Jörn Engel <[EMAIL PROTECTED]> writes: > 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. Josef did specifically state that modification to the lower layers would be allowed only if a special mount flag is given. > 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? I think that if someone can come up with consistent (and useful) semantics for a mount option that allows modifications to other layers as well, it would be a useful additional feature to support. It seems that it should be possible to add this feature at a later time in any case. Perhaps referring to the plan9 semantics could be helpful. -- Jeremy Maitin-Shepard - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
