ipvs: SH fallback and L4 hashing

By default the SH scheduler rejects connections that are hashed onto a
realserver of weight 0.  This patch adds a flag to make SH choose a
different realserver in this case, instead of rejecting the connection.

The patch also adds a flag to make SH include the source port (TCP, UDP,
SCTP) in the hash as well as the source address.  This basically allows
for deterministic round-robin load balancing (i.e., where any director
in a cluster of directors with identical config will send the same
packet the same way).

The flags are service flags (IP_VS_SVC_F_SCHED*) so that these options
can be set per service.  They are set using a new option to ipvsadm.

Signed-off-by: Alexander Frolkin <avf@eldamar.org.uk>
Acked-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Simon Horman <horms@verge.net.au>

1 files changed, 85 insertions, 15 deletions

diff --git a/net/netfilter/ipvs/ip_vs_sh.c b/net/netfilter/ipvs/ip_vs_sh.c
index e0d5d1653566..f16c027df15b 100644
--- a/net/netfilter/ipvs/ip_vs_sh.c
+++ b/net/netfilter/ipvs/ip_vs_sh.c
@@ -48,6 +48,10 @@
 
 #include <net/ip_vs.h>
 
+#include <net/tcp.h>
+#include <linux/udp.h>
+#include <linux/sctp.h>
+
 
 /*
  *      IPVS SH bucket
@@ -71,10 +75,19 @@ struct ip_vs_sh_state {
         struct ip_vs_sh_bucket          buckets[IP_VS_SH_TAB_SIZE];
 };
 
+/* Helper function to determine if server is unavailable */
+static inline bool is_unavailable(struct ip_vs_dest *dest)
+{
+        return atomic_read(&dest->weight) <= 0 ||
+               dest->flags & IP_VS_DEST_F_OVERLOAD;
+}
+
 /*
  *      Returns hash value for IPVS SH entry
  */
-static inline unsigned int ip_vs_sh_hashkey(int af, const union nf_inet_addr *addr)
+static inline unsigned int
+ip_vs_sh_hashkey(int af, const union nf_inet_addr *addr,
+                 __be16 port, unsigned int offset)
 {
         __be32 addr_fold = addr->ip;
 
@@ -83,7 +96,8 @@ static inline unsigned int ip_vs_sh_hashkey(int af, const union nf_inet_addr *ad
                 addr_fold = addr->ip6[0]^addr->ip6[1]^
                             addr->ip6[2]^addr->ip6[3];
 #endif
-        return (ntohl(addr_fold)*2654435761UL) & IP_VS_SH_TAB_MASK;
+        return (offset + (ntohs(port) + ntohl(addr_fold))*2654435761UL) &
+                IP_VS_SH_TAB_MASK;
 }
 
 
@@ -91,12 +105,42 @@ static inline unsigned int ip_vs_sh_hashkey(int af, const union nf_inet_addr *ad
  *      Get ip_vs_dest associated with supplied parameters.
  */
 static inline struct ip_vs_dest *
-ip_vs_sh_get(int af, struct ip_vs_sh_state *s, const union nf_inet_addr *addr)
+ip_vs_sh_get(struct ip_vs_service *svc, struct ip_vs_sh_state *s,
+             const union nf_inet_addr *addr, __be16 port)
 {
-        return rcu_dereference(s->buckets[ip_vs_sh_hashkey(af, addr)].dest);
+        unsigned int hash = ip_vs_sh_hashkey(svc->af, addr, port, 0);
+        struct ip_vs_dest *dest = rcu_dereference(s->buckets[hash].dest);
+
+        return (!dest || is_unavailable(dest)) ? NULL : dest;
 }
 
 
+/* As ip_vs_sh_get, but with fallback if selected server is unavailable */
+static inline struct ip_vs_dest *
+ip_vs_sh_get_fallback(struct ip_vs_service *svc, struct ip_vs_sh_state *s,
+                      const union nf_inet_addr *addr, __be16 port)
+{
+        unsigned int offset;
+        unsigned int hash;
+        struct ip_vs_dest *dest;
+
+        for (offset = 0; offset < IP_VS_SH_TAB_SIZE; offset++) {
+                hash = ip_vs_sh_hashkey(svc->af, addr, port, offset);
+                dest = rcu_dereference(s->buckets[hash].dest);
+                if (!dest)
+                        break;
+                if (is_unavailable(dest))
+                        IP_VS_DBG_BUF(6, "SH: selected unavailable server "
+                                      "%s:%d (offset %d)",
+                                      IP_VS_DBG_ADDR(svc->af, &dest->addr),
+                                      ntohs(dest->port), offset);
+                else
+                        return dest;
+        }
+
+        return NULL;
+}
+
 /*
  *      Assign all the hash buckets of the specified table with the service.
  */
@@ -213,13 +257,33 @@ static int ip_vs_sh_dest_changed(struct ip_vs_service *svc,
 }
 
 
-/*
- *      If the dest flags is set with IP_VS_DEST_F_OVERLOAD,
- *      consider that the server is overloaded here.
- */
-static inline int is_overloaded(struct ip_vs_dest *dest)
+/* Helper function to get port number */
+static inline __be16
+ip_vs_sh_get_port(const struct sk_buff *skb, struct ip_vs_iphdr *iph)
 {
-        return dest->flags & IP_VS_DEST_F_OVERLOAD;
+        __be16 port;
+        struct tcphdr _tcph, *th;
+        struct udphdr _udph, *uh;
+        sctp_sctphdr_t _sctph, *sh;
+
+        switch (iph->protocol) {
+        case IPPROTO_TCP:
+                th = skb_header_pointer(skb, iph->len, sizeof(_tcph), &_tcph);
+                port = th->source;
+                break;
+        case IPPROTO_UDP:
+                uh = skb_header_pointer(skb, iph->len, sizeof(_udph), &_udph);
+                port = uh->source;
+                break;
+        case IPPROTO_SCTP:
+                sh = skb_header_pointer(skb, iph->len, sizeof(_sctph), &_sctph);
+                port = sh->source;
+                break;
+        default:
+                port = 0;
+        }
+
+        return port;
 }
 
 
@@ -232,15 +296,21 @@ ip_vs_sh_schedule(struct ip_vs_service *svc, const struct sk_buff *skb,
 {
         struct ip_vs_dest *dest;
         struct ip_vs_sh_state *s;
+        __be16 port = 0;
 
         IP_VS_DBG(6, "ip_vs_sh_schedule(): Scheduling...\n");
 
+        if (svc->flags & IP_VS_SVC_F_SCHED_SH_PORT)
+                port = ip_vs_sh_get_port(skb, iph);
+
         s = (struct ip_vs_sh_state *) svc->sched_data;
-        dest = ip_vs_sh_get(svc->af, s, &iph->saddr);
-        if (!dest
-            || !(dest->flags & IP_VS_DEST_F_AVAILABLE)
-            || atomic_read(&dest->weight) <= 0
-            || is_overloaded(dest)) {
+
+        if (svc->flags & IP_VS_SVC_F_SCHED_SH_FALLBACK)
+                dest = ip_vs_sh_get_fallback(svc, s, &iph->saddr, port);
+        else
+                dest = ip_vs_sh_get(svc, s, &iph->saddr, port);
+
+        if (!dest) {
                 ip_vs_scheduler_err(svc, "no destination available");
                 return NULL;
         }