ovs/lib/nx-match.c

/*
 * Copyright (c) 2010-2017, 2020 Nicira, Inc.
 *
 * 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 "nx-match.h"

#include <netinet/icmp6.h>

#include "classifier.h"
#include "colors.h"
#include "openvswitch/hmap.h"
#include "openflow/nicira-ext.h"
#include "openvswitch/dynamic-string.h"
#include "openvswitch/meta-flow.h"
#include "openvswitch/ofp-actions.h"
#include "openvswitch/ofp-errors.h"
#include "openvswitch/ofp-match.h"
#include "openvswitch/ofp-port.h"
#include "openvswitch/ofpbuf.h"
#include "openvswitch/vlog.h"
#include "packets.h"
#include "openvswitch/shash.h"
#include "tun-metadata.h"
#include "unaligned.h"
#include "util.h"
#include "vl-mff-map.h"

VLOG_DEFINE_THIS_MODULE(nx_match);

/* OXM headers.
 *
 *
 * Standard OXM/NXM
 * ================
 *
 * The header is 32 bits long.  It looks like this:
 *
 * |31                              16 15            9| 8 7                0
 * +----------------------------------+---------------+--+------------------+
 * |            oxm_class             |   oxm_field   |hm|    oxm_length    |
 * +----------------------------------+---------------+--+------------------+
 *
 * where hm stands for oxm_hasmask.  It is followed by oxm_length bytes of
 * payload.  When oxm_hasmask is 0, the payload is the value of the field
 * identified by the header; when oxm_hasmask is 1, the payload is a value for
 * the field followed by a mask of equal length.
 *
 * Internally, we represent a standard OXM header as a 64-bit integer with the
 * above information in the most-significant bits.
 *
 *
 * Experimenter OXM
 * ================
 *
 * The header is 64 bits long.  It looks like the diagram above except that a
 * 32-bit experimenter ID, which we call oxm_vendor and which identifies a
 * vendor, is inserted just before the payload.  Experimenter OXMs are
 * identified by an all-1-bits oxm_class (OFPXMC12_EXPERIMENTER).  The
 * oxm_length value *includes* the experimenter ID, so that the real payload is
 * only oxm_length - 4 bytes long.
 *
 * Internally, we represent an experimenter OXM header as a 64-bit integer with
 * the standard header in the upper 32 bits and the experimenter ID in the
 * lower 32 bits.  (It would be more convenient to swap the positions of the
 * two 32-bit words, but this would be more error-prone because experimenter
 * OXMs are very rarely used, so accidentally passing one through a 32-bit type
 * somewhere in the OVS code would be hard to find.)
 */

/*
 * OXM Class IDs.
 * The high order bit differentiate reserved classes from member classes.
 * Classes 0x0000 to 0x7FFF are member classes, allocated by ONF.
 * Classes 0x8000 to 0xFFFE are reserved classes, reserved for standardisation.
 */
enum ofp12_oxm_class {
    OFPXMC12_NXM_0          = 0x0000, /* Backward compatibility with NXM */
    OFPXMC12_NXM_1          = 0x0001, /* Backward compatibility with NXM */
    OFPXMC12_OPENFLOW_BASIC = 0x8000, /* Basic class for OpenFlow */
    OFPXMC15_PACKET_REGS    = 0x8001, /* Packet registers (pipeline fields). */
    OFPXMC12_EXPERIMENTER   = 0xffff, /* Experimenter class */
};

/* Functions for extracting raw field values from OXM/NXM headers. */
static uint32_t nxm_vendor(uint64_t header) { return header; }
static int nxm_class(uint64_t header) { return header >> 48; }
static int nxm_field(uint64_t header) { return (header >> 41) & 0x7f; }
static bool nxm_hasmask(uint64_t header) { return (header >> 40) & 1; }
static int nxm_length(uint64_t header) { return (header >> 32) & 0xff; }
static uint64_t nxm_no_len(uint64_t header) { return header & 0xffffff80ffffffffULL; }

static bool
is_experimenter_oxm(uint64_t header)
{
    return nxm_class(header) == OFPXMC12_EXPERIMENTER;
}

/* The OXM header "length" field is somewhat tricky:
 *
 *     - For a standard OXM header, the length is the number of bytes of the
 *       payload, and the payload consists of just the value (and mask, if
 *       present).
 *
 *     - For an experimenter OXM header, the length is the number of bytes in
 *       the payload plus 4 (the length of the experimenter ID).  That is, the
 *       experimenter ID is included in oxm_length.
 *
 * This function returns the length of the experimenter ID field in 'header'.
 * That is, for an experimenter OXM (when an experimenter ID is present), it
 * returns 4, and for a standard OXM (when no experimenter ID is present), it
 * returns 0. */
static int
nxm_experimenter_len(uint64_t header)
{
    return is_experimenter_oxm(header) ? 4 : 0;
}

/* Returns the number of bytes that follow the header for an NXM/OXM entry
 * with the given 'header'. */
static unsigned int
nxm_payload_len(uint64_t header)
{
    ovs_assert(nxm_length(header) >= nxm_experimenter_len(header));
    return nxm_length(header) - nxm_experimenter_len(header);
}

/* Returns the number of bytes in the header for an NXM/OXM entry with the
 * given 'header'. */
static int
nxm_header_len(uint64_t header)
{
    return 4 + nxm_experimenter_len(header);
}

#define NXM_HEADER(VENDOR, CLASS, FIELD, HASMASK, LENGTH)       \
    (((uint64_t) (CLASS) << 48) |                               \
     ((uint64_t) (FIELD) << 41) |                               \
     ((uint64_t) (HASMASK) << 40) |                             \
     ((uint64_t) (LENGTH) << 32) |                              \
     (VENDOR))

#define NXM_HEADER_FMT "%#"PRIx32":%d:%d:%d:%d"
#define NXM_HEADER_ARGS(HEADER)                                 \
    nxm_vendor(HEADER), nxm_class(HEADER), nxm_field(HEADER),   \
    nxm_hasmask(HEADER), nxm_length(HEADER)

/* Functions for turning the "hasmask" bit on or off.  (This also requires
 * adjusting the length.) */
static uint64_t
nxm_make_exact_header(uint64_t header)
{
    unsigned int new_len = nxm_payload_len(header)
                           / 2 + nxm_experimenter_len(header);
    return NXM_HEADER(nxm_vendor(header), nxm_class(header),
                      nxm_field(header), 0, new_len);
}
static uint64_t
nxm_make_wild_header(uint64_t header)
{
    unsigned int new_len = nxm_payload_len(header) * 2
                           + nxm_experimenter_len(header);
    return NXM_HEADER(nxm_vendor(header), nxm_class(header),
                      nxm_field(header), 1, new_len);
}

/* Flow cookie.
 *
 * This may be used to gain the OpenFlow 1.1-like ability to restrict
 * certain NXM-based Flow Mod and Flow Stats Request messages to flows
 * with specific cookies.  See the "nx_flow_mod" and "nx_flow_stats_request"
 * structure definitions for more details.  This match is otherwise not
 * allowed. */
#define NXM_NX_COOKIE     NXM_HEADER  (0, 0x0001, 30, 0, 8)
#define NXM_NX_COOKIE_W   nxm_make_wild_header(NXM_NX_COOKIE)

struct nxm_field {
    uint64_t header;
    enum ofp_version version;
    const char *name;           /* e.g. "NXM_OF_IN_PORT". */

    enum mf_field_id id;
};

static const struct nxm_field *nxm_field_by_header(uint64_t header, bool is_action, enum ofperr *h_error);
static const struct nxm_field *nxm_field_by_name(const char *name, size_t len);
static const struct nxm_field *nxm_field_by_mf_id(enum mf_field_id,
                                                  enum ofp_version);

static void nx_put_header__(struct ofpbuf *, uint64_t header, bool masked);
static void nx_put_header_len(struct ofpbuf *, enum mf_field_id field,
                              enum ofp_version version, bool masked,
                              size_t n_bytes);

/* Rate limit for nx_match 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 rl = VLOG_RATE_LIMIT_INIT(1, 5);

static const struct nxm_field *
mf_parse_subfield_name(const char *name, int name_len, bool *wild);

/* Returns the preferred OXM header to use for field 'id' in OpenFlow version
 * 'version'.  Specify 0 for 'version' if an NXM legacy header should be
 * preferred over any standardized OXM header.  Returns 0 if field 'id' cannot
 * be expressed in NXM or OXM. */
static uint64_t
mf_oxm_header(enum mf_field_id id, enum ofp_version version)
{
    const struct nxm_field *f = nxm_field_by_mf_id(id, version);
    return f ? f->header : 0;
}

/* Returns the 32-bit OXM or NXM header to use for field 'id', preferring an
 * NXM legacy header over any standardized OXM header.  Returns 0 if field 'id'
 * cannot be expressed with a 32-bit NXM or OXM header.
 *
 * Whenever possible, use nx_pull_header() instead of this function, because
 * this function cannot support 64-bit experimenter OXM headers. */
uint32_t
mf_nxm_header(enum mf_field_id id)
{
    uint64_t oxm = mf_oxm_header(id, 0);
    return is_experimenter_oxm(oxm) ? 0 : oxm >> 32;
}

/* Returns the 32-bit OXM or NXM header to use for field 'mff'. If 'mff' is
 * a mapped variable length mf_field, update the header with the configured
 * length of 'mff'. Returns 0 if 'mff' cannot be expressed with a 32-bit NXM
 * or OXM header.*/
uint32_t
nxm_header_from_mff(const struct mf_field *mff)
{
    uint64_t oxm = mf_oxm_header(mff->id, 0);

    if (mff->mapped) {
        oxm = nxm_no_len(oxm) | ((uint64_t) mff->n_bytes << 32);
    }

    return is_experimenter_oxm(oxm) ? 0 : oxm >> 32;
}

static const struct mf_field *
mf_from_oxm_header(uint64_t header, const struct vl_mff_map *vl_mff_map,
                   bool is_action, enum ofperr *h_error)
{
    const struct nxm_field *f = nxm_field_by_header(header, is_action, h_error);

    if (f) {
        const struct mf_field *mff = mf_from_id(f->id);
        const struct mf_field *vl_mff = mf_get_vl_mff(mff, vl_mff_map);
        return vl_mff ? vl_mff : mff;
    } else {
        return NULL;
    }
}

/* Returns the "struct mf_field" that corresponds to NXM or OXM header
 * 'header', or NULL if 'header' doesn't correspond to any known field.  */
const struct mf_field *
mf_from_nxm_header(uint32_t header, const struct vl_mff_map *vl_mff_map)
{
    return mf_from_oxm_header((uint64_t) header << 32, vl_mff_map, false, NULL);
}

/* Returns the width of the data for a field with the given 'header', in
 * bytes. */
static int
nxm_field_bytes(uint64_t header)
{
    unsigned int length = nxm_payload_len(header);
    return nxm_hasmask(header) ? length / 2 : length;
}

