverbs is a library that enables user-space processes to use RDMA verbs as described in the InfiniBand Architecture Specification (see, http://www.infinibandta.org) and the RDMA Protocol Verbs Specification (see, http://tools.ietf.org/html/draft-hilland-rddp-verbs-00).
Several /dev/rdma/uverbsN character device nodes are used to handle communication between the library libibverbs and the kernel ib_uverbs layer. There is one such device per RNIC adapter registered with OFED core (uverbs1, uverbs2, etc). The library writes commands corresponding to the verb to execute on the appropriate device.