Add (guix build-system linux-module).

* guix/build/linux-module-build-system.scm: New file.
* guix/build-system/linux-module.scm: New file.
* doc/guix.texi (Build Systems): Document it.
* Makefile.am (MODULES): Add them.

4 files changed, 273 insertions, 0 deletions

diff --git a/Makefile.am b/Makefile.am
index 704f2451c3..8d523262cb 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -120,6 +120,7 @@ MODULES =					\
   guix/build-system/gnu.scm			\
   guix/build-system/guile.scm			\
   guix/build-system/haskell.scm			\
+  guix/build-system/linux-module.scm		\
   guix/build-system/perl.scm			\
   guix/build-system/python.scm			\
   guix/build-system/ocaml.scm			\
@@ -173,6 +174,7 @@ MODULES =					\
   guix/build/texlive-build-system.scm		\
   guix/build/waf-build-system.scm		\
   guix/build/haskell-build-system.scm		\
+  guix/build/linux-module-build-system.scm	\
   guix/build/store-copy.scm			\
   guix/build/utils.scm				\
   guix/build/union.scm				\
diff --git a/doc/guix.texi b/doc/guix.texi
index 7dc4e1894a..9be7d9a27b 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -6210,6 +6210,33 @@ is not enabled by default.  It can be enabled with @code{#:glib-or-gtk?}.
 @end table
 @end defvr
 
