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

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

The following reply was made to PR kern/50602; it has been noted by GNATS.

From: Ryota Ozaki <ozaki-r%netbsd.org@localhost>
To: "gnats-bugs%NetBSD.org@localhost" <gnats-bugs%netbsd.org@localhost>
Cc: kern-bug-people%netbsd.org@localhost, gnats-admin%netbsd.org@localhost, netbsd-bugs%netbsd.org@localhost, 
	Michael van Elst <mlelstv%serpens.de@localhost>
Subject: Re: kern/50602: removing ethernet cable panics the kernel
Date: Wed, 10 Feb 2016 13:24:14 +0900

 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."
 >>