v6: recover from race between git mv and git-annex get/drop

Update pointer file next time reconcileStaged is run to recover from the
race.

Note that restagePointerFile causes git to run the clean filter,
and that will run reconcileStaged. So, normally by the time the git
annex get/drop command finishes, the race has already been dealt with.
It may be that, in some case, that won't happen and the race will be
dealt with at a later point. git-annex could run reconcileStaged at
shutdown if that becomes a problem.

This does not handle the situation where the git mv is committed before
git-annex gets a chance to run again. git commit does run the clean
filter, and that happens to re-inject the content if it was supposed to
be dropped but is still populated. But, the case where the file was
supposed to be gotten but is not populated is not handled yet.

This commit was supported by the NSF-funded DataLad project.

CHANGELOG

@@ -13,6 +13,7 @@ git-annex (6.20180808) UNRELEASED; urgency=medium
     so git status will not show the files as modified.
   * v6: Update associated files database when git has staged changes
     to pointer files.
+  * v6: Fix some race conditions.
   * linux standalone: When LOCPATH is already set, use it instead of the
     bundled locales. It can be set to an empty string to use the system
     locales too.

Database/Keys.hs

@@ -15,6 +15,7 @@ module Database.Keys (
 	getAssociatedKey,
 	removeAssociatedFile,
 	storeInodeCaches,
+	storeInodeCaches',
 	addInodeCaches,
 	getInodeCaches,
 	removeInodeCaches,
@@ -32,6 +33,8 @@ import Annex.Version (versionUsesKeysDatabase)
 import qualified Annex
 import Annex.LockFile
 import Annex.CatFile
+import Annex.Content.PointerFile
+import Annex.Link
 import Utility.InodeCache
 import Annex.InodeSentinal
 import Git
@@ -136,9 +139,9 @@ openDb createdb _ = catchPermissionDenied permerr $ withExclusiveLock gitAnnexKe
 		True -> throwM e
 	
 	open db = do
-		h <- liftIO $ H.openDbQueue H.MultiWriter db SQL.containedTable
-		reconcileStaged (SQL.WriteHandle h)
-		return $ DbOpen h
+		qh <- liftIO $ H.openDbQueue H.MultiWriter db SQL.containedTable
+		reconcileStaged qh
+		return $ DbOpen qh
 
 {- Closes the database if it was open. Any writes will be flushed to it.
  -
@@ -168,8 +171,12 @@ removeAssociatedFile k = runWriterIO . SQL.removeAssociatedFile (toIKey k)
 
 {- Stats the files, and stores their InodeCaches. -}
 storeInodeCaches :: Key -> [FilePath] -> Annex ()
-storeInodeCaches k fs = withTSDelta $ \d ->
-	addInodeCaches k . catMaybes =<< liftIO (mapM (`genInodeCache` d) fs)
+storeInodeCaches k fs = storeInodeCaches' k fs []
+
+storeInodeCaches' :: Key -> [FilePath] -> [InodeCache] -> Annex ()
+storeInodeCaches' k fs ics = withTSDelta $ \d ->
+	addInodeCaches k . (++ ics) . catMaybes
+		=<< liftIO (mapM (`genInodeCache` d) fs)
 
 addInodeCaches :: Key -> [InodeCache] -> Annex ()
 addInodeCaches k is = runWriterIO $ SQL.addInodeCaches (toIKey k) is
@@ -196,9 +203,22 @@ removeInodeCaches = runWriterIO . SQL.removeInodeCaches . toIKey
  -
  - Note that this is run with a lock held, so only one process can be
  - running this at a time.
+ -
+ - This also cleans up after a race between eg a git mv and git-annex
+ - get/drop/similar. If git moves the file between this being run and the
+ - get/drop, the moved file won't be updated for the get/drop. 
+ - The next time this runs, it will see the staged change. It then checks
+ - if the worktree file's content availability does not match the git-annex
+ - content availablity, and makes changes as necessary to reconcile them.
+ -
+ - Note that if a commit happens before this runs again, it won't see
+ - the staged change. Instead, during the commit, git will run the clean
+ - filter. If a drop missed the file then the file is added back into the
+ - annex. If a get missed the file then the clean filter populates the
+ - file.
  -}
-reconcileStaged :: SQL.WriteHandle -> Annex ()
-reconcileStaged h@(SQL.WriteHandle qh) = whenM versionUsesKeysDatabase $ do
+reconcileStaged :: H.DbQueue -> Annex ()
+reconcileStaged qh = whenM versionUsesKeysDatabase $ do
 	gitindex <- inRepo currentIndexFile
 	indexcache <- fromRepo gitAnnexKeysDbIndexCache
 	withTSDelta (liftIO . genInodeCache gitindex) >>= \case
@@ -250,15 +270,28 @@ reconcileStaged h@(SQL.WriteHandle qh) = whenM versionUsesKeysDatabase $ do
 		((':':_srcmode):dstmode:_srcsha:dstsha:_change:[])
 			-- Only want files, not symlinks
 			| dstmode /= fmtTreeItemType TreeSymlink -> do
-				catKey (Ref dstsha) >>= \case
-					Nothing -> noop
-					Just k -> liftIO $ 
-						SQL.addAssociatedFileFast 
-							(toIKey k)
-							(asTopFilePath file)
-							h
+				maybe noop (reconcile (asTopFilePath file)) 
+					=<< catKey (Ref dstsha)
 				procdiff rest True
 			| otherwise -> procdiff rest changed
 		_ -> return changed -- parse failed
 	procdiff _ changed = return changed
 
+	-- Note that database writes done in here will not necessarily 
+	-- be visible to database reads also done in here.
+	reconcile file key = do
+		let ikey = toIKey key
+		liftIO $ SQL.addAssociatedFileFast ikey file (SQL.WriteHandle qh)
+		caches <- liftIO $ SQL.getInodeCaches ikey (SQL.ReadHandle qh)
+		keyloc <- calcRepo (gitAnnexLocation key)
+		keypopulated <- sameInodeCache keyloc caches
+		p <- fromRepo $ fromTopFilePath file
+		filepopulated <- sameInodeCache p caches
+		case (keypopulated, filepopulated) of
+			(True, False) ->
+				populatePointerFile (Restage True) key keyloc p >>= \case
+					Nothing -> return ()
+					Just ic -> liftIO $
+						SQL.addInodeCaches ikey [ic] (SQL.WriteHandle qh)
+			(False, True) -> depopulatePointerFile key p
+			_ -> return ()

doc/todo/smudge.mdwn

@@ -13,7 +13,7 @@ git-annex should use smudge/clean filters. v6 mode
 
   This could be partially dealt with in reconcileStaged. The next time
   git-annex runs it, it will notice the staged change, and it could update
-  the worktree file that was not gotten/dropped before.
+  the worktree file that was not gotten/dropped before. -- this is done now
 
   But, if a git mv is run, and then a git commit, reconcileStaged won't
   get a chance to notice the changes. git commit does run the clean filter.