On Tue, May 22, 2007 at 08:35:17AM -0400, Shaya Potter wrote: > Bharata B Rao wrote: > > > >In case of regular files, when we copyup a file, we are actually preventing > >any writes to the lower layers (which we have designated as read only). > > > >Applying the same logic to devices, what do we achieve by copying them up ? > >How does it matter if we write to the device through a node in the upper > >layer or in the lower layer. Both the writes eventually do the same thing. > > What happens if the lower layer is on a read only medium. But the top > layer is RW. Why can't one change permissions? In your model, one can't. > > What happens if one wants to share a lower layer read-only (I'm doing > this with my research into uses of union file systems), one doesn't want > permission change in one use of the lower layer to affect any of the > other uses. Ok, makes sense. Thanks for the clarification. So looks like in addition to copyup on open (which is what we do currently) there is a case for doing copyups for other situations also. Regards, Bharata. - 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
