[PATCH v4 08/16] tcp, flow: Replace TCP specific hash function with general flow hash

[David Gibson <david@gibson.dropbear.id.au>]

Currently we match TCP packets received on the tap connection to a TCP
connection via a hash table based on the forwarding address and both
ports.  We hope in future to allow for multiple guest side addresses, or
for multiple interfaces which means we may need to distinguish based on
the endpoint address and pif as well.  We also want a unified hash table
to cover multiple protocols, not just TCP.

Replace the TCP specific hash function with one suitable for general flows,
or rather for one side of a general flow.  This includes all the
information from struct flowside, plus the L4 protocol number.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 flow.c | 28 ++++++++++++++++++++++++++
 flow.h | 19 ++++++++++++++++++
 tcp.c  | 62 +++++++++++-----------------------------------------------
 3 files changed, 58 insertions(+), 51 deletions(-)

diff --git a/flow.c b/flow.c
index 02d6008..370d422 100644
--- a/flow.c
+++ b/flow.c
@@ -268,6 +268,34 @@ void flow_alloc_cancel(union flow *flow)
 	flow_first_free = FLOW_IDX(flow);
 }
 
+/**
+ * flow_hash() - Calculate hash value for one side of a flow
+ * @c:		Execution context
+ * @proto:	Protocol of this flow (IP L4 protocol number)
+ * @fside:	Flowside (must not have unspecified parts)
+ *
+ * Return: hash value
+ */
+uint64_t flow_hash(const struct ctx *c, uint8_t proto,
+		   const struct flowside *fside)
+{
+	struct siphash_state state = SIPHASH_INIT(c->hash_secret);
+
+	/* For the hash table to work, we need complete information in the
+	 * flowside.
+	 */
+	ASSERT(fside->pif != PIF_NONE &&
+	       !inany_is_unspecified(&fside->faddr) && fside->fport != 0 &&
+	       !inany_is_unspecified(&fside->eaddr) && fside->eport != 0);
+
+	inany_siphash_feed(&state, &fside->faddr);
+	inany_siphash_feed(&state, &fside->eaddr);
+
+	return siphash_final(&state, 38, (uint64_t)proto << 40 |
+			     (uint64_t)fside->pif << 32 |
+			     fside->fport << 16 | fside->eport);
+}
+
 /**
  * flow_defer_handler() - Handler for per-flow deferred and timed tasks
  * @c:		Execution context
diff --git a/flow.h b/flow.h
index 88caa76..218edc6 100644
--- a/flow.h
+++ b/flow.h
@@ -107,6 +107,22 @@ static inline void flowside_from_af(struct flowside *fside,
 
 #define SIDES			2
 
+/**
+ * flowside_eq() - Check if two flowsides are equal
+ * @left, @right:	Flowsides to compare
+ *
+ * Return: true if equal, false otherwise
+ */
+static inline bool flowside_eq(const struct flowside *left,
+			       const struct flowside *right)
+{
+	return left->pif == right->pif &&
+	       inany_equals(&left->eaddr, &right->eaddr) &&
+	       left->eport == right->eport &&
+	       inany_equals(&left->faddr, &right->faddr) &&
+	       left->fport == right->fport;
+}
+
 /**
  * struct flow_common - Common fields for packet flows
  * @side[]:	Information for each side of the flow
@@ -128,6 +144,9 @@ union flow *flow_start(union flow *flow, enum flow_type type,
 #define FLOW_START(flow_, t_, var_, i_)		\
 	(&flow_start((flow_), (t_), (i_))->var_)
 
+uint64_t flow_hash(const struct ctx *c, uint8_t proto,
+		   const struct flowside *fside);
+
 /**
  * struct flow_sidx - ID for one side of a specific flow
  * @side:	Side referenced (0 or 1)
diff --git a/tcp.c b/tcp.c
index 9ba2b07..2ad47c5 100644
--- a/tcp.c
+++ b/tcp.c
@@ -524,7 +524,7 @@ static struct iovec	tcp_iov			[UIO_MAXIOV];
 
 #define CONN(idx)		(&(FLOW(idx)->tcp))
 
-/* Table for lookup from remote address, local port, remote port */
+/* Table for lookup from flowside information */
 static flow_sidx_t tc_hash[TCP_HASH_TABLE_SIZE];
 
 static_assert(ARRAY_SIZE(tc_hash) >= FLOW_MAX,
@@ -1074,46 +1074,6 @@ static int tcp_opt_get(const char *opts, size_t len, uint8_t type_find,
 	return -1;
 }
 
