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RE: Varargs in AdapterVifCallbacks.
- To: "paul@xxxxxxx" <paul@xxxxxxx>, "win-pv-devel@xxxxxxxxxxxxxxxxxxxx" <win-pv-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Martin Harvey <martin.harvey@xxxxxxxxxx>
- Date: Thu, 12 May 2022 15:42:26 +0000
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- Cc: Owen Smith <owen.smith@xxxxxxxxxx>
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- Thread-topic: Varargs in AdapterVifCallbacks.
-----Original Message-----
From: win-pv-devel <win-pv-devel-bounces@xxxxxxxxxxxxxxxxxxxx> On Behalf Of
Durrant, Paul
Sent: 12 May 2022 15:39
To: win-pv-devel@xxxxxxxxxxxxxxxxxxxx
Subject: Re: Varargs in AdapterVifCallbacks.
> Not necessarily. Can you elaborate on "not as wonderful as it should be"?
There is some nastiness when you end up with a large number of parameters or
pointers to certain types - unfortunately it's a heisenbug, and keeps moving
around as I add / remove debugging statements / params to the call. However,
it's fairly clear the stack eats itself for lunch. All I did was add a single
PBOOLEAN to the parameter list of one of the callback parameters, upped the
version number of the interface, and it all went very badly wrong. Then I then
"fixed" the problem by adding a couple more ULONG's padding to the varargs and
it all works again.
However, I do notice that none of the windows kernel interfaces use varargs,
I'm not even sure they are "officially" supported for kernel development, and I
would far prefer to declare and maintain a struct/union for parameters. That
way, all the details are in fact kept in the interface, and there is good
debugging symbolic information for all of them.
> Any complaints if I remove varargs from upcoming v9 of XENVIF_VIF
> interface? Speak now or forever …
> I could be persuaded that an argument struct is a suitable replacement but
> I'd like to understand what the exact nature of the problem is.
OK. I hope my partial explanation above is at least a bit of an explanation.
That and the fact that varargs are extremely difficult to debug when they go
wrong.
One final thing: We may have things afoot here that I can't talk about on the
list. Might this be a good time for me, you and owen to meet in a pub some time?
MH.
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