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small optimisation to file copying

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Avoid statting file, just try to remove it.

Also a comment to explain why it tries to remove it, which was puzzling
me when I revisited this code until I saw that cp fails to overwrite a
mode 444 file, including perhaps one left by a previous interrupted cp.

This commit was sponsored by Fernando Jimenez on Patreon.
This commit is contained in:
Joey Hess 2019-07-17 14:22:21 -04:00
parent 21ff5e1e5a
commit 7234b1f9a7
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1 changed files with 4 additions and 4 deletions
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8
Utility/CopyFile.hs
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@ -38,8 +38,9 @@ copyMetaDataParams meta = map snd $ filter fst
- and because this allows easy access to features like cp --reflink. -} - and because this allows easy access to features like cp --reflink. -}
copyFileExternal :: CopyMetaData -> FilePath -> FilePath -> IO Bool copyFileExternal :: CopyMetaData -> FilePath -> FilePath -> IO Bool
copyFileExternal meta src dest = do copyFileExternal meta src dest = do
whenM (doesFileExist dest) $ -- Delete any existing dest file because an unwritable file
removeFile dest -- would prevent cp from working.
void $ tryIO $ removeFile dest
boolSystem "cp" $ params ++ [File src, File dest] boolSystem "cp" $ params ++ [File src, File dest]
where where
params params
@ -52,8 +53,7 @@ copyFileExternal meta src dest = do
copyCoW :: CopyMetaData -> FilePath -> FilePath -> IO Bool copyCoW :: CopyMetaData -> FilePath -> FilePath -> IO Bool
copyCoW meta src dest copyCoW meta src dest
| BuildInfo.cp_reflink_supported = do | BuildInfo.cp_reflink_supported = do
whenM (doesFileExist dest) $ void $ tryIO $ removeFile dest
removeFile dest
-- When CoW is not supported, cp will complain to stderr, -- When CoW is not supported, cp will complain to stderr,
-- so have to discard its stderr. -- so have to discard its stderr.
ok <- catchBoolIO $ do ok <- catchBoolIO $ do