[sudo-workers] Is there a way to avoid get_net_ifs() when the information won't be used?

[Rick Jones]

On 01/23/2014 11:37 AM, Todd C. Miller wrote:
> On Thu, 23 Jan 2014 10:58:20 -0800, Rick Jones wrote:
>
>> A run-time switch would be splendid.
>
> I'll implement that in the next sudo release.

I would be happy to be a pre-release guinea pig for that.

>> I've gone ahead and fired-up a FreeBSD 9.2-RELEASE VM, and created 8000
>> "gre" interfaces (without IPs assigned, just "ifconfig greN create")and
>> while there was a slight increase in time for sudo (unpatched 1.8.9p4)
>> of a few milliseconds, it wasn't nearly as bad as under Linux.  I'm
>> going to spin-up a similar, Ubuntu 13.10 VM to get a better A/B
>> comparison (everything I've mentioned thusfar has been bare-iron, but I
>> don't have the luxury of running FreeBSD on bare-iron) and perhaps
>> mention it to the Linux netdev folks.  Would you like to be cc'd on that
>> message?
>
> The first __sysctl() is probably to get the size and the other is
> to fill it in.  I think it is worth mentioning to Linux net-dev.

I've sent a missive to netdev - didn't cc you on it, but it should 
appear in the archives before long 
http://vger.kernel.org/vger-lists.html#netdev .  The subject is 
"getifaddrs performance, sudo and Linux vs FreeBSD."

I was thinking the same thing about the sysctl - the pity is that truss 
doesn't seem to know how to further decode the system call.  However, 
assuming 
https://github.com/freebsd/freebsd-head/blob/master/lib/libc/net/getifaddrs.c 
matches what I'm using in the FreeBSD VM then indeed, it is two calls - 
one to get the quantity of space needed, and then one to fetch it.

rick

> It may be possible to use recvmsg() with a scatter-gather buffer
> instead of repeated calls.
>
>   - todd
>