/* nx_pull_match() and helpers. */

/* Given NXM/OXM value 'value' and mask 'mask' associated with 'header', checks
 * for any 1-bit in the value where there is a 0-bit in the mask.  Returns 0 if
 * none, otherwise an error code. */
static bool
is_mask_consistent(uint64_t header, const uint8_t *value, const uint8_t *mask)
{
    unsigned int width = nxm_field_bytes(header);
    unsigned int i;

    for (i = 0; i < width; i++) {
        if (value[i] & ~mask[i]) {
            if (!VLOG_DROP_WARN(&rl)) {
                VLOG_WARN_RL(&rl, "Rejecting NXM/OXM entry "NXM_HEADER_FMT " "
                             "with 1-bits in value for bits wildcarded by the "
                             "mask.", NXM_HEADER_ARGS(header));
            }
            return false;
        }
    }
    return true;
}

static bool
is_cookie_pseudoheader(uint64_t header)
{
    return header == NXM_NX_COOKIE || header == NXM_NX_COOKIE_W;
}

static enum ofperr
nx_pull_header__(struct ofpbuf *b, bool allow_cookie,
                 const struct vl_mff_map *vl_mff_map, uint64_t *header,
                 const struct mf_field **field, bool is_action)
{
    if (b->size < 4) {
        goto bad_len;
    }

    *header = ((uint64_t) ntohl(get_unaligned_be32(b->data))) << 32;
    if (is_experimenter_oxm(*header)) {
        if (b->size < 8) {
            goto bad_len;
        }
        *header = ntohll(get_unaligned_be64(b->data));
    }
    if (nxm_length(*header) < nxm_experimenter_len(*header)) {
        VLOG_WARN_RL(&rl, "OXM header "NXM_HEADER_FMT" has invalid length %d "
                     "(minimum is %d)",
                     NXM_HEADER_ARGS(*header), nxm_length(*header),
                     nxm_header_len(*header));
        goto error;
    }
    ofpbuf_pull(b, nxm_header_len(*header));

    if (field) {
        enum ofperr h_error = 0;
        *field = mf_from_oxm_header(*header, vl_mff_map, is_action, &h_error);
        if (!*field && !(allow_cookie && is_cookie_pseudoheader(*header))) {
            VLOG_DBG_RL(&rl, "OXM header "NXM_HEADER_FMT" is unknown",
                        NXM_HEADER_ARGS(*header));
            if (is_action) {
                if (h_error) {
                     *field = NULL;
                     return h_error;
                }
                return OFPERR_OFPBAC_BAD_SET_TYPE;
            } else {
                return OFPERR_OFPBMC_BAD_FIELD;
            }
        } else if (mf_vl_mff_invalid(*field, vl_mff_map)) {
            return OFPERR_NXFMFC_INVALID_TLV_FIELD;
        }
    }

    return 0;

bad_len:
    VLOG_DBG_RL(&rl, "encountered partial (%"PRIu32"-byte) OXM entry",
                b->size);
error:
    *header = 0;
    if (field) {
        *field = NULL;
    }
    return OFPERR_OFPBMC_BAD_LEN;
}

static void
copy_entry_value(const struct mf_field *field, union mf_value *value,
                 const uint8_t *payload, int width)
{
    int copy_len;
    void *copy_dst;

    copy_dst = value;
    copy_len = MIN(width, field ? field->n_bytes : sizeof *value);

    if (field && field->variable_len) {
        memset(value, 0, field->n_bytes);
        copy_dst = &value->u8 + field->n_bytes - copy_len;
    }

    memcpy(copy_dst, payload, copy_len);
}

static enum ofperr
nx_pull_entry__(struct ofpbuf *b, bool allow_cookie,
                const struct vl_mff_map *vl_mff_map, uint64_t *header,
                const struct mf_field **field_,
                union mf_value *value, union mf_value *mask, bool is_action)
{
    const struct mf_field *field;
    enum ofperr header_error;
    unsigned int payload_len;
    const uint8_t *payload;
    int width;

    header_error = nx_pull_header__(b, allow_cookie, vl_mff_map, header,
                                    &field, is_action);
    if (header_error && header_error != OFPERR_OFPBMC_BAD_FIELD) {
        return header_error;
    }

    payload_len = nxm_payload_len(*header);
    payload = ofpbuf_try_pull(b, payload_len);
    if (!payload) {
        VLOG_DBG_RL(&rl, "OXM header "NXM_HEADER_FMT" calls for %u-byte "
                    "payload but only %"PRIu32" bytes follow OXM header",
                    NXM_HEADER_ARGS(*header), payload_len, b->size);
        return OFPERR_OFPBMC_BAD_LEN;
    }

    width = nxm_field_bytes(*header);
    if (nxm_hasmask(*header)
        && !is_mask_consistent(*header, payload, payload + width)) {
        return OFPERR_OFPBMC_BAD_WILDCARDS;
    }

    copy_entry_value(field, value, payload, width);

    if (mask) {
        if (nxm_hasmask(*header)) {
            copy_entry_value(field, mask, payload + width, width);
        } else {
            memset(mask, 0xff, sizeof *mask);
        }
    } else if (nxm_hasmask(*header)) {
        VLOG_DBG_RL(&rl, "OXM header "NXM_HEADER_FMT" includes mask but "
                    "masked OXMs are not allowed here",
                    NXM_HEADER_ARGS(*header));
        return OFPERR_OFPBMC_BAD_MASK;
    }

    if (field_) {
        *field_ = field;
        return header_error;
    }

    return 0;
}

/* Attempts to pull an NXM or OXM header, value, and mask (if present) from the
 * beginning of 'b'.  If successful, stores a pointer to the "struct mf_field"
 * corresponding to the pulled header in '*field', the value into '*value',
 * and the mask into '*mask', and returns 0.  On error, returns an OpenFlow
 * error; in this case, some bytes might have been pulled off 'b' anyhow, and
 * the output parameters might have been modified.
 *
 * If a NULL 'mask' is supplied, masked OXM or NXM entries are treated as
 * errors (with OFPERR_OFPBMC_BAD_MASK).
 *
 * The "bool is_action" is supplied to differentiate between match and action
 * headers. This is done in order to return appropriate error type and code for
 * bad match or bad action conditions. If set to True, indicates that the
 * OXM or NXM entries belong to an action header.
 */
enum ofperr
nx_pull_entry(struct ofpbuf *b, const struct vl_mff_map *vl_mff_map,
              const struct mf_field **field, union mf_value *value,
              union mf_value *mask, bool is_action)
{
    uint64_t header;

    return nx_pull_entry__(b, false, vl_mff_map, &header, field, value, mask, is_action);
}

/* Attempts to pull an NXM or OXM header from the beginning of 'b'.  If
 * successful, stores a pointer to the "struct mf_field" corresponding to the
 * pulled header in '*field', stores the header's hasmask bit in '*masked'
 * (true if hasmask=1, false if hasmask=0), and returns 0.  On error, returns
 * an OpenFlow error; in this case, some bytes might have been pulled off 'b'
 * anyhow, and the output parameters might have been modified.
 *
 * If NULL 'masked' is supplied, masked OXM or NXM headers are treated as
 * errors (with OFPERR_OFPBMC_BAD_MASK).
 */
enum ofperr
nx_pull_header(struct ofpbuf *b, const struct vl_mff_map *vl_mff_map,
               const struct mf_field **field, bool *masked)
{
    enum ofperr error;
    uint64_t header;

    error = nx_pull_header__(b, false, vl_mff_map,  &header, field, false);
    if (masked) {
        *masked = !error && nxm_hasmask(header);
    } else if (!error && nxm_hasmask(header)) {
        error = OFPERR_OFPBMC_BAD_MASK;
    }
    return error;
}

static enum ofperr
nx_pull_match_entry(struct ofpbuf *b, bool allow_cookie,
                    const struct vl_mff_map *vl_mff_map,
                    const struct mf_field **field,
                    union mf_value *value, union mf_value *mask)
{
    enum ofperr error;
    uint64_t header;

    error = nx_pull_entry__(b, allow_cookie, vl_mff_map, &header, field, value,
                            mask, false);
    if (error) {
        return error;
    }
    if (field && *field) {
        if (!mf_is_mask_valid(*field, mask)) {
            VLOG_DBG_RL(&rl, "bad mask for field %s", (*field)->name);
            return OFPERR_OFPBMC_BAD_MASK;
        }
        if (!mf_is_value_valid(*field, value)) {
            VLOG_DBG_RL(&rl, "bad value for field %s", (*field)->name);
            return OFPERR_OFPBMC_BAD_VALUE;
        }
    }
    return 0;
}

/* Prerequisites will only be checked when 'strict' is 'true'.  This allows
 * decoding conntrack original direction 5-tuple IP addresses without the
 * ethertype being present, when decoding metadata only. */
static enum ofperr
nx_pull_raw(const uint8_t *p, unsigned int match_len, bool strict,
            bool pipeline_fields_only, struct match *match, ovs_be64 *cookie,
            ovs_be64 *cookie_mask, const struct tun_table *tun_table,
            const struct vl_mff_map *vl_mff_map)
{
    ovs_assert((cookie != NULL) == (cookie_mask != NULL));

    match_init_catchall(match);
    match->flow.tunnel.metadata.tab = tun_table;
    if (cookie) {
        *cookie = *cookie_mask = htonll(0);
    }

    struct ofpbuf b = ofpbuf_const_initializer(p, match_len);
    while (b.size) {
        const uint8_t *pos = b.data;
        const struct mf_field *field;
        union mf_value value;
        union mf_value mask;
        enum ofperr error;

        error = nx_pull_match_entry(&b, cookie != NULL, vl_mff_map, &field,
                                    &value, &mask);
        if (error) {
            if (error == OFPERR_OFPBMC_BAD_FIELD && !strict) {
                continue;
            }
        } else if (!field) {
            if (!cookie) {
                error = OFPERR_OFPBMC_BAD_FIELD;
            } else if (*cookie_mask) {
                error = OFPERR_OFPBMC_DUP_FIELD;
            } else {
                *cookie = value.be64;
                *cookie_mask = mask.be64;
            }
        } else if (strict && !mf_are_match_prereqs_ok(field, match)) {
            error = OFPERR_OFPBMC_BAD_PREREQ;
        } else if (!mf_is_all_wild(field, &match->wc)) {
            error = OFPERR_OFPBMC_DUP_FIELD;
        } else if (pipeline_fields_only && !mf_is_pipeline_field(field)) {
            error = OFPERR_OFPBRC_PIPELINE_FIELDS_ONLY;
        } else {
            char *err_str;

            mf_set(field, &value, &mask, match, &err_str);
            if (err_str) {
                VLOG_DBG_RL(&rl, "error parsing OXM at offset %"PRIdPTR" "
                           "within match (%s)", pos - p, err_str);
                free(err_str);
                return OFPERR_OFPBMC_BAD_VALUE;
            }

            match_add_ethernet_prereq(match, field);
        }

        if (error) {
            VLOG_DBG_RL(&rl, "error parsing OXM at offset %"PRIdPTR" "
                        "within match (%s)", pos -
                        p, ofperr_to_string(error));
            return error;
        }
    }

    match->flow.tunnel.metadata.tab = NULL;
    return 0;
}

static enum ofperr
nx_pull_match__(struct ofpbuf *b, unsigned int match_len, bool strict,
                bool pipeline_fields_only, struct match *match,
                ovs_be64 *cookie, ovs_be64 *cookie_mask,
                const struct tun_table *tun_table,
                const struct vl_mff_map *vl_mff_map)
{
    uint8_t *p = NULL;

    if (match_len) {
        p = ofpbuf_try_pull(b, ROUND_UP(match_len, 8));
        if (!p) {
            VLOG_DBG_RL(&rl, "nx_match length %u, rounded up to a "
                        "multiple of 8, is longer than space in message (max "
                        "length %"PRIu32")", match_len, b->size);
            return OFPERR_OFPBMC_BAD_LEN;
        }
    }

    return nx_pull_raw(p, match_len, strict, pipeline_fields_only, match,
                       cookie, cookie_mask, tun_table, vl_mff_map);
}

