Method for intra-stack zero-copy transmit path in shared-memory-based communication mode

A method for an intra-stack zero-copy transmit (Tx) path in a shared-memory-based communication mode, characterized in comprising the steps of:

• Step 1:
• receiving an I/O request from an application by polling an I/O event queue and then forwarding the request to a session module for processing, by an event polling module of a network protocol stack;
• Step 2:
• after receiving the request, identifying a corresponding network session, identifying a data Tx queue based on information thereof recorded in the network session, determining a location and length of a Tx data, and then calling a memory coupling module and transferring the information of the Tx data to the memory coupling module, by the session module;
• Step 3:
• after acquiring the information of the data from the Tx queue, calculating required packet buffer resources, allocating them from a pool of packet buffer resources and then storing references to the data in the packet buffers, by the memory coupling module, instead of copying the data into the packet buffers, as is conventional, wherein in this process, one more packet buffer is allocated;
• Step 4:
• after the references are written in the packet buffers, handing the packet buffers over to the session module by the memory coupling module and in turn handing the packet buffers over to a transport/network layer for packet encapsulation by the session module;
• Step 5:
• receiving a session information and the packet buffers from the session module and identifying a corresponding network connection, by the transport/network layer, and generating a packet header by the network protocol stack, wherein in order to enable ready ascertainment of whether a packet buffer stores references to data in shared memory, the network protocol stack stores the packet header in a separate packet buffer from those storing the data references and labels the packet buffers storing the data references;
• the network protocol stack pre-allocates one more packet buffer in Step 3 and writes the generated packet header into this reserved packet buffer;
• and the network protocol stack then concatenates the packet buffers storing the corresponding data references at the end of the packet buffer storing the packet header so that the set of packet buffers is together taken as a single encapsulated packet with scattered payloads;
• Step 6:
• after the packet encapsulation is completed, notifying the event polling module by the session module of readiness of the packet buffers, and notifying a network interface card (NIC) driver by the network protocol stack;
• Step 7:
• retrieving the packet header from the packet buffer, or address and length information of the data in the shared memory, filling it into descriptors and placing them into a descriptor ring, by the NIC driver;
• for the concatenated packet buffers, the driver traverses them one by one, retrieves the information therefrom, fills the descriptors therewith and concatenates fields of the descriptors into a string of descriptors and writes it into the Tx descriptor ring;
• on an NIC which supports scatter/gather list (SGL) characteristics, based on the string of descriptors, the NIC reads the packet header and the data from the packet buffers and the data Tx queue, respectively, assembles them into a continuous packet within the NIC itself, and transmits the packet out;
• and after the transmission is completed, the NIC labels the string of descriptors as “done”;
• Step 8:
• after the NIC driver receiving the done string of descriptors, handing the packet buffers over to a memory decoupling module by the network protocol stack;
• and
• Step 9:
• checking the packet buffers one by one, deleting the reference information within the packet buffers for the labeled packet buffers that store the data references and thereby recovering them into regular packet buffers, and recycling them back into the pool of packet buffer resources, by the memory decoupling module.