How do I write a network device driver using SPI?

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I have implemented a device driver for the NRF24L01+ transceiver in userspace using rust. The userspace driver makes use of the kernel spi interface driver. Writing the driver as kernel module seems incredibly hard, as the documentation for linux/netdevice.h as found in linux device drivers seems outdated (or I'm just not smart enough to understand the intricate details).

A new project from the TU Munich proposes the use of vfio. From my understanding this type of driver implementation uses the iommu to manage isolation to protected memory areas for the devices. "Project Ixy" uses the network device as block device, hence it can be mapped. SPI is different as insofar it is a streaming protocol.

My question is, if it is possible to integrate the user space spi network device driver into the linux network stack, e.g. having all protocols etc handled by the network stack. Is it possible to use a similar approach as Project Ixy, like having a small component in kernel space, which is isolated for security, that builds a "bridge" to userland?

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linuxdriverspi

1 Answers

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I think it is possible in two ways:

  1. using TAP interface
  2. writing your own "bridging" interface like TAP between user space and kernel space

If ethernet-like interface is enough for you - then use TAP. I mean TAP provides functionality where physical layer is moved to user space. In your case it could work like this: data received by SPI can be pushed to TAP interface to linux network stack. The data received from TAP interface (from Linux network stack) you can push via SPI. Is that what you wanted?

If ethernet-like interace (as TAP is) is not enough for you - you can write your own interface in kernel space basing on TAP sources.