Add DMA, block, and network driver examples

[jserv]

This introduces new kernel module examples (dma.c, blkram.c, vnetloop.c) and corresponding book sections covering memory/time/data-movement, PCI, USB, block, and network driver subsystems.

It also adds poll/select/epoll, async notification, MMIO, DMA/mmap, scatter-gather, and modern-interface-choices sections to the book text, and updates the version baseline statement to reflect 5.10 minimum.

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Summary by cubic

Adds three kernel module examples (DMA demo, RAM-backed blk‑mq block device, and virtual loopback Ethernet) and expands the book with modern DMA/MMIO, poll/epoll, and PCI/USB/block/network chapters. Sets Linux v5.10 as the minimum baseline and embeds the new samples in the text.

• New Features
  • Examples: examples/dma.c (sets DMA mask, coherent + streaming DMA via synthetic platform_device, version-aware .remove for 5.10–6.11), examples/blkram.c (RAM disk using blk‑mq with guards for 5.10–6.9+, kmap and queue helper transitions), examples/vnetloop.c (virtual net_device looping TX→RX with 64‑bit stats). Updated examples/Makefile to build dma.o, blkram.o, vnetloop.o.
  • Book (lkmpg.tex): Added poll/select/epoll and fasync; a Memory/Time/Data Movement chapter (timekeeping, allocation, user–kernel copies); MMIO; DMA + mmap with scatter‑gather and debugging; modern interface choices; and subsystem chapters for PCI, USB, block, and network with sample embeds. Baseline set to Linux v5.10.

^{Written for commit 563b6db. Summary will update on new commits.}

[cubic-dev-ai]

1 issue found across 5 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="examples/vnetloop.c">

<violation number="1" location="examples/vnetloop.c:27">
P2: `u64` packet/byte counters are updated and read without synchronization, which can yield inconsistent stats under concurrent access (especially on 32-bit builds).</violation>
</file>

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