Re: struct ifnet and ifaddr handling [was: Re: Making global variables of if.c MPSAFE]

[Masao Uebayashi <uebayasi%gmail.com@localhost>]

On Wed, Nov 26, 2014 at 12:29 AM, Ryota Ozaki <ozaki-r%netbsd.org@localhost> wrote:
> Yes, we can extend if_flags to int by unifying with if__pad1, and it works
> for the kernel and for old userland programs on little endian machines.
> However, it doesn't work for old userland programs on big endian machines,
> IIUC. An old userland program, say netstat, which uses kvm(3) reads
> if_flags as short. On a LE machine, netstat can see lower-half of if_flags
> (int) of a new kernel as expected. OTOH, on a BE machine, netstat sees
> upper-half of the value.

I'd change if__pad1 to if_flags2 and define IFF2_SLOWTIMO_MPSAFE etc.

>>> I don't understand how kvm(3) works though, if we don't change existing
>>> members of struct ifnet, can old netstat(1) run on a new kernel that
>>> adds a value hidden in _KERNEL to struct ifnet?
>>
>> I think adding a new member at the tail doesn't change member offsets,
>> so netstat(1) *should* keep working.
>>
>> But for future, netstat(3) should use kvm(3), so that it keeps working
>> even after struct ifnet changes.
>
> Hmm, I fail to understand what you mean. netstat should use kvm? or
> shouldn't use?

Sorry, I meant s/kvm(3)/sysctl(3)/...