Expand kernel module guide

[jserv]

• Recommended CONFIG options for module development (KASAN, LOCKDEP, DEBUG_ATOMIC_SLEEP, DYNAMIC_DEBUG, DEBUG_INFO, MODULE_FORCE_UNLOAD).
• printk rate limiting (pr_*_ratelimited, CONFIG_LOG_BUF_SHIFT) and dynamic debug (pr_debug + dyndbg runtime control).
• Expanded vermagic explanation: what the string encodes, how CONFIG_MODVERSIONS CRC checksums reject ABI-incompatible modules.
• Canonical goto-based init error-handling pattern with reverse-order cleanup.
• IS_ERR/PTR_ERR/ERR_PTR convention, distinguishing ERR_PTR-returning APIs (class_create) from NULL-returning ones (kmalloc, proc_create).
• Module-loading race warning: register last, unregister first.
• Execution context overview: three kernel entry mechanisms, the "current" macro, and a process/softirq/hardirq capability table.
• Spinlock variant decision table and same-CPU deadlock scenario, with threaded-IRQ caveat.
• open/release/flush semantics and private_data lifecycle.
• sysfs /sys layout overview (devices, bus, class, module, kernel, firmware, power) before the coding example.
• copy_from_user exception-table mechanism and SMAP/PAN hardware enforcement explaining why raw user-pointer dereference crashes.
• Four new Common Pitfalls subsections: kernel stack limits, no floating point, buffer pre-initialization for copy_to_user, and double-underscore function conventions.

Makefile: fix blank-line rendering in HTML code blocks. make4ht emits N\n for blank source lines; the newline trapped inside the display:inline-block span collapses to zero height. Move the newline outside the span so

 renders it as a visible line break.  Tested against 1038 affected lines in the deployed HTML; zero remain after the fix.



Summary by cubic
Expands the kernel module guide with practical debugging, ABI, and concurrency guidance to prevent common bugs, and fixes HTML rendering for blank lines in code blocks.

This improves developer workflows and makes the guide safer and easier to follow.


New Features

Dev and logging: recommended CONFIGs, rate-limited printk, dynamic debug.
ABI and init: version magic and CONFIG_MODVERSIONS, goto-based cleanup, ERR_PTR/IS_ERR patterns, register-last/unregister-first.
Concurrency and locking: process/softirq/hardirq rules, current meaning, spinlock variant guidance with same-CPU deadlock note, file open/release/flush and private_data.
Interfaces and safety: sysfs map, copy_from_user + SMAP/PAN, pitfalls (small stack, no FP, zero buffers before copy_to_user, double-underscore APIs).



Bug Fixes

Fix blank-line rendering in HTML code blocks from make4ht by relocating trapped newlines so <pre> shows them.



Written for commit 1d15f7100b82a13d18dee7f92f1ad0f5aa11def3. Summary will update on new commits.

[cubic-dev-ai]

No issues found across 2 files