nfs4: Check for stale nodes when reload dir cache

* When the DirectoryCache is updated, compare the new contents with
  the old.  If any of the old entries are obsolete, treat the
  respective node as stale.
* Create FileSystem::TrashStaleNode() to avoid duplicating code.
* Possible fix for #19656.

This helps the client keep current with changes made to server files
by other users.

While the comparison will be slow for a large directory, it won't be
executed unless another user has changed the contents of a directory
since the last time the Haiku client read the directory.

Change-Id: I03e65aaaad5027c66b10265f2b4a21ed9d2b6744
Reviewed-on: https://review.haiku-os.org/c/haiku/+/9445
Tested-by: Commit checker robot <[email protected]>
Reviewed-by: waddlesplash <[email protected]>

src/add-ons/kernel/file_systems/nfs4/DirectoryCache.cpp

@@ -206,9 +206,6 @@ DirectoryCache::_LoadSnapshot(bool trash)
 	if (oldSnapshot != NULL)
 		oldSnapshot->AcquireReference();
 
-	if (trash)
-		Trash();
-
 	DirectoryCacheSnapshot* newSnapshot;
 	status_t result = fInode->GetDirSnapshot(&newSnapshot, NULL, &fChange,
 		fAttrDir);
@@ -222,6 +219,31 @@ DirectoryCache::_LoadSnapshot(bool trash)
 	_SetSnapshot(newSnapshot);
 	fExpireTime = system_time() + fExpirationTime;
 
+	if (trash) {
+		// Clear fNameCache, while checking for mismatches between its entries and the newly
+		// obtained snapshot that might indicate stale nodes.
+		while (!fNameCache.IsEmpty()) {
+			NameCacheEntry* current = fNameCache.RemoveHead();
+			bool nodeFound = false;
+			for (SinglyLinkedList<NameCacheEntry>::ConstIterator it
+					= newSnapshot->fEntries.GetIterator();
+				NameCacheEntry* snapshotEntry = it.Next();) {
+				if (current->fNode == snapshotEntry->fNode
+					&& strcmp(current->fName, snapshotEntry->fName) == 0) {
+					nodeFound = true;
+					break;
+				}
+			}
+			if (!nodeFound) {
+				// The inode-name association that was cached in 'current' is no longer valid.
+				result = fInode->GetFileSystem()->TrashStaleNode(current->fNode);
+				if (result != B_OK)
+					INFORM("_LoadSnapshot: Couldn't free stale node.\n");
+			}
+			delete current;
+		}
+	}
+
 	fTrashed = false;
 
 	if (oldSnapshot != NULL)

src/add-ons/kernel/file_systems/nfs4/FileSystem.cpp

@@ -469,6 +469,41 @@ FileSystem::GetDelegation(const FileHandle& handle)
 	return it.Current();
 }
 
+/*! If a node object with this inode number exists, free it at the FS and VFS levels to
+	ensure that no operation will try to use it.
+
+*/
+status_t
+FileSystem::TrashStaleNode(ino_t ino)
+{
+	status_t result = B_OK;
+	if (acquire_vnode(fFsVolume, ino) == B_OK) {
+		// we still have a vnode for the stale file present in memory
+
+		// mark it as stale
+		VnodeToInode* vti;
+		result = get_vnode(fFsVolume, ino, reinterpret_cast<void**>(&vti));
+		ASSERT(result == B_OK);
+		Inode* inode = vti->GetPointer();
+		if (inode != NULL)
+			inode->SetStale();
+		put_vnode(fFsVolume, ino);
+
+		// delete it
+		result = remove_vnode(fFsVolume, ino);
+		ASSERT(result == B_OK);
+		put_vnode(fFsVolume, ino);
+
+		// verify it is gone
+		if (acquire_vnode(fFsVolume, ino) == B_OK)
+			result = B_ERROR;
+		else
+			result = B_OK;
+	}
+
+	return result;
+}
+
 
 /*! Used when creating a file to check for a stale node with the same ino. If it exists,
 	the stale node is deleted.
@@ -488,28 +523,8 @@ FileSystem::EnsureNoCollision(ino_t newID, const FileHandle& handle)
 		// We are already using this file ID for a previously existing file.  If the server has
 		// assigned that ID to the file that we are now creating, it means someone else must have
 		// deleted the other file from the server, and the server is recycling the file ID.
-		result = acquire_vnode(fFsVolume, newID);
-		if (result == B_OK) {
-			// we still have a vnode for the stale file present in memory
-
-			// mark it as stale
-			VnodeToInode* vti;
-			result = get_vnode(fFsVolume, newID, reinterpret_cast<void**>(&vti));
-			ASSERT(result == B_OK);
-			Inode* inode = vti->GetPointer();
-			if (inode != NULL)
-				inode->SetStale();
-			put_vnode(fFsVolume, newID);
-
-			// delete it
-			result = remove_vnode(fFsVolume, newID);
-			ASSERT(result == B_OK);
-			put_vnode(fFsVolume, newID);
-
-			// verify it is gone
-			result = acquire_vnode(fFsVolume, newID);
-			ASSERT(result != B_OK);
-		}
+		result = TrashStaleNode(newID);
+		ASSERT(result == B_OK);
 	}
 
 	return;

src/add-ons/kernel/file_systems/nfs4/FileSystem.h

@@ -84,6 +84,7 @@ public:
 
 	inline	mutex&				CreateFileLock();
 
+			status_t			TrashStaleNode(ino_t ino);
 			void				EnsureNoCollision(ino_t newID, const FileHandle& handle);
 
 			void				Dump(void (*xprintf)(const char*, ...) = dprintf);