Red Bear OS — microkernel OS in Rust, based on Redox

Derivative of Redox OS (https://www.redox-os.org) adding:
- AMD GPU driver (amdgpu) via LinuxKPI compat layer
- ext4 filesystem support (ext4d scheme daemon)
- ACPI fixes for AMD bare metal (x2APIC, DMAR, IVRS, MCFG)
- Custom branding (hostname, os-release, boot identity)

Build system is full upstream Redox with RBOS overlay in local/.
Patches for kernel, base, and relibc are symlinked from local/patches/
and protected from make clean/distclean. Custom recipes live in
local/recipes/ with symlinks into the recipes/ search path.

Build:  make all CONFIG_NAME=redbear-full
Sync:   ./local/scripts/sync-upstream.sh

local/recipes/drivers/linux-kpi/source/build.rs

@@ -0,0 +1,53 @@
+use std::env;
+use std::fs;
+use std::path::Path;
+
+fn copy_dir_recursive(src: &Path, dst: &Path) -> std::io::Result<()> {
+    fs::create_dir_all(dst)?;
+    for entry in fs::read_dir(src)? {
+        let entry = entry?;
+        let src_path = entry.path();
+        let dst_path = dst.join(entry.file_name());
+        if src_path.is_dir() {
+            copy_dir_recursive(&src_path, &dst_path)?;
+        } else {
+            fs::copy(&src_path, &dst_path)?;
+        }
+    }
+    Ok(())
+}
+
+fn main() {
+    let out_dir = env::var("OUT_DIR").expect("OUT_DIR not set");
+    let manifest_dir = env::var("CARGO_MANIFEST_DIR").expect("CARGO_MANIFEST_DIR not set");
+
+    let headers_src = Path::new(&manifest_dir).join("src/c_headers");
+    let headers_dst = Path::new(&out_dir).join("include");
+
+    if headers_src.exists() {
+        copy_dir_recursive(&headers_src, &headers_dst)
+            .expect("failed to copy C headers to OUT_DIR");
+
+        println!("cargo:include={}", headers_dst.display());
+    }
+
+    let sysroot = env::var("COOKBOOK_SYSROOT").ok();
+    if let Some(ref sysroot_path) = sysroot {
+        let sysroot_include = Path::new(sysroot_path).join("include/linux-kpi");
+        if headers_src.exists() {
+            copy_dir_recursive(&headers_src, &sysroot_include)
+                .expect("failed to copy C headers to COOKBOOK_SYSROOT");
+        }
+    }
+
+    let stage = env::var("COOKBOOK_STAGE").ok();
+    if let Some(ref stage_path) = stage {
+        let stage_include = Path::new(stage_path).join("usr/include/linux-kpi");
+        if headers_src.exists() {
+            copy_dir_recursive(&headers_src, &stage_include)
+                .expect("failed to copy C headers to COOKBOOK_STAGE");
+        }
+    }
+
+    println!("cargo:rerun-if-changed=src/c_headers");
+}