Merge branch 'joeyconfig'

1 files changed, 17 insertions, 2 deletions

diff --git a/src/Propellor/Bootstrap.hs b/src/Propellor/Bootstrap.hs
index 6812b4ab..089def51 100644
--- a/src/Propellor/Bootstrap.hs
+++ b/src/Propellor/Bootstrap.hs
@@ -104,9 +104,24 @@ build = catchBoolIO $ do
 		void $ cabal ["configure"]
 		unlessM (cabal ["build"]) $
 			error "cabal build failed"
-	nukeFile "propellor"
-	createSymbolicLink "dist/build/propellor-config/propellor-config" "propellor"
+	-- For safety against eg power loss in the middle of the build,
+	-- make a copy of the binary, and move it into place atomically.
+	-- This ensures that the propellor symlink only ever points at
+	-- a binary that is fully built. Also, avoid ever removing
+	-- or breaking the symlink.
+	--
+	-- Need cp -a to make build timestamp checking work.
+	unlessM (boolSystem "cp" [Param "-a", Param cabalbuiltbin, Param (tmpfor safetycopy)]) $
+		error "cp of binary failed"
+	rename (tmpfor safetycopy) safetycopy
+	createSymbolicLink safetycopy (tmpfor dest)
+	rename (tmpfor dest) dest
 	return True
+  where
+	dest = "propellor"
+	cabalbuiltbin = "dist/build/propellor-config/propellor-config"
+	safetycopy = cabalbuiltbin ++ ".built"
+	tmpfor f = f ++ ".propellortmp"
 
 make :: FilePath -> [FilePath] -> IO Bool -> IO ()
 make dest srcs builder = do