Re: [TUHS] moving directories in svr2

[Bakul Shah <bakul@iitbombay.org>]

On Dec 30, 2021, at 2:31 PM, Dan Cross <crossd@gmail.com> wrote:
> 
> On Thu, Dec 30, 2021 at 11:41 AM Theodore Ts'o <tytso@mit.edu> wrote:
>> 
>> The other problem with storing the path as a string is that if
>> higher-level directories get renamed, the path would become
>> invalidated.  If you store the cwd as "/foo/bar/baz/quux", and someone
>> renames "/foo/bar" to "/foo/sadness" the cwd-stored-as-a-string would
>> become invalidated.
> 
> Why? Presumably as you traversed the filesystem, you'd cache, (path
> component, inode) pairs and keep a ref on the inode.  For any given
> file, including $CWD, you'd know it's pathname from the root as you
> accessed it, but if it got renamed, it wouldn't matter because you'd
> have cached a reference to the inode.

Without the ".." entry you can't map a dir inode back to a path.
Note that something similar can happen even today:

$ mkdir ~/a; cd ~/a; rm -rf ~/a; cd ..
cd: no such file or directory: ..

$ mkdir -p ~/a/b; ln -s ~/a/b b; cd b; mv ~/a/b ~/a/c; cd ../b
ls: ../b: No such file or directory

You can't protect the user from every such case. Storing a path
instead of the cwd inode simply changes the symptoms.