gnu: Add brightnessctl.

* gnu/packages/linux.scm (brightnessctl): New variable.

Signed-off-by: Ricardo Wurmus <rekado@elephly.net>

gnu/packages/linux.scm

@@ -4304,6 +4304,45 @@ (define-public light
 Light is the successor of lightscript.")
     (license license:gpl3+)))
 
+(define-public brightnessctl
+  (let ((commit "6a791e7694aeeb5d027f71c6098e5182cf03371c"))
+    (package
+      (name "brightnessctl")
+      (version (git-version "0.4" "0" commit))
+      (source (origin
+                (method git-fetch)
+                (uri (git-reference
+                      (url "https://github.com/Hummer12007/brightnessctl/")
+                      (commit commit)))
+                (file-name (git-file-name name version))
+                (sha256
+                 (base32
+                  "1n1gb8ldgqv3vs565yhk1w4jfvrviczp94r8wqlkv5q6ab43c8w9"))))
+      (build-system gnu-build-system)
+      (arguments
+       '(#:tests? #f                    ; no tests
+         #:make-flags (list "CC=gcc"
+                            (string-append "PREFIX=" %output)
+                            (string-append "UDEVDIR=" %output "/lib/udev/rules.d/"))
+         #:phases
+         (modify-phases %standard-phases
+           (delete 'configure)
+           (add-after 'unpack 'adjust-udev-rules
+             (lambda _
+               (substitute* "90-brightnessctl.rules"
+                 (("/bin/") "/run/current-system/profile/bin/"))
+               #t)))))
+      (home-page "https://github.com/Hummer12007/brightnessctl")
+      (synopsis "Backlight and LED brightness control")
+      (description
+       "This program allows you read and control device brightness.  Devices
+include backlight and LEDs.  It can also preserve current brightness before
+applying the operation, such as on lid close.
+
+The appropriate permissions must be set on the backlight or LED control
+interface in sysfs, which can be accomplished with the included udev rules.")
+      (license license:expat))))
+
 (define-public tlp
   (package
     (name "tlp")