-/**
- * tcp_hash_match() - Check if a connection entry matches address and ports
- * @conn:	Connection entry to match against
- * @faddr:	Guest side forwarding address
- * @eport:	Guest side endpoint port
- * @fport:	Guest side forwarding port
- *
- * Return: 1 on match, 0 otherwise
- */
-static int tcp_hash_match(const struct tcp_tap_conn *conn,
-			  const union inany_addr *faddr,
-			  in_port_t eport, in_port_t fport)
-{
-	const struct flowside *tapside = &conn->f.side[TAPSIDE];
-
-	if (inany_equals(&tapside->faddr, faddr) &&
-	    tapside->eport == eport && tapside->fport == fport)
-		return 1;
-
-	return 0;
-}
-
-/**
- * tcp_hash() - Calculate hash value for connection given address and ports
- * @c:		Execution context
- * @faddr:	Guest side forwarding address
- * @eport:	Guest side endpoint port
- * @fport:	Guest side forwarding port
- *
- * Return: hash value, needs to be adjusted for table size
- */
-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);
-
-	inany_siphash_feed(&state, faddr);
-	return siphash_final(&state, 20, (uint64_t)eport << 16 | fport);
-}
-
 /**
  * tcp_conn_hash() - Calculate hash bucket of an existing connection
  * @c:		Execution context
@@ -1124,9 +1084,7 @@ static uint64_t tcp_hash(const struct ctx *c, const union inany_addr *faddr,
 static uint64_t tcp_conn_hash(const struct ctx *c,
 			      const struct tcp_tap_conn *conn)
 {
-	const struct flowside *tapside = &conn->f.side[TAPSIDE];
-
-	return tcp_hash(c, &tapside->faddr, tapside->eport, tapside->fport);
+	return flow_hash(c, IPPROTO_TCP, &conn->f.side[TAPSIDE]);
 }
 
 /**
@@ -1201,25 +1159,26 @@ static void tcp_hash_remove(const struct ctx *c,
  * tcp_hash_lookup() - Look up connection given remote address and ports
  * @c:		Execution context
  * @af:		Address family, AF_INET or AF_INET6
+ * @eaddr:	Guest side endpoint address (guest local address)
  * @faddr:	Guest side forwarding address (guest remote address)
  * @eport:	Guest side endpoint port (guest local port)
  * @fport:	Guest side forwarding port (guest remote port)
  *
  * Return: connection pointer, if found, -ENOENT otherwise
  */
-static struct tcp_tap_conn *tcp_hash_lookup(const struct ctx *c,
-					    sa_family_t af, const void *faddr,
+static struct tcp_tap_conn *tcp_hash_lookup(const struct ctx *c, sa_family_t af,
+					    const void *eaddr, const void *faddr,
 					    in_port_t eport, in_port_t fport)
 {
-	union inany_addr aany;
+	struct flowside fside;
 	union flow *flow;
 	unsigned b;
 
-	inany_from_af(&aany, af, faddr);
+	flowside_from_af(&fside, PIF_TAP, af, faddr, fport, eaddr, eport);
 
-	b = tcp_hash(c, &aany, eport, fport) % TCP_HASH_TABLE_SIZE;
+	b = flow_hash(c, IPPROTO_TCP, &fside) % TCP_HASH_TABLE_SIZE;
 	while ((flow = flow_at_sidx(tc_hash[b])) &&
-	       !tcp_hash_match(&flow->tcp, &aany, eport, fport))
+	       !flowside_eq(&flow->f.side[TAPSIDE], &fside))
 		b = mod_sub(b, 1, TCP_HASH_TABLE_SIZE);
 
 	return &flow->tcp;
@@ -2522,7 +2481,8 @@ int tcp_tap_handler(struct ctx *c, uint8_t pif, sa_family_t af,
 	optlen = MIN(optlen, ((1UL << 4) /* from doff width */ - 6) * 4UL);
 	opts = packet_get(p, idx, sizeof(*th), optlen, NULL);
 
-	conn = tcp_hash_lookup(c, af, daddr, ntohs(th->source), ntohs(th->dest));
+	conn = tcp_hash_lookup(c, af, saddr, daddr,
+			       ntohs(th->source), ntohs(th->dest));
 
 	/* New connection from tap */
 	if (!conn) {
-- 
@@ -524,7 +524,7 @@ static struct iovec	tcp_iov			[UIO_MAXIOV];
 
 #define CONN(idx)		(&(FLOW(idx)->tcp))
 
