vconn: Move OpenFlow utility functions into new file ofp-util.c.

The main purpose of the vconn code is to ship OpenFlow messages across
network connections.  Over time a large number of utility functions related
to OpenFlow messages have also crept into vconn.c, but that's really
logically separate.  This commit breaks those functions out into a new
file.

1 files changed, 701 insertions, 0 deletions

diff --git a/lib/ofp-util.c b/lib/ofp-util.c
new file mode 100644
index 000000000..d773a3fa9
--- /dev/null
+++ b/lib/ofp-util.c
@@ -0,0 +1,701 @@
+/*
+ * Copyright (c) 2008, 2009, 2010 Nicira Networks.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <config.h>
+#include "ofp-print.h"
+#include <inttypes.h>
+#include <stdlib.h>
+#include "ofp-util.h"
+#include "ofpbuf.h"
+#include "packets.h"
+#include "random.h"
+
+#define THIS_MODULE VLM_ofp_util
+#include "vlog.h"
+
+/* Rate limit for OpenFlow message parse errors.  These always indicate a bug
+ * in the peer and so there's not much point in showing a lot of them. */
+static struct vlog_rate_limit bad_ofmsg_rl = VLOG_RATE_LIMIT_INIT(1, 5);
+
+/* XXX we should really use consecutive xids to avoid probabilistic
+ * failures. */
+static inline uint32_t
+alloc_xid(void)
+{
+    return random_uint32();
+}
+
+/* Allocates and stores in '*bufferp' a new ofpbuf with a size of
+ * 'openflow_len', starting with an OpenFlow header with the given 'type' and
+ * an arbitrary transaction id.  Allocated bytes beyond the header, if any, are
+ * zeroed.
+ *
+ * The caller is responsible for freeing '*bufferp' when it is no longer
+ * needed.
+ *
+ * The OpenFlow header length is initially set to 'openflow_len'; if the
+ * message is later extended, the length should be updated with
+ * update_openflow_length() before sending.
+ *
+ * Returns the header. */
+void *
+make_openflow(size_t openflow_len, uint8_t type, struct ofpbuf **bufferp)
+{
+    *bufferp = ofpbuf_new(openflow_len);
+    return put_openflow_xid(openflow_len, type, alloc_xid(), *bufferp);
+}
+
+/* Allocates and stores in '*bufferp' a new ofpbuf with a size of
+ * 'openflow_len', starting with an OpenFlow header with the given 'type' and
+ * transaction id 'xid'.  Allocated bytes beyond the header, if any, are
+ * zeroed.
+ *
+ * The caller is responsible for freeing '*bufferp' when it is no longer
+ * needed.
+ *
+ * The OpenFlow header length is initially set to 'openflow_len'; if the
+ * message is later extended, the length should be updated with
+ * update_openflow_length() before sending.
+ *
+ * Returns the header. */
+void *
+make_openflow_xid(size_t openflow_len, uint8_t type, uint32_t xid,
+                  struct ofpbuf **bufferp)
+{
+    *bufferp = ofpbuf_new(openflow_len);
+    return put_openflow_xid(openflow_len, type, xid, *bufferp);
+}
+
+/* Appends 'openflow_len' bytes to 'buffer', starting with an OpenFlow header
+ * with the given 'type' and an arbitrary transaction id.  Allocated bytes
+ * beyond the header, if any, are zeroed.
+ *
+ * The OpenFlow header length is initially set to 'openflow_len'; if the
+ * message is later extended, the length should be updated with
+ * update_openflow_length() before sending.
+ *
+ * Returns the header. */
+void *
+put_openflow(size_t openflow_len, uint8_t type, struct ofpbuf *buffer)
+{
+    return put_openflow_xid(openflow_len, type, alloc_xid(), buffer);
+}
+
+/* Appends 'openflow_len' bytes to 'buffer', starting with an OpenFlow header
+ * with the given 'type' and an transaction id 'xid'.  Allocated bytes beyond
+ * the header, if any, are zeroed.
+ *
+ * The OpenFlow header length is initially set to 'openflow_len'; if the
+ * message is later extended, the length should be updated with
+ * update_openflow_length() before sending.
+ *
+ * Returns the header. */
+void *
+put_openflow_xid(size_t openflow_len, uint8_t type, uint32_t xid,
+                 struct ofpbuf *buffer)
+{
+    struct ofp_header *oh;
+
+    assert(openflow_len >= sizeof *oh);
+    assert(openflow_len <= UINT16_MAX);
+
+    oh = ofpbuf_put_uninit(buffer, openflow_len);
+    oh->version = OFP_VERSION;
+    oh->type = type;
+    oh->length = htons(openflow_len);
+    oh->xid = xid;
+    memset(oh + 1, 0, openflow_len - sizeof *oh);
+    return oh;
+}
+
+/* Updates the 'length' field of the OpenFlow message in 'buffer' to
+ * 'buffer->size'. */
+void
+update_openflow_length(struct ofpbuf *buffer) 
+{
+    struct ofp_header *oh = ofpbuf_at_assert(buffer, 0, sizeof *oh);
+    oh->length = htons(buffer->size); 
+}
+
+struct ofpbuf *
+make_flow_mod(uint16_t command, const flow_t *flow, size_t actions_len)
+{
+    struct ofp_flow_mod *ofm;
+    size_t size = sizeof *ofm + actions_len;
+    struct ofpbuf *out = ofpbuf_new(size);
+    ofm = ofpbuf_put_zeros(out, sizeof *ofm);
+    ofm->header.version = OFP_VERSION;
+    ofm->header.type = OFPT_FLOW_MOD;
+    ofm->header.length = htons(size);
+    ofm->cookie = 0;
+    ofm->match.wildcards = htonl(0);
+    ofm->match.in_port = htons(flow->in_port == ODPP_LOCAL ? OFPP_LOCAL
+                               : flow->in_port);
+    memcpy(ofm->match.dl_src, flow->dl_src, sizeof ofm->match.dl_src);
+    memcpy(ofm->match.dl_dst, flow->dl_dst, sizeof ofm->match.dl_dst);
+    ofm->match.dl_vlan = flow->dl_vlan;
+    ofm->match.dl_vlan_pcp = flow->dl_vlan_pcp;
+    ofm->match.dl_type = flow->dl_type;
+    ofm->match.nw_src = flow->nw_src;
+    ofm->match.nw_dst = flow->nw_dst;
+    ofm->match.nw_proto = flow->nw_proto;
+    ofm->match.nw_tos = flow->nw_tos;
+    ofm->match.tp_src = flow->tp_src;
+    ofm->match.tp_dst = flow->tp_dst;
+    ofm->command = htons(command);
+    return out;
+}
+
+struct ofpbuf *
+make_add_flow(const flow_t *flow, uint32_t buffer_id,
+              uint16_t idle_timeout, size_t actions_len)
+{
+    struct ofpbuf *out = make_flow_mod(OFPFC_ADD, flow, actions_len);
+    struct ofp_flow_mod *ofm = out->data;
+    ofm->idle_timeout = htons(idle_timeout);
+    ofm->hard_timeout = htons(OFP_FLOW_PERMANENT);
+    ofm->buffer_id = htonl(buffer_id);
+    return out;
+}
+
+struct ofpbuf *
+make_del_flow(const flow_t *flow)
+{
+    struct ofpbuf *out = make_flow_mod(OFPFC_DELETE_STRICT, flow, 0);
+    struct ofp_flow_mod *ofm = out->data;
+    ofm->out_port = htons(OFPP_NONE);
+    return out;
+}
+
+struct ofpbuf *
+make_add_simple_flow(const flow_t *flow,
+                     uint32_t buffer_id, uint16_t out_port,
+                     uint16_t idle_timeout)
+{
+    struct ofp_action_output *oao;
+    struct ofpbuf *buffer = make_add_flow(flow, buffer_id, idle_timeout,
+                                          sizeof *oao);
+    oao = ofpbuf_put_zeros(buffer, sizeof *oao);
+    oao->type = htons(OFPAT_OUTPUT);
+    oao->len = htons(sizeof *oao);
+    oao->port = htons(out_port);
+    return buffer;
+}
+
+struct ofpbuf *
+make_packet_in(uint32_t buffer_id, uint16_t in_port, uint8_t reason,
+               const struct ofpbuf *payload, int max_send_len)
+{
+    struct ofp_packet_in *opi;
+    struct ofpbuf *buf;
+    int send_len;
+
+    send_len = MIN(max_send_len, payload->size);
+    buf = ofpbuf_new(sizeof *opi + send_len);
+    opi = put_openflow_xid(offsetof(struct ofp_packet_in, data),
