[jboss-user] [JBoss Microcontainer Development] New message: "Re: VFS3 and symlinks"

Jason Greene do-not-reply at jboss.com
Fri Feb 26 17:22:33 EST 2010

User development,

A new message was posted in the thread "VFS3 and symlinks":


Author  : Jason Greene
Profile : http://community.jboss.org/people/jason.greene@jboss.com

> johnbailey wrote:
> After discussing with Jason on IRC, it seems any behavior related to symbolic link support would really have to rely in the FileSystem instances.  The FileSystem instances may need to support symbolic links in different ways, or not at all.  Handling symbolic links in the VFS or VirtualFile classes would break certain functionality allowing FileSystems to be mounted at any path. 
> Ex. 
>   RealPath --> /real/path/to/archive.jar
>   SymLinkedPath --> /link/to/archive.jar  ('link' is symlink to /real/path)
> If you mount mount any FileSystem (maybe real, zip, assembled ...) at '/link' in the VFS, regardless of if it has anything to do with 'archive.jar', it would not be possible to get to  the contents of the FileSystem if you force paths to be canonical in the VFS or VirtualFile layer.  It would take the VFS path and convert it to the canonical path, and never get to the mounted FileSystem.  In essence, the FileSystem does not exist in the VFS.
> What would make sense is if you asked a RealFileSystem for a specific path and it does the JDK File based canonical path conversion automatically.  There may not necessarily be any other FileSystem that supports it, but there is nothing stopping a specific FileSystem from adding support.
> So I think it just makes sense to make sure we aren't switching between path types, and just leave it to the FileSystems to support it.
Where symlinks on vfs really break down is relative paths. If you have a symlink in a mount's root that points to "../sibling.jar", then it should refer to the parent of the mount in VFS. Unfortunately we don't know what a symlink points to since java doesn't know. If we could, however, read the link (say via an lstat call), it would be possible to canonicalize them correctly. We could bundle a JNI module that would allow for RealFileSystem to pull the link info, however, that would be a big effort for an uncommon feature. IMO we should wait to see if there is demand for it, and add it later.


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