/* Parses the nx_match formatted match description in 'b' with length
 * 'match_len'.  Stores the results in 'match'.  If 'cookie' and 'cookie_mask'
 * are valid pointers, then stores the cookie and mask in them if 'b' contains
 * a "NXM_NX_COOKIE*" match.  Otherwise, stores 0 in both.
 * If 'pipeline_fields_only' is true, this function returns
 * OFPERR_OFPBRC_PIPELINE_FIELDS_ONLY if there is any non pipeline fields
 * in 'b'.
 *
 * 'vl_mff_map" is an optional parameter that is used to validate the length
 * of variable length mf_fields in 'match'. If it is not provided, the
 * default mf_fields with maximum length will be used.
 *
 * Fails with an error upon encountering an unknown NXM header.
 *
 * Returns 0 if successful, otherwise an OpenFlow error code. */
enum ofperr
nx_pull_match(struct ofpbuf *b, unsigned int match_len, struct match *match,
              ovs_be64 *cookie, ovs_be64 *cookie_mask,
              bool pipeline_fields_only, const struct tun_table *tun_table,
              const struct vl_mff_map *vl_mff_map)
{
    return nx_pull_match__(b, match_len, true, pipeline_fields_only, match,
                           cookie, cookie_mask, tun_table, vl_mff_map);
}

/* Behaves the same as nx_pull_match(), but skips over unknown NXM headers,
 * instead of failing with an error, and does not check for field
 * prerequisites. */
enum ofperr
nx_pull_match_loose(struct ofpbuf *b, unsigned int match_len,
                    struct match *match, ovs_be64 *cookie,
                    ovs_be64 *cookie_mask, bool pipeline_fields_only,
                    const struct tun_table *tun_table)
{
    return nx_pull_match__(b, match_len, false, pipeline_fields_only, match,
                           cookie, cookie_mask, tun_table, NULL);
}

static enum ofperr
oxm_pull_match__(struct ofpbuf *b, bool strict, bool pipeline_fields_only,
                 const struct tun_table *tun_table,
                 const struct vl_mff_map *vl_mff_map, struct match *match)
{
    struct ofp11_match_header *omh = b->data;
    uint8_t *p;
    uint16_t match_len;

    if (b->size < sizeof *omh) {
        return OFPERR_OFPBMC_BAD_LEN;
    }

    match_len = ntohs(omh->length);
    if (match_len < sizeof *omh) {
        return OFPERR_OFPBMC_BAD_LEN;
    }

    if (omh->type != htons(OFPMT_OXM)) {
        return OFPERR_OFPBMC_BAD_TYPE;
    }

    p = ofpbuf_try_pull(b, ROUND_UP(match_len, 8));
    if (!p) {
        VLOG_DBG_RL(&rl, "oxm length %u, rounded up to a "
                    "multiple of 8, is longer than space in message (max "
                    "length %"PRIu32")", match_len, b->size);
        return OFPERR_OFPBMC_BAD_LEN;
    }

    return nx_pull_raw(p + sizeof *omh, match_len - sizeof *omh,
                       strict, pipeline_fields_only, match, NULL, NULL,
                       tun_table, vl_mff_map);
}

/* Parses the oxm formatted match description preceded by a struct
 * ofp11_match_header in 'b'.  Stores the result in 'match'.
 * If 'pipeline_fields_only' is true, this function returns
 * OFPERR_OFPBRC_PIPELINE_FIELDS_ONLY if there is any non pipeline fields
 * in 'b'.
 *
 * 'vl_mff_map' is an optional parameter that is used to validate the length
 * of variable length mf_fields in 'match'. If it is not provided, the
 * default mf_fields with maximum length will be used.
 *
 * Fails with an error when encountering unknown OXM headers.
 *
 * Returns 0 if successful, otherwise an OpenFlow error code. */
enum ofperr
oxm_pull_match(struct ofpbuf *b, bool pipeline_fields_only,
               const struct tun_table *tun_table,
               const struct vl_mff_map *vl_mff_map, struct match *match)
{
    return oxm_pull_match__(b, true, pipeline_fields_only, tun_table,
                            vl_mff_map, match);
}

/* Behaves the same as oxm_pull_match() with two exceptions.  Skips over
 * unknown OXM headers instead of failing with an error when they are
 * encountered, and does not check for field prerequisites. */
enum ofperr
oxm_pull_match_loose(struct ofpbuf *b, bool pipeline_fields_only,
                     const struct tun_table *tun_table, struct match *match)
{
    return oxm_pull_match__(b, false, pipeline_fields_only, tun_table, NULL,
                            match);
}

/* Parses the OXM match description in the 'oxm_len' bytes in 'oxm'.  Stores
 * the result in 'match'.
 *
 * Returns 0 if successful, otherwise an OpenFlow error code.
 *
 * If 'loose' is true, encountering unknown OXM headers or missing field
 * prerequisites are not considered as error conditions.
 */
enum ofperr
oxm_decode_match(const void *oxm, size_t oxm_len, bool loose,
                 const struct tun_table *tun_table,
                 const struct vl_mff_map *vl_mff_map, struct match *match)
{
    return nx_pull_raw(oxm, oxm_len, !loose, false, match, NULL, NULL,
                       tun_table, vl_mff_map);
}

/* Verify an array of OXM TLVs treating value of each TLV as a mask,
 * disallowing masks in each TLV and ignoring pre-requisites. */
enum ofperr
oxm_pull_field_array(const void *fields_data, size_t fields_len,
                     struct field_array *fa)
{
    struct ofpbuf b = ofpbuf_const_initializer(fields_data, fields_len);
    while (b.size) {
        const uint8_t *pos = b.data;
        const struct mf_field *field;
        union mf_value value;
        enum ofperr error;
        uint64_t header;

        error = nx_pull_entry__(&b, false, NULL, &header, &field, &value,
                                NULL, false);
        if (error) {
            VLOG_DBG_RL(&rl, "error pulling field array field");
        } else if (!field) {
            VLOG_DBG_RL(&rl, "unknown field array field");
            error = OFPERR_OFPBMC_BAD_FIELD;
        } else if (bitmap_is_set(fa->used.bm, field->id)) {
            VLOG_DBG_RL(&rl, "duplicate field array field '%s'", field->name);
            error = OFPERR_OFPBMC_DUP_FIELD;
        } else if (!mf_is_mask_valid(field, &value)) {
            VLOG_DBG_RL(&rl, "bad mask in field array field '%s'", field->name);
            error = OFPERR_OFPBMC_BAD_MASK;
        } else {
            field_array_set(field->id, &value, fa);
        }

        if (error) {
            const uint8_t *start = fields_data;

            VLOG_DBG_RL(&rl, "error parsing OXM at offset %"PRIdPTR" "
                        "within field array (%s)", pos - start,
                        ofperr_to_string(error));

            free(fa->values);
            fa->values = NULL;
            return error;
        }
    }

    return 0;
}

/* nx_put_match() and helpers.
 *
 * 'put' functions whose names end in 'w' add a wildcarded field.
 * 'put' functions whose names end in 'm' add a field that might be wildcarded.
 * Other 'put' functions add exact-match fields.
 */

struct nxm_put_ctx {
    struct ofpbuf *output;
    bool implied_ethernet;
};

void
nxm_put_entry_raw(struct ofpbuf *b,
                  enum mf_field_id field, enum ofp_version version,
                  const void *value, const void *mask, size_t n_bytes)
{
    nx_put_header_len(b, field, version, !!mask, n_bytes);
    ofpbuf_put(b, value, n_bytes);
    if (mask) {
        ofpbuf_put(b, mask, n_bytes);
    }
}

static void
nxm_put__(struct nxm_put_ctx *ctx,
          enum mf_field_id field, enum ofp_version version,
          const void *value, const void *mask, size_t n_bytes)
{
    nxm_put_entry_raw(ctx->output, field, version, value, mask, n_bytes);
    if (!ctx->implied_ethernet && mf_from_id(field)->prereqs != MFP_NONE) {
        ctx->implied_ethernet = true;
    }
}

static void
nxm_put(struct nxm_put_ctx *ctx,
        enum mf_field_id field, enum ofp_version version,
        const void *value, const void *mask, size_t n_bytes)
{
    if (!is_all_zeros(mask, n_bytes)) {
        bool masked = !is_all_ones(mask, n_bytes);
        nxm_put__(ctx, field, version, value, masked ? mask : NULL, n_bytes);
    }
}

static void
nxm_put_8m(struct nxm_put_ctx *ctx,
           enum mf_field_id field, enum ofp_version version,
           uint8_t value, uint8_t mask)
{
    nxm_put(ctx, field, version, &value, &mask, sizeof value);
}

static void
nxm_put_8(struct nxm_put_ctx *ctx,
          enum mf_field_id field, enum ofp_version version, uint8_t value)
{
    nxm_put__(ctx, field, version, &value, NULL, sizeof value);
}

static void
nxm_put_16m(struct nxm_put_ctx *ctx,
            enum mf_field_id field, enum ofp_version version,
            ovs_be16 value, ovs_be16 mask)
{
    nxm_put(ctx, field, version, &value, &mask, sizeof value);
}

static void
nxm_put_16(struct nxm_put_ctx *ctx,
           enum mf_field_id field, enum ofp_version version, ovs_be16 value)
{
    nxm_put__(ctx, field, version, &value, NULL, sizeof value);
}

static void
nxm_put_32m(struct nxm_put_ctx *ctx,
            enum mf_field_id field, enum ofp_version version,
            ovs_be32 value, ovs_be32 mask)
{
    nxm_put(ctx, field, version, &value, &mask, sizeof value);
}

static void
nxm_put_32(struct nxm_put_ctx *ctx,
           enum mf_field_id field, enum ofp_version version, ovs_be32 value)
{
    nxm_put__(ctx, field, version, &value, NULL, sizeof value);
}

