widgets: Add hwmontemp_linux

Introduce hwmontemp_linux widget, which provides name-based access to hwmon
sensors via sysfs.

README.md

@@ -264,6 +264,22 @@ Supported platforms: GNU/Linux, requiring `hddtemp` and `curl`.
 * Returns a table with string keys, using hard drives as a base, e.g.
   `${/dev/sda}` and `${/dev/sdc}`.
 
+### vicious.widgets.hwmontemp
+
+Provides name-based access to hwmon devices via sysfs.
+
+Supported platforms: GNU/Linux
+
+* Argument: table with sensor name and (optional) input number, e.g.
+  `{ "radeon", 2 }` (input no. is assumed to be 1 if omitted)
+* Returns a table with just the temperature value: `$1`
+* Usage example:
+
+```lua
+gputemp = wibox.widget.textbox()
+vicious.register(gputemp, vicious.contrib.hwmontemp, " $1°C", 5, { "radeon" })
+```
+
 ### vicious.widgets.mbox
 
 Provides the subject of last e-mail in a mbox file.

widgets/hwmontemp_linux.lua

@@ -0,0 +1,60 @@
+----------------------------------------------------------------
+--   Licensed under the GNU General Public License v2
+--   (C) 2019, Alexander Koch <lynix47@gmail.com>
+----------------------------------------------------------------
+
+-- environment
+local io = { popen = io.popen, open = io.open }
+local assert = assert
+local setmetatable = setmetatable
+
+-- sysfs prefix for hwmon devices
+local sys_hwmon = "/sys/class/hwmon/"
+-- cache table for hwmon device names
+local paths = {}
+
+-- transparently caching hwmon device name lookup
+function name_to_path(name)
+    if paths[name] then return paths[name] end
+
+    for sensor in io.popen("ls -1 " .. sys_hwmon):lines() do
+        local path = sys_hwmon .. sensor
+        local f = assert(io.open(path .. "/name", "r"))
+        local sname = f:read("*line")
+        f:close()
+        if sname == name then
+            paths[name] = path
+            return path
+        end
+    end
+
+    return nil
+end
+
+-- hwmontemp: provides name-indexed temps from /sys/class/hwmon
+-- vicious.widgets.hwmontemp
+local hwmontemp_linux = {}
+
+function worker(format, warg)
+    assert(type(warg) == "table", "invalid hwmontemp argument: must be a table")
+    name = warg[1]
+
+    if not warg[2] then
+        input = 1
+    else
+        input = warg[2]
+    end
+
+    local sensor = name_to_path(name)
+    if not sensor then return { "N/A" } end
+
+    local f = assert(io.open(("%s/temp%d_input"):format(sensor, input), "r"))
+    local temp = f:read("*line")
+    f:close()
+
+    return { temp / 1000 }
+end
+
+return setmetatable(hwmontemp_linux, { __call = function(_, ...) return worker(...) end })
+
+-- vim: ts=4:sw=4:expandtab