[RESEND PATCH net-next v3 5/5] ipv6: ioam: Documentation for new IOAM sysctls

[Justin Iurman <justin.iurman@uliege.be>]

Add documentation for new IOAM sysctls:
 - ioam6_id: a namespace sysctl
 - ioam6_enabled and ioam6_id: two per-interface sysctls

Example of IOAM configuration based on the following simple topology:

 _____              _____              _____
|     | eth0  eth0 |     | eth1  eth0 |     |
|  A  |.----------.|  B  |.----------.|  C  |
|_____|            |_____|            |_____|

1) Node and interface IDs can be configured for IOAM:

  # IOAM ID of A = 1, IOAM ID of A.eth0 = 11
  (A) sysctl -w net.ipv6.ioam6_id=1
  (A) sysctl -w net.ipv6.conf.eth0.ioam6_id=11

  # IOAM ID of B = 2, IOAM ID of B.eth0 = 21, IOAM ID of B.eth1 = 22
  (B) sysctl -w net.ipv6.ioam6_id=2
  (B) sysctl -w net.ipv6.conf.eth0.ioam6_id=21
  (B) sysctl -w net.ipv6.conf.eth1.ioam6_id=22

  # IOAM ID of C = 3, IOAM ID of C.eth0 = 31
  (C) sysctl -w net.ipv6.ioam6_id=3
  (C) sysctl -w net.ipv6.conf.eth0.ioam6_id=31

2) Each node can be configured to form an IOAM domain. For instance,
   we allow IOAM from A to C, i.e. enable IOAM on ingress for B.eth0
   and C.eth0:

  (B) sysctl -w net.ipv6.conf.eth0.ioam6_enabled=1
  (C) sysctl -w net.ipv6.conf.eth0.ioam6_enabled=1

3) An IOAM domain (e.g. ID=123) is defined and made known to each node:

  (A) ip ioam namespace add 123
  (B) ip ioam namespace add 123
  (C) ip ioam namespace add 123

4) Finally, an IOAM Pre-allocated Trace can be inserted in traffic sent
   by A when C (e.g. db02::2) is the destination:

  (A) ip -6 route add db02::2/128 encap ioam6 trace type 0x800000 ns 123
      size 12 dev eth0

Signed-off-by: Justin Iurman <justin.iurman@uliege.be>
---
 Documentation/networking/ioam6-sysctl.rst | 20 ++++++++++++++++++++
 Documentation/networking/ip-sysctl.rst    |  5 +++++
 2 files changed, 25 insertions(+)
 create mode 100644 Documentation/networking/ioam6-sysctl.rst

diff --git a/Documentation/networking/ioam6-sysctl.rst b/Documentation/networking/ioam6-sysctl.rst
new file mode 100644
index 000000000000..37a9b4e731a0
--- /dev/null
+++ b/Documentation/networking/ioam6-sysctl.rst
@@ -0,0 +1,20 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=====================
+IOAM6 Sysfs variables
+=====================
+
+
+/proc/sys/net/conf/<iface>/ioam6_* variables:
+=============================================
+
+ioam6_enabled - BOOL
+	Accept or ignore IPv6 IOAM options for ingress on this interface.
+
+	* 0 - disabled (default)
+	* not 0 - enabled
+
+ioam6_id - INTEGER
+	Define the IOAM id of this interface.
+
+	Default is 0.
diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index a5c250044500..d472c4f0972e 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -1901,6 +1901,11 @@ fib_notify_on_flag_change - INTEGER
         - 1 - Emit notifications.
         - 2 - Emit notifications only for RTM_F_OFFLOAD_FAILED flag change.
 
+ioam6_id - INTEGER
+	Define the IOAM id of this node.
+
+	Default: 0
+
 IPv6 Fragmentation:
 
 ip6frag_high_thresh - INTEGER
-- 
2.17.1