static void
nxm_put_64m(struct nxm_put_ctx *ctx,
            enum mf_field_id field, enum ofp_version version,
            ovs_be64 value, ovs_be64 mask)
{
    nxm_put(ctx, field, version, &value, &mask, sizeof value);
}

static void
nxm_put_128m(struct nxm_put_ctx *ctx,
             enum mf_field_id field, enum ofp_version version,
             const ovs_be128 value, const ovs_be128 mask)
{
    nxm_put(ctx, field, version, &value, &mask, sizeof(value));
}

static void
nxm_put_eth_masked(struct nxm_put_ctx *ctx,
                   enum mf_field_id field, enum ofp_version version,
                   const struct eth_addr value, const struct eth_addr mask)
{
    nxm_put(ctx, field, version, value.ea, mask.ea, ETH_ADDR_LEN);
}

static void
nxm_put_ipv6(struct nxm_put_ctx *ctx,
             enum mf_field_id field, enum ofp_version version,
             const struct in6_addr *value, const struct in6_addr *mask)
{
    nxm_put(ctx, field, version, value->s6_addr, mask->s6_addr,
            sizeof value->s6_addr);
}

static void
nxm_put_frag(struct nxm_put_ctx *ctx, const struct match *match,
             enum ofp_version version)
{
    uint8_t nw_frag = match->flow.nw_frag & FLOW_NW_FRAG_MASK;
    uint8_t nw_frag_mask = match->wc.masks.nw_frag & FLOW_NW_FRAG_MASK;

    nxm_put_8m(ctx, MFF_IP_FRAG, version, nw_frag,
               nw_frag_mask == FLOW_NW_FRAG_MASK ? UINT8_MAX : nw_frag_mask);
}

/* Appends to 'b' a set of OXM or NXM matches for the IPv4 or IPv6 fields in
 * 'match'.  */
static void
nxm_put_ip(struct nxm_put_ctx *ctx,
           const struct match *match, enum ofp_version oxm)
{
    const struct flow *flow = &match->flow;
    ovs_be16 dl_type = get_dl_type(flow);

    if (dl_type == htons(ETH_TYPE_IP)) {
        nxm_put_32m(ctx, MFF_IPV4_SRC, oxm,
                    flow->nw_src, match->wc.masks.nw_src);
        nxm_put_32m(ctx, MFF_IPV4_DST, oxm,
                    flow->nw_dst, match->wc.masks.nw_dst);
    } else {
        nxm_put_ipv6(ctx, MFF_IPV6_SRC, oxm,
                     &flow->ipv6_src, &match->wc.masks.ipv6_src);
        nxm_put_ipv6(ctx, MFF_IPV6_DST, oxm,
                     &flow->ipv6_dst, &match->wc.masks.ipv6_dst);
    }

    nxm_put_frag(ctx, match, oxm);

    if (match->wc.masks.nw_tos & IP_DSCP_MASK) {
        if (oxm) {
            nxm_put_8(ctx, MFF_IP_DSCP_SHIFTED, oxm,
                      flow->nw_tos >> 2);
        } else {
            nxm_put_8(ctx, MFF_IP_DSCP, oxm,
                      flow->nw_tos & IP_DSCP_MASK);
        }
    }

    if (match->wc.masks.nw_tos & IP_ECN_MASK) {
        nxm_put_8(ctx, MFF_IP_ECN, oxm,
                  flow->nw_tos & IP_ECN_MASK);
    }

    if (match->wc.masks.nw_ttl) {
        nxm_put_8(ctx, MFF_IP_TTL, oxm, flow->nw_ttl);
    }

    nxm_put_32m(ctx, MFF_IPV6_LABEL, oxm,
                flow->ipv6_label, match->wc.masks.ipv6_label);

    if (match->wc.masks.nw_proto) {
        nxm_put_8(ctx, MFF_IP_PROTO, oxm, flow->nw_proto);

        if (flow->nw_proto == IPPROTO_TCP) {
            nxm_put_16m(ctx, MFF_TCP_SRC, oxm,
                        flow->tp_src, match->wc.masks.tp_src);
            nxm_put_16m(ctx, MFF_TCP_DST, oxm,
                        flow->tp_dst, match->wc.masks.tp_dst);
            nxm_put_16m(ctx, MFF_TCP_FLAGS, oxm,
                        flow->tcp_flags, match->wc.masks.tcp_flags);
        } else if (flow->nw_proto == IPPROTO_UDP) {
            nxm_put_16m(ctx, MFF_UDP_SRC, oxm,
                        flow->tp_src, match->wc.masks.tp_src);
            nxm_put_16m(ctx, MFF_UDP_DST, oxm,
                        flow->tp_dst, match->wc.masks.tp_dst);
        } else if (flow->nw_proto == IPPROTO_SCTP) {
            nxm_put_16m(ctx, MFF_SCTP_SRC, oxm, flow->tp_src,
                        match->wc.masks.tp_src);
            nxm_put_16m(ctx, MFF_SCTP_DST, oxm, flow->tp_dst,
                        match->wc.masks.tp_dst);
        } else if (is_icmpv4(flow, NULL)) {
            if (match->wc.masks.tp_src) {
                nxm_put_8(ctx, MFF_ICMPV4_TYPE, oxm,
                          ntohs(flow->tp_src));
            }
            if (match->wc.masks.tp_dst) {
                nxm_put_8(ctx, MFF_ICMPV4_CODE, oxm,
                          ntohs(flow->tp_dst));
            }
        } else if (is_icmpv6(flow, NULL)) {
            if (match->wc.masks.tp_src) {
                nxm_put_8(ctx, MFF_ICMPV6_TYPE, oxm,
                          ntohs(flow->tp_src));
            }
            if (match->wc.masks.tp_dst) {
                nxm_put_8(ctx, MFF_ICMPV6_CODE, oxm,
                          ntohs(flow->tp_dst));
            }
            if (is_nd(flow, NULL)) {
                if (match->wc.masks.igmp_group_ip4) {
                    nxm_put_32(ctx, MFF_ND_RESERVED, oxm,
                           flow->igmp_group_ip4);
                }
                nxm_put_ipv6(ctx, MFF_ND_TARGET, oxm,
                             &flow->nd_target, &match->wc.masks.nd_target);
                if (match->wc.masks.tcp_flags) {
                   nxm_put_8(ctx, MFF_ND_OPTIONS_TYPE, oxm,
                             ntohs(flow->tcp_flags));
                }
                if (flow->tp_src == htons(ND_NEIGHBOR_SOLICIT)) {
                    nxm_put_eth_masked(ctx, MFF_ND_SLL, oxm,
                                       flow->arp_sha, match->wc.masks.arp_sha);
                }
                if (flow->tp_src == htons(ND_NEIGHBOR_ADVERT)) {
                    nxm_put_eth_masked(ctx, MFF_ND_TLL, oxm,
                                       flow->arp_tha, match->wc.masks.arp_tha);
                }
            }
        }
    }
}

/* Appends to 'b' the nx_match format that expresses 'match'.  For Flow Mod and
 * Flow Stats Requests messages, a 'cookie' and 'cookie_mask' may be supplied.
 * Otherwise, 'cookie_mask' should be zero.
 *
 * Specify 'oxm' as 0 to express the match in NXM format; otherwise, specify
 * 'oxm' as the OpenFlow version number for the OXM format to use.
 *
 * This function can cause 'b''s data to be reallocated.
 *
 * Returns the number of bytes appended to 'b', excluding padding.
 *
 * If 'match' is a catch-all rule that matches every packet, then this function
 * appends nothing to 'b' and returns 0. */
static int
nx_put_raw(struct ofpbuf *b, enum ofp_version oxm, const struct match *match,
           ovs_be64 cookie, ovs_be64 cookie_mask)
{
    const struct flow *flow = &match->flow;
    const size_t start_len = b->size;
    ovs_be16 dl_type = get_dl_type(flow);
    ovs_be32 spi_mask;
    int match_len;

    BUILD_ASSERT_DECL(FLOW_WC_SEQ == 42);

    struct nxm_put_ctx ctx = { .output = b, .implied_ethernet = false };

    /* OpenFlow Packet Type. Must be first. */
    if (match->wc.masks.packet_type && !match_has_default_packet_type(match)) {
        nxm_put_32m(&ctx, MFF_PACKET_TYPE, oxm, flow->packet_type,
                    match->wc.masks.packet_type);
    }

    /* Metadata. */
    if (match->wc.masks.dp_hash) {
        nxm_put_32m(&ctx, MFF_DP_HASH, oxm,
                    htonl(flow->dp_hash), htonl(match->wc.masks.dp_hash));
    }

    if (match->wc.masks.recirc_id) {
        nxm_put_32(&ctx, MFF_RECIRC_ID, oxm, htonl(flow->recirc_id));
    }

    if (match->wc.masks.conj_id) {
        nxm_put_32(&ctx, MFF_CONJ_ID, oxm, htonl(flow->conj_id));
    }

    if (match->wc.masks.in_port.ofp_port) {
        ofp_port_t in_port = flow->in_port.ofp_port;
        if (oxm) {
            nxm_put_32(&ctx, MFF_IN_PORT_OXM, oxm,
                       ofputil_port_to_ofp11(in_port));
        } else {
            nxm_put_16(&ctx, MFF_IN_PORT, oxm,
                       htons(ofp_to_u16(in_port)));
        }
    }
    if (match->wc.masks.actset_output) {
        nxm_put_32(&ctx, MFF_ACTSET_OUTPUT, oxm,
                   ofputil_port_to_ofp11(flow->actset_output));
    }

    /* Ethernet. */
    nxm_put_eth_masked(&ctx, MFF_ETH_SRC, oxm,
                       flow->dl_src, match->wc.masks.dl_src);
    nxm_put_eth_masked(&ctx, MFF_ETH_DST, oxm,
                       flow->dl_dst, match->wc.masks.dl_dst);
    nxm_put_16m(&ctx, MFF_ETH_TYPE, oxm,
                ofputil_dl_type_to_openflow(flow->dl_type),
                match->wc.masks.dl_type);

    /* 802.1Q. */
    if (oxm) {
        ovs_be16 VID_CFI_MASK = htons(VLAN_VID_MASK | VLAN_CFI);
        ovs_be16 vid = flow->vlans[0].tci & VID_CFI_MASK;
        ovs_be16 mask = match->wc.masks.vlans[0].tci & VID_CFI_MASK;

        if (mask == htons(VLAN_VID_MASK | VLAN_CFI)) {
            nxm_put_16(&ctx, MFF_VLAN_VID, oxm, vid);
        } else if (mask) {
            nxm_put_16m(&ctx, MFF_VLAN_VID, oxm, vid, mask);
        }

        if (vid && vlan_tci_to_pcp(match->wc.masks.vlans[0].tci)) {
            nxm_put_8(&ctx, MFF_VLAN_PCP, oxm,
                      vlan_tci_to_pcp(flow->vlans[0].tci));
        }

