KFA, the Kernel Flow Allocation Manger. The KFA is in charge of flow management related functionalities such as creation, binding to IPC processes, de-allocation, etc. These functionalities are offered to both the KIPCM via its northbound interface, and to the IPC Processes via its southbound interface. The management of port identifiers and its association to flow instances is the most important functionality provided by the KFA through its Port ID Manager (PIDM). This solves synchronization issues during the flow creation process due to race conditions. The destination applications started to invoke system calls on port-ids before the kernel completed the flow allocation process. Thus, there was a short period where the read and write operations on this port id failed since this situation was not properly handled by the KIPCM. With the introduction of the KFA, the internal kernel flow structures that support the port-ids are created before notifying the application of an incoming flow allocation request, with the status of ‘PENDING’. When the application confirms that the flow is accepted, the status of the flow structure is updated to ‘ALLOCATED’. If the application invokes a read/write system call on the port-id before the flow status is ‘ALLOCATED’, the KFA simply deschedule the calling process until the flow allocation is complete. Complementary to the port id management, the KFA binds the KIPCM and IPC Processes by means of the flow it manages. For this reason, the KFA creates a flow structure for each flow and binds together its port identifier and the identifier of the IPC Process supporting the flow. The flow structure also contains information such as the flow instance allocation state – as described in the previous paragraph - and the queue of SDUs ready to be consumed by user space applications. By means of the allocation state, the KFA controls the life cycle of a flow, since the possible states (pending, allocated, de-allocated) are set as result of the management actions and impose constraints about the possible actions that can be applied over the flow. The following figure shows the main interactions of the KFA. Figure 3 KFA Interactions (details)
