Re: [Xen-devel] Xen Project policy on feature flags

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Sep 29, 2014 at 10:00:13AM +0100, George Dunlap wrote:
> On 09/26/2014 03:49 PM, Stefano Stabellini wrote:
> >>Let me rephrase - will it boot in the same fashion (And with the same
> >>bugs) as it did prior to this functionality being introduced?
> >3.15 -> dom0 on ARM broken (if netback is used)
> >3.17 -> dom0 on ARM is fixed, only if the kernel is compiled with 
> >CONFIG_ARM_LPAE
> >
> >Reverting the XENFEAT_grant_map_identity related changes would give you
> >a system broken even with CONFIG_ARM_LPAE.
> >Reverting Zoltan's changes to netback would give you a working system.
> 

FWIW reverting isn't practical as many more fixes have gone in.

I think a possible workaround is to copy directly xen-netback directory
from 3.14 and build it against new kernel. Netback itself is quite
self-contained.

> So the *only* reason to include this flag at this point is to allow people
> to run an unmodified 3.17 kernel with netback, is that right?  It seems like
> a really jerk move to encourage people to put 3.17 on their systems, and
> then deliberately break it on a subsequent release.
> 

I think this applies to all netback > 3.15. That means all unmodified
kernels released during our next release cycle.

(Not suggesting we should have this flag or not, just providing some
information to clarify current situation)

Wei.

> Particularly with ARM, where people are used to doing platform-specific
> things, it seems like encouraging people to either use pre-3.15 or to revert
> Zoltan's changes would be a better option.
> 
>  -George
> 
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