    } else {
        nxm_put_16m(&ctx, MFF_VLAN_TCI, oxm, flow->vlans[0].tci,
                    match->wc.masks.vlans[0].tci);
    }

    /* MPLS. */
    if (eth_type_mpls(dl_type)) {
        if (match->wc.masks.mpls_lse[0] & htonl(MPLS_TC_MASK)) {
            nxm_put_8(&ctx, MFF_MPLS_TC, oxm,
                      mpls_lse_to_tc(flow->mpls_lse[0]));
        }

        if (match->wc.masks.mpls_lse[0] & htonl(MPLS_BOS_MASK)) {
            nxm_put_8(&ctx, MFF_MPLS_BOS, oxm,
                      mpls_lse_to_bos(flow->mpls_lse[0]));
        }

        if (match->wc.masks.mpls_lse[0] & htonl(MPLS_TTL_MASK)) {
            nxm_put_8(&ctx, MFF_MPLS_TTL, oxm,
                      mpls_lse_to_ttl(flow->mpls_lse[0]));
        }

        if (match->wc.masks.mpls_lse[0] & htonl(MPLS_LABEL_MASK)) {
            nxm_put_32(&ctx, MFF_MPLS_LABEL, oxm,
                       htonl(mpls_lse_to_label(flow->mpls_lse[0])));
        }
    }

    /* L3. */
    if (is_ip_any(flow)) {
        nxm_put_ip(&ctx, match, oxm);
    } else if (dl_type == htons(ETH_TYPE_ARP) ||
               dl_type == htons(ETH_TYPE_RARP)) {
        /* ARP. */
        if (match->wc.masks.nw_proto) {
            nxm_put_16(&ctx, MFF_ARP_OP, oxm,
                       htons(flow->nw_proto));
        }
        nxm_put_32m(&ctx, MFF_ARP_SPA, oxm,
                    flow->nw_src, match->wc.masks.nw_src);
        nxm_put_32m(&ctx, MFF_ARP_TPA, oxm,
                    flow->nw_dst, match->wc.masks.nw_dst);
        nxm_put_eth_masked(&ctx, MFF_ARP_SHA, oxm,
                           flow->arp_sha, match->wc.masks.arp_sha);
        nxm_put_eth_masked(&ctx, MFF_ARP_THA, oxm,
                           flow->arp_tha, match->wc.masks.arp_tha);
    }

    /* Tunnel ID. */
    nxm_put_64m(&ctx, MFF_TUN_ID, oxm,
                flow->tunnel.tun_id, match->wc.masks.tunnel.tun_id);

    /* Other tunnel metadata. */
    nxm_put_16m(&ctx, MFF_TUN_FLAGS, oxm,
                htons(flow->tunnel.flags), htons(match->wc.masks.tunnel.flags));
    nxm_put_32m(&ctx, MFF_TUN_SRC, oxm,
                flow->tunnel.ip_src, match->wc.masks.tunnel.ip_src);
    nxm_put_32m(&ctx, MFF_TUN_DST, oxm,
                flow->tunnel.ip_dst, match->wc.masks.tunnel.ip_dst);
    nxm_put_ipv6(&ctx, MFF_TUN_IPV6_SRC, oxm,
                 &flow->tunnel.ipv6_src, &match->wc.masks.tunnel.ipv6_src);
    nxm_put_ipv6(&ctx, MFF_TUN_IPV6_DST, oxm,
                 &flow->tunnel.ipv6_dst, &match->wc.masks.tunnel.ipv6_dst);
    nxm_put_16m(&ctx, MFF_TUN_GBP_ID, oxm,
                flow->tunnel.gbp_id, match->wc.masks.tunnel.gbp_id);
    nxm_put_8m(&ctx, MFF_TUN_GBP_FLAGS, oxm,
               flow->tunnel.gbp_flags, match->wc.masks.tunnel.gbp_flags);
    tun_metadata_to_nx_match(b, oxm, match);

    /* ERSPAN */
    nxm_put_32m(&ctx, MFF_TUN_ERSPAN_IDX, oxm,
                htonl(flow->tunnel.erspan_idx),
                htonl(match->wc.masks.tunnel.erspan_idx));
    nxm_put_8m(&ctx, MFF_TUN_ERSPAN_VER, oxm,
                flow->tunnel.erspan_ver, match->wc.masks.tunnel.erspan_ver);
    nxm_put_8m(&ctx, MFF_TUN_ERSPAN_DIR, oxm,
                flow->tunnel.erspan_dir, match->wc.masks.tunnel.erspan_dir);
    nxm_put_8m(&ctx, MFF_TUN_ERSPAN_HWID, oxm,
                flow->tunnel.erspan_hwid, match->wc.masks.tunnel.erspan_hwid);

    /* GTP-U */
    nxm_put_8m(&ctx, MFF_TUN_GTPU_FLAGS, oxm, flow->tunnel.gtpu_flags,
               match->wc.masks.tunnel.gtpu_flags);
    nxm_put_8m(&ctx, MFF_TUN_GTPU_MSGTYPE, oxm, flow->tunnel.gtpu_msgtype,
               match->wc.masks.tunnel.gtpu_msgtype);

    /* Network Service Header */
    nxm_put_8m(&ctx, MFF_NSH_FLAGS, oxm, flow->nsh.flags,
            match->wc.masks.nsh.flags);
    nxm_put_8m(&ctx, MFF_NSH_TTL, oxm, flow->nsh.ttl,
            match->wc.masks.nsh.ttl);
    nxm_put_8m(&ctx, MFF_NSH_MDTYPE, oxm, flow->nsh.mdtype,
            match->wc.masks.nsh.mdtype);
    nxm_put_8m(&ctx, MFF_NSH_NP, oxm, flow->nsh.np,
            match->wc.masks.nsh.np);
    spi_mask = nsh_path_hdr_to_spi(match->wc.masks.nsh.path_hdr);
    if (spi_mask == htonl(NSH_SPI_MASK >> NSH_SPI_SHIFT)) {
        spi_mask = OVS_BE32_MAX;
    }
    nxm_put_32m(&ctx, MFF_NSH_SPI, oxm,
                nsh_path_hdr_to_spi(flow->nsh.path_hdr),
                spi_mask);
    nxm_put_8m(&ctx, MFF_NSH_SI, oxm,
                nsh_path_hdr_to_si(flow->nsh.path_hdr),
                nsh_path_hdr_to_si(match->wc.masks.nsh.path_hdr));
    for (int i = 0; i < 4; i++) {
        nxm_put_32m(&ctx, MFF_NSH_C1 + i, oxm, flow->nsh.context[i],
                    match->wc.masks.nsh.context[i]);
    }

    /* Registers. */
    if (oxm < OFP15_VERSION) {
        for (int i = 0; i < FLOW_N_REGS; i++) {
            nxm_put_32m(&ctx, MFF_REG0 + i, oxm,
                        htonl(flow->regs[i]), htonl(match->wc.masks.regs[i]));
        }
    } else {
        for (int i = 0; i < FLOW_N_XREGS; i++) {
            nxm_put_64m(&ctx, MFF_XREG0 + i, oxm,
                        htonll(flow_get_xreg(flow, i)),
                        htonll(flow_get_xreg(&match->wc.masks, i)));
        }
    }

    /* Packet mark. */
    nxm_put_32m(&ctx, MFF_PKT_MARK, oxm, htonl(flow->pkt_mark),
                htonl(match->wc.masks.pkt_mark));

    /* Connection tracking. */
    nxm_put_32m(&ctx, MFF_CT_STATE, oxm, htonl(flow->ct_state),
                htonl(match->wc.masks.ct_state));
    nxm_put_16m(&ctx, MFF_CT_ZONE, oxm, htons(flow->ct_zone),
                htons(match->wc.masks.ct_zone));
    nxm_put_32m(&ctx, MFF_CT_MARK, oxm, htonl(flow->ct_mark),
                htonl(match->wc.masks.ct_mark));
    nxm_put_128m(&ctx, MFF_CT_LABEL, oxm, hton128(flow->ct_label),
                 hton128(match->wc.masks.ct_label));
    nxm_put_32m(&ctx, MFF_CT_NW_SRC, oxm,
                flow->ct_nw_src, match->wc.masks.ct_nw_src);
    nxm_put_ipv6(&ctx, MFF_CT_IPV6_SRC, oxm,
                 &flow->ct_ipv6_src, &match->wc.masks.ct_ipv6_src);
    nxm_put_32m(&ctx, MFF_CT_NW_DST, oxm,
                flow->ct_nw_dst, match->wc.masks.ct_nw_dst);
    nxm_put_ipv6(&ctx, MFF_CT_IPV6_DST, oxm,
                 &flow->ct_ipv6_dst, &match->wc.masks.ct_ipv6_dst);
    if (flow->ct_nw_proto) {
        nxm_put_8m(&ctx, MFF_CT_NW_PROTO, oxm, flow->ct_nw_proto,
                   match->wc.masks.ct_nw_proto);
        nxm_put_16m(&ctx, MFF_CT_TP_SRC, oxm,
                    flow->ct_tp_src, match->wc.masks.ct_tp_src);
        nxm_put_16m(&ctx, MFF_CT_TP_DST, oxm,
                    flow->ct_tp_dst, match->wc.masks.ct_tp_dst);
    }
    /* OpenFlow 1.1+ Metadata. */
    nxm_put_64m(&ctx, MFF_METADATA, oxm,
                flow->metadata, match->wc.masks.metadata);

    /* Cookie. */
    if (cookie_mask) {
        bool masked = cookie_mask != OVS_BE64_MAX;

        cookie &= cookie_mask;
        nx_put_header__(b, NXM_NX_COOKIE, masked);
        ofpbuf_put(b, &cookie, sizeof cookie);
        if (masked) {
            ofpbuf_put(b, &cookie_mask, sizeof cookie_mask);
        }
    }

    if (match_has_default_packet_type(match) && !ctx.implied_ethernet) {
        uint64_t pt_stub[16 / 8];
        struct ofpbuf pt;
        ofpbuf_use_stack(&pt, pt_stub, sizeof pt_stub);
        nxm_put_entry_raw(&pt, MFF_PACKET_TYPE, oxm, &flow->packet_type,
                          NULL, sizeof flow->packet_type);

        ofpbuf_insert(b, start_len, pt.data, pt.size);
    }

    match_len = b->size - start_len;
    return match_len;
}

/* Appends to 'b' the nx_match format that expresses 'match', plus enough zero
 * bytes to pad the nx_match out to a multiple of 8.  For Flow Mod and Flow
 * Stats Requests messages, a 'cookie' and 'cookie_mask' may be supplied.
 * Otherwise, 'cookie_mask' should be zero.
 *
 * This function can cause 'b''s data to be reallocated.
 *
 * Returns the number of bytes appended to 'b', excluding padding.  The return
 * value can be zero if it appended nothing at all to 'b' (which happens if
 * 'cr' is a catch-all rule that matches every packet). */
int
nx_put_match(struct ofpbuf *b, const struct match *match,
             ovs_be64 cookie, ovs_be64 cookie_mask)
{
    int match_len = nx_put_raw(b, 0, match, cookie, cookie_mask);

    ofpbuf_put_zeros(b, PAD_SIZE(match_len, 8));
    return match_len;
}

/* Appends to 'b' an struct ofp11_match_header followed by the OXM format that
 * expresses 'match', plus enough zero bytes to pad the data appended out to a
 * multiple of 8.
 *
 * OXM differs slightly among versions of OpenFlow.  Specify the OpenFlow
 * version in use as 'version'.
 *
 * This function can cause 'b''s data to be reallocated.
 *
 * Returns the number of bytes appended to 'b', excluding the padding.  Never
 * returns zero. */
int
oxm_put_match(struct ofpbuf *b, const struct match *match,
              enum ofp_version version)
{
    int match_len;
    struct ofp11_match_header *omh;
    size_t start_len = b->size;
    ovs_be64 cookie = htonll(0), cookie_mask = htonll(0);

    ofpbuf_put_uninit(b, sizeof *omh);
    match_len = (nx_put_raw(b, version, match, cookie, cookie_mask)
                 + sizeof *omh);
    ofpbuf_put_zeros(b, PAD_SIZE(match_len, 8));

    omh = ofpbuf_at(b, start_len, sizeof *omh);
    omh->type = htons(OFPMT_OXM);
    omh->length = htons(match_len);

    return match_len;
}

/* Appends to 'b' the OXM formats that expresses 'match', without header or
 * padding.
 *
 * OXM differs slightly among versions of OpenFlow.  Specify the OpenFlow
 * version in use as 'version'.
 *
 * This function can cause 'b''s data to be reallocated. */
void
oxm_put_raw(struct ofpbuf *b, const struct match *match,
            enum ofp_version version)
{
    nx_put_raw(b, version, match, 0, 0);
}

/* Appends to 'b' the nx_match format that expresses the tlv corresponding
 * to 'id'. If mask is not all-ones then it is also formated as the value
 * of the tlv. */
static void
nx_format_mask_tlv(struct ds *ds, enum mf_field_id id,
                   const union mf_value *mask)
{
    const struct mf_field *mf = mf_from_id(id);

    ds_put_format(ds, "%s", mf->name);

    if (!is_all_ones(mask, mf->n_bytes)) {
        ds_put_char(ds, '=');
        mf_format(mf, mask, NULL, NULL, ds);
    }

    ds_put_char(ds, ',');
}

/* Appends a string representation of 'fa_' to 'ds'.
 * The TLVS value of 'fa_' is treated as a mask and
 * only the name of fields is formated if it is all ones. */
void
oxm_format_field_array(struct ds *ds, const struct field_array *fa)
{
    size_t start_len = ds->length;
    size_t i, offset = 0;

    BITMAP_FOR_EACH_1 (i, MFF_N_IDS, fa->used.bm) {
        const struct mf_field *mf = mf_from_id(i);
        union mf_value value;

        memcpy(&value, fa->values + offset, mf->n_bytes);
        nx_format_mask_tlv(ds, i, &value);
        offset += mf->n_bytes;
    }

    if (ds->length > start_len) {
        ds_chomp(ds, ',');
    }
}

/* Appends to 'b' a series of OXM TLVs corresponding to the series
 * of enum mf_field_id and value tuples in 'fa_'.
 *
 * OXM differs slightly among versions of OpenFlow.  Specify the OpenFlow
 * version in use as 'version'.
 *
 * This function can cause 'b''s data to be reallocated.
 *
 * Returns the number of bytes appended to 'b'.  May return zero. */
int
oxm_put_field_array(struct ofpbuf *b, const struct field_array *fa,
                    enum ofp_version version)
{
    size_t start_len = b->size;

    /* XXX Some care might need to be taken of different TLVs that handle the
     * same flow fields. In particular:

     * - VLAN_TCI, VLAN_VID and MFF_VLAN_PCP
     * - IP_DSCP_MASK and DSCP_SHIFTED
     * - REGS and XREGS
     */

    size_t i, offset = 0;

    BITMAP_FOR_EACH_1 (i, MFF_N_IDS, fa->used.bm) {
        const struct mf_field *mf = mf_from_id(i);
        union mf_value value;

        memcpy(&value, fa->values + offset, mf->n_bytes);

        int len = mf_field_len(mf, &value, NULL, NULL);
        nxm_put_entry_raw(b, i, version,
                          &value + mf->n_bytes - len, NULL, len);
        offset += mf->n_bytes;
    }

    return b->size - start_len;
}

static void
nx_put_header__(struct ofpbuf *b, uint64_t header, bool masked)
{
    uint64_t masked_header = masked ? nxm_make_wild_header(header) : header;
    ovs_be64 network_header = htonll(masked_header);

    ofpbuf_put(b, &network_header, nxm_header_len(header));
}

void
nx_put_header(struct ofpbuf *b, enum mf_field_id field,
              enum ofp_version version, bool masked)
{
    nx_put_header__(b, mf_oxm_header(field, version), masked);
}

void nx_put_mff_header(struct ofpbuf *b, const struct mf_field *mff,
                       enum ofp_version version, bool masked)
{
    if (mff->mapped) {
        nx_put_header_len(b, mff->id, version, masked, mff->n_bytes);
    } else {
        nx_put_header(b, mff->id, version, masked);
    }
}

static void
nx_put_header_len(struct ofpbuf *b, enum mf_field_id field,
                  enum ofp_version version, bool masked, size_t n_bytes)
{
    uint64_t header = mf_oxm_header(field, version);

    header = NXM_HEADER(nxm_vendor(header), nxm_class(header),
                        nxm_field(header), false,
                        nxm_experimenter_len(header) + n_bytes);

    nx_put_header__(b, header, masked);
}

void
nx_put_entry(struct ofpbuf *b, const struct mf_field *mff,
             enum ofp_version version, const union mf_value *value,
             const union mf_value *mask)
{
    bool masked;
    int len, offset;

    len = mf_field_len(mff, value, mask, &masked);
    offset = mff->n_bytes - len;

    nxm_put_entry_raw(b, mff->id, version,
                      &value->u8 + offset, masked ? &mask->u8 + offset : NULL,
                      len);
}

/* nx_match_to_string() and helpers. */

static void format_nxm_field_name(struct ds *, uint64_t header);

char *
nx_match_to_string(const uint8_t *p, unsigned int match_len)
{
    if (!match_len) {
        return xstrdup("<any>");
    }

    struct ofpbuf b = ofpbuf_const_initializer(p, match_len);
    struct ds s = DS_EMPTY_INITIALIZER;
    while (b.size) {
        union mf_value value;
        union mf_value mask;
        enum ofperr error;
        uint64_t header;
        int value_len;

        error = nx_pull_entry__(&b, true, NULL, &header, NULL, &value, &mask, false);
        if (error) {
            break;
        }
        value_len = MIN(sizeof value, nxm_field_bytes(header));

        if (s.length) {
            ds_put_cstr(&s, ", ");
        }

        format_nxm_field_name(&s, header);
        ds_put_char(&s, '(');

        for (int i = 0; i < value_len; i++) {
            ds_put_format(&s, "%02x", ((const uint8_t *) &value)[i]);
        }
        if (nxm_hasmask(header)) {
            ds_put_char(&s, '/');
            for (int i = 0; i < value_len; i++) {
                ds_put_format(&s, "%02x", ((const uint8_t *) &mask)[i]);
            }
        }
        ds_put_char(&s, ')');
    }

    if (b.size) {
        if (s.length) {
            ds_put_cstr(&s, ", ");
        }

        ds_put_format(&s, "<%u invalid bytes>", b.size);
    }

    return ds_steal_cstr(&s);
}

char *
oxm_match_to_string(const struct ofpbuf *p, unsigned int match_len)
{
    const struct ofp11_match_header *omh = p->data;
    uint16_t match_len_;
    struct ds s;

    ds_init(&s);

    if (match_len < sizeof *omh) {
        ds_put_format(&s, "<match too short: %u>", match_len);
        goto err;
    }

    if (omh->type != htons(OFPMT_OXM)) {
        ds_put_format(&s, "<bad match type field: %u>", ntohs(omh->type));
        goto err;
    }

    match_len_ = ntohs(omh->length);
    if (match_len_ < sizeof *omh) {
        ds_put_format(&s, "<match length field too short: %u>", match_len_);
        goto err;
    }

    if (match_len_ != match_len) {
        ds_put_format(&s, "<match length field incorrect: %u != %u>",
                      match_len_, match_len);
        goto err;
    }

    return nx_match_to_string(ofpbuf_at(p, sizeof *omh, 0),
                              match_len - sizeof *omh);

err:
    return ds_steal_cstr(&s);
}

void
nx_format_field_name(enum mf_field_id id, enum ofp_version version,
                     struct ds *s)
{
    format_nxm_field_name(s, mf_oxm_header(id, version));
}

static void
format_nxm_field_name(struct ds *s, uint64_t header)
{
    const struct nxm_field *f = nxm_field_by_header(header, false, NULL);
    if (f) {
        ds_put_cstr(s, f->name);
        if (nxm_hasmask(header)) {
            ds_put_cstr(s, "_W");
        }
    } else if (header == NXM_NX_COOKIE) {
        ds_put_cstr(s, "NXM_NX_COOKIE");
    } else if (header == NXM_NX_COOKIE_W) {
        ds_put_cstr(s, "NXM_NX_COOKIE_W");
    } else {
        ds_put_format(s, "%d:%d", nxm_class(header), nxm_field(header));
    }
}

static bool
streq_len(const char *a, size_t a_len, const char *b)
{
    return strlen(b) == a_len && !memcmp(a, b, a_len);
}

static uint64_t
parse_nxm_field_name(const char *name, int name_len)
{
    const struct nxm_field *f;
    bool wild;

    f = mf_parse_subfield_name(name, name_len, &wild);
    if (f) {
        if (!wild) {
            return f->header;
        } else if (mf_from_id(f->id)->maskable != MFM_NONE) {
            return nxm_make_wild_header(f->header);
        }
    }

    if (streq_len(name, name_len, "NXM_NX_COOKIE")) {
        return NXM_NX_COOKIE;
    } else if (streq_len(name, name_len, "NXM_NX_COOKIE_W")) {
        return NXM_NX_COOKIE_W;
    }

    /* Check whether it's a field header value as hex.
     * (This isn't ordinarily useful except for testing error behavior.) */
    if (name_len == 8) {
        uint64_t header;
        bool ok;

        header = hexits_value(name, name_len, &ok) << 32;
        if (ok) {
            return header;
        }
    } else if (name_len == 16) {
        uint64_t header;
        bool ok;

        header = hexits_value(name, name_len, &ok);
        if (ok && is_experimenter_oxm(header)) {
            return header;
        }
    }

    return 0;
}

/* nx_match_from_string(). */

static int
nx_match_from_string_raw(const char *s, struct ofpbuf *b)
{
    const char *full_s = s;
    const size_t start_len = b->size;

    if (!strcmp(s, "<any>")) {
        /* Ensure that 'b->data' isn't actually null. */
        ofpbuf_prealloc_tailroom(b, 1);
        return 0;
    }

    for (s += strspn(s, ", "); *s; s += strspn(s, ", ")) {
        const char *name;
        uint64_t header;
        ovs_be64 nw_header;
        int name_len;
        size_t n;

        name = s;
        name_len = strcspn(s, "(");
        if (s[name_len] != '(') {
            ovs_fatal(0, "%s: missing ( at end of nx_match", full_s);
        }

        header = parse_nxm_field_name(name, name_len);
        if (!header) {
            ovs_fatal(0, "%s: unknown field `%.*s'", full_s, name_len, s);
        }

        s += name_len + 1;

        b->header = ofpbuf_put_uninit(b, nxm_header_len(header));
        s = ofpbuf_put_hex(b, s, &n);
        if (n != nxm_field_bytes(header)) {
            const struct mf_field *field = mf_from_oxm_header(header, NULL, false, NULL);

            if (field && field->variable_len) {
                if (n <= field->n_bytes) {
                    int len = (nxm_hasmask(header) ? n * 2 : n) +
                              nxm_experimenter_len(header);

                    header = NXM_HEADER(nxm_vendor(header), nxm_class(header),
                                        nxm_field(header),
                                        nxm_hasmask(header) ? 1 : 0, len);
                } else {
                    ovs_fatal(0, "expected to read at most %d bytes but got "
                              "%"PRIuSIZE, field->n_bytes, n);
                }
            } else {
                ovs_fatal(0, "expected to read %d bytes but got %"PRIuSIZE,
                          nxm_field_bytes(header), n);
            }
        }
        nw_header = htonll(header);
        memcpy(b->header, &nw_header, nxm_header_len(header));

        if (nxm_hasmask(header)) {
            s += strspn(s, " ");
            if (*s != '/') {
                ovs_fatal(0, "%s: missing / in masked field %.*s",
                          full_s, name_len, name);
            }
            s = ofpbuf_put_hex(b, s + 1, &n);
            if (n != nxm_field_bytes(header)) {
                ovs_fatal(0, "%.2s: hex digits expected", s);
            }
        }

        s += strspn(s, " ");
        if (*s != ')') {
            ovs_fatal(0, "%s: missing ) following field %.*s",
                      full_s, name_len, name);
        }
        s++;
    }

    return b->size - start_len;
}

int
nx_match_from_string(const char *s, struct ofpbuf *b)
{
    int match_len = nx_match_from_string_raw(s, b);
    ofpbuf_put_zeros(b, PAD_SIZE(match_len, 8));
    return match_len;
}

int
oxm_match_from_string(const char *s, struct ofpbuf *b)
{
    int match_len;
    struct ofp11_match_header *omh;
    size_t start_len = b->size;

    ofpbuf_put_uninit(b, sizeof *omh);
    match_len = nx_match_from_string_raw(s, b) + sizeof *omh;
    ofpbuf_put_zeros(b, PAD_SIZE(match_len, 8));

    omh = ofpbuf_at(b, start_len, sizeof *omh);
    omh->type = htons(OFPMT_OXM);
    omh->length = htons(match_len);

    return match_len;
}

/* Parses 's' as a "move" action, in the form described in ovs-actions(7), into
 * '*move'.
 *
 * Returns NULL if successful, otherwise a malloc()'d string describing the
 * error.  The caller is responsible for freeing the returned string. */
char * OVS_WARN_UNUSED_RESULT
nxm_parse_reg_move(struct ofpact_reg_move *move, const char *s)
{
    const char *full_s = s;
    char *error;

    error = mf_parse_subfield__(&move->src, &s);
    if (error) {
        return error;
    }
    if (strncmp(s, "->", 2)) {
        return xasprintf("%s: missing `->' following source", full_s);
    }
    s += 2;
    error = mf_parse_subfield(&move->dst, s);
    if (error) {
        return error;
    }

    if (move->src.n_bits != move->dst.n_bits) {
        return xasprintf("%s: source field is %d bits wide but destination is "
                         "%d bits wide", full_s,
                         move->src.n_bits, move->dst.n_bits);
    }
    return NULL;
}

/* nxm_format_reg_move(). */

void
nxm_format_reg_move(const struct ofpact_reg_move *move, struct ds *s)
{
    ds_put_format(s, "%smove:%s", colors.special, colors.end);
    mf_format_subfield(&move->src, s);
    ds_put_format(s, "%s->%s", colors.special, colors.end);
    mf_format_subfield(&move->dst, s);
}


enum ofperr
nxm_reg_move_check(const struct ofpact_reg_move *move,
                   const struct match *match)
{
    enum ofperr error;

    error = mf_check_src(&move->src, match);
    if (error) {
        return error;
    }

    return mf_check_dst(&move->dst, match);
}

/* nxm_execute_reg_move(). */

void
nxm_reg_load(const struct mf_subfield *dst, uint64_t src_data,
             struct flow *flow, struct flow_wildcards *wc)
{
    union mf_subvalue src_subvalue;
    union mf_subvalue mask_value;
    ovs_be64 src_data_be = htonll(src_data);

    memset(&mask_value, 0xff, sizeof mask_value);
    mf_write_subfield_flow(dst, &mask_value, &wc->masks);

    bitwise_copy(&src_data_be, sizeof src_data_be, 0,
                 &src_subvalue, sizeof src_subvalue, 0,
                 sizeof src_data_be * 8);
    mf_write_subfield_flow(dst, &src_subvalue, flow);
}

/* nxm_parse_stack_action, works for both push() and pop(). */

/* Parses 's' as a "push" or "pop" action, in the form described in
 * ovs-actions(7), into '*stack_action'.
 *
 * Returns NULL if successful, otherwise a malloc()'d string describing the
 * error.  The caller is responsible for freeing the returned string. */
char * OVS_WARN_UNUSED_RESULT
nxm_parse_stack_action(struct ofpact_stack *stack_action, const char *s)
{
    char *error;

    error = mf_parse_subfield__(&stack_action->subfield, &s);
    if (error) {
        return error;
    }

    if (*s != '\0') {
        return xasprintf("%s: trailing garbage following push or pop", s);
    }

    return NULL;
}

void
nxm_format_stack_push(const struct ofpact_stack *push, struct ds *s)
{
    ds_put_format(s, "%spush:%s", colors.param, colors.end);
    mf_format_subfield(&push->subfield, s);
}

void
nxm_format_stack_pop(const struct ofpact_stack *pop, struct ds *s)
{
    ds_put_format(s, "%spop:%s", colors.param, colors.end);
    mf_format_subfield(&pop->subfield, s);
}

enum ofperr
nxm_stack_push_check(const struct ofpact_stack *push,
                     const struct match *match)
{
    return mf_check_src(&push->subfield, match);
}

enum ofperr
nxm_stack_pop_check(const struct ofpact_stack *pop,
                    const struct match *match)
{
    return mf_check_dst(&pop->subfield, match);
}

/* nxm_execute_stack_push(), nxm_execute_stack_pop().
 *
 * A stack is an ofpbuf with 'data' pointing to the bottom of the stack and
 * 'size' indexing the top of the stack.  Each value of some byte length is
 * stored to the stack immediately followed by the length of the value as an
 * unsigned byte.  This way a POP operation can first read the length byte, and
 * then the appropriate number of bytes from the stack.  This also means that
 * it is only possible to traverse the stack from top to bottom.  It is
 * possible, however, to push values also to the bottom of the stack, which is
 * useful when a stack has been serialized to a wire format in reverse order
 * (topmost value first).
 */

/* Push value 'v' of length 'bytes' to the top of 'stack'. */
void
nx_stack_push(struct ofpbuf *stack, const void *v, uint8_t bytes)
{
    ofpbuf_put(stack, v, bytes);
    ofpbuf_put(stack, &bytes, sizeof bytes);
}

/* Push value 'v' of length 'bytes' to the bottom of 'stack'. */
void
nx_stack_push_bottom(struct ofpbuf *stack, const void *v, uint8_t bytes)
{
    ofpbuf_push(stack, &bytes, sizeof bytes);
    ofpbuf_push(stack, v, bytes);
}

/* Pop the topmost value from 'stack', returning a pointer to the value in the
 * stack and the length of the value in '*bytes'.  In case of underflow a NULL
 * is returned and length is returned as zero via '*bytes'. */
void *
nx_stack_pop(struct ofpbuf *stack, uint8_t *bytes)
{
    if (!stack->size) {
        *bytes = 0;
        return NULL;
    }

    stack->size -= sizeof *bytes;
    memcpy(bytes, ofpbuf_tail(stack), sizeof *bytes);

    ovs_assert(stack->size >= *bytes);
    stack->size -= *bytes;
    return ofpbuf_tail(stack);
}

void
nxm_execute_stack_push(const struct ofpact_stack *push,
                       const struct flow *flow, struct flow_wildcards *wc,
                       struct ofpbuf *stack)
{
    union mf_subvalue dst_value;

    mf_write_subfield_flow(&push->subfield,
                           (union mf_subvalue *)&exact_match_mask,
                           &wc->masks);

    mf_read_subfield(&push->subfield, flow, &dst_value);
    uint8_t bytes = DIV_ROUND_UP(push->subfield.n_bits, 8);
    nx_stack_push(stack, &dst_value.u8[sizeof dst_value - bytes], bytes);
}

bool
nxm_execute_stack_pop(const struct ofpact_stack *pop,
                      struct flow *flow, struct flow_wildcards *wc,
                      struct ofpbuf *stack)
{
    uint8_t src_bytes;
    const void *src = nx_stack_pop(stack, &src_bytes);
    if (src) {
        union mf_subvalue src_value;
        uint8_t dst_bytes = DIV_ROUND_UP(pop->subfield.n_bits, 8);

        if (src_bytes < dst_bytes) {
            memset(&src_value.u8[sizeof src_value - dst_bytes], 0,
                   dst_bytes - src_bytes);
        }
        memcpy(&src_value.u8[sizeof src_value - src_bytes], src, src_bytes);
        mf_write_subfield_flow(&pop->subfield,
                               (union mf_subvalue *)&exact_match_mask,
                               &wc->masks);
        mf_write_subfield_flow(&pop->subfield, &src_value, flow);
        return true;
    } else {
        /* Attempted to pop from an empty stack. */
        return false;
    }
}

/* Parses a field from '*s' into '*field'.  If successful, stores the
 * reference to the field in '*field', and returns NULL.  On failure,
 * returns a malloc()'ed error message.
 */
char * OVS_WARN_UNUSED_RESULT
mf_parse_field(const struct mf_field **field, const char *s)
{
    const struct nxm_field *f;
    int s_len = strlen(s);

    f = nxm_field_by_name(s, s_len);
    (*field) = f ? mf_from_id(f->id) : mf_from_name_len(s, s_len);
    if (!*field) {
        return xasprintf("unknown field `%s'", s);
    }
    return NULL;
}

