ofp-msgs: New approach to encoding and decoding OpenFlow headers.

OpenFlow headers are not as uniform as they could be, with size, alignment,
and numbering changes from one version to another and across varieties
(e.g. ordinary messages vs. "stats" messages).  Until now the Open vSwitch
internal APIs haven't done a good job of abstracting those differences in
header formats.  This commit changes that; from this commit forward very
little code actually needs to understand the header format or numbering.
Instead, it can just encode or decode, or pull or put, the header using
a more abstract API using the ofpraw_, ofptype_, and other APIs in the
new ofp-msgs module.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Tested-by: Simon Horman <horms@verge.net.au>
Reviewed-by: Simon Horman <horms@verge.net.au>

1 files changed, 962 insertions, 0 deletions

diff --git a/lib/ofp-msgs.c b/lib/ofp-msgs.c
new file mode 100644
index 00000000..1d11e7f3
--- /dev/null
+++ b/lib/ofp-msgs.c
@@ -0,0 +1,962 @@
+/*
+ * Copyright (c) 2012 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 "ofp-msgs.h"
+#include <assert.h>
+#include "byte-order.h"
+#include "dynamic-string.h"
+#include "hash.h"
+#include "hmap.h"
+#include "ofpbuf.h"
+#include "openflow/nicira-ext.h"
+#include "openflow/openflow.h"
+#include "vlog.h"
+
+VLOG_DEFINE_THIS_MODULE(ofp_msgs);
+
+#define OFPT_VENDOR 4
+#define OFPT10_STATS_REQUEST 16
+#define OFPT10_STATS_REPLY 17
+#define OFPT11_STATS_REQUEST 18
+#define OFPT11_STATS_REPLY 19
+#define OFPST_VENDOR 0xffff
+
+/* A thin abstraction of OpenFlow headers:
+ *
+ *   - 'version' and 'type' come straight from struct ofp_header, so these are
+ *     always present and meaningful.
+ *
+ *   - 'stat' comes from the 'type' member in statistics messages only.  It is
+ *     meaningful, therefore, only if 'version' and 'type' taken together
+ *     specify a statistics request or reply.  Otherwise it is 0.
+ *
+ *   - 'vendor' is meaningful only for vendor messages, that is, if 'version'
+ *     and 'type' specify a vendor message or if 'version' and 'type' specify
+ *     a statistics message and 'stat' specifies a vendor statistic type.
+ *     Otherwise it is 0.
+ *
+ *   - 'subtype' is meaningful only for vendor messages and otherwise 0.  It
+ *     specifies a vendor-defined subtype.  There is no standard format for
+ *     these but 32 bits seems like it should be enough. */
+struct ofphdrs {
+    uint8_t version;            /* From ofp_header. */
+    uint8_t type;               /* From ofp_header. */
+    uint16_t stat;              /* From ofp10_stats_msg or ofp11_stats_msg. */
+    uint32_t vendor;            /* From ofp_vendor_header,
+                                 * ofp10_vendor_stats_msg, or
+                                 * ofp11_vendor_stats_msg. */
+    uint32_t subtype;           /* From nicira_header, nicira10_stats_msg, or
+                                 * nicira11_stats_msg. */
+};
+BUILD_ASSERT_DECL(sizeof(struct ofphdrs) == 12);
+
+/* A mapping from OpenFlow headers to OFPRAW_*.  */
+struct raw_instance {
+    struct hmap_node hmap_node; /* In 'raw_instance_map'. */
+    struct ofphdrs hdrs;        /* Key. */
+    enum ofpraw raw;            /* Value. */
+    unsigned int hdrs_len;      /* ofphdrs_len(hdrs). */
+};
+
+/* Information about a particular 'enum ofpraw'. */
+struct raw_info {
+    /* All possible instantiations of this OFPRAW_* into OpenFlow headers. */
+    struct raw_instance *instances; /* min_version - max_version + 1 elems. */
+    uint8_t min_version;
+    uint8_t max_version;
+
+    unsigned int min_body;
+    unsigned int extra_multiple;
+    enum ofptype type;
+    const char *name;
+};
+
+/* All understood OpenFlow message types, indexed by their 'struct ofphdrs'. */
