ofp-actions: Add truncate action.

The patch adds a new action to support packet truncation.  The new action
is formatted as 'output(port=n,max_len=m)', as output to port n, with
packet size being MIN(original_size, m).

One use case is to enable port mirroring to send smaller packets to the
destination port so that only useful packet information is mirrored/copied,
saving some performance overhead of copying entire packet payload.  Example
use case is below as well as shown in the testcases:

    - Output to port 1 with max_len 100 bytes.
    - The output packet size on port 1 will be MIN(original_packet_size, 100).
    # ovs-ofctl add-flow br0 'actions=output(port=1,max_len=100)'

    - The scope of max_len is limited to output action itself.  The following
      packet size of output:1 and output:2 will be intact.
    # ovs-ofctl add-flow br0 \
            'actions=output(port=1,max_len=100),output:1,output:2'
    - The Datapath actions shows:
    # Datapath actions: trunc(100),1,1,2

Tested-at: https://travis-ci.org/williamtu/ovs-travis/builds/140037134
Signed-off-by: William Tu <u9012063@gmail.com>
Acked-by: Pravin B Shelar <pshelar@ovn.org>

lib/ofp-actions.c

@@ -301,6 +301,9 @@ enum ofp_raw_action_type {
     /* NX1.0+(36): struct nx_action_nat, ... */
     NXAST_RAW_NAT,
 
+    /* NX1.0+(39): struct nx_action_output_trunc. */
+    NXAST_RAW_OUTPUT_TRUNC,
+
 /* ## ------------------ ## */
 /* ## Debugging actions. ## */
 /* ## ------------------ ## */
@@ -381,6 +384,7 @@ ofpact_next_flattened(const struct ofpact *ofpact)
     case OFPACT_CONTROLLER:
     case OFPACT_ENQUEUE:
     case OFPACT_OUTPUT_REG:
+    case OFPACT_OUTPUT_TRUNC:
     case OFPACT_BUNDLE:
     case OFPACT_SET_FIELD:
     case OFPACT_SET_VLAN_VID:
@@ -537,6 +541,40 @@ encode_OUTPUT(const struct ofpact_output *output,
     }
 }
 
+static char * OVS_WARN_UNUSED_RESULT
+parse_truncate_subfield(struct ofpact_output_trunc *output_trunc,
+                        const char *arg_)
+{
+    char *key, *value;
+    char *arg = CONST_CAST(char *, arg_);
+
+    while (ofputil_parse_key_value(&arg, &key, &value)) {
+        if (!strcmp(key, "port")) {
+            if (!ofputil_port_from_string(value, &output_trunc->port)) {
+                return xasprintf("output to unknown truncate port: %s",
+                                  value);
+            }
+            if (ofp_to_u16(output_trunc->port) > ofp_to_u16(OFPP_MAX)) {
+                if (output_trunc->port != OFPP_LOCAL &&
+                    output_trunc->port != OFPP_IN_PORT)
+                return xasprintf("output to unsupported truncate port: %s",
+                                 value);
+            }
+        } else if (!strcmp(key, "max_len")) {
+            char *err;
+
+            err = str_to_u32(value, &output_trunc->max_len);
+            if (err) {
+                return err;
+            }
+        } else {
+            return xasprintf("invalid key '%s' in output_trunc argument",
+                                key);
+        }
+    }
+    return NULL;
+}
+
 static char * OVS_WARN_UNUSED_RESULT
 parse_OUTPUT(const char *arg, struct ofpbuf *ofpacts,
              enum ofputil_protocol *usable_protocols OVS_UNUSED)
@@ -547,6 +585,11 @@ parse_OUTPUT(const char *arg, struct ofpbuf *ofpacts,
         output_reg = ofpact_put_OUTPUT_REG(ofpacts);
         output_reg->max_len = UINT16_MAX;
         return mf_parse_subfield(&output_reg->src, arg);
+    } else if (strstr(arg, "port") && strstr(arg, "max_len")) {
+        struct ofpact_output_trunc *output_trunc;
+
+        output_trunc = ofpact_put_OUTPUT_TRUNC(ofpacts);
+        return parse_truncate_subfield(output_trunc, arg);
     } else {
         struct ofpact_output *output;
 
@@ -5603,6 +5646,61 @@ parse_NAT(char *arg, struct ofpbuf *ofpacts,
     return NULL;
 }
 
