Re: [Xen-devel] [PATCH net-next v5 4/9] xen-netback: Change RX path for mapped SKB fragments

[Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>]

On 24/02/14 13:49, Zoltan Kiss wrote:
> On 22/02/14 23:18, Zoltan Kiss wrote:
> > On 18/02/14 17:45, Ian Campbell wrote:
> > > On Mon, 2014-01-20 at 21:24 +0000, Zoltan Kiss wrote:
> > >
> > > Re the Subject: change how? Perhaps "handle foreign mapped pages on the
> > > guest RX path" would be clearer.
> > Ok, I'll do that.
> >
> > > > RX path need to know if the SKB fragments are stored on pages from 
> > > > another
> > > > domain.
> > > Does this not need to be done either before the mapping change or at 
> > > the
> > > same time? -- otherwise you have a window of a couple of commits where
> > > things are broken, breaking bisectability.
> > I can move this to the beginning, to keep bisectability. I've put it 
> > here originally because none of these makes sense without the 
> > previous patches.
> Well, I gave it a close look: to move this to the beginning as a 
> separate patch I would need to put move a lot of definitions from the 
> first patch to here (ubuf_to_vif helper, xenvif_zerocopy_callback 
> etc.). That would be the best from bisect point of view, but from 
> patch review point of view even worse than now. So the only option I 
> see is to merge this with the first 2 patches, so it will be even bigger. 
Actually I was stupid, we can move this patch earlier and introduce 
stubs for those 2 functions. But for the another two patches (#6 and #8) 
it's still true that we can't move them before, only merge them into the 
main, as they heavily rely on the main patch. #6 is necessary for 
Windows frontends, as they are keen to send too many slots. #8 is quite 
a rare case, happens only if a guest wedge or malicious, and sits on the 
packet.
So my question is still up: do you prefer perfect bisectability or more 
segmented patches which are not that pain to review?
> And based on that principle, patch #6 and #8 should be merged there as 
> well, as they solve corner cases introduced by the grant mapping.
> I don't know how much the bisecting requirements are written in stone. 
> At this moment, all the separate patches compile, but after #2 there 
> are new problems solved in #4, #6 and #8. If someone bisect in the 
> middle of this range and run into these problems, they could quite 
> easily figure out what went wrong looking at the adjacent patches. So 
> I would recommend to keep this current order.
> What's your opinion?
>
> Zoli

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