Re: [HVM} xen_platform_pci=0 doesn't prevent platform device creation and disk and nic take over by PV drivers.

[George Dunlap <george.dunlap@eu.citrix.com>]

On 09/10/13 13:49, Sander Eikelenboom wrote:
> Wednesday, October 9, 2013, 2:00:02 PM, you wrote:
>
>> create ^
>> title it xen_platform_pci=0 doesn't work with qemu-xen
>> owner it Anthony Perard <anthony.perard@citrix.com>
>> thanks
> Perhaps in general looking at the libxl and xend .. and .. qemu-xen and qemu-xen-traditonal compatibility shoud be added too.
>
> Perhaps i'm a bit blunt ..
> but for users it's quite a mess and PITA now for quite some time, the transition of both is now smeared out over quite some major and minor releases.
>
> With some features not working since .. some features are working again but have a gap of not working,
> since old features becoming usable again are (understandably) not backported.

Well thank you for being blunt -- we'd much rather you complain than 
just silently disappear. :-)  I can certainly see where you're coming 
from.  But on the flip side -- how are developers supposed to know what 
is broken if nobody tests it, or reports it?  We had several test days 
before the 4.3 release; if anyone had reported this feature broken, it 
would have been fixed immediately.

Something similar with xend -- many of the Xen developers were 
considering removing xend for 4.4, because xl seemed to be mature enough 
for everyone.  When we discussed it on the list, immediately a number of 
people stood up and listed features they wanted that were missing from 
xl, or ways in which xl didn't meet their needs.

We're not mind-readers, and our software doesn't have a call-home 
feature to let us know who is using what feature.  The core developers 
have already been looking at libxl, xend, and qemu-xen for some time; we 
made the switch because it looked like we had feature parity for the 
important features.  Us taking a longer look at this point isn't going 
to help things: we've seen all we're going to see.

If you have features that are missing from xl/qemu-xen that are not on 
my 4.4 development list, and not in xenbugs, the best thing you can do 
is report them, so we can put them on our list.  Better yet, as Stefano 
said, write a test case for them, to make sure that they are never 
broken in any release ever again. :-)

As for the future -- it is unfortunate that with a major transition, 
like from xend->libxl and qemu-traditional->qemu-xen, there is going to 
be some "catch-up" as bugs are ironed out and important functionality 
"faulted in".  This same thing happens in other open source projects; 
KDE, Gnome, Ubuntu's move to Unity, all come to mind as things that have 
had this happen. Even Linux: the Linux driver for the SD card reader 
broke on my 8-year-old laptop 4 years ago, and still hasn't been fixed.  
KVM isn't an exception: they just haven't had to do any major 
refactorings yet (as far as I know). Maybe that's because they have 
superior process, developers, or design; or maybe it's just because it's 
a younger project by about 4 years, and there's a major refactoring 
coming up right around the corner. :-)

I don't forsee any more big transitions like that for Xen any time on 
the horizon: once libxl and qemu-xen settle down, things should be 
stable for quite a while.  We're putting a lot more effort into writing 
test cases, and making it easy for others to do so; as our test suite 
grows and becomes more comprehensive, the number of features that can 
get broken without us noticing will get smaller and smaller.

  -George