-/* Table for lookup from remote address, local port, remote port */
+/* Table for lookup from flowside information */
 static flow_sidx_t tc_hash[TCP_HASH_TABLE_SIZE];
 
 static_assert(ARRAY_SIZE(tc_hash) >= FLOW_MAX,
@@ -1074,46 +1074,6 @@ static int tcp_opt_get(const char *opts, size_t len, uint8_t type_find,
 	return -1;
 }
 
-/**
- * tcp_hash_match() - Check if a connection entry matches address and ports
- * @conn:	Connection entry to match against
- * @faddr:	Guest side forwarding address
- * @eport:	Guest side endpoint port
- * @fport:	Guest side forwarding port
- *
- * Return: 1 on match, 0 otherwise
- */
-static int tcp_hash_match(const struct tcp_tap_conn *conn,
-			  const union inany_addr *faddr,
-			  in_port_t eport, in_port_t fport)
-{
-	const struct flowside *tapside = &conn->f.side[TAPSIDE];
-
-	if (inany_equals(&tapside->faddr, faddr) &&
-	    tapside->eport == eport && tapside->fport == fport)
-		return 1;
-
-	return 0;
-}
-
-/**
- * tcp_hash() - Calculate hash value for connection given address and ports
- * @c:		Execution context
- * @faddr:	Guest side forwarding address
- * @eport:	Guest side endpoint port
- * @fport:	Guest side forwarding port
- *
- * Return: hash value, needs to be adjusted for table size
- */
-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);
-
-	inany_siphash_feed(&state, faddr);
-	return siphash_final(&state, 20, (uint64_t)eport << 16 | fport);
-}
-
 /**
  * tcp_conn_hash() - Calculate hash bucket of an existing connection
  * @c:		Execution context
@@ -1124,9 +1084,7 @@ static uint64_t tcp_hash(const struct ctx *c, const union inany_addr *faddr,
 static uint64_t tcp_conn_hash(const struct ctx *c,
 			      const struct tcp_tap_conn *conn)
 {
-	const struct flowside *tapside = &conn->f.side[TAPSIDE];
-
-	return tcp_hash(c, &tapside->faddr, tapside->eport, tapside->fport);
+	return flow_hash(c, IPPROTO_TCP, &conn->f.side[TAPSIDE]);
 }
 
 /**
@@ -1201,25 +1159,26 @@ static void tcp_hash_remove(const struct ctx *c,
  * tcp_hash_lookup() - Look up connection given remote address and ports
  * @c:		Execution context
  * @af:		Address family, AF_INET or AF_INET6
+ * @eaddr:	Guest side endpoint address (guest local address)
  * @faddr:	Guest side forwarding address (guest remote address)
  * @eport:	Guest side endpoint port (guest local port)
  * @fport:	Guest side forwarding port (guest remote port)
  *
  * Return: connection pointer, if found, -ENOENT otherwise
  */
-static struct tcp_tap_conn *tcp_hash_lookup(const struct ctx *c,
-					    sa_family_t af, const void *faddr,
+static struct tcp_tap_conn *tcp_hash_lookup(const struct ctx *c, sa_family_t af,
+					    const void *eaddr, const void *faddr,
 					    in_port_t eport, in_port_t fport)
 {
-	union inany_addr aany;
+	struct flowside fside;
 	union flow *flow;
 	unsigned b;
 
-	inany_from_af(&aany, af, faddr);
+	flowside_from_af(&fside, PIF_TAP, af, faddr, fport, eaddr, eport);
 
-	b = tcp_hash(c, &aany, eport, fport) % TCP_HASH_TABLE_SIZE;
+	b = flow_hash(c, IPPROTO_TCP, &fside) % TCP_HASH_TABLE_SIZE;
 	while ((flow = flow_at_sidx(tc_hash[b])) &&
-	       !tcp_hash_match(&flow->tcp, &aany, eport, fport))
+	       !flowside_eq(&flow->f.side[TAPSIDE], &fside))
 		b = mod_sub(b, 1, TCP_HASH_TABLE_SIZE);
 
 	return &flow->tcp;
@@ -2522,7 +2481,8 @@ int tcp_tap_handler(struct ctx *c, uint8_t pif, sa_family_t af,
 	optlen = MIN(optlen, ((1UL << 4) /* from doff width */ - 6) * 4UL);
 	opts = packet_get(p, idx, sizeof(*th), optlen, NULL);
 
-	conn = tcp_hash_lookup(c, af, daddr, ntohs(th->source), ntohs(th->dest));
+	conn = tcp_hash_lookup(c, af, saddr, daddr,
+			       ntohs(th->source), ntohs(th->dest));
 
 	/* New connection from tap */
 	if (!conn) {
-- 
2.44.0