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 -- A surrounded army must be given a way out. -- Sun Tzu - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
