Re: kern/50602: removing ethernet cable panics the kernel

[Ryota Ozaki <ozaki-r%netbsd.org@localhost>]

So I've revisited this change.

I rebased mlelstv's patch:
http://www.netbsd.org/~ozaki-r/softint-if_link_state_change.diff

It works for me. I tested plugging/unplugging a cable repeatedly
under load or no load. I didn't see any panic and inconsistency
of the link state.

I think we can commit this change. Any thoughts?

  ozaki-r

On Mon, Jan 4, 2016 at 6:37 PM, Ryota Ozaki <ozaki-r%netbsd.org@localhost> wrote:
> On Mon, Jan 4, 2016 at 4:15 PM, Michael van Elst <mlelstv%serpens.de@localhost> wrote:
>> The following reply was made to PR kern/50602; it has been noted by GNATS.
>>
>> From: mlelstv%serpens.de@localhost (Michael van Elst)
>> To: gnats-bugs%netbsd.org@localhost
>> Cc:
>> Subject: Re: kern/50602: removing ethernet cable panics the kernel
>> Date: Mon, 4 Jan 2016 07:09:51 +0000 (UTC)
>>
>>  ozaki-r%netbsd.org@localhost (Ryota Ozaki) writes:
>>
>>  >I remember that riastradh suggested me that we don't need the
>>  >ifdef for kvm(3). IIUC, the added variables aren't accessed
>>  >by kvm(3) so that we don't need to hide them to userland.
>>
>>  >I'd remove it if nobody objects.
>>
>>  The point is that the structure to userland must not change
>>  without adding appropriate compatibility code.
>>
>>  But since the added variables are only accessed by the kernel
>>  the simple solution is to put them inside #ifdef _KERNEL
>>  as it was already done for the if_slowtimo_ch variable.
>
> Hm. My understanding is that we can keep compatibility by
> appending new variables to a data structure while inserting
> variables to middle of a data structure or removing variables
> breaks compatibility. Basically struct ifnet is accessed from
> userland via struct ifreq and one exception is kvm(3) that is
> used by netstat(1) and vmstat(1). The former guarantees
> compatibility on changing ifnet and the compatibility for
> the latter is guaranteed by always appending new variables
> to ifnet when we change ifnet.
>
> Correct me if I'm wrong (probably I am!).
>
>   ozaki-r
>
>>
>>  --
>>  --
>>                                  Michael van Elst
>>  Internet: mlelstv%serpens.de@localhost
>>                                  "A potential Snark may lurk in every tree."
>>