On 9 June 2011 05:52, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > On Thu, 9 Jun 2011 11:59:34 +1000 NeilBrown <neilb@xxxxxxx> wrote: > >> On Wed, 8 Jun 2011 15:32:08 -0700 Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> >> wrote: >> >> > On Wed, Â1 Jun 2011 14:46:13 +0200 >> > Miklos Szeredi <miklos@xxxxxxxxxx> wrote: >> > >> > > I'd like to ask for overlayfs to be merged into 3.1. >> > >> > Dumb questions: >> > >> > I've never really understood the need for fs overlaying. ÂWho wants it? >> > What are the use-cases? >> >> https://lwn.net/Articles/324291/ >> >> I think the strongest use case is that LIVE-DVD's want it to have a write-able >> root filesystem which is stored on the DVD. > > Well, these things have been around for over 20 years. ÂWhat motivated > the developers of other OS's to develop these things and how are their > users using them? FWIW there is an union solution in NetBSD. I am not sure it is used in the LiveCD but you can definitely use it to build a piece of software without actually touching the source directory. > >> > >> > This sort of thing could be implemented in userspace and wired up via >> > fuse, I assume. ÂHas that been attempted and why is it inadequate? >> >> I think that would be a valid question if the proposal was large and >> complex. ÂBut overlayfs is really quite small and self-contained. > > Not merging it would be even smaller and simpler. ÂIf there is a > userspace alternative then that option should be evaluated and compared > in a rational manner. The problem with the userspace alternative is that it does not work. I tried to run my live CD on top of unionfs-fuse and the filesystem would fail intermittently leading to random errors during boot. > > > > Another issue: there have been numerous attempts at Linux overlay > filesystems from numerous parties. ÂDoes (or will) this implementation > satisfy all their requirements? No implementation will satisfy all needs. There is always some compromise between availability (userspace/in-tree/easy to patch in) feature completeness (eg. AuFS is not so easy to forward-port to new kernels but has numerous features) performance, reliability. > > Because if not, we're in a situation where the in-kernel code is > unfixably inadequate so we end up merging another similar-looking > thing, or the presence of this driver makes it harder for them to get > other drivers merged and the other parties' requirements remain > unsatisfied. One of the major use cases is building live CDs. That and other things can be done with overlayfs. Thanks Michal -- 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
