mpls: Add a sysctl to control the size of the mpls label table

This sysctl gives two benefits.  By defaulting the table size to 0
mpls even when compiled in and enabled defaults to not forwarding
any packets.  This prevents unpleasant surprises for users.

The other benefit is that as mpls labels are allocated locally a dense
table a small dense label table may be used which saves memory and
is extremely simple and efficient to implement.

This sysctl allows userspace to choose the restrictions on the label
table size userspace applications need to cope with.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 20 insertions, 0 deletions

diff --git a/Documentation/networking/mpls-sysctl.txt b/Documentation/networking/mpls-sysctl.txt
new file mode 100644
index 000000000000..639ddf0ece9b
--- /dev/null
+++ b/Documentation/networking/mpls-sysctl.txt
@@ -0,0 +1,20 @@
+/proc/sys/net/mpls/* Variables:
+
+platform_labels - INTEGER
+	Number of entries in the platform label table.  It is not
+	possible to configure forwarding for label values equal to or
+	greater than the number of platform labels.
+
+	A dense utliziation of the entries in the platform label table
+	is possible and expected aas the platform labels are locally
+	allocated.
+
+	If the number of platform label table entries is set to 0 no
+	label will be recognized by the kernel and mpls forwarding
+	will be disabled.
+
+	Reducing this value will remove all label routing entries that
+	no longer fit in the table.
+
+	Possible values: 0 - 1048575
+	Default: 0