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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