Re: [Xen-devel] Removing building qemu from xen ?

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2014-01-23 at 17:40 -0800, Luis R. Rodriguez wrote:
> I see xen by default builds qemu on x86 / x86_64, and by default it will
> build it on tools/qemu-xen-dir, and regardless of x86 32/64 bit architecture
> it will call the binary qemu-system-i386. I see recently also support
> was added to avoid having to build qemu and let distributions specify
> their own binary path for qemu. That's great! I see though that by
> default xen builds a different repo version of qemu:
> 
> git://xenbits.xen.org/qemu-upstream-unstable.git
> tag: qemu-xen-4.4.0-rc1
> 
> At first glance I am not seeing much delta between what's upstream and
> at least the latest commit of qemu-upstream-unstable.git is already
> upstream on the *real* qemu upstream tree [0]. This begs the question of
> whether or not xen needs to have the qemu building infrastructure as
> part of its own build system.

The xenbits qemu tree serves a useful purpose as a "stable xen branch",
that is it is the qemu stable branch + patches which are very useful for
Xen but perhaps not suitable for the upstream stable branch for one
reason or another (maybe they are risky for some non-Xen use case).
Obviously such patches are quite rare, which is why the delta is
normally small.

>  Can we rip it out?

At a minimum someone would first need to teach Xen's automated test
system to fetch & build the separate qemu.

Probably more bank for buck short term would be a test flight targeting
the upstream qemu development and stable branches to help us spot
regressions there early.

In fact one of those additional flights would be a prerequisite for the
first thing because the outputs of it would need to serve as input to
the main Xen flight (in order to only vary one thing per flight).

But if you are interested in removing build integration cruft from the
Xen tree then the first thing to target would be the Linux kernel build
stuff, which is unused by most people (disabled by default, obsolete
etc) but which osstest.git still uses for some small pieces (at least
xen.git/buildconfigs/enable-xen-config, maybe other bits) which would
need moving to osstest.git.

http://xenbits.xen.org/gitweb/?p=osstest.git is the thing to send
patches against. I'd certainly welcome patches to remove the need for
the kernel build stuff. Probably best to let the conversation re: qemu
play out before digging into that side of things too much.

Ian.


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