merge from git-annex

Fixes 2 bugs, one a data loss bug. It is possible to get those fixes
without merging all the other changes, if a backport is wanted.

1 files changed, 83 insertions, 0 deletions

diff --git a/Utility/CopyFile.hs b/Utility/CopyFile.hs
new file mode 100644
index 0000000..f851326
--- /dev/null
+++ b/Utility/CopyFile.hs
@@ -0,0 +1,83 @@
+{- file copying
+ -
+ - Copyright 2010-2019 Joey Hess <id@joeyh.name>
+ -
+ - License: BSD-2-clause
+ -}
+
+module Utility.CopyFile (
+	copyFileExternal,
+	copyCoW,
+	createLinkOrCopy,
+	CopyMetaData(..)
+) where
+
+import Common
+import qualified BuildInfo
+
+data CopyMetaData 
+	-- Copy timestamps when possible, but no other metadata, and
+	-- when copying a symlink, makes a copy of its content.
+	= CopyTimeStamps
+	-- Copy all metadata when possible.
+	| CopyAllMetaData
+	deriving (Eq)
+
+copyMetaDataParams :: CopyMetaData -> [CommandParam]
+copyMetaDataParams meta = map snd $ filter fst
+	[ (allmeta && BuildInfo.cp_a, Param "-a")
+	, (allmeta && BuildInfo.cp_p && not BuildInfo.cp_a
+		, Param "-p")
+	, (not allmeta && BuildInfo.cp_preserve_timestamps
+		, Param "--preserve=timestamps")
+	]
+  where
+	allmeta = meta == CopyAllMetaData
+
+{- The cp command is used, because I hate reinventing the wheel,
+ - and because this allows easy access to features like cp --reflink
+ - and preserving metadata. -}
+copyFileExternal :: CopyMetaData -> FilePath -> FilePath -> IO Bool
+copyFileExternal meta src dest = do
+	-- Delete any existing dest file because an unwritable file
+	-- would prevent cp from working.
+	void $ tryIO $ removeFile dest
+	boolSystem "cp" $ params ++ [File src, File dest]
+  where
+	params
+		| BuildInfo.cp_reflink_supported =
+			Param "--reflink=auto" : copyMetaDataParams meta
+		| otherwise = copyMetaDataParams meta
+
+{- When a filesystem supports CoW (and cp does), uses it to make
+ - an efficient copy of a file. Otherwise, returns False. -}
+copyCoW :: CopyMetaData -> FilePath -> FilePath -> IO Bool
+copyCoW meta src dest
+	| BuildInfo.cp_reflink_supported = do
+		void $ tryIO $ removeFile dest
+		-- When CoW is not supported, cp will complain to stderr,
+		-- so have to discard its stderr.
+		ok <- catchBoolIO $ withNullHandle $ \nullh ->
+			let p = (proc "cp" $ toCommand $ params ++ [File src, File dest])
+				{ std_out = UseHandle nullh
+				, std_err = UseHandle nullh
+				}
+			in withCreateProcess p $ \_ _ _ -> checkSuccessProcess
+		-- When CoW is not supported, cp creates the destination
+		-- file but leaves it empty.
+		unless ok $
+			void $ tryIO $ removeFile dest
+		return ok
+	| otherwise = return False
+  where
+	params = Param "--reflink=always" : copyMetaDataParams meta
+
+{- Create a hard link if the filesystem allows it, and fall back to copying
+ - the file. -}
+createLinkOrCopy :: FilePath -> FilePath -> IO Bool
+createLinkOrCopy src dest = go `catchIO` const fallback
+  where
+	go = do
+		createLink src dest
+		return True
+	fallback = copyFileExternal CopyAllMetaData src dest