[PATCH 3/3] NET: Generic network statistics/estimator documentation

[Thomas Graf <tgraf@suug.ch>]

Documentation of generic network statistics and estimator API.

Signed-off-by: Thomas Graf <tgraf@suug.ch>


--- linux-2.6.9-rc3.orig/Documentation/networking/gen_stats.txt	1970-01-01 01:00:00.000000000 +0100
+++ linux-2.6.9-rc3/Documentation/networking/gen_stats.txt	2004-10-03 22:33:57.000000000 +0200
@@ -0,0 +1,117 @@
+Generic networking statistics for netlink users
+======================================================================
+
+Statistic counters are grouped into structs:
+
+Struct               TLV type              Description
+----------------------------------------------------------------------
+gnet_stats_basic     TCA_STATS_BASIC       Basic statistics
+gnet_stats_rate_est  TCA_STATS_RATE_EST    Rate estimator
+gnet_stats_queue     TCA_STATS_QUEUE       Queue statistics
+none                 TCA_STATS_APP         Application specific
+
+
+Collecting:
+-----------
+
+Declare the statistic structs you need:
+struct mystruct {
+	struct gnet_stats_basic	bstats;
+	struct gnet_stats_queue	qstats;
+	...
+};
+
+Update statistics:
+mystruct->tstats.packet++;
+mystruct->qstats.backlog += skb->pkt_len;
+
+
+Export to userspace (Dump):
+---------------------------
+
+my_dumping_routine(struct sk_buff *skb, ...)
+{
+	struct gnet_dump dump;
+
+	if (gnet_stats_start_copy(skb, TCA_STATS2, &mystruct->lock, &dump) < 0)
+		goto rtattr_failure;
+
+	if (gnet_stats_copy_basic(&dump, &mystruct->bstats) < 0 ||
+	    gnet_stats_copy_queue(&dump, &mystruct->qstats) < 0 ||
+		gnet_stats_copy_app(&dump, &xstats, sizeof(xstats)) < 0)
+		goto rtattr_failure;
+
+	if (gnet_stats_finish_copy(&dump) < 0)
+		goto rtattr_failure;
+	...
+}
+
+TCA_STATS/TCA_XSTATS backward compatibility:
+--------------------------------------------
+
+Prior users of struct tc_stats and xstats can maintain backward
+compatibility by calling the compat wrappers to keep providing the
+existing TLV types.
+
+my_dumping_routine(struct sk_buff *skb, ...)
+{
+    if (gnet_stats_start_copy_compat(skb, TCA_STATS2, TCA_STATS,
+		TCA_XSTATS, &mystruct->lock, &dump) < 0)
+		goto rtattr_failure;
+	...
+}
+
+A struct tc_stats will be filled out during gnet_stats_copy_* calls
+and appended to the skb. TCA_XSTATS is provided if gnet_stats_copy_app
+was called.
+
+
+Locking:
+--------
+
+Locks are taken before writing and released once all statistics have
+been written. Locks are always released in case of an error. You
+are responsible for making sure that the lock is initialized.
+
+
+Rate Estimator:
+--------------
+
+0) Prepare an estimator attribute. Most likely this would be in user
+   space. The value of this TLV should contain a tc_estimator structure.
+   As usual, such a TLV nees to be 32 bit aligned and therefore the
+   length needs to be appropriately set etc. The estimator interval
+   and ewma log need to be converted to the appropriate values.
+   tc_estimator.c::tc_setup_estimator() is advisable to be used as the
+   conversion routine. It does a few clever things. It takes a time
+   interval in microsecs, a time constant also in microsecs and a struct
+   tc_estimator to  be populated. The returned tc_estimator can be
+   transported to the kernel.  Transfer such a structure in a TLV of type
+   TCA_RATE to your code in the kernel.
+
+In the kernel when setting up:
+1) make sure you have basic stats and rate stats setup first.
+2) make sure you have initialized stats lock that is used to setup such
+   stats.
+3) Now initialize a new estimator:
+
+   int ret = gen_new_estimator(my_basicstats,my_rate_est_stats,
+       mystats_lock, attr_with_tcestimator_struct);
+
+   if ret == 0
+       success
+   else
+       failed
+
+From now on, everytime you dump my_rate_est_stats it will contain
+uptodate info.
+
+Once you are done, call gen_kill_estimator(my_basicstats,
+my_rate_est_stats) Make sure that my_basicstats and my_rate_est_stats
+are still valid (i.e still exist) at the time of making this call.
+
+
+Authors:
+--------
+Thomas Graf <tgraf@suug.ch>
+Jamal Hadi Salim <hadi@cyberus.ca>