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|
{- Caching a file's inode, size, and modification time
- to see when it's changed.
-
- Copyright 2013, 2014 Joey Hess <joey@kitenet.net>
-
- License: BSD-2-clause
-}
{-# LANGUAGE CPP #-}
module Utility.InodeCache (
InodeCache,
InodeComparisonType(..),
compareStrong,
compareWeak,
compareBy,
readInodeCache,
showInodeCache,
genInodeCache,
toInodeCache,
InodeCacheKey,
inodeCacheToKey,
inodeCacheToMtime,
SentinalFile(..),
SentinalStatus(..),
TSDelta,
noTSDelta,
writeSentinalFile,
checkSentinalFile,
sentinalFileExists,
prop_read_show_inodecache
) where
import Common
import System.PosixCompat.Types
import Utility.QuickCheck
data InodeCachePrim = InodeCachePrim FileID FileOffset EpochTime
deriving (Show, Eq, Ord)
newtype InodeCache = InodeCache InodeCachePrim
deriving (Show)
{- Inode caches can be compared in two different ways, either weakly
- or strongly. -}
data InodeComparisonType = Weakly | Strongly
deriving (Eq, Ord)
{- Strong comparison, including inodes. -}
compareStrong :: InodeCache -> InodeCache -> Bool
compareStrong (InodeCache x) (InodeCache y) = x == y
{- Weak comparison of the inode caches, comparing the size and mtime,
- but not the actual inode. Useful when inodes have changed, perhaps
- due to some filesystems being remounted.
-
- The weak mtime comparison treats any mtimes that are within 2 seconds
- of one-anther as the same. This is because FAT has only a 2 second
- resolution. When a FAT filesystem is used on Linux, higher resolution
- timestamps are cached and used by Linux, but this is lost on unmount,
- so after a remount, the timestamp can appear to have changed.
-}
compareWeak :: InodeCache -> InodeCache -> Bool
compareWeak (InodeCache (InodeCachePrim _ size1 mtime1)) (InodeCache (InodeCachePrim _ size2 mtime2)) =
size1 == size2 && (abs (mtime1 - mtime2) < 2)
compareBy :: InodeComparisonType -> InodeCache -> InodeCache -> Bool
compareBy Strongly = compareStrong
compareBy Weakly = compareWeak
{- For use in a Map; it's determined at creation time whether this
- uses strong or weak comparison for Eq. -}
data InodeCacheKey = InodeCacheKey InodeComparisonType InodeCachePrim
deriving (Ord)
instance Eq InodeCacheKey where
(InodeCacheKey ctx x) == (InodeCacheKey cty y) =
compareBy (maximum [ctx,cty]) (InodeCache x ) (InodeCache y)
inodeCacheToKey :: InodeComparisonType -> InodeCache -> InodeCacheKey
inodeCacheToKey ct (InodeCache prim) = InodeCacheKey ct prim
inodeCacheToMtime :: InodeCache -> EpochTime
inodeCacheToMtime (InodeCache (InodeCachePrim _ _ mtime)) = mtime
showInodeCache :: InodeCache -> String
showInodeCache (InodeCache (InodeCachePrim inode size mtime)) = unwords
[ show inode
, show size
, show mtime
]
readInodeCache :: String -> Maybe InodeCache
readInodeCache s = case words s of
(inode:size:mtime:_) ->
let prim = InodeCachePrim
<$> readish inode
<*> readish size
<*> readish mtime
in InodeCache <$> prim
_ -> Nothing
genInodeCache :: FilePath -> TSDelta -> IO (Maybe InodeCache)
genInodeCache f delta = catchDefaultIO Nothing $
toInodeCache delta =<< getFileStatus f
toInodeCache :: TSDelta -> FileStatus -> IO (Maybe InodeCache)
toInodeCache (TSDelta getdelta) s
| isRegularFile s = do
delta <- getdelta
return $ Just $ InodeCache $ InodeCachePrim
(fileID s)
(fileSize s)
(modificationTime s + delta)
| otherwise = pure Nothing
{- Some filesystem get new random inodes each time they are mounted.
- To detect this and other problems, a sentinal file can be created.
- Its InodeCache at the time of its creation is written to the cache file,
- so changes can later be detected. -}
data SentinalFile = SentinalFile
{ sentinalFile :: FilePath
, sentinalCacheFile :: FilePath
}
deriving (Show)
{- On Windows, the mtime of a file appears to change when the time zone is
- changed. To deal with this, a TSDelta can be used; the delta is added to
- the mtime when generating an InodeCache. The current delta can be found
- by looking at the SentinalFile. Effectively, this makes all InodeCaches
- use the same time zone that was in use when the sential file was
- originally written. -}
newtype TSDelta = TSDelta (IO EpochTime)
noTSDelta :: TSDelta
noTSDelta = TSDelta (pure 0)
writeSentinalFile :: SentinalFile -> IO ()
writeSentinalFile s = do
writeFile (sentinalFile s) ""
maybe noop (writeFile (sentinalCacheFile s) . showInodeCache)
=<< genInodeCache (sentinalFile s) noTSDelta
data SentinalStatus = SentinalStatus
{ sentinalInodesChanged :: Bool
, sentinalTSDelta :: TSDelta
}
{- Checks if the InodeCache of the sentinal file is the same
- as it was when it was originally created.
-
- On Windows, time stamp differences are ignored, since they change
- with the timezone.
-
- When the sential file does not exist, InodeCaches canot reliably be
- compared, so the assumption is that there is has been a change.
-}
checkSentinalFile :: SentinalFile -> IO SentinalStatus
checkSentinalFile s = do
mold <- loadoldcache
case mold of
Nothing -> return dummy
(Just old) -> do
mnew <- gennewcache
case mnew of
Nothing -> return dummy
Just new -> return $ calc old new
where
loadoldcache = catchDefaultIO Nothing $
readInodeCache <$> readFile (sentinalCacheFile s)
gennewcache = genInodeCache (sentinalFile s) noTSDelta
calc (InodeCache (InodeCachePrim oldinode oldsize oldmtime)) (InodeCache (InodeCachePrim newinode newsize newmtime)) =
SentinalStatus (not unchanged) tsdelta
where
#ifdef mingw32_HOST_OS
unchanged = oldinode == newinode && oldsize == newsize
tsdelta = TSDelta $ do
-- Run when generating an InodeCache,
-- to get the current delta.
mnew <- gennewcache
return $ case mnew of
Just (InodeCache (InodeCachePrim _ _ currmtime)) ->
oldmtime - currmtime
Nothing -> 0
#else
unchanged = oldinode == newinode && oldsize == newsize && oldmtime == newmtime
tsdelta = noTSDelta
#endif
dummy = SentinalStatus True noTSDelta
sentinalFileExists :: SentinalFile -> IO Bool
sentinalFileExists s = allM doesFileExist [sentinalCacheFile s, sentinalFile s]
instance Arbitrary InodeCache where
arbitrary =
let prim = InodeCachePrim
<$> arbitrary
<*> arbitrary
<*> arbitrary
in InodeCache <$> prim
prop_read_show_inodecache :: InodeCache -> Bool
prop_read_show_inodecache c = case readInodeCache (showInodeCache c) of
Nothing -> False
Just c' -> compareStrong c c'
|
