Date: Thu, 23 Aug 2007 09:40:30 -0700 (PDT) From: Weiguang Shi <wgshizz@yahoo.com> To: glebius@freebsd.org, maxim@freebsd.org Cc: freebsd-net@freebsd.org Subject: questions wrt ng_netflow Message-ID: <957582.10686.qm@web43133.mail.sp1.yahoo.com>
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Hi there,=0A=0AI've been reading netlfow.c in FreeBSD-6.2 and this piece o=
f code confuses me.=0A 484 /*=0A 485 * Go th=
rough hash and find our entry. If we encounter an=0A 486 * =
entry, that should be expired, purge it. We do a reverse=0A 487 =
* search since most active entries are first, and most=0A 488 =
* searches are done on most active entries.=0A 489 =
*/=0A 490 TAILQ_FOREACH_REVERSE_SAFE(fle, &hsh->head, fhead,=
fle_hash, fle1) {=0A 491 if (bcmp(&r, &fle->f.r, si=
zeof(struct flow_rec)) =3D=3D 0)=0A 492 brea=
k;=0A 493 if ((INACTIVE(fle) && SMALL(fle)) || AGED(=
fle)) {=0A 494 TAILQ_REMOVE(&hsh->head, fle,=
fle_hash);=0A 495 expire_flow(priv, &item, =
fle, NG_QUEUE);=0A 496 atomic_add_32(&priv->=
info.nfinfo_act_exp, 1);=0A 497 }=0A 498 =
}=0A=0A +-------------+ +--------+ +--------+ +------=
--+ +--------+=0A | Bucket Head |----->| RecA |----->| RecB |--=
--->| RecC |----->| RecD |=0A +-------------+ +--------+ +=
--------+ +--------+ +--------+=0A=0AIn the figure above, let's s=
ay our packet matches RecC. So before the=0Amatch, RecD is examined to see =
if it's AGED, i.e., it's lasted for too=0Along, or if it's too small and in=
active. As the match is found, the=0Acode stops searching.=0A=0AFirst, isn'=
t INACTIVE alone enough to expire a flow? Why must INACTIVE=0A_and_ SMALL?=
=0A=0ARecA and RecB would not be examined for expiration but since they are=
=0Ato the beginning of the queue and therefore actually less recently=0Aacc=
essed, they are more likely to be INACTIVE and could be more AGED.=0AI must=
be missing something, but what justifies examining RecD but not =0ARecA an=
d RecB?=0A=0AThank you very much for your time.=0AWei=0A=0A=0A=0A=0A =
=0A________________________________________________________________________=
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