gnu: kmod: Honor $LINUX_MODULE_DIRECTORY.

* gnu/packages/patches/kmod-module-directory.patch: New file.
* gnu-system.am (dist_patch_DATA): Add it.
* gnu/packages/linux.scm (kmod)[origin]: Use it.

gnu-system.am

@@ -318,6 +318,7 @@ dist_patch_DATA =						\
   gnu/packages/patches/hop-bigloo-4.0b.patch			\
   gnu/packages/patches/icu4c-test-date-format.patch		\
   gnu/packages/patches/inkscape-stray-comma.patch               \
+  gnu/packages/patches/kmod-module-directory.patch		\
   gnu/packages/patches/libevent-dns-tests.patch			\
   gnu/packages/patches/libffi-mips-n32-fix.patch		\
   gnu/packages/patches/liboop-mips64-deplibs-fix.patch		\

gnu/packages/linux.scm

@@ -1204,7 +1204,8 @@ to use Linux' inotify mechanism, which allows file accesses to be monitored.")
                               "kmod-" version ".tar.xz"))
               (sha256
                (base32
-                "1yid3a9b64a60ybj66fk2ysrq5klnl0ijl4g624cl16y8404g9rv"))))
+                "1yid3a9b64a60ybj66fk2ysrq5klnl0ijl4g624cl16y8404g9rv"))
+              (patches (list (search-patch "kmod-module-directory.patch")))))
     (build-system gnu-build-system)
     (native-inputs
      `(("pkg-config" ,pkg-config)))

gnu/packages/patches/kmod-module-directory.patch

@@ -0,0 +1,31 @@
+This patch changes libkmod so it honors the 'LINUX_MODULE_DIRECTORY'
+environment variable, rather than looking for modules exclusively in
+/lib/modules.
+
+Patch by Shea Levy, from Nixpkgs; adjusted to use 'LINUX_MODULE_DIRECTORY'
+rather than 'MODULE_DIR' as the variable name.
+
+
+--- kmod-7/libkmod/libkmod.c	2012-03-15 08:19:16.750010226 -0400
++++ kmod-7/libkmod/libkmod.c	2012-04-04 15:21:29.532074313 -0400
+@@ -200,7 +200,7 @@
+ static char *get_kernel_release(const char *dirname)
+ {
+ 	struct utsname u;
+-	char *p;
++	char *p, *dirname_prefix;
+ 
+ 	if (dirname != NULL)
+ 		return path_make_absolute_cwd(dirname);
+@@ -208,7 +208,10 @@
+ 	if (uname(&u) < 0)
+ 		return NULL;
+ 
+-	if (asprintf(&p, "%s/%s", dirname_default_prefix, u.release) < 0)
++	if ((dirname_prefix = getenv("LINUX_MODULE_DIRECTORY")) == NULL)
++		dirname_prefix = dirname_default_prefix;
++
++	if (asprintf(&p, "%s/%s", dirname_prefix, u.release) < 0)
+ 		return NULL;
+ 
+ 	return p;