+static struct hmap raw_instance_map;
+#include "ofp-msgs.inc"
+
+static ovs_be32 alloc_xid(void);
+
+/* ofphdrs functions. */
+static uint32_t ofphdrs_hash(const struct ofphdrs *);
+static bool ofphdrs_equal(const struct ofphdrs *a, const struct ofphdrs *b);
+static enum ofperr ofphdrs_decode(struct ofphdrs *,
+                                  const struct ofp_header *oh, size_t length);
+static void ofphdrs_decode_assert(struct ofphdrs *,
+                                  const struct ofp_header *oh, size_t length);
+size_t ofphdrs_len(const struct ofphdrs *);
+
+static const struct raw_info *raw_info_get(enum ofpraw);
+static struct raw_instance *raw_instance_get(const struct raw_info *,
+                                             uint8_t version);
+
+static enum ofperr ofpraw_from_ofphdrs(enum ofpraw *, const struct ofphdrs *);
+
+/* Returns a transaction ID to use for an outgoing OpenFlow message. */
+static ovs_be32
+alloc_xid(void)
+{
+    static uint32_t next_xid = 1;
+    return htonl(next_xid++);
+}
+
+static uint32_t
+ofphdrs_hash(const struct ofphdrs *hdrs)
+{
+    BUILD_ASSERT_DECL(sizeof *hdrs == 12);
+    return hash_words((const uint32_t *) hdrs, 3, 0);
+}
+
+static bool
+ofphdrs_equal(const struct ofphdrs *a, const struct ofphdrs *b)
+{
+    return !memcmp(a, b, sizeof *a);
+}
+
+static void
+log_bad_vendor(uint32_t vendor)
+{
+    static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 1);
+
+    VLOG_WARN_RL(&rl, "OpenFlow message has unknown vendor %#"PRIx32, vendor);
+}
+
+static enum ofperr
+ofphdrs_decode(struct ofphdrs *hdrs,
+               const struct ofp_header *oh, size_t length)
+{
+    memset(hdrs, 0, sizeof *hdrs);
+    if (length < sizeof *oh) {
+        return OFPERR_OFPBRC_BAD_LEN;
+    }
+
+    /* Get base message version and type (OFPT_*). */
+    hdrs->version = oh->version;
+    hdrs->type = oh->type;
+
+    if (hdrs->type == OFPT_VENDOR) {
+        /* Get vendor. */
+        const struct ofp_vendor_header *ovh;
+
+        if (length < sizeof *ovh) {
+            return OFPERR_OFPBRC_BAD_LEN;
+        }
+
+        ovh = (const struct ofp_vendor_header *) oh;
+        hdrs->vendor = ntohl(ovh->vendor);
+        if (hdrs->vendor == NX_VENDOR_ID) {
+            /* Get Nicira message subtype (NXT_*). */
+            const struct nicira_header *nh;
+
+            if (length < sizeof *nh) {
+                return OFPERR_OFPBRC_BAD_LEN;
+            }
+            nh = (const struct nicira_header *) oh;
+            hdrs->subtype = ntohl(nh->subtype);
+        } else {
+            log_bad_vendor(hdrs->vendor);
+            return OFPERR_OFPBRC_BAD_VENDOR;
+        }
+    } else if (hdrs->version == OFP10_VERSION
+               && (hdrs->type == OFPT10_STATS_REQUEST ||
+                   hdrs->type == OFPT10_STATS_REPLY)) {
+        const struct ofp_stats_msg *osm;
+
+        /* Get statistic type (OFPST_*). */
+        if (length < sizeof *osm) {
+            return OFPERR_OFPBRC_BAD_LEN;
+        }
+        osm = (const struct ofp_stats_msg *) oh;
+        hdrs->stat = ntohs(osm->type);
+
+        if (hdrs->stat == OFPST_VENDOR) {
+            /* Get vendor. */
+            const struct ofp10_vendor_stats_msg *ovsm;
+
+            if (length < sizeof *ovsm) {
+                return OFPERR_OFPBRC_BAD_LEN;
+            }
+
+            ovsm = (const struct ofp10_vendor_stats_msg *) oh;
+            hdrs->vendor = ntohl(ovsm->vendor);
+            if (hdrs->vendor == NX_VENDOR_ID) {
+                /* Get Nicira statistic type (NXST_*). */
+                const struct nicira10_stats_msg *nsm;
+
+                if (length < sizeof *nsm) {
+                    return OFPERR_OFPBRC_BAD_LEN;
+                }
+                nsm = (const struct nicira10_stats_msg *) oh;
