[net-next,v2] doc: add nf_conntrack sysctl api documentation

I grepped through the code and picked bits about nf_conntrack sysctl api
and put that into one documentation file.

Signed-off-by: Jiri Pirko <jiri@resnulli.us>
---

v1->v2:
processed in changes suggested by Florian Westphal

 Documentation/networking/nf_conntrack-sysctl.txt | 172 +++++++++++++++++++++++
 1 file changed, 172 insertions(+)
 create mode 100644 Documentation/networking/nf_conntrack-sysctl.txt

On Wed, Jan 16, 2013 at 03:56:33PM +0100, Jiri Pirko wrote:
> I grepped through the code and picked bits about nf_conntrack sysctl api
> and put that into one documentation file.

Excellent, I was looking for documentation of some of these values
only yesterday :)
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Hi Jiri,

Thanks for working on this, some comments and suggestions.

On Wed, Jan 16, 2013 at 03:56:33PM +0100, Jiri Pirko wrote:
> I grepped through the code and picked bits about nf_conntrack sysctl api
> and put that into one documentation file.
> 
> Signed-off-by: Jiri Pirko <jiri@resnulli.us>
> ---
> 
> v1->v2:
> processed in changes suggested by Florian Westphal
> 
>  Documentation/networking/nf_conntrack-sysctl.txt | 172 +++++++++++++++++++++++
>  1 file changed, 172 insertions(+)
>  create mode 100644 Documentation/networking/nf_conntrack-sysctl.txt
> 
> diff --git a/Documentation/networking/nf_conntrack-sysctl.txt b/Documentation/networking/nf_conntrack-sysctl.txt
> new file mode 100644
> index 0000000..61b66e6
> --- /dev/null
> +++ b/Documentation/networking/nf_conntrack-sysctl.txt
> @@ -0,0 +1,172 @@
> +/proc/sys/net/netfilter/nf_conntrack_* Variables:
> +
> +nf_conntrack_acct - BOOLEAN
> +	0 - disabled (default)
> +	not 0 - enabled
> +
> +	Enable connection tracking flow accounting.

You can probably these add 64-bits byte and packet counters per flow.

> +
> +nf_conntrack_buckets - INTEGER (read-only)
> +	Size of hash table. Value is computed in nf_conntrack_init_init_net()
> +	and it basically depends on total memory size.

Instead of pointing to the function, you can say that we "use 1/16384
of memory. On i386: 32MB machine has 512 buckets. >= 1GB machines have
16384 as default" (extracted from comment on the source code).

> +
> +nf_conntrack_checksum - BOOLEAN
> +	0 - disabled
> +	not 0 - enabled (default)
> +
> +	Verify checksum of incoming packets.  Packets with bad checksum
> +	will not be considered for connection tracking, i.e. such packets
> +	will be in INVALID state.
> +
> +nf_conntrack_count - INTEGER (read-only)
> +	Number of currently allocated conntracks.

Probably use `flow entries' or simply `flows' instead of conntracks?
I'm familiar with the conntrack term, but the reader may be not.

> +
> +nf_conntrack_events - BOOLEAN
> +	0 - disabled
> +	not 0 - enabled (default)
> +
> +	If this option is enabled, the connection tracking code will
> +	provide userspace with connection tracking events via ctnetlink.
> +
> +nf_conntrack_events_retry_timeout - INTEGER (seconds)
> +	default 15
> +
> +	This option is only relevant when "reliable connection tracking
> +	events" are used.  Normally, ctnetlink is "lossy", i.e. when
> +	userspace listeners can't keep up, events are dropped.
> +
> +	Userspace can request "reliable event mode".  When this mode is
> +	active, the conntrack will only be destroyed after the event was
> +	delivered.  If event delivery fails, the kernel periodically
> +	re-tries to send the event to userspace.
> +
> +	This is the maximum interval the kernel should use when re-trying
> +	to deliver the destroy event.
> +
> +	Higher number means less delivery re-tries (but it will then take
> +	longer for a backlog to be processed).
> +
> +nf_conntrack_expect_max - INTEGER
> +	Maximum size of expectation table.  Default value is computed in
> +	nf_conntrack_expect_init() and depends on nf_conntrack_buckets value.
> +
> +nf_conntrack_frag6_high_thresh - INTEGER
> +	default 262144
> +
> +	Maximum memory used to reassemble IPv6 fragments.  When
> +	nf_conntrack_frag6_high_thresh bytes of memory is allocated for this
> +	purpose, the fragment handler will toss packets until
> +	nf_conntrack_frag6_low_thresh is reached.
> +
> +nf_conntrack_frag6_low_thresh - INTEGER
> +	default 196608
> +
> +	See nf_conntrack_frag6_low_thresh
> +
> +nf_conntrack_frag6_timeout - INTEGER (seconds)
> +	default 60
> +
> +	Time to keep an IPv6 fragment in memory.
> +
> +nf_conntrack_generic_timeout - INTEGER (seconds)
> +	default 600
> +
> +	Default for generic timeout.

