bonding: Implement user key part of port_key in an AD system.

The port key has three components - user-key, speed-part, and duplex-part.
The LSBit is for the duplex-part, next 5 bits are for the speed while the
remaining 10 bits are the user defined key bits. Get these 10 bits
from the user-space (through the SysFs interface) and use it to form the
admin port-key. Allowed range for the user-key is 0 - 1023 (10 bits). If
it is not provided then use zero for the user-key-bits (default).

It can set using following example code -

   # modprobe bonding mode=4
   # usr_port_key=$(( RANDOM & 0x3FF ))
   # echo $usr_port_key > /sys/class/net/bond0/bonding/ad_user_port_key
   # echo +eth1 > /sys/class/net/bond0/bonding/slaves
   ...
   # ip link set bond0 up

Signed-off-by: Mahesh Bandewar <maheshb@google.com>
Reviewed-by: Nikolay Aleksandrov <nikolay@redhat.com>
[jt: * fixed up style issues reported by checkpatch
     * fixed up context from change in ad_actor_sys_prio patch]
Signed-off-by: Jonathan Toppins <jtoppins@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_sysfs.c

@@ -721,6 +721,20 @@ static ssize_t bonding_show_ad_actor_system(struct device *d,
 static DEVICE_ATTR(ad_actor_system, S_IRUGO | S_IWUSR,
 		   bonding_show_ad_actor_system, bonding_sysfs_store_option);
 
+static ssize_t bonding_show_ad_user_port_key(struct device *d,
+					     struct device_attribute *attr,
+					     char *buf)
+{
+	struct bonding *bond = to_bond(d);
+
+	if (BOND_MODE(bond) == BOND_MODE_8023AD)
+		return sprintf(buf, "%hu\n", bond->params.ad_user_port_key);
+
+	return 0;
+}
+static DEVICE_ATTR(ad_user_port_key, S_IRUGO | S_IWUSR,
+		   bonding_show_ad_user_port_key, bonding_sysfs_store_option);
+
 static struct attribute *per_bond_attrs[] = {
 	&dev_attr_slaves.attr,
 	&dev_attr_mode.attr,
@@ -756,6 +770,7 @@ static struct attribute *per_bond_attrs[] = {
 	&dev_attr_tlb_dynamic_lb.attr,
 	&dev_attr_ad_actor_sys_prio.attr,
 	&dev_attr_ad_actor_system.attr,
+	&dev_attr_ad_user_port_key.attr,
 	NULL,
 };