get another node in FS call

[lquenti]

Hey. I am currently trying to build something very wild, and I know that. But effectively, I would love to try out to read another file in another directory from within an Open FUSE call. I know thats a bad idea (will also be a very very cold path), but I am currently struggling with my approach, maybe you have an idea how I misuse the API:

func findNodeByPath(ctx context.Context, rn *RootNode, path string) (*Node, syscall.Errno) {
	// Normalize the path and split into components
	parts := strings.Split(filepath.Clean(path), string(filepath.Separator))

	var currentNode fs.InodeEmbedder = rn
	var currentInode = &rn.Inode

	for _, part := range parts {
		if part == "" || part == "." {
			continue
		}

		var out fuse.EntryOut
		childInode, errno := toNode(currentNode).Lookup(ctx, part, &out)
		if errno != 0 {
			return nil, errno
		}
		// Descend into the next level
		currentNode = childInode.Operations().(fs.InodeEmbedder)
		currentInode = childInode

                // debug
		tlog.Debug.Printf("%s survived", part)
		ps, pino := toNode(currentNode).Parent()
		tlog.Debug.Printf("%v %v parent", ps, pino)
	}
	return toNode(currentInode.Operations().(*Node)), 0
}



// Open - FUSE call. Open already-existing file.
//
// Symlink-safe through Openat().
func (n *Node) Open(ctx context.Context, flags uint32) (fh fs.FileHandle, fuseFlags uint32, errno syscall.Errno) {
	debug, debugerr := findNodeByPath(ctx, n.rootNode(), "/lua/lglq/scratchpad.lua")
	tlog.Debug.Logger.Println("duck", debug, debugerr);
        // ...
}

Assume that the part was created with an unpatched version and exists.

Now, I get something very curious:

• The first iteration works. I can toNode the root inode, can call Lookup (or even successfully Readdir) on it and I get what I expect.
• In the second iteration, the /lua Inode doesnt have its .Parent() set (its Nil), so in the Lookup, in the n.PrepareAtSyscall, in the n.prepareAtSyscallMyself, the following fails

	myName, p1 := n.Parent()
	if p1 == nil || myName == "" {
		errno = syscall.ENOENT
		return
	}

So, when I get a Node myself, it seems like I forget to do something to properly set the parent. Do you have any idea on how I misuse it?

PS: Or just any pointers on where to look?

[lquenti]

Nevermind, I fully change my approach, sorry I just needed some fresh air and a pause, will instead do raw I/O and translate the cipher dirs myself... also seems the saner choice

[rfjakob]

To translate, check the EncryptPath helper https://github.com/rfjakob/gocryptfs/blob/master/internal/fusefrontend/ctlsock_interface.go#L20

[rfjakob]

Check what rawBridge.Lookup() does ( https://github.com/hanwen/go-fuse/blob/master/fs/bridge.go#L356 ). I think the missing call to addNewChild() is your problem.

Using (faking) a symlink is not an option?

[lquenti]

for the future reference: I actually only needed the file ids (and some stuff I patched in), so the ciphered was sufficient.
Thus, I took the rootnode fd, took its nametransform, split the plain path into parts, and iteratively did the following:

• apply nametransform
• call syscallscompat.Openat
• use that as new fd for next one until I arrive
  Then I extracted the file id.

Unfortunately I think my code is changed too much to be useful here, as I partially changed the crypto.