+/* Truncate output action. */
+struct nx_action_output_trunc {
+    ovs_be16 type;              /* OFPAT_VENDOR. */
+    ovs_be16 len;               /* At least 16. */
+    ovs_be32 vendor;            /* NX_VENDOR_ID. */
+    ovs_be16 subtype;           /* NXAST_OUTPUT_TRUNC. */
+    ovs_be16 port;              /* Output port */
+    ovs_be32 max_len;           /* Truncate packet to size bytes */
+};
+OFP_ASSERT(sizeof(struct nx_action_output_trunc) == 16);
+
+static enum ofperr
+decode_NXAST_RAW_OUTPUT_TRUNC(const struct nx_action_output_trunc *natrc,
+                            enum ofp_version ofp_version OVS_UNUSED,
+                            struct ofpbuf *out)
+{
+    struct ofpact_output_trunc *output_trunc;
+
+    output_trunc = ofpact_put_OUTPUT_TRUNC(out);
+    output_trunc->max_len = ntohl(natrc->max_len);
+    output_trunc->port = u16_to_ofp(ntohs(natrc->port));
+
+    if (output_trunc->max_len < ETH_HEADER_LEN) {
+        return OFPERR_OFPBAC_BAD_ARGUMENT;
+    }
+    return 0;
+}
+
+static void
+encode_OUTPUT_TRUNC(const struct ofpact_output_trunc *output_trunc,
+                  enum ofp_version ofp_version OVS_UNUSED,
+                  struct ofpbuf *out)
+{
+    struct nx_action_output_trunc *natrc = put_NXAST_OUTPUT_TRUNC(out);
+
+    natrc->max_len = htonl(output_trunc->max_len);
+    natrc->port = htons(ofp_to_u16(output_trunc->port));
+}
+
+static char * OVS_WARN_UNUSED_RESULT
+parse_OUTPUT_TRUNC(const char *arg, struct ofpbuf *ofpacts OVS_UNUSED,
+                 enum ofputil_protocol *usable_protocols OVS_UNUSED)
+{
+    /* Disable output_trunc parsing.  Expose as output(port=N,max_len=M) and
+     * reuse parse_OUTPUT to parse output_trunc action. */
+    return xasprintf("unknown action %s", arg);
+}
+
+static void
+format_OUTPUT_TRUNC(const struct ofpact_output_trunc *a, struct ds *s)
+{
+     ds_put_format(s, "%soutput%s(port=%"PRIu16",max_len=%"PRIu32")",
+                   colors.special, colors.end, a->port, a->max_len);
+}
+
 
 /* Meter instruction. */
 
@@ -5997,6 +6095,7 @@ ofpact_is_set_or_move_action(const struct ofpact *a)
     case OFPACT_NOTE:
     case OFPACT_OUTPUT:
     case OFPACT_OUTPUT_REG:
+    case OFPACT_OUTPUT_TRUNC:
     case OFPACT_POP_MPLS:
     case OFPACT_POP_QUEUE:
     case OFPACT_PUSH_MPLS:
@@ -6025,6 +6124,7 @@ ofpact_is_allowed_in_actions_set(const struct ofpact *a)
     case OFPACT_DEC_TTL:
     case OFPACT_GROUP:
     case OFPACT_OUTPUT:
+    case OFPACT_OUTPUT_TRUNC:
     case OFPACT_POP_MPLS:
     case OFPACT_PUSH_MPLS:
     case OFPACT_PUSH_VLAN:
@@ -6249,6 +6349,7 @@ ovs_instruction_type_from_ofpact_type(enum ofpact_type type)
     case OFPACT_CONTROLLER:
     case OFPACT_ENQUEUE:
     case OFPACT_OUTPUT_REG:
+    case OFPACT_OUTPUT_TRUNC:
     case OFPACT_BUNDLE:
     case OFPACT_SET_VLAN_VID:
     case OFPACT_SET_VLAN_PCP:
@@ -6677,6 +6778,10 @@ ofpact_check__(enum ofputil_protocol *usable_protocols, struct ofpact *a,
     case OFPACT_OUTPUT_REG:
         return mf_check_src(&ofpact_get_OUTPUT_REG(a)->src, flow);
 
+    case OFPACT_OUTPUT_TRUNC:
+        return ofpact_check_output_port(ofpact_get_OUTPUT_TRUNC(a)->port,
+                                        max_ports);
+
     case OFPACT_BUNDLE:
         return bundle_check(ofpact_get_BUNDLE(a), max_ports, flow);
 
@@ -7354,6 +7459,7 @@ ofpact_outputs_to_port(const struct ofpact *ofpact, ofp_port_t port)
         return port == OFPP_CONTROLLER;
 
     case OFPACT_OUTPUT_REG:
+    case OFPACT_OUTPUT_TRUNC:
     case OFPACT_BUNDLE:
     case OFPACT_SET_VLAN_VID:
     case OFPACT_SET_VLAN_PCP: