Linux Kernel Drivers

Four Linux kernel modules, each working through a different driver subsystem and the contract it imposes between kernel and user space, hardware, or the networking stack. None require physical hardware: every driver builds and runs end-to-end in Docker + QEMU against a real kernel, on Linux, macOS, or Windows.

Driver	Subsystem	Core mechanisms
linux-character-device-driver	Character device	file_operations, mutex, wait queues, blocking I/O, ioctl
linux-block-device-driver	Block I/O (gendisk/blk-mq)	bio/request segment iteration, spinlock-protected memcpy, page cache vs. O_DIRECT
linux-network-device-driver	Networking (net_device)	sk_buff, descriptor rings, NAPI, TX queue backpressure
linux-pcie-device-driver	PCI / PCIe	BAR-mapped MMIO, MSI interrupts, DMA buffer management

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Overview

Each project targets a different kernel subsystem on purpose, so that together they cover most of the contracts a driver author has to get right:

• circbuf — a virtual circular-buffer character device. No hardware dependency, so it isolates the kernel/user-space boundary itself: copy_to_user/copy_from_user, mutex vs. spinlock choice, wait-queue-based blocking I/O, and ioctl design.
• vblk — a virtual RAM-backed block device exposed as /dev/vblk0. Covers the block layer's gendisk/blk-mq contract: request dispatch, bio/request segment iteration, the spinlock-vs-mutex tradeoff once user-copies are off the table, and the page-cache-vs-O_DIRECT distinction that governs when I/O actually reaches the driver.
• netdrv — a software point-to-point Ethernet pair (vnet0 ↔ vnet1) built around the same structures a real NIC driver uses: TX/RX descriptor rings, NAPI interrupt-mitigated reception, and netif_stop_queue/wake_queue backpressure.
• pcie-edu-driver — a driver for QEMU's edu educational PCI device, covering the full PCI driver lifecycle: bus enumeration, BAR-mapped MMIO, MSI interrupt handling, and dma_alloc_coherent DMA buffer management.

The character device project establishes the kernel/user-space boundary and synchronization primitives; the block device project moves that contract into the block layer's request/bio model; the networking and PCIe projects each build further on that foundation while introducing their own subsystem-specific object model (net_device/sk_buff vs. pci_dev/MMIO/MSI) and context rules (softirq NAPI polling vs. hardirq interrupt handling).

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Repository Layout

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├── linux-character-device-driver/   # circbuf — virtual character device
├── linux-block-device-driver/       # vblk    — virtual RAM-backed block device
├── linux-network-device-driver/     # netdrv  — virtual Ethernet driver pair
├── linux-pcie-device-driver/        # pcie-edu-driver — QEMU "edu" PCIe driver
└── LICENSE                          # MIT

Each subdirectory is self-contained, with its own Makefile, docker/ test harness, and README.md covering architecture, key concepts, build/test instructions, and verified test results.

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Building and Testing

Every driver follows the same pattern: build against real kernel headers in Docker, then boot a real kernel under QEMU to load and exercise the module — not a build-only check. From within any of the three subdirectories:

./docker/run.sh test     # circbuf, vblk, pcie-edu-driver

docker build -f docker/Dockerfile -t netdrv-e2e . && docker run --rm netdrv-e2e   # netdrv

See each project's README for native (non-Docker) build instructions, architecture diagrams, design tradeoffs, and the last verified test run.

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References

• Linux Device Drivers, 3rd Edition — Corbet, Rubini, Kroah-Hartman (free at lwn.net)
• Linux Kernel Development, 3rd Edition — Robert Love
• Rosen, R. Linux Kernel Networking: Implementation and Theory
• Documentation/driver-api/, Documentation/block/, Documentation/networking/napi.rst, Documentation/PCI/pci.rst in the Linux kernel source tree

License

MIT — see LICENSE.