Messages in this thread | | | Date | Thu, 2 Aug 2007 19:50:09 +0200 | From | Jörn Engel <> | Subject | Re: [RFC 12/26] ext2 white-out support |
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On Wed, 1 August 2007 15:33:30 -0400, Josef Sipek wrote: > > This brings up an very interesting (but painful) question...which makes more > sense? Allowing the modifications in only the top-most branch, or any branch > (given the user allows it at mount-time)? > > This is really question to the community at large, not just you, Dave :)
Only write to top-most layer.
There are two reasons for this. First it allows users to create a union mount, test something (e.g. update the distribution) and remove every trace from the test by umounting the top-most layer. Such a thing can be quite valuable.
The second reason is simplicity. I personally couldn't even start to describe the semantics. If the user does a rename, which layer will the change end up in? What if source or target exist in multiple layers? How to rename a directory in a lower layer containing a new file in an upper layer?
Finding new and interesting corner cases for such a beast can be quite entertaining. And until someone has properly documented the semantics for _all_ the corner cases, my enthusiasm is below freezing point. Does such a documentation exist?
Jörn
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