+@defvr {Scheme Variable} linux-module-build-system
+@var{linux-module-build-system} allows building Linux kernel modules.
+
+@cindex build phases
+This build system is an extension of @var{gnu-build-system}, but with the
+following phases changed:
+
+@table @code
+
+@item configure
+This phase configures the environment so that the Linux kernel's Makefile
+can be used to build the external kernel module.
+
+@item build
+This phase uses the Linux kernel's Makefile in order to build the external
+kernel module.
+
+@item install
+This phase uses the Linux kernel's Makefile in order to install the external
+kernel module.
+@end table
+
+It is possible and useful to specify the Linux kernel to use for building
+the module (in the "arguments" form of a package using the
+linux-module-build-system, use the key #:linux to specify it).
+@end defvr
+
 Lastly, for packages that do not need anything as sophisticated, a
 ``trivial'' build system is provided.  It is trivial in the sense that
 it provides basically no support: it does not pull any implicit inputs,
diff --git a/guix/build-system/linux-module.scm b/guix/build-system/linux-module.scm
new file mode 100644
index 0000000000..3ed3351353
--- /dev/null
+++ b/guix/build-system/linux-module.scm
@@ -0,0 +1,166 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2019 Danny Milosavljevic <dannym@scratchpost.org>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix build-system linux-module)
+  #:use-module (guix store)
+  #:use-module (guix utils)
+  #:use-module (guix derivations)
+  #:use-module (guix search-paths)
+  #:use-module (guix build-system)
+  #:use-module (guix build-system gnu)
+  #:use-module (guix packages)
+  #:use-module (ice-9 match)
+  #:export (%linux-module-build-system-modules
+            linux-module-build
+            linux-module-build-system))
+
+;; Commentary:
+;;
+;; Code:
+
+(define %linux-module-build-system-modules
+  ;; Build-side modules imported by default.
+  `((guix build linux-module-build-system)
+    ,@%gnu-build-system-modules))
+
+(define (default-linux)
+  "Return the default Linux package."
+
+  ;; Do not use `@' to avoid introducing circular dependencies.
+  (let ((module (resolve-interface '(gnu packages linux))))
+    (module-ref module 'linux-libre)))
+
+(define (default-kmod)
+  "Return the default kmod package."
+
+  ;; Do not use `@' to avoid introducing circular dependencies.
+  (let ((module (resolve-interface '(gnu packages linux))))
+    (module-ref module 'kmod)))
+
+(define (default-gcc)
+  "Return the default gcc package."
+
+  ;; Do not use `@' to avoid introducing circular dependencies.
+  (let ((module (resolve-interface '(gnu packages gcc))))
+    (module-ref module 'gcc-7)))
+
+(define (make-linux-module-builder linux)
+  (package
+    (inherit linux)
+    (name (string-append (package-name linux) "-module-builder"))
+    (arguments
+     (substitute-keyword-arguments (package-arguments linux)
+      ((#:phases phases)
+       `(modify-phases ,phases
+          (replace 'build
+            (lambda _
+              (invoke "make" "modules_prepare")))
+          (delete 'strip) ; faster.
+          (replace 'install
+            (lambda* (#:key outputs #:allow-other-keys)
+              (let* ((out (assoc-ref outputs "out"))
+                     (out-lib-build (string-append out "/lib/modules/build")))
+                ; TODO: Only preserve the minimum, i.e. [Kbuild], Kconfig, scripts, include, ".config".
+                (copy-recursively "." out-lib-build)
+                #t)))))))))
+
+(define* (lower name
+                #:key source inputs native-inputs outputs
+                system target
+                (linux (default-linux))
+                #:allow-other-keys
+                #:rest arguments)
+  "Return a bag for NAME."
+  (define private-keywords
+    '(#:source #:target #:gcc #:kmod #:linux #:inputs #:native-inputs))
+
+  (and (not target)                               ;XXX: no cross-compilation
+       (bag
+         (name name)
+         (system system)
+         (host-inputs `(,@(if source
+                              `(("source" ,source))
+                              '())
+                        ,@inputs
+                        ,@(standard-packages)))
+         (build-inputs `(("linux" ,linux) ; for "Module.symvers".
+                         ("linux-module-builder"
+                         ,(make-linux-module-builder linux))
+                         ,@native-inputs
+                         ;; TODO: Remove "gmp", "mpfr", "mpc" since they are only needed to compile the gcc plugins.  Maybe remove "flex", "bison", "elfutils", "perl", "openssl".  That leaves very little ("bc", "gcc", "kmod").
+                         ,@(package-native-inputs linux)))
+         (outputs outputs)
+         (build linux-module-build)
+         (arguments (strip-keyword-arguments private-keywords arguments)))))
+
+(define* (linux-module-build store name inputs
+                             #:key
+                             (search-paths '())
+                             (tests? #t)
+                             (phases '(@ (guix build linux-module-build-system)
+                                         %standard-phases))
+                             (outputs '("out"))
+                             (system (%current-system))
+                             (guile #f)
+                             (imported-modules
+                              %linux-module-build-system-modules)
+                             (modules '((guix build linux-module-build-system)
+                                        (guix build utils))))
+  "Build SOURCE using LINUX, and with INPUTS."
+  (define builder
+    `(begin
+       (use-modules ,@modules)
+       (linux-module-build #:name ,name
+                     #:source ,(match (assoc-ref inputs "source")
+                                      (((? derivation? source))
+                                       (derivation->output-path source))
+                                      ((source)
+                                       source)
+                                      (source
+                                        source))
+                     #:search-paths ',(map search-path-specification->sexp
+                                           search-paths)
+                     #:phases ,phases
+                     #:system ,system
+                     #:tests? ,tests?
+                     #:outputs %outputs
+                     #:inputs %build-inputs)))
+
+  (define guile-for-build
+    (match guile
+      ((? package?)
+       (package-derivation store guile system #:graft? #f))
+      (#f                                         ; the default
+       (let* ((distro (resolve-interface '(gnu packages commencement)))
+              (guile  (module-ref distro 'guile-final)))
+         (package-derivation store guile system #:graft? #f)))))
+
+  (build-expression->derivation store name builder
+                                #:system system
+                                #:inputs inputs
+                                #:modules imported-modules
+                                #:outputs outputs
+                                #:guile-for-build guile-for-build))
+
+(define linux-module-build-system
+  (build-system
+    (name 'linux-module)
+    (description "The Linux module build system")
+    (lower lower)))
+
+;;; linux-module.scm ends here
diff --git a/guix/build/linux-module-build-system.scm b/guix/build/linux-module-build-system.scm
new file mode 100644
index 0000000000..a6664f1eca
--- /dev/null
+++ b/guix/build/linux-module-build-system.scm
@@ -0,0 +1,78 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2019 Danny Milosavljevic <dannym@scratchpost.org>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix build linux-module-build-system)
+  #:use-module ((guix build gnu-build-system) #:prefix gnu:)
+  #:use-module (guix build utils)
+  #:use-module (ice-9 ftw)
+  #:use-module (ice-9 match)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-26)
+  #:export (%standard-phases
+            linux-module-build))
+
+;; Commentary:
+;;
+;; Builder-side code of linux-module build.
+;;
+;; Code:
+
+;; TODO: It might make sense to provide "Module.symvers" in the future.
+(define* (configure #:key inputs #:allow-other-keys)
+  #t)
+
+(define* (build #:key inputs make-flags #:allow-other-keys)
+  (apply invoke "make" "-C"
+         (string-append (assoc-ref inputs "linux-module-builder")
+                        "/lib/modules/build")
+         (string-append "M=" (getcwd))
+         (or make-flags '())))
+
+;; This block was copied from make-linux-libre--only took the "modules_install"
+;; part.
+(define* (install #:key inputs native-inputs outputs #:allow-other-keys)
+  (let* ((out (assoc-ref outputs "out"))
+         (moddir (string-append out "/lib/modules"))
+         (kmod (assoc-ref (or native-inputs inputs) "kmod")))
+    ;; Install kernel modules
+    (mkdir-p moddir)
+    (invoke "make" "-C"
+            (string-append (assoc-ref inputs "linux-module-builder")
+                           "/lib/modules/build")
+            (string-append "M=" (getcwd))
+            (string-append "DEPMOD=" kmod "/bin/depmod")
+            (string-append "MODULE_DIR=" moddir)
+            (string-append "INSTALL_PATH=" out)
+            (string-append "INSTALL_MOD_PATH=" out)
+            "INSTALL_MOD_STRIP=1"
+            "modules_install")))
+
+(define %standard-phases
+  (modify-phases gnu:%standard-phases
+    (replace 'configure configure)
+    (replace 'build build)
+    (replace 'install install)))
+
+(define* (linux-module-build #:key inputs (phases %standard-phases)
+                       #:allow-other-keys #:rest args)
+  "Build the given package, applying all of PHASES in order, with a Linux kernel in attendance."
+  (apply gnu:gnu-build
+         #:inputs inputs #:phases phases
+         args))
+
+;;; linux-module-build-system.scm ends here