A network adapter includes a network interface, a bus interface, a hardware-implemented data-path and a programmable Data-Plane Accelerator (DPA). The network interface is to communicate with a network. The bus interface is to communicate with an external device over a peripheral bus. The hardware-implemented data-path includes a plurality of packet-processing engines to process data units exchanged between the network and the external device. The DPA is to expose on the peripheral bus a User-Defined Peripheral-bus Device (UDPD), to run user-programmable logic that implements the UDPD, and to process transactions issued from the external device to the UDPD by reusing one or more of the packet-processing engines of the data-path.