Date: Mon, 13 Sep 2004 20:38:45 GMT From: Matthew Luckie <mjl@luckie.org.nz> To: freebsd-gnats-submit@FreeBSD.org Subject: kern/71711: [PATCH] generate a single bpf timestamp for each packet Message-ID: <200409132038.i8DKcjaa002101@www.freebsd.org> Resent-Message-ID: <200409132040.i8DKeVni018473@freefall.freebsd.org>
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>Number: 71711
>Category: kern
>Synopsis: [PATCH] generate a single bpf timestamp for each packet
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: change-request
>Submitter-Id: current-users
>Arrival-Date: Mon Sep 13 20:40:29 GMT 2004
>Closed-Date:
>Last-Modified:
>Originator: Matthew Luckie
>Release: FreeBSD 4.10
>Organization:
University of Waikato
>Environment:
FreeBSD neoprene.luckie.org.nz 4.10-RELEASE FreeBSD 4.10-RELEASE #8: Tue Sep 14 08:14:46 NZST 2004 root@neoprene.luckie.org.nz:/usr/src/sys/compile/neoprene i386
>Description:
I'm using BPF to obtain the transmit timestamp of packets I send. I noticed that the timestamps differed slightly between what I was seeing and what tcpdump saw. The cause of this is that timestamps are generated for each bpf fd if the packet passes the filter. The bpf(4) documentation is accurate for this case, but I'm wondering if it makes more sense to generate the timestamp once for each packet, as it allows a more accurate estimation of when the packet might have hit the wire.
>How-To-Repeat:
Open two tcpdump sessions that capture the same packets. You'll notice the timestamps differ slightly.
>Fix:
I took the liberty of optimising bpf_mtap a little while generating the patch. I also removed code for generating timestamps based on the kernel being run, as the code would be duplicated in two places. I'm happy to generate a macro and stick it in bpf_compat.h
--- net/bpf.c.orig Tue Sep 14 07:40:02 2004
+++ net/bpf.c Tue Sep 14 08:14:38 2004
@@ -126,7 +126,8 @@
static inline void
bpf_wakeup __P((struct bpf_d *));
static void catchpacket __P((struct bpf_d *, u_char *, u_int,
- u_int, void (*)(const void *, void *, size_t)));
+ u_int, void (*)(const void *, void *, size_t),
+ struct timeval *));
static void reset_d __P((struct bpf_d *));
static int bpf_setf __P((struct bpf_d *, struct bpf_program *));
@@ -1188,17 +1189,22 @@
struct bpf_if *bp;
register struct bpf_d *d;
register u_int slen;
+ struct timeval tv;
+
+ bp = ifp->if_bpf;
+ if (bp->bif_dlist != NULL)
+ microtime(&tv);
+
/*
* Note that the ipl does not have to be raised at this point.
* The only problem that could arise here is that if two different
* interfaces shared any data. This is not the case.
*/
- bp = ifp->if_bpf;
for (d = bp->bif_dlist; d != 0; d = d->bd_next) {
++d->bd_rcount;
slen = bpf_filter(d->bd_filter, pkt, pktlen, pktlen);
if (slen != 0)
- catchpacket(d, pkt, pktlen, slen, bcopy);
+ catchpacket(d, pkt, pktlen, slen, bcopy, &tv);
}
}
@@ -1241,18 +1247,27 @@
struct bpf_d *d;
u_int pktlen, slen;
struct mbuf *m0;
+ struct timeval tv;
- pktlen = 0;
- for (m0 = m; m0 != 0; m0 = m0->m_next)
- pktlen += m0->m_len;
-
- for (d = bp->bif_dlist; d != 0; d = d->bd_next) {
- if (!d->bd_seesent && (m->m_pkthdr.rcvif == NULL))
- continue;
- ++d->bd_rcount;
- slen = bpf_filter(d->bd_filter, (u_char *)m, pktlen, 0);
- if (slen != 0)
- catchpacket(d, (u_char *)m, pktlen, slen, bpf_mcopy);
+ d = bp->bif_dlist;
+ if (d != NULL) {
+ microtime(&tv);
+
+ pktlen = 0;
+ for (m0 = m; m0 != 0; m0 = m0->m_next)
+ pktlen += m0->m_len;
+
+ do {
+ if (!d->bd_seesent && (m->m_pkthdr.rcvif == NULL))
+ continue;
+ ++d->bd_rcount;
+ slen = bpf_filter(d->bd_filter, (u_char *)m, pktlen, 0);
+ if (slen != 0)
+ catchpacket(d, (u_char *)m, pktlen, slen,
+ bpf_mcopy, &tv);
+ d = d->bd_next;
+ }
+ while (d != NULL);
}
}
@@ -1265,11 +1280,12 @@
* pkt is really an mbuf.
*/
static void
-catchpacket(d, pkt, pktlen, snaplen, cpfn)
+catchpacket(d, pkt, pktlen, snaplen, cpfn, tv)
register struct bpf_d *d;
register u_char *pkt;
register u_int pktlen, snaplen;
register void (*cpfn) __P((const void *, void *, size_t));
+ register struct timeval *tv;
{
register struct bpf_hdr *hp;
register int totlen, curlen;
@@ -1318,13 +1334,7 @@
* Append the bpf header.
*/
hp = (struct bpf_hdr *)(d->bd_sbuf + curlen);
-#if BSD >= 199103
- microtime(&hp->bh_tstamp);
-#elif defined(sun)
- uniqtime(&hp->bh_tstamp);
-#else
- hp->bh_tstamp = time;
-#endif
+ bcopy(tv, &hp->bh_tstamp, sizeof(hp->bh_tstamp));
hp->bh_datalen = pktlen;
hp->bh_hdrlen = hdrlen;
/*
>Release-Note:
>Audit-Trail:
>Unformatted:
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