e17342b2a0
Including them breaking permissions setting on some NFS servers. Sponsored-by: Dartmouth College's Datalad project
89 lines
2.8 KiB
Haskell
89 lines
2.8 KiB
Haskell
{- file copying
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-
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- Copyright 2010-2021 Joey Hess <id@joeyh.name>
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-
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- License: BSD-2-clause
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-}
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module Utility.CopyFile (
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copyFileExternal,
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copyCoW,
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createLinkOrCopy,
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CopyMetaData(..)
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) where
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import Common
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import qualified BuildInfo
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data CopyMetaData
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-- Copy timestamps when possible, but no other metadata, and
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-- when copying a symlink, makes a copy of its content.
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= CopyTimeStamps
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-- Copy all metadata when possible.
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| CopyAllMetaData
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deriving (Eq)
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copyMetaDataParams :: CopyMetaData -> [CommandParam]
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copyMetaDataParams meta = map snd $ filter fst
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[ (allmeta && BuildInfo.cp_a, Param "-a")
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, (allmeta && BuildInfo.cp_p && not BuildInfo.cp_a
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, Param "-p")
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, (not allmeta && BuildInfo.cp_preserve_timestamps
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, Param "--preserve=timestamps")
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-- cp -a may preserve xattrs that have special meaning,
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-- eg to NFS, and have even been observed to prevent later
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-- changing the permissions of the file. So prevent preserving
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-- xattrs.
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, (allmeta && BuildInfo.cp_a && BuildInfo.cp_no_preserve_xattr_supported
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, Param "--no-preserve=xattr")
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]
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where
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allmeta = meta == CopyAllMetaData
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{- The cp command is used, because I hate reinventing the wheel,
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- and because this allows easy access to features like cp --reflink
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- and preserving metadata. -}
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copyFileExternal :: CopyMetaData -> FilePath -> FilePath -> IO Bool
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copyFileExternal meta src dest = do
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-- Delete any existing dest file because an unwritable file
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-- would prevent cp from working.
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void $ tryIO $ removeFile dest
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boolSystem "cp" $ params ++ [File src, File dest]
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where
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params
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| BuildInfo.cp_reflink_supported =
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Param "--reflink=auto" : copyMetaDataParams meta
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| otherwise = copyMetaDataParams meta
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{- When a filesystem supports CoW (and cp does), uses it to make
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- an efficient copy of a file. Otherwise, returns False. -}
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copyCoW :: CopyMetaData -> FilePath -> FilePath -> IO Bool
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copyCoW meta src dest
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| BuildInfo.cp_reflink_supported = do
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void $ tryIO $ removeFile dest
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-- When CoW is not supported, cp will complain to stderr,
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-- so have to discard its stderr.
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ok <- catchBoolIO $ withNullHandle $ \nullh ->
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let p = (proc "cp" $ toCommand $ params ++ [File src, File dest])
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{ std_out = UseHandle nullh
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, std_err = UseHandle nullh
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}
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in withCreateProcess p $ \_ _ _ -> checkSuccessProcess
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-- When CoW is not supported, cp creates the destination
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-- file but leaves it empty.
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unless ok $
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void $ tryIO $ removeFile dest
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return ok
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| otherwise = return False
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where
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params = Param "--reflink=always" : copyMetaDataParams meta
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{- Create a hard link if the filesystem allows it, and fall back to copying
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- the file. -}
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createLinkOrCopy :: FilePath -> FilePath -> IO Bool
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createLinkOrCopy src dest = go `catchIO` const fallback
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where
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go = do
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createLink src dest
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return True
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fallback = copyFileExternal CopyAllMetaData src dest
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