Fix build #49: Replace umount with sys_umount for kernel 4.9

[Crybyte]

Automated fix for crDroid++ kernel build failure.

Issue: Build #48 failed with undefined reference to umount in function ksu_umount_mnt at core_hook.c:566

Root Cause: The ksu_umount_mnt function calls umount() which does not exist in kernel 4.9. Previous fix v34 attempted to use ksys_umount but that also is not available.

Fix:

• Added fix_kernelsu_49_v35.py script that replaces umount() with sys_umount()
• Added proper includes (linux/syscalls.h) and declarations
• Updated workflow to run v35 fix AFTER the pre-patched file override to catch any remaining issues

Related: Build #48 failed with linker error

cc: @coderabbitai

Summary by CodeRabbit

• Bug Fixes
  • Critical fix for kernel 4.9 compatibility with system call handling in kernel builds.

[coderabbitai]

Caution

Review failed

Pull request was closed or merged during review

📝 Walkthrough

Walkthrough

A new kernel 4.9 compatibility patch (v35) was added to fix umount() function usage in KernelSU's core_hook.c. The changes include a GitHub Actions workflow step that executes a new Python script to replace umount() calls with sys_umount() and inject the necessary syscall declaration.

Changes

Cohort / File(s)	Summary
Workflow Enhancement .github/workflows/crdroid-plus-kernel-build.yml	Added "CRITICAL FIX v35" step to execute kernel 4.9 compatibility patch script after v34 pre-patched core_hook.c override, before verification of line 591.
Kernel 4.9 Compatibility Script build-scripts/fix_kernelsu_49_v35.py	New Python script that locates core_hook.c, replaces kernel-4.9-incompatible umount() calls with sys_umount(), and injects #include <linux/syscalls.h> with an asmlinkage long sys_umount() declaration when needed.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• Fix build #26: KernelSU-Next 'flags undeclared' error #1: Targets the same drivers/kernelsu/core_hook.c region with alternative umount-related fixes and function replacements.
• Fix build #45: Comprehensive multi-location core_hook.c patching #21: Implements kernel-4.9 compatibility patches (v31) that pre-patch core_hook.c and verify the same line 591 flag/umount issue that v35 addresses.

Poem

🐰 Hops through kernel land with glee,
Fixing umount for 4.9's spree,
sys_umount now shall reign supreme,
Declarations flowing like a dream! 🌙✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately and specifically describes the main change: replacing umount with sys_umount for kernel 4.9 compatibility, which is the core purpose of this PR.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/build-49-umount-sys

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