yas3fs deletes the /tmp directory

[ollietreend]

Hi,

I've discovered a specific set of conditions under which the entire /tmp directory is deleted when yas3fs cleans its cache.

This causes all sorts of problems in Linux since /tmp is a system directory that should always exist.

How to recreate

1. Start with an empty /tmp directory.
2. Run yas3fs and add a new file to the mounted directory.
   • The local filesystem cache is created at /tmp/yas3fs/...
3. Delete the file you just added to the mounted directory.
   • yas3fs removes that file from its cache
   • empty cache directories are recursively deleted using python's os.removedirs method
   • because that was the only file in the cache, the entire /tmp/yas3fs directory is deleted
   • /tmp is now empty so it gets deleted

Why it happens

This happens because FSCache.delete() calls FSData.delete(), which calls remove_empty_dirs_for_file(), which calls remove_empty_dirs(), which uses os.removedirs().

The docs for os.removedirs() say that:

removedirs() tries to successively remove every parent directory mentioned in path until an error is raised (which is ignored, because it generally means that a parent directory is not empty).

Therefore if /tmp is empty after deleting /tmp/yas3fs, then it will be deleted too.

What should happen

yas3fs shouldn't recursively delete beyond its own cache path (i.e. the --cache-path option, in this case /tmp/yas3fs)

It might be necessary to implement a custom recursive delete function rather than use os.removedirs(), since it doesn't look like it's possible to limit that to a specific root directory.

[dacut]

<sigh> This isn't the first time I've seen os.removedirs() misused. It's an unintuitive API.

[liath]

Would shutil.rmtree be the correct choice here?

[jazzl0ver]

it's fixed