+                           OFPT_PACKET_IN, 0, buf);
+    opi->buffer_id = htonl(buffer_id);
+    opi->total_len = htons(payload->size);
+    opi->in_port = htons(in_port);
+    opi->reason = reason;
+    ofpbuf_put(buf, payload->data, send_len);
+    update_openflow_length(buf);
+
+    return buf;
+}
+
+struct ofpbuf *
+make_packet_out(const struct ofpbuf *packet, uint32_t buffer_id,
+                uint16_t in_port,
+                const struct ofp_action_header *actions, size_t n_actions)
+{
+    size_t actions_len = n_actions * sizeof *actions;
+    struct ofp_packet_out *opo;
+    size_t size = sizeof *opo + actions_len + (packet ? packet->size : 0);
+    struct ofpbuf *out = ofpbuf_new(size);
+
+    opo = ofpbuf_put_uninit(out, sizeof *opo);
+    opo->header.version = OFP_VERSION;
+    opo->header.type = OFPT_PACKET_OUT;
+    opo->header.length = htons(size);
+    opo->header.xid = htonl(0);
+    opo->buffer_id = htonl(buffer_id);
+    opo->in_port = htons(in_port == ODPP_LOCAL ? OFPP_LOCAL : in_port);
+    opo->actions_len = htons(actions_len);
+    ofpbuf_put(out, actions, actions_len);
+    if (packet) {
+        ofpbuf_put(out, packet->data, packet->size);
+    }
+    return out;
+}
+
+struct ofpbuf *
+make_unbuffered_packet_out(const struct ofpbuf *packet,
+                           uint16_t in_port, uint16_t out_port)
+{
+    struct ofp_action_output action;
+    action.type = htons(OFPAT_OUTPUT);
+    action.len = htons(sizeof action);
+    action.port = htons(out_port);
+    return make_packet_out(packet, UINT32_MAX, in_port,
+                           (struct ofp_action_header *) &action, 1);
+}
+
+struct ofpbuf *
+make_buffered_packet_out(uint32_t buffer_id,
+                         uint16_t in_port, uint16_t out_port)
+{
+    struct ofp_action_output action;
+    action.type = htons(OFPAT_OUTPUT);
+    action.len = htons(sizeof action);
+    action.port = htons(out_port);
+    return make_packet_out(NULL, buffer_id, in_port,
+                           (struct ofp_action_header *) &action, 1);
+}
+
+/* Creates and returns an OFPT_ECHO_REQUEST message with an empty payload. */
+struct ofpbuf *
+make_echo_request(void)
+{
+    struct ofp_header *rq;
+    struct ofpbuf *out = ofpbuf_new(sizeof *rq);
+    rq = ofpbuf_put_uninit(out, sizeof *rq);
+    rq->version = OFP_VERSION;
+    rq->type = OFPT_ECHO_REQUEST;
+    rq->length = htons(sizeof *rq);
+    rq->xid = 0;
+    return out;
+}
+
+/* Creates and returns an OFPT_ECHO_REPLY message matching the
+ * OFPT_ECHO_REQUEST message in 'rq'. */
+struct ofpbuf *
+make_echo_reply(const struct ofp_header *rq)
+{
+    size_t size = ntohs(rq->length);
+    struct ofpbuf *out = ofpbuf_new(size);
+    struct ofp_header *reply = ofpbuf_put(out, rq, size);
+    reply->type = OFPT_ECHO_REPLY;
+    return out;
+}
+
+static int
+check_message_type(uint8_t got_type, uint8_t want_type) 
+{
+    if (got_type != want_type) {
+        char *want_type_name = ofp_message_type_to_string(want_type);
+        char *got_type_name = ofp_message_type_to_string(got_type);
+        VLOG_WARN_RL(&bad_ofmsg_rl,
+                     "received bad message type %s (expected %s)",
+                     got_type_name, want_type_name);
+        free(want_type_name);
+        free(got_type_name);
+        return ofp_mkerr(OFPET_BAD_REQUEST, OFPBRC_BAD_TYPE);
+    }
+    return 0;
+}
+
+/* Checks that 'msg' has type 'type' and that it is exactly 'size' bytes long.
