Date: Sat, 18 Sep 2004 13:42:24 -0400 (EDT) From: Robert Watson <rwatson@FreeBSD.org> To: Brooks Davis <brooks@one-eyed-alien.net> Cc: current@FreeBSD.org Subject: Re: 5.3-RELEASE TODO Message-ID: <Pine.NEB.3.96L.1040918134100.91851A-100000@fledge.watson.org> In-Reply-To: <20040918171216.GA27533@odin.ac.hmc.edu>
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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? Robert N M Watson FreeBSD Core Team, TrustedBSD Projects robert@fledge.watson.org Principal Research Scientist, McAfee Research
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