Messages in this thread | | | Date | Thu, 13 May 2004 12:56:13 +0200 | From | Jörn Engel <> | Subject | Re: [ANNOUNCEMENT PATCH COW] proof of concept impementation of cowlinks |
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On Wed, 12 May 2004 01:26:06 +0100, Jamie Lokier wrote: > Jörn Engel wrote: > > What about ino? I currently return 1, so diff remains fast without > > any changes. If someone really needs the difference between inode 2 > > and 3, I would introduce a cstat() system call similar to lstat(), > > which would return ino=2. > > > > Is this sane? Should it be reversed and cstat() return ino=1, while > > stat returns ino=2? I can imagine that "tar -x" would create hard > > links for every cowlink that "tar -c" saw, but I'm not sure yet. > > I think it should be reversed.
Aye.
> One very useful application for cowlinks is for virtual machine (UML) > and chroot jail setups, where an entire filesystem tree is copied > perhaps hundreds of times on a single disk. I'm surprised we didn't > think of this earlier, as it's potentially one of the most useful > applications for cowlinks. > > In that scenario, cowlinks would save enormous amounts of storage and > potentially save memory too. However to be useful at all, they'd need > to have accurate POSIX semantics: that is, cowlinks must behave very > much as a storage optimisation only. > > That means stat() should return ino==2.
Hmm, true. Up 'till now, that was done with disk images and block based diffs/snapshots. Nice application.
Jörn
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