+ * Returns 0 if the checks pass, otherwise an OpenFlow error code (produced
+ * with ofp_mkerr()). */
+int
+check_ofp_message(const struct ofp_header *msg, uint8_t type, size_t size)
+{
+    size_t got_size;
+    int error;
+
+    error = check_message_type(msg->type, type);
+    if (error) {
+        return error;
+    }
+
+    got_size = ntohs(msg->length);
+    if (got_size != size) {
+        char *type_name = ofp_message_type_to_string(type);
+        VLOG_WARN_RL(&bad_ofmsg_rl,
+                     "received %s message of length %zu (expected %zu)",
+                     type_name, got_size, size);
+        free(type_name);
+        return ofp_mkerr(OFPET_BAD_REQUEST, OFPBRC_BAD_LEN);
+    }
+
+    return 0;
+}
+
+/* Checks that 'msg' has type 'type' and that 'msg' is 'size' plus a
+ * nonnegative integer multiple of 'array_elt_size' bytes long.  Returns 0 if
+ * the checks pass, otherwise an OpenFlow error code (produced with
+ * ofp_mkerr()).
+ *
+ * If 'n_array_elts' is nonnull, then '*n_array_elts' is set to the number of
+ * 'array_elt_size' blocks in 'msg' past the first 'min_size' bytes, when
+ * successful. */
+int
+check_ofp_message_array(const struct ofp_header *msg, uint8_t type,
+                        size_t min_size, size_t array_elt_size,
+                        size_t *n_array_elts)
+{
+    size_t got_size;
+    int error;
+
+    assert(array_elt_size);
+
+    error = check_message_type(msg->type, type);
+    if (error) {
+        return error;
+    }
+
+    got_size = ntohs(msg->length);
+    if (got_size < min_size) {
+        char *type_name = ofp_message_type_to_string(type);
+        VLOG_WARN_RL(&bad_ofmsg_rl, "received %s message of length %zu "
+                     "(expected at least %zu)",
+                     type_name, got_size, min_size);
+        free(type_name);
+        return ofp_mkerr(OFPET_BAD_REQUEST, OFPBRC_BAD_LEN);
+    }
+    if ((got_size - min_size) % array_elt_size) {
+        char *type_name = ofp_message_type_to_string(type);
+        VLOG_WARN_RL(&bad_ofmsg_rl,
+                     "received %s message of bad length %zu: the "
+                     "excess over %zu (%zu) is not evenly divisible by %zu "
+                     "(remainder is %zu)",
+                     type_name, got_size, min_size, got_size - min_size,
+                     array_elt_size, (got_size - min_size) % array_elt_size);
+        free(type_name);
+        return ofp_mkerr(OFPET_BAD_REQUEST, OFPBRC_BAD_LEN);
+    }
+    if (n_array_elts) {
+        *n_array_elts = (got_size - min_size) / array_elt_size;
+    }
+    return 0;
+}
+
+int
+check_ofp_packet_out(const struct ofp_header *oh, struct ofpbuf *data,
+                     int *n_actionsp, int max_ports)
+{
+    const struct ofp_packet_out *opo;
+    unsigned int actions_len, n_actions;
+    size_t extra;
+    int error;
+
+    *n_actionsp = 0;
+    error = check_ofp_message_array(oh, OFPT_PACKET_OUT,
+                                    sizeof *opo, 1, &extra);
+    if (error) {
+        return error;
+    }
+    opo = (const struct ofp_packet_out *) oh;
+
+    actions_len = ntohs(opo->actions_len);
+    if (actions_len > extra) {
