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RE: [Xen-devel] Repositories and build system

To: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>, Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Subject: RE: [Xen-devel] Repositories and build system
From: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Date: Wed, 29 Apr 2009 09:38:26 -0700 (PDT)
Cc: Yuji Shimada <shimada-yxb@xxxxxxxxxxxxxxx>, Xen Developers <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx>, "Zhai, Edwin" <edwin.zhai@xxxxxxxxx>
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A few thoughts:

I fear that the real issue is that knowledge of the
locksteps are hidden in people's brains, or at best
in cryptic comments in some sub-repos.  For any
solution to work, this knowledge needs to be made
available, at least in human-readable format and
preferably (or perhaps additionally) in machine-parseable

The problem is that each developer is working on a
different component and has little interest in the
other components other than to ensure they don't
break "the component I care about".  (And sometimes
a developer cares about two or more components...
and may become the "lockstep culprit".)  Furthermore,
there are sometimes "partial locksteps", where
say, a new qemu is required beyond this changeset
in Xen, but only if you are using stub domains.

Generally, I think the idea of a meta-pull and
meta-make are good (and maybe a meta-install?),
but in order to be useful, they need to work not
only on "latest" but older branches of components
as well.  For example:

"Pull and build all latest known stable components
that work with xen-unstable changeset 19314"

Without the "lockstep database", this is impossible.
And without this functionality, binary searching
for a problem is also impossible.

> -----Original Message-----
> From: Ian Jackson [mailto:Ian.Jackson@xxxxxxxxxxxxx]
> Sent: Wednesday, April 29, 2009 9:42 AM
> To: Stefano Stabellini
> Cc: Yuji Shimada; Xen Developers; Keir Fraser; Zhai, Edwin
> Subject: [Xen-devel] Repositories and build system
> Stefano Stabellini writes ("Re: [Xen-devel] [PATCH] [Xend] 
> Fix HVM PCI hot removal failure"):
> > A two way synchronization between the qemu hg mirror and 
> the qemu git
> > repo would mean trouble.
> > 
> > Maybe we could find a way to mirror the qemu git repo inside the
> > xen-unstable hg repo, but it would still just a mirror.
> I agree that the current situation isn't ideal.  I had hoped that we
> could avoid constantly making changes that introduce cross-repository
> incompatibilities but it seems to be too difficult to do that.  We
> keep introducing new lockstep changes.
> Stefano's idea of mirroring the qemu git repo inside the xen-unstable
> hg repo would be one approach.  It could probably be done, although it
> would be a novel arrangement.
> I think a better thing to try would be to make it easier for people to
> pull and update all of the sub-repos at once.  It's not just qemu - we
> have linux (which is in at least two major branches: 2.6.18 and pvops)
> and now some of the Ocaml work too.  Perhaps it's time to create a
> meta-component which permits `make pull', `make world', etc. ?
> Ian.
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