Date: Mon, 16 Oct 2000 17:05:11 -0400 (EDT) From: "Andrew R. Reiter" <arr@watson.org> To: Peter Van Epp <vanepp@sfu.ca> Cc: freebsd-hackers@FreeBSD.ORG Subject: OOPS Re: bpf.c select fix for review Message-ID: <Pine.NEB.3.96L.1001016170453.31935B-100000@fledge.watson.org> In-Reply-To: <200010162026.NAA01828@fraser.sfu.ca>
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woops.. I meant bd_rdstart.
On Mon, 16 Oct 2000, Peter Van Epp wrote:
> While working on the new argus version I discovered that there is a
> bug in the /sys/net/bpf.c code if you are doing select with a timeout (which
> tcpdump isn't). Basically if you set up tcpreplay on another machine and send
> a less than full buffer (9 packets 2300 bytes in my case) to a FreeBSD 4.1
> RELEASE machine, argus won't see the packets. It turns out that because it
> is using select (and not immediate mode) the partially full buffer won't get
> passed up to libpcap. The OpenBSD folks have a partial fix (which only gets
> the first packet up and leaves the other 8 dangling). I ported that to FreeBSD
> and then made a fix which appears to work based on what their code looked to
> be trying to do (as opposed to what it does which is incorrect).
> Basically at receive packet time the tick counter is stored in a
> variable in the capture structure. When the select/poll timeout occurs it
> checks if the current tick time is > then the last received packet count +
> the timeout value. If so it rotates the (partially full) packet buffer and
> signals to wake up the process. While this appears to work (and match the
> Solaris behavior on the same file) I figured I'd see if anyone sees a glaring
> hole in the fix before submitting a bug report on it.
>
> Peter Van Epp / Operations and Technical Support
> Simon Fraser University, Burnaby, B.C. Canada
>
> *** /sys/net/bpf.c.orig Sat Oct 14 19:00:59 2000
> --- /sys/net/bpf.c Mon Oct 16 09:30:24 2000
> ***************
> *** 1054,1061 ****
> if (events & (POLLIN | POLLRDNORM)) {
> if (d->bd_hlen != 0 || (d->bd_immediate && d->bd_slen != 0))
> revents |= events & (POLLIN | POLLRDNORM);
> ! else
> ! selrecord(p, &d->bd_sel);
> }
> splx(s);
> return (revents);
> --- 1054,1076 ----
> if (events & (POLLIN | POLLRDNORM)) {
> if (d->bd_hlen != 0 || (d->bd_immediate && d->bd_slen != 0))
> revents |= events & (POLLIN | POLLRDNORM);
> ! else {
> ! /*
> ! * If there is a timeout and no data in the hold buffer
> ! * see if there has been data in the capture buffer
> ! * for more than a timeout interval. If so rotate the
> ! * buffer to push the packets to the user.
> ! */
> ! if ((d->bd_slen != 0) && (d->bd_hlen == 0)) {
> ! if ((d->bd_rtout != -1) &&
> ! (d->bd_rdStart + d->bd_rtout) > ticks) {
> ! ROTATE_BUFFERS(d);
> ! revents |= events & (POLLIN | POLLRDNORM);
> ! }
> ! } else
> ! selrecord(p, &d->bd_sel);
> !
> ! }
> }
> splx(s);
> return (revents);
> ***************
> *** 1219,1224 ****
> --- 1234,1245 ----
> */
> (*cpfn)(pkt, (u_char *)hp + hdrlen, (hp->bh_caplen = totlen - hdrlen));
> d->bd_slen = curlen + totlen;
> +
> + /*
> + * Mark the time the last packet was seen for poll timeout processing.
> + */
> +
> + d->bd_rdStart = ticks;
> }
>
> /*
>
>
>
> *** /sys/net/bpfdesc.h.orig Sat Oct 14 19:16:07 2000
> --- /sys/net/bpfdesc.h Sat Oct 14 19:21:54 2000
> ***************
> *** 69,74 ****
> --- 69,75 ----
>
> struct bpf_if * bd_bif; /* interface descriptor */
> u_long bd_rtout; /* Read timeout in 'ticks' */
> + u_long bd_rdStart; /* when the read started */
> struct bpf_insn *bd_filter; /* filter code */
> u_long bd_rcount; /* number of packets received */
> u_long bd_dcount; /* number of packets dropped */
>
>
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*-------------.................................................
| Andrew R. Reiter
| arr@fledge.watson.org
| "It requires a very unusual mind
| to undertake the analysis of the obvious" -- A.N. Whitehead
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