+                hdrs->subtype = ntohl(nsm->subtype);
+            } else {
+                log_bad_vendor(hdrs->vendor);
+                return OFPERR_OFPBRC_BAD_VENDOR;
+            }
+        }
+    } else if (hdrs->version != OFP10_VERSION
+               && (hdrs->type == OFPT11_STATS_REQUEST ||
+                   hdrs->type == OFPT11_STATS_REPLY)) {
+        const struct ofp11_stats_msg *osm;
+
+        /* Get statistic type (OFPST_*). */
+        if (length < sizeof *osm) {
+            return OFPERR_OFPBRC_BAD_LEN;
+        }
+        osm = (const struct ofp11_stats_msg *) oh;
+        hdrs->stat = ntohs(osm->type);
+
+        if (hdrs->stat == OFPST_VENDOR) {
+            /* Get vendor. */
+            const struct ofp11_vendor_stats_msg *ovsm;
+
+            if (length < sizeof *ovsm) {
+                return OFPERR_OFPBRC_BAD_LEN;
+            }
+
+            ovsm = (const struct ofp11_vendor_stats_msg *) oh;
+            hdrs->vendor = ntohl(ovsm->vendor);
+            if (hdrs->vendor == NX_VENDOR_ID) {
+                /* Get Nicira statistic type (NXST_*). */
+                const struct nicira11_stats_msg *nsm;
+
+                if (length < sizeof *nsm) {
+                    return OFPERR_OFPBRC_BAD_LEN;
+                }
+                nsm = (const struct nicira11_stats_msg *) oh;
+                hdrs->subtype = ntohl(nsm->subtype);
+            } else {
+                log_bad_vendor(hdrs->vendor);
+                return OFPERR_OFPBRC_BAD_VENDOR;
+            }
+        }
+    }
+
+    return 0;
+}
+
+static void
+ofphdrs_decode_assert(struct ofphdrs *hdrs,
+                      const struct ofp_header *oh, size_t length)
+{
+    enum ofperr error = ofphdrs_decode(hdrs, oh, length);
+    assert(!error);
+}
+
+static bool
+ofphdrs_is_stat(const struct ofphdrs *hdrs)
+{
+    return (hdrs->version == OFP10_VERSION
+            ? (hdrs->type == OFPT10_STATS_REQUEST ||
+               hdrs->type == OFPT10_STATS_REPLY)
+            : (hdrs->type == OFPT11_STATS_REQUEST ||
+               hdrs->type == OFPT11_STATS_REPLY));
+}
+
+size_t
+ofphdrs_len(const struct ofphdrs *hdrs)
+{
+    if (hdrs->type == OFPT_VENDOR) {
+        return sizeof(struct nicira_header);
+    }
+
+    if (hdrs->version == OFP10_VERSION) {
+        if (hdrs->type == OFPT10_STATS_REQUEST ||
+            hdrs->type == OFPT10_STATS_REPLY) {
+            return (hdrs->stat == OFPST_VENDOR
+                    ? sizeof(struct nicira10_stats_msg)
+                    : sizeof(struct ofp_stats_msg));
+        }
+    } else {
+        if (hdrs->type == OFPT11_STATS_REQUEST ||
+            hdrs->type == OFPT11_STATS_REPLY) {
+            return (hdrs->stat == OFPST_VENDOR
+                    ? sizeof(struct nicira11_stats_msg)
+                    : sizeof(struct ofp11_stats_msg));
+        }
+    }
+
+    return sizeof(struct ofp_header);
+}
+
+/* Determines the OFPRAW_* type of the OpenFlow message at 'oh', which has
+ * length 'oh->length'.  (The caller must ensure that 'oh->length' bytes of
+ * data are readable at 'oh'.)  On success, returns 0 and stores the type into
+ * '*raw'.  On failure, returns an OFPERR_* error code and zeros '*raw'.
+ *
+ * This function checks that 'oh' is a valid length for its particular type of
+ * message, and returns an error if not. */
+enum ofperr
+ofpraw_decode(enum ofpraw *raw, const struct ofp_header *oh)
+{
+    struct ofpbuf msg;
+
+    ofpbuf_use_const(&msg, oh, ntohs(oh->length));
+    return ofpraw_pull(raw, &msg);
+}
+
+/* Determines the OFPRAW_* type of the OpenFlow message in 'msg', which starts
+ * at 'msg->data' and has length 'msg->size' bytes.  On success, returns 0 and
+ * stores the type into '*rawp'.  On failure, returns an OFPERR_* error code
+ * and zeros '*rawp'.
