devout: add functions to read sysfs attributes

pkgs/devout/devout.fnl

@@ -1,3 +1,4 @@
+(local { : dirname } (require :anoia))
 (local ll (require :lualinux))
 (local {
         : AF_LOCAL
@@ -145,6 +146,25 @@
     :_tbl #(do fds)                    ;exposed for tests
      }))
 
+(fn read-if-exists [pathname]
+  (match (ll.open pathname 0 0)
+    fd (let [s (ll.read fd 4096)
+             s1 (string.gsub s "[ \n]*(.-)[ \n]*" "%1")]
+         (ll.close fd)
+         s1)
+    nil nil))
+
+(fn sysfs [fspath]
+  {
+   :attr (fn [_ path name]
+           (read-if-exists (.. fspath "/" path "/" name)))
+   :attrs (fn [self path name]
+            (when path
+              (or (self:attr path name)
+                  (self:attrs (dirname path) name))))
+   })
+
+
 (fn run []
   (let [[sockname nl-groups] arg
         s (check-errno (unix-socket sockname))
@@ -170,4 +190,4 @@
         (ll.poll pollfds 5000)
         (loop:feed (unpack-pollfds pollfds))))))
 
-{ : database : run : event-loop : parse-event }
+{ : database : run : event-loop : parse-event : sysfs }

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"))