Linux Ethernet Bonding Driver HOWTO
 
-               Latest update: 12 November 2007
+               Latest update: 23 September 2009
 
 Initial release : Thomas Davis <tadavis at lbl.gov>
 Corrections, HA extensions : 2000/10/03-15 :
 
        The primary option is only valid for active-backup mode.
 
+primary_reselect
+
+       Specifies the reselection policy for the primary slave.  This
+       affects how the primary slave is chosen to become the active slave
+       when failure of the active slave or recovery of the primary slave
+       occurs.  This option is designed to prevent flip-flopping between
+       the primary slave and other slaves.  Possible values are:
+
+       always or 0 (default)
+
+               The primary slave becomes the active slave whenever it
+               comes back up.
+
+       better or 1
+
+               The primary slave becomes the active slave when it comes
+               back up, if the speed and duplex of the primary slave is
+               better than the speed and duplex of the current active
+               slave.
+
+       failure or 2
+
+               The primary slave becomes the active slave only if the
+               current active slave fails and the primary slave is up.
+
+       The primary_reselect setting is ignored in two cases:
+
+               If no slaves are active, the first slave to recover is
+               made the active slave.
+
+               When initially enslaved, the primary slave is always made
+               the active slave.
+
+       Changing the primary_reselect policy via sysfs will cause an
+       immediate selection of the best active slave according to the new
+       policy.  This may or may not result in a change of the active
+       slave, depending upon the circumstances.
+
+       This option was added for bonding version 3.6.0.
+
 updelay
 
        Specifies the time, in milliseconds, to wait before enabling a
 
 static int use_carrier = 1;
 static char *mode;
 static char *primary;
+static char *primary_reselect;
 static char *lacp_rate;
 static char *ad_select;
 static char *xmit_hash_policy;
                       "6 for balance-alb");
 module_param(primary, charp, 0);
 MODULE_PARM_DESC(primary, "Primary network device to use");
+module_param(primary_reselect, charp, 0);
+MODULE_PARM_DESC(primary_reselect, "Reselect primary slave "
+                                  "once it comes up; "
+                                  "0 for always (default), "
+                                  "1 for only if speed of primary is "
+                                  "better, "
+                                  "2 for only on active slave "
+                                  "failure");
 module_param(lacp_rate, charp, 0);
 MODULE_PARM_DESC(lacp_rate, "LACPDU tx rate to request from 802.3ad partner "
                            "(slow/fast)");
 {      NULL,                   -1},
 };
 
+const struct bond_parm_tbl pri_reselect_tbl[] = {
+{      "always",               BOND_PRI_RESELECT_ALWAYS},
+{      "better",               BOND_PRI_RESELECT_BETTER},
+{      "failure",              BOND_PRI_RESELECT_FAILURE},
+{      NULL,                   -1},
+};
+
 struct bond_parm_tbl ad_select_tbl[] = {
 {      "stable",       BOND_AD_STABLE},
 {      "bandwidth",    BOND_AD_BANDWIDTH},
 
 }
 
+static bool bond_should_change_active(struct bonding *bond)
+{
+       struct slave *prim = bond->primary_slave;
+       struct slave *curr = bond->curr_active_slave;
+
+       if (!prim || !curr || curr->link != BOND_LINK_UP)
+               return true;
+       if (bond->force_primary) {
+               bond->force_primary = false;
+               return true;
+       }
+       if (bond->params.primary_reselect == BOND_PRI_RESELECT_BETTER &&
+           (prim->speed < curr->speed ||
+            (prim->speed == curr->speed && prim->duplex <= curr->duplex)))
+               return false;
+       if (bond->params.primary_reselect == BOND_PRI_RESELECT_FAILURE)
+               return false;
+       return true;
+}
 
 /**
  * find_best_interface - select the best available slave to be the active one
        }
 
        if ((bond->primary_slave) &&
-           bond->primary_slave->link == BOND_LINK_UP) {
+           bond->primary_slave->link == BOND_LINK_UP &&
+           bond_should_change_active(bond)) {
                new_active = bond->primary_slave;
        }
 
 
        if (USES_PRIMARY(bond->params.mode) && bond->params.primary[0]) {
                /* if there is a primary slave, remember it */
-               if (strcmp(bond->params.primary, new_slave->dev->name) == 0)
+               if (strcmp(bond->params.primary, new_slave->dev->name) == 0) {
                        bond->primary_slave = new_slave;
+                       bond->force_primary = true;
+               }
        }
 
        write_lock_bh(&bond->curr_slave_lock);
        }
 
        if (USES_PRIMARY(bond->params.mode)) {
-               seq_printf(seq, "Primary Slave: %s\n",
+               seq_printf(seq, "Primary Slave: %s",
                           (bond->primary_slave) ?
                           bond->primary_slave->dev->name : "None");
+               if (bond->primary_slave)
+                       seq_printf(seq, " (primary_reselect %s)",
+                  pri_reselect_tbl[bond->params.primary_reselect].modename);
 
-               seq_printf(seq, "Currently Active Slave: %s\n",
+               seq_printf(seq, "\nCurrently Active Slave: %s\n",
                           (curr) ? curr->dev->name : "None");
        }
 
 
 static int bond_check_params(struct bond_params *params)
 {
-       int arp_validate_value, fail_over_mac_value;
+       int arp_validate_value, fail_over_mac_value, primary_reselect_value;
 
