ofproto: Add relaxed group_mod command ADD_OR_MOD

This patch adds support for a new Group Mod command OFPGC_ADD_OR_MOD to
OVS for all OpenFlow versions that support groups (OF11 and higher).
The new ADD_OR_MOD creates a group that does not yet exist (like ADD)
and modifies an existing group (like MODIFY).

Rational: In OpenFlow 1.x the Group Mod commands OFPGC_ADD and
OFPGC_MODIFY have strict semantics: ADD fails if the group exists,
while MODIFY fails if the group does not exist. This requires a
controller to exactly know the state of the switch when programming a
group in order not run the risk of getting an OFP Error message in
response. This is hard to achieve and maintain at all times in view of
possible switch and controller restarts or other connection losses
between switch and controller.

Due to the un-acknowledged nature of the Group Mod message programming
groups safely and efficiently at the same time is virtually impossible
as the controller has to either query the existence of the group prior
to each Group Mod message or to insert a Barrier Request/Reply after
every group to be sure that no Error can be received at a later stage
and require a complicated roll-back of any dependent actions taken
between the failed Group Mod and the Error.

In the ovs-ofctl command line the ADD_OR_MOD command is made available
through the new option --may-create in the mod-group command:

$ ovs-ofctl -Oopenflow13 del-groups br-int group_id=100

$ ovs-ofctl -Oopenflow13 mod-group br-int
group_id=100,type=indirect,bucket=actions=2 OFPT_ERROR (OF1.3)
(xid=0x2): OFPGMFC_UNKNOWN_GROUP OFPT_GROUP_MOD (OF1.3) (xid=0x2):
 MOD group_id=100,type=indirect,bucket=actions=output:2

$ ovs-ofctl -Oopenflow13 --may-create mod-group br-int
group_id=100,type=indirect,bucket=actions=2

$ ovs-ofctl -Oopenflow13 dump-groups br-int
OFPST_GROUP_DESC reply (OF1.3) (xid=0x2):
 group_id=100,type=indirect,bucket=actions=output:2

$ ovs-ofctl -Oopenflow13 --may-create mod-group br-int
group_id=100,type=indirect,bucket=actions=3

$ ovs-ofctl -Oopenflow13 dump-groups br-int
OFPST_GROUP_DESC reply (OF1.3) (xid=0x2):
 group_id=100,type=indirect,bucket=actions=output:3

Signed-off-by: Jan Scheurich <jan.scheurich at web.de>
Signed-off-by: Ben Pfaff <blp@ovn.org>

1 files changed, 7 insertions, 3 deletions

diff --git a/utilities/ovs-ofctl.8.in b/utilities/ovs-ofctl.8.in
index 208f67177..94e78d788 100644
--- a/utilities/ovs-ofctl.8.in
+++ b/utilities/ovs-ofctl.8.in
@@ -431,10 +431,14 @@ zero or more groups in the same syntax, one per line.
 .IQ "\fBadd\-groups \fIswitch file\fR"
 Add each group entry to \fIswitch\fR's tables.
 .
-.IP "\fBmod\-group \fIswitch group\fR"
-.IQ "\fBmod\-group \fIswitch \fB\- < \fIfile\fR"
+.IP "[\fB\-\-may\-create\fR] \fBmod\-group \fIswitch group\fR"
+.IQ "[\fB\-\-may\-create\fR] \fBmod\-group \fIswitch \fB\- < \fIfile\fR"
 Modify the action buckets in entries from \fIswitch\fR's tables for
-each group entry.
+each group entry.  If a specified group does not already exist, then
+without \fB\-\-may\-create\fR, this command has no effect; with
+\fB\-\-may\-create\fR, it creates a new group.  The
+\fB\-\-may\-create\fR option uses an Open vSwitch extension to
+OpenFlow only implemented in Open vSwitch 2.6 and later.
 .
 .IP "\fBdel\-groups \fIswitch\fR"
 .IQ "\fBdel\-groups \fIswitch \fR[\fIgroup\fR]"