+        VLOG_WARN_RL(&bad_ofmsg_rl, "packet-out claims %u bytes of actions "
+                     "but message has room for only %zu bytes",
+                     actions_len, extra);
+        return ofp_mkerr(OFPET_BAD_REQUEST, OFPBRC_BAD_LEN);
+    }
+    if (actions_len % sizeof(union ofp_action)) {
+        VLOG_WARN_RL(&bad_ofmsg_rl, "packet-out claims %u bytes of actions, "
+                     "which is not a multiple of %zu",
+                     actions_len, sizeof(union ofp_action));
+        return ofp_mkerr(OFPET_BAD_REQUEST, OFPBRC_BAD_LEN);
+    }
+
+    n_actions = actions_len / sizeof(union ofp_action);
+    error = validate_actions((const union ofp_action *) opo->actions,
+                             n_actions, max_ports);
+    if (error) {
+        return error;
+    }
+
+    data->data = (void *) &opo->actions[n_actions];
+    data->size = extra - actions_len;
+    *n_actionsp = n_actions;
+    return 0;
+}
+
+const struct ofp_flow_stats *
+flow_stats_first(struct flow_stats_iterator *iter,
+                 const struct ofp_stats_reply *osr)
+{
+    iter->pos = osr->body;
+    iter->end = osr->body + (ntohs(osr->header.length)
+                             - offsetof(struct ofp_stats_reply, body));
+    return flow_stats_next(iter);
+}
+
+const struct ofp_flow_stats *
+flow_stats_next(struct flow_stats_iterator *iter)
+{
+    ptrdiff_t bytes_left = iter->end - iter->pos;
+    const struct ofp_flow_stats *fs;
+    size_t length;
+
+    if (bytes_left < sizeof *fs) {
+        if (bytes_left != 0) {
+            VLOG_WARN_RL(&bad_ofmsg_rl,
+                         "%td leftover bytes in flow stats reply", bytes_left);
+        }
+        return NULL;
+    }
+
+    fs = (const void *) iter->pos;
+    length = ntohs(fs->length);
+    if (length < sizeof *fs) {
+        VLOG_WARN_RL(&bad_ofmsg_rl, "flow stats length %zu is shorter than "
+                     "min %zu", length, sizeof *fs);
+        return NULL;
+    } else if (length > bytes_left) {
+        VLOG_WARN_RL(&bad_ofmsg_rl, "flow stats length %zu but only %td "
+                     "bytes left", length, bytes_left);
+        return NULL;
+    } else if ((length - sizeof *fs) % sizeof fs->actions[0]) {
+        VLOG_WARN_RL(&bad_ofmsg_rl, "flow stats length %zu has %zu bytes "
+                     "left over in final action", length,
+                     (length - sizeof *fs) % sizeof fs->actions[0]);
+        return NULL;
+    }
+    iter->pos += length;
+    return fs;
+}
+
+/* Alignment of ofp_actions. */
+#define ACTION_ALIGNMENT 8
+
+static int
+check_action_exact_len(const union ofp_action *a, unsigned int len,
+                       unsigned int required_len)
+{
+    if (len != required_len) {
+        VLOG_DBG_RL(&bad_ofmsg_rl,
+                    "action %u has invalid length %"PRIu16" (must be %u)\n",
+                    a->type, ntohs(a->header.len), required_len);
+        return ofp_mkerr(OFPET_BAD_ACTION, OFPBAC_BAD_LEN);
+    }
+    return 0;
+}
+
+static int
+check_action_port(int port, int max_ports)
+{
+    switch (port) {
+    case OFPP_IN_PORT:
+    case OFPP_TABLE:
+    case OFPP_NORMAL:
+    case OFPP_FLOOD:
+    case OFPP_ALL:
+    case OFPP_CONTROLLER:
+    case OFPP_LOCAL:
+        return 0;
+
+    default:
+        if (port >= 0 && port < max_ports) {
+            return 0;
+        }
+        VLOG_WARN_RL(&bad_ofmsg_rl, "unknown output port %x", port);
+        return ofp_mkerr(OFPET_BAD_ACTION, OFPBAC_BAD_OUT_PORT);
+    }
+}
+
+static int
+check_nicira_action(const union ofp_action *a, unsigned int len)
+{
+    const struct nx_action_header *nah;
+
+    if (len < 16) {
+        VLOG_DBG_RL(&bad_ofmsg_rl,
+                    "Nicira vendor action only %u bytes", len);
+        return ofp_mkerr(OFPET_BAD_ACTION, OFPBAC_BAD_LEN);
+    }
+    nah = (const struct nx_action_header *) a;
+
+    switch (ntohs(nah->subtype)) {
+    case NXAST_RESUBMIT:
+    case NXAST_SET_TUNNEL:
+        return check_action_exact_len(a, len, 16);
+    default:
+        return ofp_mkerr(OFPET_BAD_ACTION, OFPBAC_BAD_VENDOR_TYPE);
+    }
+}
+
+static int
+check_action(const union ofp_action *a, unsigned int len, int max_ports)
+{
+    int error;
+
+    switch (ntohs(a->type)) {
+    case OFPAT_OUTPUT:
+        error = check_action_port(ntohs(a->output.port), max_ports);
+        return error ? error : check_action_exact_len(a, len, 8);
+
+    case OFPAT_SET_VLAN_VID:
+    case OFPAT_SET_VLAN_PCP:
+    case OFPAT_STRIP_VLAN:
+    case OFPAT_SET_NW_SRC:
+    case OFPAT_SET_NW_DST:
+    case OFPAT_SET_NW_TOS:
+    case OFPAT_SET_TP_SRC:
+    case OFPAT_SET_TP_DST:
+        return check_action_exact_len(a, len, 8);
+
+    case OFPAT_SET_DL_SRC:
+    case OFPAT_SET_DL_DST:
+        return check_action_exact_len(a, len, 16);
+
+    case OFPAT_VENDOR:
+        return (a->vendor.vendor == htonl(NX_VENDOR_ID)
+                ? check_nicira_action(a, len)
+                : ofp_mkerr(OFPET_BAD_ACTION, OFPBAC_BAD_VENDOR));
+
+    default:
+        VLOG_WARN_RL(&bad_ofmsg_rl, "unknown action type %"PRIu16,
+                ntohs(a->type));
+        return ofp_mkerr(OFPET_BAD_ACTION, OFPBAC_BAD_TYPE);
+    }
+}
+
+int
+validate_actions(const union ofp_action *actions, size_t n_actions,
+                 int max_ports)
+{
+    const union ofp_action *a;
+
+    for (a = actions; a < &actions[n_actions]; ) {
+        unsigned int len = ntohs(a->header.len);
+        unsigned int n_slots = len / ACTION_ALIGNMENT;
+        unsigned int slots_left = &actions[n_actions] - a;
+        int error;
+
+        if (n_slots > slots_left) {
+            VLOG_DBG_RL(&bad_ofmsg_rl,
+                        "action requires %u slots but only %u remain",
+                        n_slots, slots_left);
+            return ofp_mkerr(OFPET_BAD_ACTION, OFPBAC_BAD_LEN);
+        } else if (!len) {
+            VLOG_DBG_RL(&bad_ofmsg_rl, "action has invalid length 0");
+            return ofp_mkerr(OFPET_BAD_ACTION, OFPBAC_BAD_LEN);
+        } else if (len % ACTION_ALIGNMENT) {
+            VLOG_DBG_RL(&bad_ofmsg_rl, "action length %u is not a multiple "
+                        "of %d", len, ACTION_ALIGNMENT);
+            return ofp_mkerr(OFPET_BAD_ACTION, OFPBAC_BAD_LEN);
+        }
+
+        error = check_action(a, len, max_ports);
+        if (error) {
+            return error;
+        }
+        a += n_slots;
+    }
+    return 0;
+}
+
+/* The set of actions must either come from a trusted source or have been
+ * previously validated with validate_actions(). */
+const union ofp_action *
+actions_first(struct actions_iterator *iter,
+              const union ofp_action *oa, size_t n_actions)
+{
+    iter->pos = oa;
+    iter->end = oa + n_actions;
+    return actions_next(iter);
+}
+
+const union ofp_action *
+actions_next(struct actions_iterator *iter)
+{
+    if (iter->pos < iter->end) {
+        const union ofp_action *a = iter->pos;
+        unsigned int len = ntohs(a->header.len);
+        iter->pos += len / ACTION_ALIGNMENT;
+        return a;
+    } else {
+        return NULL;
+    }
+}
+
+void
+normalize_match(struct ofp_match *m)
+{
+    enum { OFPFW_NW = OFPFW_NW_SRC_MASK | OFPFW_NW_DST_MASK | OFPFW_NW_PROTO };
+    enum { OFPFW_TP = OFPFW_TP_SRC | OFPFW_TP_DST };
+    uint32_t wc;
+
+    wc = ntohl(m->wildcards) & OVSFW_ALL;
+    if (wc & OFPFW_DL_TYPE) {
+        m->dl_type = 0;
+
+        /* Can't sensibly match on network or transport headers if the
+         * data link type is unknown. */
+        wc |= OFPFW_NW | OFPFW_TP;
+        m->nw_src = m->nw_dst = m->nw_proto = 0;
+        m->tp_src = m->tp_dst = 0;
+    } else if (m->dl_type == htons(ETH_TYPE_IP)) {
+        if (wc & OFPFW_NW_PROTO) {
+            m->nw_proto = 0;
+
+            /* Can't sensibly match on transport headers if the network
+             * protocol is unknown. */
+            wc |= OFPFW_TP;
+            m->tp_src = m->tp_dst = 0;
+        } else if (m->nw_proto == IPPROTO_TCP ||
+                   m->nw_proto == IPPROTO_UDP ||
+                   m->nw_proto == IPPROTO_ICMP) {
+            if (wc & OFPFW_TP_SRC) {
+                m->tp_src = 0;
+            }
+            if (wc & OFPFW_TP_DST) {
+                m->tp_dst = 0;
+            }
+        } else {
+            /* Transport layer fields will always be extracted as zeros, so we
+             * can do an exact-match on those values.  */
+            wc &= ~OFPFW_TP;
+            m->tp_src = m->tp_dst = 0;
+        }
+        if (wc & OFPFW_NW_SRC_MASK) {
+            m->nw_src &= flow_nw_bits_to_mask(wc, OFPFW_NW_SRC_SHIFT);
+        }
+        if (wc & OFPFW_NW_DST_MASK) {
+            m->nw_dst &= flow_nw_bits_to_mask(wc, OFPFW_NW_DST_SHIFT);
+        }
+    } else if (m->dl_type == htons(ETH_TYPE_ARP)) {
+        if (wc & OFPFW_NW_PROTO) {
+            m->nw_proto = 0;
+        }
+        if (wc & OFPFW_NW_SRC_MASK) {
+            m->nw_src &= flow_nw_bits_to_mask(wc, OFPFW_NW_SRC_SHIFT);
+        }
+        if (wc & OFPFW_NW_DST_MASK) {
+            m->nw_dst &= flow_nw_bits_to_mask(wc, OFPFW_NW_DST_SHIFT);
+        }
+        m->tp_src = m->tp_dst = 0;
+    } else {
+        /* Network and transport layer fields will always be extracted as
+         * zeros, so we can do an exact-match on those values. */
+        wc &= ~(OFPFW_NW | OFPFW_TP);
+        m->nw_proto = m->nw_src = m->nw_dst = 0;
+        m->tp_src = m->tp_dst = 0;
+    }
+    if (wc & OFPFW_DL_SRC) {
+        memset(m->dl_src, 0, sizeof m->dl_src);
+    }
+    if (wc & OFPFW_DL_DST) {
+        memset(m->dl_dst, 0, sizeof m->dl_dst);
+    }
+    m->wildcards = htonl(wc);
+}
+