devout: add functions to read sysfs attributes

pkgs/devout/test.fnl

@@ -1,4 +1,4 @@
-(local { : database : event-loop : parse-event } (require :devout))
+(local { : database : event-loop : parse-event : sysfs } (require :devout))
 (local { : view } (require :fennel))
 (local ll (require :lualinux))
 (import-macros { : expect : expect= } :anoia.assert)
@@ -207,4 +207,35 @@ MINOR=17")
    ))
 
 
+;; tests for sysfs attrs
+
+(example
+ "read attributes from sysfs"
+ (let [sysfs (sysfs "./fixtures/sys")]
+   ;; finds attr at path
+   (expect=
+    (sysfs:attr "devices/pci0000:00/0000:00:14.0/usb1/1-2" "idVendor")
+    "1199")
+   ;; finds attr in ancestor directory
+   (expect=
+    (sysfs:attrs
+     "devices/pci0000:00/0000:00:14.0/usb1/1-7/1-7:1.0/bluetooth/hci0"
+     "idVendor")
+    "8087")
+   ;; nil if no attr
+   (expect=
+    (sysfs:attrs
+     "devices/pci0000:00/0000:00:14.0/usb1/1-7/1-7:1.0/bluetooth/hci0"
+     "idOfWizard")
+    nil)
+   ;; closer ancestor wins against more distant one
+   (expect=
+    (sysfs:attrs
+     "devices/pci0000:00/0000:00:14.0/usb1/1-7/1-7:1.0/bluetooth/hci0"
+     "modalias")
+    "usb:v8087p0A2Bd0001dcE0dsc01dp01icE0isc01ip01in00")))
+
+
+
+
 (if failed (os.exit 1) (print "OK"))