You can add here "this refers to layer 4 unknown/unsupported
protocols"

> +
> +nf_conntrack_helper - BOOLEAN
> +	0 - disabled
> +	not 0 - enabled (default)
> +
> +	Enable automatic conntrack helper assignment.
> +
> +nf_conntrack_icmp_timeout - INTEGER (seconds)
> +	default 30
> +
> +	Default for ICMP timeout.
> +
> +nf_conntrack_icmpv6_timeout - INTEGER (seconds)
> +	default 30
> +
> +	Default for ICMP6 timeout.
> +
> +nf_conntrack_log_invalid - INTEGER
> +	0   - disable (default)
> +	1   - log ICMP packets
> +	6   - log TCP packets
> +	17  - log UDP packets
> +	33  - log DCCP packets
> +	41  - log ICMPv6 packets
> +	136 - log UDPLITE packets
> +	255 - log packets of any protocol
> +
> +	Log invalid packets of a type specified by value.
> +
> +nf_conntrack_max - INTEGER
> +	Size of connection tracking table.  Default value is computed in
> +	nf_conntrack_init_init_net() and depends on nf_conntrack_buckets value.

By default is 4 * number of buckets in the hashtable.

> +
> +nf_conntrack_tcp_be_liberal - BOOLEAN
> +	0 - disabled (default)
> +	not 0 - enabled
> +
> +	Be conservative in what you do, be liberal in what you accept from others.
> +	If it's non-zero, we mark only out of window RST segments as INVALID.
> +
> +nf_conntrack_tcp_loose - BOOLEAN
> +	0 - disabled
> +	not 0 - enabled (default)
> +
> +	If it is set to zero, we disable picking up already established
> +	connections.
> +
> +nf_conntrack_tcp_max_retrans - INTEGER
> +	default 3
> +
> +	Max number of the retransmitted packets without receiving an
> +	(acceptable) ACK from the destination.  If this number is reached,
> +	a shorter timer will be started.
> +
> +nf_conntrack_tcp_timeout_close - INTEGER (seconds)
> +	default 10
> +
> +nf_conntrack_tcp_timeout_close_wait - INTEGER (seconds)
> +	default 60
> +
> +nf_conntrack_tcp_timeout_established - INTEGER (seconds)
> +	default 432000 (5 days)
> +
> +nf_conntrack_tcp_timeout_fin_wait - INTEGER (seconds)
> +	default 120
> +
> +nf_conntrack_tcp_timeout_last_ack - INTEGER (seconds)
> +	default 30
> +
> +nf_conntrack_tcp_timeout_max_retrans - INTEGER (seconds)
> +	default 300
> +
> +nf_conntrack_tcp_timeout_syn_recv - INTEGER (seconds)
> +	default 60
> +
> +nf_conntrack_tcp_timeout_syn_sent - INTEGER (seconds)
> +	default 120
> +
> +nf_conntrack_tcp_timeout_time_wait - INTEGER (seconds)
> +	default 120
> +
> +nf_conntrack_tcp_timeout_unacknowledged - INTEGER (seconds)
> +	default 300
> +
> +nf_conntrack_timestamp - BOOLEAN
> +	0 - disabled (default)
> +	not 0 - enabled
> +
> +	Enable connection tracking flow timestamping.
> +
> +nf_conntrack_udp_timeout - INTEGER (seconds)
> +	default 30
> +
> +nf_conntrack_udp_timeout_stream2 - INTEGER (seconds)
> +	default 180
> +
> +	This extended timeout will be used in case there is an UDP stream
> +	detected.
> -- 
> 1.8.1
> 
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