ply: Allow building for git-fetched kernels

pkgs/os-specific/linux/ply/default.nix

@@ -16,9 +16,17 @@ in stdenv.mkDerivation {
   };
 
   preAutoreconf = ''
-    # ply wants to install header fails to its build directory
-    # use 7z to handle multiple archive formats transparently
-    7z x ${kernel.src} -so | 7z x -aoa -si -ttar
+    # If kernel sources are a folder (i.e. fetched from git), we just copy them in
+    # Since they are owned by uid 0 and read-only, we need to fix permissions
+    if [ -d ${kernel.src} ]; then
+      cp -r ${kernel.src} linux-${kernel.version}
+      chown -R $(whoami): linux-${kernel.version}
+      chmod -R a+w linux-${kernel.version}
+    else
+      # ply wants to install header files to its build directory
+      # use 7z to handle multiple archive formats transparently
+      7z x ${kernel.src} -so | 7z x -aoa -si -ttar
+    fi
 
     configureFlagsArray+=(--with-kerneldir=$(echo $(pwd)/linux-*))
     ./autogen.sh --prefix=$out