/* Formats 'sf' into 's' in a format normally acceptable to
 * mf_parse_subfield().  (It won't be acceptable if sf->field is NULL or if
 * sf->field has no NXM name.) */
void
mf_format_subfield(const struct mf_subfield *sf, struct ds *s)
{
    if (!sf->field) {
        ds_put_cstr(s, "<unknown>");
    } else {
        const struct nxm_field *f = nxm_field_by_mf_id(sf->field->id, 0);
        ds_put_cstr(s, f ? f->name : sf->field->name);
    }

    if (sf->field && sf->ofs == 0 && sf->n_bits == sf->field->n_bits) {
        ds_put_cstr(s, "[]");
    } else if (sf->n_bits == 1) {
        ds_put_format(s, "[%d]", sf->ofs);
    } else {
        ds_put_format(s, "[%d..%d]", sf->ofs, sf->ofs + sf->n_bits - 1);
    }
}

static const struct nxm_field *
mf_parse_subfield_name(const char *name, int name_len, bool *wild)
{
    *wild = name_len > 2 && !memcmp(&name[name_len - 2], "_W", 2);
    if (*wild) {
        name_len -= 2;
    }

    return nxm_field_by_name(name, name_len);
}

/* Parses a subfield from the beginning of '*sp' into 'sf'.  If successful,
 * returns NULL and advances '*sp' to the first byte following the parsed
 * string.  On failure, returns a malloc()'d error message, does not modify
 * '*sp', and does not properly initialize 'sf'.
 *
 * The syntax parsed from '*sp' takes the form "header[start..end]" where
 * 'header' is the name of an NXM field and 'start' and 'end' are (inclusive)
 * bit indexes.  "..end" may be omitted to indicate a single bit.  "start..end"
 * may both be omitted (the [] are still required) to indicate an entire
 * field. */
char * OVS_WARN_UNUSED_RESULT
mf_parse_subfield__(struct mf_subfield *sf, const char **sp)
{
    const struct mf_field *field = NULL;
    const struct nxm_field *f;
    const char *name;
    int start, end;
    const char *s;
    int name_len;
    bool wild;

    s = *sp;
    name = s;
    name_len = strcspn(s, "[-");

    f = mf_parse_subfield_name(name, name_len, &wild);
    field = f ? mf_from_id(f->id) : mf_from_name_len(name, name_len);
    if (!field) {
        return xasprintf("%s: unknown field `%.*s'", *sp, name_len, s);
    }

    s += name_len;
    /* Assume full field. */
    start = 0;
    end = field->n_bits - 1;
    if (*s == '[') {
        if (!strncmp(s, "[]", 2)) {
            /* Nothing to do. */
        } else if (ovs_scan(s, "[%d..%d]", &start, &end)) {
            /* Nothing to do. */
        } else if (ovs_scan(s, "[%d]", &start)) {
            end = start;
        } else {
            return xasprintf("%s: syntax error expecting [] or [<bit>] or "
                             "[<start>..<end>]", *sp);
        }
        s = strchr(s, ']') + 1;
    }

    if (start > end) {
        return xasprintf("%s: starting bit %d is after ending bit %d",
                         *sp, start, end);
    } else if (start >= field->n_bits) {
        return xasprintf("%s: starting bit %d is not valid because field is "
                         "only %d bits wide", *sp, start, field->n_bits);
    } else if (end >= field->n_bits){
        return xasprintf("%s: ending bit %d is not valid because field is "
                         "only %d bits wide", *sp, end, field->n_bits);
    }

    sf->field = field;
    sf->ofs = start;
    sf->n_bits = end - start + 1;

    *sp = s;
    return NULL;
}

/* Parses a subfield from the entirety of 's' into 'sf'.  Returns NULL if
 * successful, otherwise a malloc()'d string describing the error.  The caller
 * is responsible for freeing the returned string.
 *
 * The syntax parsed from 's' takes the form "header[start..end]" where
 * 'header' is the name of an NXM field and 'start' and 'end' are (inclusive)
 * bit indexes.  "..end" may be omitted to indicate a single bit.  "start..end"
 * may both be omitted (the [] are still required) to indicate an entire
 * field.  */
char * OVS_WARN_UNUSED_RESULT
mf_parse_subfield(struct mf_subfield *sf, const char *s)
{
    char *error = mf_parse_subfield__(sf, &s);
    if (!error && s[0]) {
        error = xstrdup("unexpected input following field syntax");
    }
    return error;
}

/* Returns an bitmap in which each bit corresponds to the like-numbered field
 * in the OFPXMC12_OPENFLOW_BASIC OXM class, in which the bit values are taken
 * from the 'fields' bitmap.  Only fields defined in OpenFlow 'version' are
 * considered.
 *
 * This is useful for encoding OpenFlow 1.2 table stats messages. */
ovs_be64
oxm_bitmap_from_mf_bitmap(const struct mf_bitmap *fields,
                          enum ofp_version version)
{
    uint64_t oxm_bitmap = 0;
    enum mf_field_id id;

    BITMAP_FOR_EACH_1 (id, MFF_N_IDS, fields->bm) {
        uint64_t oxm = mf_oxm_header(id, version);
        uint32_t class = nxm_class(oxm);
        int field = nxm_field(oxm);

        if (class == OFPXMC12_OPENFLOW_BASIC && field < 64) {
            oxm_bitmap |= UINT64_C(1) << field;
        }
    }
    return htonll(oxm_bitmap);
}

/* Opposite conversion from oxm_bitmap_from_mf_bitmap().
 *
 * This is useful for decoding OpenFlow 1.2 table stats messages. */
struct mf_bitmap
oxm_bitmap_to_mf_bitmap(ovs_be64 oxm_bitmap, enum ofp_version version)
{
    struct mf_bitmap fields = MF_BITMAP_INITIALIZER;

    for (enum mf_field_id id = 0; id < MFF_N_IDS; id++) {
        uint64_t oxm = mf_oxm_header(id, version);
        if (oxm && version >= nxm_field_by_header(oxm, false, NULL)->version) {
            uint32_t class = nxm_class(oxm);
            int field = nxm_field(oxm);

            if (class == OFPXMC12_OPENFLOW_BASIC
                && field < 64
                && oxm_bitmap & htonll(UINT64_C(1) << field)) {
                bitmap_set1(fields.bm, id);
            }
        }
    }
    return fields;
}

/* Returns a bitmap of fields that can be encoded in OXM and that can be
 * modified with a "set_field" action.  */
struct mf_bitmap
oxm_writable_fields(void)
{
    struct mf_bitmap b = MF_BITMAP_INITIALIZER;
    int i;

    for (i = 0; i < MFF_N_IDS; i++) {
        if (mf_oxm_header(i, 0) && mf_from_id(i)->writable) {
            bitmap_set1(b.bm, i);
        }
    }
    return b;
}

/* Returns a bitmap of fields that can be encoded in OXM and that can be
 * matched in a flow table.  */
struct mf_bitmap
oxm_matchable_fields(void)
{
    struct mf_bitmap b = MF_BITMAP_INITIALIZER;
    int i;

    for (i = 0; i < MFF_N_IDS; i++) {
        if (mf_oxm_header(i, 0)) {
            bitmap_set1(b.bm, i);
        }
    }
    return b;
}

/* Returns a bitmap of fields that can be encoded in OXM and that can be
 * matched in a flow table with an arbitrary bitmask.  */
struct mf_bitmap
oxm_maskable_fields(void)
{
    struct mf_bitmap b = MF_BITMAP_INITIALIZER;
    int i;

    for (i = 0; i < MFF_N_IDS; i++) {
        if (mf_oxm_header(i, 0) && mf_from_id(i)->maskable == MFM_FULLY) {
            bitmap_set1(b.bm, i);
        }
    }
    return b;
}

struct nxm_field_index {
    struct hmap_node header_node; /* In nxm_header_map. */
    struct hmap_node name_node;   /* In nxm_name_map. */
    struct ovs_list mf_node;      /* In mf_mf_map[nf.id]. */
    const struct nxm_field nf;
};

#include "nx-match.inc"

static struct hmap nxm_header_map;
static struct hmap nxm_name_map;
static struct ovs_list nxm_mf_map[MFF_N_IDS];

static void
nxm_init(void)
{
    static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
    if (ovsthread_once_start(&once)) {
        hmap_init(&nxm_header_map);
        hmap_init(&nxm_name_map);
        for (int i = 0; i < MFF_N_IDS; i++) {
            ovs_list_init(&nxm_mf_map[i]);
        }
        for (struct nxm_field_index *nfi = all_nxm_fields;
             nfi < &all_nxm_fields[ARRAY_SIZE(all_nxm_fields)]; nfi++) {
            hmap_insert(&nxm_header_map, &nfi->header_node,
                        hash_uint64(nxm_no_len(nfi->nf.header)));
            hmap_insert(&nxm_name_map, &nfi->name_node,
                        hash_string(nfi->nf.name, 0));
            ovs_list_push_back(&nxm_mf_map[nfi->nf.id], &nfi->mf_node);
        }
        ovsthread_once_done(&once);
    }
}


static const struct nxm_field *
nxm_field_by_header(uint64_t header, bool is_action, enum ofperr *h_error)
{
    const struct nxm_field_index *nfi;
    uint64_t header_no_len;

    nxm_init();
    if (nxm_hasmask(header)) {
        header = nxm_make_exact_header(header);
    }

    header_no_len = nxm_no_len(header);

    HMAP_FOR_EACH_IN_BUCKET (nfi, header_node, hash_uint64(header_no_len),
                             &nxm_header_map) {
        if (is_action && nxm_length(header) > 0) {
            if (nxm_length(header) != nxm_length(nfi->nf.header) && h_error ) {
               *h_error = OFPERR_OFPBAC_BAD_SET_LEN;
            }
        }
        if (header_no_len == nxm_no_len(nfi->nf.header)) {
            if (nxm_length(header) == nxm_length(nfi->nf.header) ||
                mf_from_id(nfi->nf.id)->variable_len) {
                return &nfi->nf;
            } else {
                return NULL;
            }
        }
    }
    return NULL;
}

static const struct nxm_field *
nxm_field_by_name(const char *name, size_t len)
{
    const struct nxm_field_index *nfi;

    nxm_init();
    HMAP_FOR_EACH_WITH_HASH (nfi, name_node, hash_bytes(name, len, 0),
                             &nxm_name_map) {
        if (strlen(nfi->nf.name) == len && !memcmp(nfi->nf.name, name, len)) {
            return &nfi->nf;
        }
    }
    return NULL;
}

static const struct nxm_field *
nxm_field_by_mf_id(enum mf_field_id id, enum ofp_version version)
{
    const struct nxm_field_index *nfi;
    const struct nxm_field *f;

    nxm_init();

    f = NULL;
    LIST_FOR_EACH (nfi, mf_node, &nxm_mf_map[id]) {
        if (!f || version >= nfi->nf.version) {
            f = &nfi->nf;
        }
    }
    return f;
}