From 94b74da9de8d79d74769c7937ef9c969d89ba42f Mon Sep 17 00:00:00 2001
From: Tomas Janousek <tomi@nomi.cz>
Date: Mon, 23 Jan 2017 14:40:20 +0100
Subject: Fix Net monitor for large uptimes/bytecounts

My laptop currently has rx/tx bytes in 10s of gigabytes and it's only
been up for 20 days. Normally it's several times more. At this point,
Float can only tell the difference of 4KB and up:

Prelude> let x = (50 * 2^30 :: Float) in (x + 2000) - x
0.0
Prelude> let x = (50 * 2^30 :: Float) in (x + 3000) - x
4096.0

This commit makes the Net monitor read Word64 which is exactly what the
kernel prints into /proc/net/dev [1] and converts to Float only after
subtracting the two numbers.

[1] https://github.com/torvalds/linux/blob/7a308bb3016f57e5be11a677d15b821536419d36/net/core/net-procfs.c#L82

Still, I think it's time to switch from Float to Double. At half-gigabit
speeds (easily attainable at home while rsyncing over a direct UTP cable
between two post-2010 laptops), Float can only tell the difference of
8 bytes and up (and I'm not even considering takeDigits!). That's
probably okay for a Net monitor in xmobar, but we're so close to the
limit it makes sense to move to Double just in case.
---
 src/Plugins/Monitors/Net.hs | 29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

(limited to 'src/Plugins/Monitors')

diff --git a/src/Plugins/Monitors/Net.hs b/src/Plugins/Monitors/Net.hs
index 5954a77..7df8889 100644
--- a/src/Plugins/Monitors/Net.hs
+++ b/src/Plugins/Monitors/Net.hs
@@ -20,6 +20,7 @@ module Plugins.Monitors.Net (
 
 import Plugins.Monitors.Common
 
+import Data.Word (Word64)
 import Data.IORef (IORef, newIORef, readIORef, writeIORef)
 import Data.Time.Clock (UTCTime, getCurrentTime, diffUTCTime)
 import Control.Monad (forM, filterM, liftM)
@@ -63,16 +64,20 @@ instance Show UnitPerSec where
     show MBs = "MB/s"
     show GBs = "GB/s"
 
-data NetDev = NA
-            | NI String
-            | ND String Float Float deriving (Eq,Show,Read)
+data NetDev num
+    = NA
+    | NI String
+    | ND String num num deriving (Eq,Show,Read)
 
-type NetDevRef = IORef (NetDev, UTCTime)
+type NetDevRawTotal = NetDev Word64
+type NetDevRate = NetDev Float
+
+type NetDevRef = IORef (NetDevRawTotal, UTCTime)
 
 -- The more information available, the better.
 -- Note that names don't matter. Therefore, if only the names differ,
 -- a compare evaluates to EQ while (==) evaluates to False.
-instance Ord NetDev where
+instance Ord num => Ord (NetDev num) where
     compare NA NA              = EQ
     compare NA _               = LT
     compare _  NA              = GT
@@ -104,7 +109,7 @@ isUp d = do
   operstate <- B.readFile (operstateDir d)
   return $ (B.unpack . head . B.lines) operstate `elem`  ["up", "unknown"]
 
-readNetDev :: [String] -> IO NetDev
+readNetDev :: [String] -> IO NetDevRawTotal
 readNetDev (d:x:y:_) = do
   up <- isUp d
   return (if up then ND d (r x) (r y) else NI d)
@@ -113,7 +118,7 @@ readNetDev (d:x:y:_) = do
 
 readNetDev _ = return NA
 
-netParser :: B.ByteString -> IO [NetDev]
+netParser :: B.ByteString -> IO [NetDevRawTotal]
 netParser = mapM (readNetDev . splitDevLine) . readDevLines
   where readDevLines = drop 2 . B.lines
         splitDevLine = selectCols . wordsBy (`elem` " :") . B.unpack
@@ -122,7 +127,7 @@ netParser = mapM (readNetDev . splitDevLine) . readDevLines
           [] -> []
           s' -> w : wordsBy f s'' where (w, s'') = break f s'
 
-findNetDev :: String -> IO NetDev
+findNetDev :: String -> IO NetDevRawTotal
 findNetDev dev = do
   nds <- B.readFile "/proc/net/dev" >>= netParser
   case filter isDev nds of
@@ -145,7 +150,7 @@ formatNet mipat d = do
     x <- showWithColors (str s) d
     return (x, b, vb, ipat)
 
-printNet :: NetOpts -> NetDev -> Monitor String
+printNet :: NetOpts -> NetDevRate -> Monitor String
 printNet opts nd =
   case nd of
     ND d r t -> do
@@ -155,7 +160,7 @@ printNet opts nd =
     NI _ -> return ""
     NA -> getConfigValue naString
 
-parseNet :: NetDevRef -> String -> IO NetDev
+parseNet :: NetDevRef -> String -> IO NetDevRate
 parseNet nref nd = do
   (n0, t0) <- readIORef nref
   n1 <- findNetDev nd
@@ -163,7 +168,7 @@ parseNet nref nd = do
   writeIORef nref (n1, t1)
   let scx = realToFrac (diffUTCTime t1 t0)
       scx' = if scx > 0 then scx else 1
-      rate da db = takeDigits 2 $ (db - da) / scx'
+      rate da db = takeDigits 2 $ fromIntegral (db - da) / scx'
       diffRate (ND d ra ta) (ND _ rb tb) = ND d (rate ra rb) (rate ta tb)
       diffRate (NI d) _ = NI d
       diffRate _ (NI d) = NI d
@@ -176,7 +181,7 @@ runNet nref i argv = do
   opts <- io $ parseOpts argv
   printNet opts dev
 
-parseNets :: [(NetDevRef, String)] -> IO [NetDev]
+parseNets :: [(NetDevRef, String)] -> IO [NetDevRate]
 parseNets = mapM $ uncurry parseNet
 
 runNets :: [(NetDevRef, String)] -> [String] -> Monitor String
-- 
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