Re: 5.3-RELEASE TODO

On Sat, Sep 18, 2004 at 01:42:24PM -0400, Robert Watson wrote:
> 
> On Sat, 18 Sep 2004, Brooks Davis wrote:
> 
> > > Have you tried seeing just how many addresses you can add before
> > > getifaddrs() fails to return the complete list?  128k seems like a lot,
> > > but I instrumente ifconf() locally a couple of weeks ago when I first
> > > became aware of this problem, and discovered that even on my notebook
> > > (which has a wireless card with one IP, and an unused ethernet card) that
> > > I see moderately large buffers being read from user space:
> > > 
> > > ifconf: 16384 space
> > 
> > Those allocations don't seem to make any sense.  The actual space
> > required is quite small.  All you do is copy one struct ifreq out for
> > each address, plus one for each interface with no addresses.  The base
> > size of a struct ifreq is 32 bytes and it extends to 34 for IPv6
> > addresses.  The maximum size allowed by the data types is 273 (for a 255
> > byte address).  Since I think IPv6 are the largest addresses used in
> > practice, MAXPHYS is probably not too bad, though it does put a new cap
> > on the number of interfaces at ~4k. 
> > 
> > If we want to keep kernel allocations small and allow all the itnerfaces
> > to be reliably reported, we probably need to go back to my origional
> > plan where we loop repeatidly.  I might do it differently by allocating
> > up to MAXPHYS and only reallocating if we overflow.  That would avoid
> > doing it twice (or more) on normal machines while still being correct. 
> 
> I'm not too worried about theory, mostly about practice.  I.e., if you add
> a few thousand IP addresses to a tap device, does all go happily?

After adding the missing sbuf_delete(), I was able to create 2000
aliases on a vlan.  I think the current practical limit is ~4090.
I'm working on a new version that initially caps the allocation at
MAXPHYS and then retries if it doesn't have enough space.

-- Brooks

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