+ *
+ * This function checks that the message has a valid length for its particular
+ * type of message, and returns an error if not.
+ *
+ * In addition to setting '*rawp', this function pulls off the OpenFlow header
+ * (including the stats headers, vendor header, and any subtype header) with
+ * ofpbuf_pull().  It also sets 'msg->l2' to the start of the OpenFlow header
+ * and 'msg->l3' just beyond the headers (that is, to the final value of
+ * msg->data). */
+enum ofperr
+ofpraw_pull(enum ofpraw *rawp, struct ofpbuf *msg)
+{
+    static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
+
+    const struct raw_instance *instance;
+    const struct raw_info *info;
+    struct ofphdrs hdrs;
+
+    unsigned int min_len;
+    unsigned int len;
+
+    enum ofperr error;
+    enum ofpraw raw;
+
+    /* Set default outputs. */
+    msg->l2 = msg->l3 = msg->data;
+    *rawp = 0;
+
+    len = msg->size;
+    error = ofphdrs_decode(&hdrs, msg->data, len);
+    if (error) {
+        return error;
+    }
+
+    error = ofpraw_from_ofphdrs(&raw, &hdrs);
+    if (error) {
+        return error;
+    }
+
+    info = raw_info_get(raw);
+    instance = raw_instance_get(info, hdrs.version);
+    msg->l2 = ofpbuf_pull(msg, instance->hdrs_len);
+    msg->l3 = msg->data;
+
+    min_len = instance->hdrs_len + info->min_body;
+    switch (info->extra_multiple) {
+    case 0:
+        if (len != min_len) {
+            VLOG_WARN_RL(&rl, "received %s with incorrect length %u (expected "
+                         "length %u)", info->name, len, min_len);
+            return OFPERR_OFPBRC_BAD_LEN;
+        }
+        break;
+
+    case 1:
+        if (len < min_len) {
+            VLOG_WARN_RL(&rl, "received %s with incorrect length %u (expected "
+                         "length at least %u bytes)",
+                         info->name, len, min_len);
+            return OFPERR_OFPBRC_BAD_LEN;
+        }
+        break;
+
+    default:
+        if (len < min_len || (len - min_len) % info->extra_multiple) {
+            VLOG_WARN_RL(&rl, "received %s with incorrect length %u (must be "
+                         "exactly %u bytes or longer by an integer multiple "
+                         "of %u bytes)",
+                         info->name, len, min_len, info->extra_multiple);
+            return OFPERR_OFPBRC_BAD_LEN;
+        }
+        break;
+    }
+
+    *rawp = raw;
+    return 0;
+}
+
+/* Does the same job as ofpraw_pull(), except that it assert-fails if
+ * ofpbuf_pull() would have reported an error.  Thus, it's able to use the
+ * return value for the OFPRAW_* message type instead of an error code.
+ *
+ * (It only makes sense to use this function if you previously called
+ * ofpbuf_decode() on the message and thus know that it's OK.) */
+enum ofpraw
+ofpraw_pull_assert(struct ofpbuf *msg)
+{
+    enum ofperr error;
+    enum ofpraw raw;
+
+    error = ofpraw_pull(&raw, msg);
+    assert(!error);
+    return raw;
+}
+
+/* Determines the OFPRAW_* type of the OpenFlow message that starts at 'oh' and
+ * has length 'length' bytes.  On success, returns 0 and stores the type into
+ * '*rawp'.  On failure, returns an OFPERR_* error code and zeros '*rawp'.
+ *
+ * Unlike other functions for decoding message types, this one is not picky
+ * about message length.  For example, it will successfully decode a message
+ * whose body is shorter than the minimum length for a message of its type.
