Re: Fallthrus as full-length symlinks?

[AYAN TYAGI <ayan.tyagi@gmail.com>]

On Tue, Nov 17, 2009 at 1:44 AM, Jamie Lokier <jamie@shareable.org> wrote:
> AYAN TYAGI wrote:
>> > >Another idea that I first had when reading the suggestion was to use a
>> > >symlink to self (ln -s x x) as the encoding for a fallthrough. It does
>> > >not allow renames like what you really describe, but it has another advantage
>> > >in that it does not require extensions to the upper file system layout
>> > >while not conflicting with any use case I can see.
>>
>> It seems to be a great idea to make use of self referenced symlinks .
>> Could you please describe the whole process u are proposing?
>>
>> If possible give some example and code .
>
> That'll do surprising things when the user _really_ makes a
> self-referencing symlink with "ln -s x x", which can happen
> unexpectedly, for example by untarring some archive.
>
> If a fallthrough is encoded that way, there should probably be an
> error when the user tries to make a self-referencing symlink.
>
> -- Jamie
>

>> > The interesting thing about
> > >this idea is that it could theoretically let us rename a file from the
> > >low level file system to another place in the low-level file system
> > >without copying the contents of the file up.  Basically, we can
> > >arbitrarily swizzle the namespace of the low-level by maintaining a
> > >set of symlinks above.

So do you mean that the need of copyup in case of renaming is
virtually eliminated ?
If yes, this would mean that by playing somewhat smart we can even
alter the RO file contents without copyup (that seems to be really
impractical)
Also what changes in the existing model would you envision ? Does the
idea of self referencing symlinks do any good or is it just an eye
candy ?

Does anyone know about any filesystem that implements a similar
paradigm ? btw Aufs implements whiteouts and fallthrus by hard links
...