We implement our hash table with pointers to the entry for each bucket (or
NULL). However, the entries are always allocated within the flow table,
meaning that a flow index will suffice, halving the size of the hash table.
For TCP, just a flow index would be enough, but future uses will want to
expand the hash table to cover indexing either side of a flow, so use a
flow_sidx_t as the type for each hash bucket.
Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
---
flow.h | 11 +++++++++++
tcp.c | 33 ++++++++++++++++++++++-----------
2 files changed, 33 insertions(+), 11 deletions(-)
diff --git a/flow.h b/flow.h
index c2a5190..959b461 100644
--- a/flow.h
+++ b/flow.h
@@ -53,6 +53,17 @@ static_assert(sizeof(flow_sidx_t) <= sizeof(uint32_t),
#define FLOW_SIDX_NONE ((flow_sidx_t){ .flow = FLOW_MAX })
+/**
+ * flow_sidx_eq() - Test if two sidx values are equal
+ * @a, @b: sidx values
+ *
+ * Return: true iff @a and @b refer to the same side of the same flow
+ */
+static inline bool flow_sidx_eq(flow_sidx_t a, flow_sidx_t b)
+{
+ return (a.flow == b.flow) && (a.side == b.side);
+}
+
union flow;
void flow_table_compact(struct ctx *c, union flow *hole);
diff --git a/tcp.c b/tcp.c
index cd8e64e..8dc9f31 100644
--- a/tcp.c
+++ b/tcp.c
@@ -574,7 +574,7 @@ static unsigned int tcp6_l2_flags_buf_used;
#define CONN(idx) (&(FLOW(idx)->tcp))
/* Table for lookup from remote address, local port, remote port */
-static struct tcp_tap_conn *tc_hash[TCP_HASH_TABLE_SIZE];
+static flow_sidx_t tc_hash[TCP_HASH_TABLE_SIZE];
static_assert(ARRAY_SIZE(tc_hash) >= FLOW_MAX,
"Safe linear probing requires hash table larger than connection table");
@@ -1197,10 +1197,12 @@ static unsigned int tcp_conn_hash(const struct ctx *c,
static inline unsigned tcp_hash_probe(const struct ctx *c,
const struct tcp_tap_conn *conn)
{
+ flow_sidx_t sidx = FLOW_SIDX(conn, TAPSIDE);
unsigned b = tcp_conn_hash(c, conn);
/* Linear probing */
- while (tc_hash[b] && tc_hash[b] != conn)
+ while (!flow_sidx_eq(tc_hash[b], FLOW_SIDX_NONE) &&
+ !flow_sidx_eq(tc_hash[b], sidx))
b = mod_sub(b, 1, TCP_HASH_TABLE_SIZE);
return b;
@@ -1215,7 +1217,7 @@ static void tcp_hash_insert(const struct ctx *c, struct tcp_tap_conn
*conn)
{
unsigned b = tcp_hash_probe(c, conn);
- tc_hash[b] = conn;
+ tc_hash[b] = FLOW_SIDX(conn, TAPSIDE);
flow_dbg(conn, "hash table insert: sock %i, bucket: %u", conn->sock, b);
}
@@ -1228,16 +1230,18 @@ static void tcp_hash_remove(const struct ctx *c,
const struct tcp_tap_conn *conn)
{
unsigned b = tcp_hash_probe(c, conn), s;
+ union flow *flow = flow_at_sidx(tc_hash[b]);
- if (!tc_hash[b])
+ if (!flow)
return; /* Redundant remove */
flow_dbg(conn, "hash table remove: sock %i, bucket: %u", conn->sock, b);
/* Scan the remainder of the cluster */
- for (s = mod_sub(b, 1, TCP_HASH_TABLE_SIZE); tc_hash[s];
+ for (s = mod_sub(b, 1, TCP_HASH_TABLE_SIZE);
+ (flow = flow_at_sidx(tc_hash[s]));
s = mod_sub(s, 1, TCP_HASH_TABLE_SIZE)) {
- unsigned h = tcp_conn_hash(c, tc_hash[s]);
+ unsigned h = tcp_conn_hash(c, &flow->tcp);
if (!mod_between(h, s, b, TCP_HASH_TABLE_SIZE)) {
/* tc_hash[s] can live in tc_hash[b]'s slot */
@@ -1247,7 +1251,7 @@ static void tcp_hash_remove(const struct ctx *c,
}
}
- tc_hash[b] = NULL;
+ tc_hash[b] = FLOW_SIDX_NONE;
}
/**
@@ -1262,10 +1266,10 @@ void tcp_tap_conn_update(const struct ctx *c, struct tcp_tap_conn
*old,
{
unsigned b = tcp_hash_probe(c, old);
- if (!tc_hash[b])
+ if (!flow_at_sidx(tc_hash[b]))
return; /* Not in hash table, nothing to update */
- tc_hash[b] = new;
+ tc_hash[b] = FLOW_SIDX(new, TAPSIDE);
debug("TCP: hash table update: old index %u, new index %u, sock %i, "
"bucket: %u", FLOW_IDX(old), FLOW_IDX(new), new->sock, b);
@@ -1288,15 +1292,17 @@ static struct tcp_tap_conn *tcp_hash_lookup(const struct ctx *c,
in_port_t eport, in_port_t fport)
{
union inany_addr aany;
+ union flow *flow;
unsigned b;
inany_from_af(&aany, af, faddr);
b = tcp_hash(c, &aany, eport, fport);
- while (tc_hash[b] && !tcp_hash_match(tc_hash[b], &aany, eport, fport))
+ while ((flow = flow_at_sidx(tc_hash[b])) &&
+ !tcp_hash_match(&flow->tcp, &aany, eport, fport))
b = mod_sub(b, 1, TCP_HASH_TABLE_SIZE);
- return tc_hash[b];
+ return &flow->tcp;
}
/**
@@ -3087,6 +3093,11 @@ static void tcp_sock_refill_init(const struct ctx *c)
*/
int tcp_init(struct ctx *c)
{
+ unsigned b;
+
+ for (b = 0; b < TCP_HASH_TABLE_SIZE; b++)
+ tc_hash[b] = FLOW_SIDX_NONE;
+
if (c->ifi4)
tcp_sock4_iov_init(c);
--
2.43.0