+ * Thus, this is the correct function to use for decoding the type of a message
+ * that might have been truncated, such as the payload of an OpenFlow error
+ * message (which is allowed to be truncated to 64 bytes). */
+enum ofperr
+ofpraw_decode_partial(enum ofpraw *raw,
+                      const struct ofp_header *oh, size_t length)
+{
+    struct ofphdrs hdrs;
+    enum ofperr error;
+
+    error = ofphdrs_decode(&hdrs, oh, length);
+    if (!error) {
+        error = ofpraw_from_ofphdrs(raw, &hdrs);
+    }
+
+    if (error) {
+        *raw = 0;
+    }
+    return error;
+}
+
+/* Encoding messages using OFPRAW_* values. */
+
+static void ofpraw_put__(enum ofpraw, uint8_t version, ovs_be32 xid,
+                         size_t extra_tailroom, struct ofpbuf *);
+
+/* Allocates and returns a new ofpbuf that contains an OpenFlow header for
+ * 'raw' with OpenFlow version 'version' and a fresh OpenFlow transaction ID.
+ * The ofpbuf has enough tailroom for the minimum body length of 'raw', plus
+ * 'extra_tailroom' additional bytes.
+ *
+ * Each 'raw' value is valid only for certain OpenFlow versions.  The caller
+ * must specify a valid (raw, version) pair.
+ *
+ * In the returned ofpbuf, 'l2' points to the beginning of the OpenFlow header
+ * and 'l3' points just after it, to where the message's body will start.  The
+ * caller must actually allocate the body into the space reserved for it,
+ * e.g. with ofpbuf_put_uninit().
+ *
+ * The caller owns the returned ofpbuf and must free it when it is no longer
+ * needed, e.g. with ofpbuf_delete(). */
+struct ofpbuf *
+ofpraw_alloc(enum ofpraw raw, uint8_t version, size_t extra_tailroom)
+{
+    return ofpraw_alloc_xid(raw, version, alloc_xid(), extra_tailroom);
+}
+
+/* Same as ofpraw_alloc() but the caller provides the transaction ID. */
+struct ofpbuf *
+ofpraw_alloc_xid(enum ofpraw raw, uint8_t version, ovs_be32 xid,
+                 size_t extra_tailroom)
+{
+    struct ofpbuf *buf = ofpbuf_new(0);
+    ofpraw_put__(raw, version, xid, extra_tailroom, buf);
+    return buf;
+}
+
+/* Same as ofpraw_alloc(), but obtains the OpenFlow version and transaction ID
+ * from 'request->version' and 'request->xid', respectively.
+ *
+ * Even though the version comes from 'request->version', the caller must still
+ * know what it is doing, by specifying a valid pairing of 'raw' and
+ * 'request->version', just like ofpraw_alloc(). */
+struct ofpbuf *
+ofpraw_alloc_reply(enum ofpraw raw, const struct ofp_header *request,
+                   size_t extra_tailroom)
+{
+    return ofpraw_alloc_xid(raw, request->version, request->xid,
+                            extra_tailroom);
+}
+
+/* Allocates and returns a new ofpbuf that contains an OpenFlow header that is
+ * a stats reply to the stats request in 'request', using the same OpenFlow
+ * version and transaction ID as 'request'.  The ofpbuf has enough tailroom for
+ * the stats reply's minimum body length, plus 'extra_tailroom' additional
+ * bytes.
+ *
+ * 'request' must be a stats request, that is, an OFPRAW_OFPST* or OFPRAW_NXST*
+ * value.  Every stats request has a corresponding reply, so the (raw, version)
+ * pairing pitfalls of the other ofpraw_alloc_*() functions don't apply here.
+ *
+ * In the returned ofpbuf, 'l2' points to the beginning of the OpenFlow header
+ * and 'l3' points just after it, to where the message's body will start.  The
+ * caller must actually allocate the body into the space reserved for it,
+ * e.g. with ofpbuf_put_uninit().
+ *
+ * The caller owns the returned ofpbuf and must free it when it is no longer
+ * needed, e.g. with ofpbuf_delete(). */
+struct ofpbuf *
+ofpraw_alloc_stats_reply(const struct ofp_header *request,
+                         size_t extra_tailroom)
+{
+    enum ofpraw request_raw;
+    enum ofpraw reply_raw;
+    enum ofperr error;
+
+    error = ofpraw_decode_partial(&request_raw, request,
+                                  ntohs(request->length));
+    assert(!error);
+
+    reply_raw = ofpraw_stats_request_to_reply(request_raw, request->version);
+    assert(reply_raw);
+
+    return ofpraw_alloc_reply(reply_raw, request, extra_tailroom);
+}
+
+/* Appends to 'buf' an OpenFlow header for 'raw' with OpenFlow version
+ * 'version' and a fresh OpenFlow transaction ID.  Preallocates enough tailroom
+ * in 'buf' for the minimum body length of 'raw', plus 'extra_tailroom'
+ * additional bytes.
