VFS improvements

[kevinaboos]

✔️ The ls app has redundant code that has been copy-pasted for two identical cases: when the path is specified, and when there is no path specified. Condense those into one case.

✔️ All file creation should accept a &DirRef rather than a WeakDirRef. This eliminates the potential error of not being able to upgrade the weak ref to the parent.

✔️ Don't use the return keyword at the end of a function, that violates Rust's style conventions.

✔️ TaskFiles are never actually created. Mmi files are pretty worthless at the moment.

[kevinaboos]

We also need the ability to create symlinks (symbolic links) for both files and directories. These types should basically just be simple wrappers around FileRef and DirRef.

[kevinaboos]

I don't understand parts of the Path crate, especially how canonicalize works. In my mind, canonicalize would have a similar fn signature as get(), in that it accepts just one directory, the starting/working directory from which to begin the path traversal.

Also, there are two types of canonicalization/verification for paths. One operates purely at the String level and does not access the filesystem. You can think of it as Path reduction/simplification. The other kind is "full canonicalization" that actually checks whether the files and directories really exist. A full canonicalization would then transform the Path's inner String into an absolute path.

[kevinaboos]

✔️ a lot of functions don't need to borrow self mutably, e.g., get_child(). Fixed already.

[kevinaboos]

✔️ your existing canonicalize() and relative() functions in the Path struct appended a slash instead of prepending it. I've fixed that.

[kevinaboos]

✔️ The Path::get() function didn't allow you to get a File path, only a directory path. Fixed.

[kevinaboos]

✔️ Absolute paths don't work, such as cd /root/namespaces when you're in some other directory.
(perhaps my changes caused this)

[kevinaboos]

✔️ When adding nodes with something like insert_child(), we always must check if the child exists already. If it does, then we need to return an Err. You could optionally add an overwrite boolean parameter that if true, will result in the child node being replaced with the new one.
Note that when inserting a child, it should always be an error if you try to replace a file with a directory, or vice versa.

[kevinaboos]

✔️ separate the creation of a file from the writing of its contents.

[kevinaboos]

✔️ Two other problems:

• path traversal doesn't work for absolute paths... every path is treated as if it's relative, even when it begins with a /.
• The root directory should just be /, not /root. There's no need to give it a name, that breaks expectations.

[kevinaboos]

Thanks to @christinewang5, commit 5bc3fa1 addresses the problems of absolute path traversal and root directory naming.

[kevinaboos]

Commit 9237398 covers all features, except for symlinks (see #114).