[IPVS]: Add sysctl documentation

* Derived from http://www.linuxvirtualserver.org/docs/sysctl.html, v1.4
  maintained by Wensong Zhang

* Adjusted preample to match ip-sysctl.txt

* Sorted options into alphabetical order

* Added expire_quiescent_template

* Removed timeout_* which are no longer present

* Incoporated doc/debug-levels.txt from IPVS source tree into
  description of ipvs_debug

* Minor spelling fixes

* Further editing more than welcome

Signed-Off-By: Horms <horms@verge.net.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/ipvs-sysctl.txt

@@ -0,0 +1,143 @@
+/proc/sys/net/ipv4/vs/* Variables:
+
+am_droprate - INTEGER
+        default 10
+
+        It sets the always mode drop rate, which is used in the mode 3
+        of the drop_rate defense.
+
+amemthresh - INTEGER
+        default 1024
+
+        It sets the available memory threshold (in pages), which is
+        used in the automatic modes of defense. When there is no
+        enough available memory, the respective strategy will be
+        enabled and the variable is automatically set to 2, otherwise
+        the strategy is disabled and the variable is  set  to 1.
+
+cache_bypass - BOOLEAN
+        0 - disabled (default)
+        not 0 - enabled
+
+        If it is enabled, forward packets to the original destination
+        directly when no cache server is available and destination
+        address is not local (iph->daddr is RTN_UNICAST). It is mostly
+        used in transparent web cache cluster.
+
+debug_level - INTEGER
+	0          - transmission error messages (default)
+	1          - non-fatal error messages
+	2          - configuration
+	3          - destination trash
+	4          - drop entry
+	5          - service lookup
+	6          - scheduling
+	7          - connection new/expire, lookup and synchronization
+	8          - state transition
+	9          - binding destination, template checks and applications
+	10         - IPVS packet transmission
+	11         - IPVS packet handling (ip_vs_in/ip_vs_out)
+	12 or more - packet traversal
+
+	Only available when IPVS is compiled with the CONFIG_IPVS_DEBUG
+
+	Higher debugging levels include the messages for lower debugging
+	levels, so setting debug level 2, includes level 0, 1 and 2
+	messages. Thus, logging becomes more and more verbose the higher
+	the level.
+
+drop_entry - INTEGER
+        0  - disabled (default)
+
+        The drop_entry defense is to randomly drop entries in the
+        connection hash table, just in order to collect back some
+        memory for new connections. In the current code, the
+        drop_entry procedure can be activated every second, then it
+        randomly scans 1/32 of the whole and drops entries that are in
+        the SYN-RECV/SYNACK state, which should be effective against
+        syn-flooding attack.
+
+        The valid values of drop_entry are from 0 to 3, where 0 means
+        that this strategy is always disabled, 1 and 2 mean automatic
+        modes (when there is no enough available memory, the strategy
+        is enabled and the variable is automatically set to 2,
+        otherwise the strategy is disabled and the variable is set to
+        1), and 3 means that that the strategy is always enabled.
+
+drop_packet - INTEGER
+        0  - disabled (default)
+
+        The drop_packet defense is designed to drop 1/rate packets
+        before forwarding them to real servers. If the rate is 1, then
+        drop all the incoming packets.
+
+        The value definition is the same as that of the drop_entry. In
+        the automatic mode, the rate is determined by the follow
+        formula: rate = amemthresh / (amemthresh - available_memory)
+        when available memory is less than the available memory
+        threshold. When the mode 3 is set, the always mode drop rate
+        is controlled by the /proc/sys/net/ipv4/vs/am_droprate.
+
+expire_nodest_conn - BOOLEAN
+        0 - disabled (default)
+        not 0 - enabled
+
+        The default value is 0, the load balancer will silently drop
+        packets when its destination server is not available. It may
+        be useful, when user-space monitoring program deletes the
+        destination server (because of server overload or wrong
+        detection) and add back the server later, and the connections
+        to the server can continue.
+
+        If this feature is enabled, the load balancer will expire the
+        connection immediately when a packet arrives and its
+        destination server is not available, then the client program
+        will be notified that the connection is closed. This is
+        equivalent to the feature some people requires to flush
+        connections when its destination is not available.
+
+expire_quiescent_template - BOOLEAN
+	0 - disabled (default)
+	not 0 - enabled
+
+	When set to a non-zero value, the load balancer will expire
+	persistent templates when the destination server is quiescent.
+	This may be useful, when a user makes a destination server
+	quiescent by setting its weight to 0 and it is desired that
+	subsequent otherwise persistent connections are sent to a
+	different destination server.  By default new persistent
+	connections are allowed to quiescent destination servers.
+
+	If this feature is enabled, the load balancer will expire the
+	persistence template if it is to be used to schedule a new
+	connection and the destination server is quiescent.
+
+nat_icmp_send - BOOLEAN
+        0 - disabled (default)
+        not 0 - enabled
+
+        It controls sending icmp error messages (ICMP_DEST_UNREACH)
+        for VS/NAT when the load balancer receives packets from real
+        servers but the connection entries don't exist.
+
+secure_tcp - INTEGER
+        0  - disabled (default)
+
+        The secure_tcp defense is to use a more complicated state
+        transition table and some possible short timeouts of each
+        state. In the VS/NAT, it delays the entering the ESTABLISHED
+        until the real server starts to send data and ACK packet
+        (after 3-way handshake).
+
+        The value definition is the same as that of drop_entry or
+        drop_packet.
+
+sync_threshold - INTEGER
+        default 3
+
+        It sets synchronization threshold, which is the minimum number
+        of incoming packets that a connection needs to receive before
+        the connection will be synchronized. A connection will be
+        synchronized, every time the number of its incoming packets
+        modulus 50 equals the threshold. The range of the threshold is
+        from 0 to 49.