linux-testing: Fix arg list too long in modinst

With the default kernel and thus with the build I have tested in
74ec94bfa2e57e2c0beeee0e469de58391d04a7b, we get an error during
modules_install:

make[2]: execvp: /nix/store/.../bin/bash: Argument list too long

I haven't noticed this build until I actually tried booting using this
kernel because make didn't fail here.

The reason this happens within Nix and probably didn't yet surface in
other distros is that programs only have a limited amount of memory
available for storing the environment and the arguments.

Environment variables however are quite common on Nix and thus we
stumble on problems like this way earlier - in this case Linux 4.8 - but
I have noticed this in 4.7-next as well already.

The fix is far from perfect and suffers performance overhead because we
now run grep for every *.mod file instead of passing all *.mod files
into one single invocation of grep.

But comparing the performance overhead (around 1s on my machine) with
the overall build time of the kernel I think the overhead really is
neglicible.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

pkgs/os-specific/linux/kernel/modinst-arg-list-too-long.patch

@@ -0,0 +1,14 @@
+diff --git a/scripts/Makefile.modinst b/scripts/Makefile.modinst
+index 07650ee..934a7a8 100644
+--- a/scripts/Makefile.modinst
++++ b/scripts/Makefile.modinst
+@@ -9,7 +9,8 @@ include scripts/Kbuild.include
+ 
+ #
+ 
+-__modules := $(sort $(shell grep -h '\.ko$$' /dev/null $(wildcard $(MODVERDIR)/*.mod)))
++__modules := $(sort $(foreach f,$(wildcard $(MODVERDIR)/*.mod),$(shell \
++    grep -h '\.ko$$' '$f')))
+ modules := $(patsubst %.o,%.ko,$(wildcard $(__modules:.ko=.o)))
+ 
+ PHONY += $(modules)

pkgs/os-specific/linux/kernel/patches.nix

@@ -74,6 +74,11 @@ rec {
       patch = ./mips-ext3-n32.patch;
     };
 
+  modinst_arg_list_too_long =
+    { name = "modinst-arglist-too-long";
+      patch = ./modinst-arg-list-too-long.patch;
+    };
+
   ubuntu_fan_4_4 =
     { name = "ubuntu-fan";
       patch = ./ubuntu-fan-4.4.patch;

pkgs/top-level/all-packages.nix

@@ -11185,9 +11185,11 @@ in
   };
 
   linux_testing = callPackage ../os-specific/linux/kernel/linux-testing.nix {
-    kernelPatches = [ kernelPatches.bridge_stp_helper ]
-      ++ lib.optionals ((platform.kernelArch or null) == "mips")
-      [ kernelPatches.mips_fpureg_emu
+    kernelPatches = [
+      kernelPatches.bridge_stp_helper
+      kernelPatches.modinst_arg_list_too_long
+    ] ++ lib.optionals ((platform.kernelArch or null) == "mips") [
+      kernelPatches.mips_fpureg_emu
       kernelPatches.mips_fpu_sigill
       kernelPatches.mips_ext3_n32
     ];