ipvs: improved SH fallback strategy

}

/* As ip_vs_sh_get, but with fallback if selected server is unavailable */

/* As ip_vs_sh_get, but with fallback if selected server is unavailable

 *

 * The fallback strategy loops around the table starting from a "random"

 * point (in fact, it is chosen to be the original hash value to make the

 * algorithm deterministic) to find a new server.

 */

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;

	unsigned int offset, roffset;

	unsigned int hash, ihash;

	struct ip_vs_dest *dest;

	/* first try the dest it's supposed to go to */

	ihash = ip_vs_sh_hashkey(svc->af, addr, port, 0);

	dest = rcu_dereference(s->buckets[ihash].dest);

	if (!dest)

		return NULL;

	if (!is_unavailable(dest))

		return dest;

	IP_VS_DBG_BUF(6, "SH: selected unavailable server %s:%d, reselecting",

		      IP_VS_DBG_ADDR(svc->af, &dest->addr), ntohs(dest->port));

	/* if the original dest is unavailable, loop around the table

	 * starting from ihash to find a new dest

	 */

	for (offset = 0; offset < IP_VS_SH_TAB_SIZE; offset++) {

		hash = ip_vs_sh_hashkey(svc->af, addr, port, offset);

		roffset = (offset + ihash) % IP_VS_SH_TAB_SIZE;

		hash = ip_vs_sh_hashkey(svc->af, addr, port, roffset);

		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

		if (!is_unavailable(dest))

			return dest;

		IP_VS_DBG_BUF(6, "SH: selected unavailable "

			      "server %s:%d (offset %d), reselecting",

			      IP_VS_DBG_ADDR(svc->af, &dest->addr),

			      ntohs(dest->port), roffset);

	}

	return NULL;