Investigate the use of zero-copy from kernel to vsocket driver

[MatiasVara]

We can reduce one copy if we use the content of the packet in the buffer descriptor instead of copying into temporal buffers.

[MatiasVara]

Toro could use the pointer to the data to the packet and then free it when the packet is sent. The network stack must not free the packet after send it. This will save one copy.

[MatiasVara]

If we use the data from kernel, we should use tell the kernel when the packet has been sent so that it can free the packet, i.e., DequeueOutgoingPacket().

[MatiasVara]

TODO: to illustrate the different buffers by using a picture.

[MatiasVara]

To reduce a copy, data should point to a different block of memory and the driver must be in charge of release it. The struct should have a flag that would allow such a mechanism. Then, the kernel can release the packet without release the data. The kernel has to inform the driver about this functionality:

  TPacket = record
    Size: LongInt;
    Data: Pointer;
    Status: Boolean;
    Scattered: Boolean;
    Ready: Boolean;
    Delete: Boolean;
    Next: PPacket;
  end;

[MatiasVara]

You can just use the current flag "Delete". To do this, the driver has to 1) enqueue packets in the outgoing queue, 2) consumes packets from the outgoing queue after a packet is sent. The driver calls DeQueueOnGoingPacket() to inform the kernel that the last packet has been sent.

[MatiasVara]

This is going to save one copy from the kernel buffer to the driver buffer. After packet is sent, the packet and the data are released.

[MatiasVara]

This issue remains open. I reverted the changes that were committed before. The problem was that the vsocket driver was telling the kernel that packets have been sent when it was not the case. This is because the driver does not know when a packet has been sent. So for each interruption, it was telling the kernel that the last packet has been sent. This ends up by corruption the queue of sent packets. I have to investigate this issue again.

[MatiasVara]

We would need something like transferTo() function to send data from disk to socket to avoid copying to application buffer.

[MatiasVara]

You only need to change

torokernel/rtl/Network.pas

Line 1063 in 3bb2b08

Packet.Data := Pointer(PtrUInt(Packet)+ sizeof(TPacket));

to use in Data a pointer to the user's buffers.

[MatiasVara]

The issue breaks down into the following tasks:

• Remove Packet.Ready, Packet.Delete and Packet.Ready, assume that when using SysNetworkSend() sender loses ownership on the packet.
• Remove OutgoingPackets and OutgoingPacketTail queues. This only worked when the network is able to send only one packet at time.
• DequeueOutgoingPacket() shall tell the kernel that a packet has been sent and release it memory if Delete = True.
• The vsocket stack shall not release the packet. The network stack will do it if Delete = True.
• The Vsocket driver shall tell the Network stack that a Packet has been sent by using DequeueOutgoingPacket().
• The Packet.data shall be PAGE_SIZE aligned
• The VSocket driver shall not require to allocate buffers.
• The allocation of packets shall be done by a dedicated function.
• To document the Network Stack and the interaction with the network driver. The documentation is at https://github.com/torokernel/documentation.