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|
{- file copying
-
- Copyright 2010-2021 Joey Hess <id@joeyh.name>
-
- License: BSD-2-clause
-}
module Utility.CopyFile (
copyFileExternal,
copyCoW,
createLinkOrCopy,
CopyMetaData(..)
) where
import Common
import qualified BuildInfo
import qualified Utility.RawFilePath as R
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")
-- cp -a may preserve xattrs that have special meaning,
-- eg to NFS, and have even been observed to prevent later
-- changing the permissions of the file. So prevent preserving
-- xattrs.
, (allmeta && BuildInfo.cp_a && BuildInfo.cp_no_preserve_xattr_supported
, Param "--no-preserve=xattr")
]
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.
-
- The dest file must not exist yet, or it will fail to make a CoW copy,
- and will return False.
-}
copyCoW :: CopyMetaData -> FilePath -> FilePath -> IO Bool
copyCoW meta src dest
| BuildInfo.cp_reflink_supported = do
-- 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
-- Note that in coreutils 9.0, cp uses CoW by default,
-- without needing an option. This s only needed to support
-- older versions.
params = Param "--reflink=always" : copyMetaDataParams meta
{- Create a hard link if the filesystem allows it, and fall back to copying
- the file. -}
createLinkOrCopy :: RawFilePath -> RawFilePath -> IO Bool
createLinkOrCopy src dest = go `catchIO` const fallback
where
go = do
R.createLink src dest
return True
fallback = copyFileExternal CopyAllMetaData (fromRawFilePath src) (fromRawFilePath dest)
|
