internal/rosa: kernel patching

The side effect of this is to work around zfs performance issue with chmod on overlay mount.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/kernel.go

@@ -8,6 +8,7 @@ import (
 
 // newKernel is a helper for interacting with Kbuild.
 func (t Toolchain) newKernel(
+	patches [][2]string,
 	script string,
 	extra ...pkg.Artifact,
 ) pkg.Artifact {
@@ -20,18 +21,20 @@ func (t Toolchain) newKernel(
 	}, extra), nil, nil, `
 export LLVM=1
 export HOSTLDFLAGS="${LDFLAGS}"
-chmod -R +w /usr/src/linux && cd /usr/src/linux
-`+script, pkg.Path(AbsUsrSrc.Append("linux"), true, pkg.NewHTTPGetTar(
-		nil,
-		"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/"+
-			"snapshot/linux-"+version+".tar.gz",
-		mustDecode(checksum),
-		pkg.TarGzip,
+cd /usr/src/linux
+`+script, pkg.Path(AbsUsrSrc.Append("linux"), true, t.NewPatchedSource(
+		"kernel", pkg.NewHTTPGetTar(
+			nil,
+			"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/"+
+				"snapshot/linux-"+version+".tar.gz",
+			mustDecode(checksum),
+			pkg.TarGzip,
+		), false, patches...,
 	)))
 }
 
 func (t Toolchain) newKernelHeaders() pkg.Artifact {
-	return t.newKernel(`
+	return t.newKernel(nil, `
 make "-j$(nproc)" \
 	INSTALL_HDR_PATH=/work/system \
 	headers_install