[Pbuilder-maint] Re: pbuilder: cowdancer/cowbuilder status update

[Robert Collins]

On Fri, 2006-01-13 at 08:42 +0900, Junichi Uekawa wrote:
> Hi,
> 
> > > This is an update on using userland COW method with pbuilder.
> > > 
> > > cowdancer is a tool that allows you to "cp -al" (hardlink) a tree, and
> > > break the hardlink when a write-open to a file is performed. The
> > > adventurous part of cowdancer COW implementation is that it's trying
> > > to do this from within userland only.
> > > 
> > > cowbuilder doesn't really exist yet; it's a name for pbuilder ported
> > > to fully use cowdancer. cowdancer is under development, and Debian
> > > package exists in unstable. It seems like it's getting nearly there
> > > with the feature set. With version 0.8, performance is improved
> > > against a large tree (I profiled against building the kernel), and
> > > with version 0.9, I fixed a bug which you could not replace /lib/ld.so
> > > while cowdancer was running.
> > 
> > Are you aware of fl-cow, which is a LD_PRELOAD userspace COW tool ?
> 
> It seems to be the tool with a same kind of goal. If I knew it
> existed, I might have started from it. However, it only supports
> 'open', so it will have problems when used with pbuilder; for example,
> file permissions are shared between files with same i-nodes.  The
> scope of implementation between the two applications is a bit
> different.
...
> Considering the difference, it might be better to improve desciprtions
> of both packages.
> 
> 
> 
> Another difference I noticed is that fl-cow takes a list of
> directories to protect in FL_COW, and seems to copy files
> unconditionally on 'open'.
> 
> cowdancer caches a list of i-nodes so that it won't try to break
> hardlinks more than once. (cow-shell does this much work).

Nice. I'm not sure both tools need to be in debian. How mature is
cowdancer - can it replace fl-cow at this point? (fl-cows primary use is
to be told 'these paths may contain hardlinked files, please unhardlink
any of them on write').

Rob

-- 
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