Re: libpcap on Mac Os X 10.6 Snow Leopard

[Guy Harris <guy () alum mit edu>]

On Feb 12, 2010, at 11:02 AM, Marco De Angelis wrote:

> Guy Harris <guy <at> alum.mit.edu> writes:
>
> > Can you cut your application down to the smallest code 
> > snippet that shows the problem, and send that to me? 
>
> I managed to extrapolate the core. It's a little messy because
> of the many tests I made recently and the 80-chars line 
> limitation, but it show the original  problem. 
> If you uncomment the call to ioctl with
> BIOCIMMEDIATE setting, packets get delivered immediately.

...and if I "#if 0" out the code that puts the pcap into non-blocking mode, packets don't get delivered immediately, 
but they *do* arrive, so it appears to be an issue with non-blocking mode.

> From looking at both the FreeBSD and OS X BPF code path in the kernel, I suspect the problem would also show up on 
> FreeBSD 7.x and 8.x, at least, as well as 9.0-CURRENT; there are probably older versions that have it as well.  
> However, if you use select() to wait for packets, it probably won't occur on FreeBSD, but would still occur on OS X.  
> Top-of-tree NetBSD looks as if it fixes this, and I don't know if OpenBSD ever had it (the top-of-tree code looks as 
> if the change that introduced this was never added).  DragonFly BSD appears to be the same as FreeBSD here.

If you have an Apple Developer Connection account, go to

        http://developer.apple.com/bugreporter/

and log in to Apple Bug Reporter and file a bug; please send me the bug number when you do so.  If you don't have an 
ADC account, that page has a "Sign up to become a free ADC Member" link.

This problem was introduced in Snow Leopard as a result of picking up from FreeBSD a fix to another bug; the existence 
in FreeBSD of that fix is the reason why I suspect the same problem would show up there (and the existence in FreeBSD 
of a fix to the way BPF works with select() is the reason why I suspect using select() to wait for packets would 
prevent the bug from appearing there - that fix is *not* in OS X).

Anybody else seeing this problem should also file a bug and send me the bug number.  (The more bugs filed, the more 
likely I suspect it'll be to get fixed in a software update.)

If it shows up in FreeBSD, I'll look at submitting fixes for it and DragonFly BSD as well.  (If it doesn't, I need to 
think about this a little more.)-
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