Currently tcp_hash() returns the hash bucket for a value, that is the hash
modulo the size of the hash table. Usually it's a bit more flexible to
have hash functions return a "raw" hash value and perform the modulus in
the callers. That allows the same hash function to be used for multiple
tables of different sizes, or to re-use the hash for other purposes.
We don't do anything like that with tcp_hash() at present, but we have some
plans to do so. Prepare for that by making tcp_hash() and tcp_conn_hash()
return raw hash values.
Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
---
tcp.c | 23 ++++++++++-------------
1 file changed, 10 insertions(+), 13 deletions(-)
diff --git a/tcp.c b/tcp.c
index 8dc9f31..63b39e0 100644
--- a/tcp.c
+++ b/tcp.c
@@ -1159,18 +1159,15 @@ static int tcp_hash_match(const struct tcp_tap_conn *conn,
* @eport: Guest side endpoint port
* @fport: Guest side forwarding port
*
- * Return: hash value, already modulo size of the hash table
+ * Return: hash value, needs to be adjusted for table size
*/
-static unsigned int tcp_hash(const struct ctx *c, const union inany_addr *faddr,
- in_port_t eport, in_port_t fport)
+static uint64_t tcp_hash(const struct ctx *c, const union inany_addr *faddr,
+ in_port_t eport, in_port_t fport)
{
struct siphash_state state = SIPHASH_INIT(c->hash_secret);
- uint64_t hash;
inany_siphash_feed(&state, faddr);
- hash = siphash_final(&state, 20, (uint64_t)eport << 16 | fport);
-
- return (unsigned int)(hash % TCP_HASH_TABLE_SIZE);
+ return siphash_final(&state, 20, (uint64_t)eport << 16 | fport);
}
/**
@@ -1178,10 +1175,10 @@ static unsigned int tcp_hash(const struct ctx *c, const union
inany_addr *faddr,
* @c: Execution context
* @conn: Connection
*
- * Return: hash value, already modulo size of the hash table
+ * Return: hash value, needs to be adjusted for table size
*/
-static unsigned int tcp_conn_hash(const struct ctx *c,
- const struct tcp_tap_conn *conn)
+static uint64_t tcp_conn_hash(const struct ctx *c,
+ const struct tcp_tap_conn *conn)
{
return tcp_hash(c, &conn->faddr, conn->eport, conn->fport);
}
@@ -1198,7 +1195,7 @@ 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);
+ unsigned b = tcp_conn_hash(c, conn) % TCP_HASH_TABLE_SIZE;
/* Linear probing */
while (!flow_sidx_eq(tc_hash[b], FLOW_SIDX_NONE) &&
@@ -1241,7 +1238,7 @@ static void tcp_hash_remove(const struct ctx *c,
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, &flow->tcp);
+ unsigned h = tcp_conn_hash(c, &flow->tcp) % TCP_HASH_TABLE_SIZE;
if (!mod_between(h, s, b, TCP_HASH_TABLE_SIZE)) {
/* tc_hash[s] can live in tc_hash[b]'s slot */
@@ -1297,7 +1294,7 @@ static struct tcp_tap_conn *tcp_hash_lookup(const struct ctx *c,
inany_from_af(&aany, af, faddr);
- b = tcp_hash(c, &aany, eport, fport);
+ b = tcp_hash(c, &aany, eport, fport) % TCP_HASH_TABLE_SIZE;
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);
--
2.43.0