        /*
         * Convert string parameters.
                primary = NULL;
        }
 
+       if (primary && primary_reselect) {
+               primary_reselect_value = bond_parse_parm(primary_reselect,
+                                                        pri_reselect_tbl);
+               if (primary_reselect_value == -1) {
+                       pr_err(DRV_NAME
+                              ": Error: Invalid primary_reselect \"%s\"\n",
+                              primary_reselect ==
+                                       NULL ? "NULL" : primary_reselect);
+                       return -EINVAL;
+               }
+       } else {
+               primary_reselect_value = BOND_PRI_RESELECT_ALWAYS;
+       }
+
        if (fail_over_mac) {
                fail_over_mac_value = bond_parse_parm(fail_over_mac,
                                                      fail_over_mac_tbl);
        params->use_carrier = use_carrier;
        params->lacp_fast = lacp_fast;
        params->primary[0] = 0;
+       params->primary_reselect = primary_reselect_value;
        params->fail_over_mac = fail_over_mac_value;
 
        if (primary) {
 
 static DEVICE_ATTR(primary, S_IRUGO | S_IWUSR,
                   bonding_show_primary, bonding_store_primary);
 
+/*
+ * Show and set the primary_reselect flag.
+ */
+static ssize_t bonding_show_primary_reselect(struct device *d,
+                                            struct device_attribute *attr,
+                                            char *buf)
+{
+       struct bonding *bond = to_bond(d);
+
+       return sprintf(buf, "%s %d\n",
+                      pri_reselect_tbl[bond->params.primary_reselect].modename,
+                      bond->params.primary_reselect);
+}
+
+static ssize_t bonding_store_primary_reselect(struct device *d,
+                                             struct device_attribute *attr,
+                                             const char *buf, size_t count)
+{
+       int new_value, ret = count;
+       struct bonding *bond = to_bond(d);
+
+       if (!rtnl_trylock())
+               return restart_syscall();
+
+       new_value = bond_parse_parm(buf, pri_reselect_tbl);
+       if (new_value < 0)  {
+               pr_err(DRV_NAME
+                      ": %s: Ignoring invalid primary_reselect value %.*s.\n",
+                      bond->dev->name,
+                      (int) strlen(buf) - 1, buf);
+               ret = -EINVAL;
+               goto out;
+       }
+
+       bond->params.primary_reselect = new_value;
+       pr_info(DRV_NAME ": %s: setting primary_reselect to %s (%d).\n",
+               bond->dev->name, pri_reselect_tbl[new_value].modename,
+               new_value);
+
+       read_lock(&bond->lock);
+       write_lock_bh(&bond->curr_slave_lock);
+       bond_select_active_slave(bond);
+       write_unlock_bh(&bond->curr_slave_lock);
+       read_unlock(&bond->lock);
+out:
+       rtnl_unlock();
+       return ret;
+}
+static DEVICE_ATTR(primary_reselect, S_IRUGO | S_IWUSR,
+                  bonding_show_primary_reselect,
+                  bonding_store_primary_reselect);
+
 /*
  * Show and set the use_carrier flag.
  */
        &dev_attr_num_unsol_na.attr,
        &dev_attr_miimon.attr,
        &dev_attr_primary.attr,
+       &dev_attr_primary_reselect.attr,
        &dev_attr_use_carrier.attr,
        &dev_attr_active_slave.attr,
        &dev_attr_mii_status.attr,
 
 #include "bond_3ad.h"
 #include "bond_alb.h"
 
-#define DRV_VERSION    "3.5.0"
-#define DRV_RELDATE    "November 4, 2008"
+#define DRV_VERSION    "3.6.0"
+#define DRV_RELDATE    "September 26, 2009"
 #define DRV_NAME       "bonding"
 #define DRV_DESCRIPTION        "Ethernet Channel Bonding Driver"
 
        int lacp_fast;
        int ad_select;
        char primary[IFNAMSIZ];
+       int primary_reselect;
        __be32 arp_targets[BOND_MAX_ARP_TARGETS];
 };
 
        struct   slave *curr_active_slave;
        struct   slave *current_arp_slave;
        struct   slave *primary_slave;
+       bool     force_primary;
        s32      slave_cnt; /* never change this value outside the attach/detach wrappers */
        rwlock_t lock;
        rwlock_t curr_slave_lock;
                || bond->params.mode == BOND_MODE_ALB;
 }
 
+#define BOND_PRI_RESELECT_ALWAYS       0
+#define BOND_PRI_RESELECT_BETTER       1
+#define BOND_PRI_RESELECT_FAILURE      2
+
 #define BOND_FOM_NONE                  0
 #define BOND_FOM_ACTIVE                        1
 #define BOND_FOM_FOLLOW                        2
 extern const struct bond_parm_tbl xmit_hashtype_tbl[];
 extern const struct bond_parm_tbl arp_validate_tbl[];
 extern const struct bond_parm_tbl fail_over_mac_tbl[];
+extern const struct bond_parm_tbl pri_reselect_tbl[];
 extern struct bond_parm_tbl ad_select_tbl[];
 
 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)