frag6: add "big picture"

Add some ASCII relation of how the bits plug together.  The terminology
difference of "fragmented packets" and "fragment packets" is subtle.
While here clear up more whitespace and comments.

No functional change.

MFC after:	3 weeks
Sponsored by:	Netflix

1 files changed, 22 insertions, 5 deletions

diff --git a/sys/netinet6/frag6.c b/sys/netinet6/frag6.c
index 936fa959b742..b1b24260231b 100644
--- a/sys/netinet6/frag6.c
+++ b/sys/netinet6/frag6.c
@@ -69,6 +69,22 @@ __FBSDID("$FreeBSD$");
 #include <security/mac/mac_framework.h>
 #endif
 
+/*
+ * A "big picture" of how IPv6 fragment queues are all linked together.
+ *
+ * struct ip6qbucket ip6qb[...];			hashed buckets
+ * ||||||||
+ * |
+ * +--- TAILQ(struct ip6q, packets) *q6;		tailq entries holding
+ *      ||||||||					fragmented packets
+ *      |						(1 per original packet)
+ *      |
+ *      +--- TAILQ(struct ip6asfrag, ip6q_frags) *af6;	tailq entries of IPv6
+ *           |                                   *ip6af;fragment packets
+ *           |						for one original packet
+ *           + *mbuf
+ */
+
 /* Reassembly headers are stored in hash buckets. */
 #define	IP6REASS_NHASH_LOG2	10
 #define	IP6REASS_NHASH		(1 << IP6REASS_NHASH_LOG2)
@@ -84,10 +100,10 @@ struct ip6qbucket {
 struct ip6asfrag {
 	TAILQ_ENTRY(ip6asfrag) ip6af_tq;
 	struct mbuf	*ip6af_m;
-	int		ip6af_offset;	/* offset in ip6af_m to next header */
-	int		ip6af_frglen;	/* fragmentable part length */
-	int		ip6af_off;	/* fragment offset */
-	bool		ip6af_mff;	/* more fragment bit in frag off */
+	int		ip6af_offset;	/* Offset in ip6af_m to next header. */
+	int		ip6af_frglen;	/* Fragmentable part length. */
+	int		ip6af_off;	/* Fragment offset. */
+	bool		ip6af_mff;	/* More fragment bit in frag off. */
 };
 
 #define IP6_REASS_MBUF(ip6af) (*(struct mbuf **)&((ip6af)->ip6af_m))
@@ -309,7 +325,7 @@ frag6_cleanup(void *arg __unused, struct ifnet *ifp)
 
 				m = IP6_REASS_MBUF(af6);
 
-				/* clear no longer valid rcvif pointer */
+				/* Clear no longer valid rcvif pointer. */
 				if (m->m_pkthdr.rcvif == ifp)
 					m->m_pkthdr.rcvif = NULL;
 			}
@@ -563,6 +579,7 @@ frag6_input(struct mbuf **mp, int *offp, int proto)
 		IP6QB_UNLOCK(bucket);
 		return (IPPROTO_DONE);
 	}
+
 	/*
 	 * If it is the first fragment, do the above check for each
 	 * fragment already stored in the reassembly queue.