+ *
+ * Each 'raw' value is valid only for certain OpenFlow versions.  The caller
+ * must specify a valid (raw, version) pair.
+ *
+ * Upon return, 'buf->l2' points to the beginning of the OpenFlow header and
+ * 'buf->l3' points just after it, to where the message's body will start.  The
+ * caller must actually allocating the body into the space reserved for it,
+ * e.g. with ofpbuf_put_uninit(). */
+void
+ofpraw_put(enum ofpraw raw, uint8_t version, struct ofpbuf *buf)
+{
+    ofpraw_put__(raw, version, alloc_xid(), 0, buf);
+}
+
+/* Same as ofpraw_put() but the caller provides the transaction ID. */
+void
+ofpraw_put_xid(enum ofpraw raw, uint8_t version, ovs_be32 xid,
+               struct ofpbuf *buf)
+{
+    ofpraw_put__(raw, version, xid, 0, buf);
+}
+
+/* Same as ofpraw_put(), but obtains the OpenFlow version and transaction ID
+ * from 'request->version' and 'request->xid', respectively.
+ *
+ * Even though the version comes from 'request->version', the caller must still
+ * know what it is doing, by specifying a valid pairing of 'raw' and
+ * 'request->version', just like ofpraw_put(). */
+void
+ofpraw_put_reply(enum ofpraw raw, const struct ofp_header *request,
+                 struct ofpbuf *buf)
+{
+    ofpraw_put__(raw, request->version, request->xid, 0, buf);
+}
+
+/* Appends to 'buf' an OpenFlow header that is a stats reply to the stats
+ * request in 'request', using the same OpenFlow version and transaction ID as
+ * 'request'.  Preallocate enough tailroom in 'buf for the stats reply's
+ * minimum body length, plus 'extra_tailroom' additional bytes.
+ *
+ * 'request' must be a stats request, that is, an OFPRAW_OFPST* or OFPRAW_NXST*
+ * value.  Every stats request has a corresponding reply, so the (raw, version)
+ * pairing pitfalls of the other ofpraw_alloc_*() functions don't apply here.
+ *
+ * In the returned ofpbuf, 'l2' points to the beginning of the OpenFlow header
+ * and 'l3' points just after it, to where the message's body will start.  The
+ * caller must actually allocate the body into the space reserved for it,
+ * e.g. with ofpbuf_put_uninit().
+ *
+ * The caller owns the returned ofpbuf and must free it when it is no longer
+ * needed, e.g. with ofpbuf_delete(). */
+void
+ofpraw_put_stats_reply(const struct ofp_header *request, struct ofpbuf *buf)
+{
+    enum ofperr error;
+    enum ofpraw raw;
+
+    error = ofpraw_decode_partial(&raw, request, ntohs(request->length));
+    assert(!error);
+
+    raw = ofpraw_stats_request_to_reply(raw, request->version);
+    assert(raw);
+
+    ofpraw_put__(raw, request->version, request->xid, 0, buf);
+}
+
+static void
+ofpraw_put__(enum ofpraw raw, uint8_t version, ovs_be32 xid,
+             size_t extra_tailroom, struct ofpbuf *buf)
+{
+    const struct raw_info *info = raw_info_get(raw);
+    const struct raw_instance *instance = raw_instance_get(info, version);
+    const struct ofphdrs *hdrs = &instance->hdrs;
+    struct ofp_header *oh;
+
+    ofpbuf_prealloc_tailroom(buf, (instance->hdrs_len + info->min_body
+                                   + extra_tailroom));
+    buf->l2 = ofpbuf_put_uninit(buf, instance->hdrs_len);
+    buf->l3 = ofpbuf_tail(buf);
+
+    oh = buf->l2;
+    oh->version = version;
+    oh->type = hdrs->type;
+    oh->length = htons(buf->size);
+    oh->xid = xid;
+
+    if (hdrs->type == OFPT_VENDOR) {
+        struct nicira_header *nh = buf->l2;
+
+        assert(hdrs->vendor == NX_VENDOR_ID);
+        nh->vendor = htonl(hdrs->vendor);
+        nh->subtype = htonl(hdrs->subtype);
+    } else if (version == OFP10_VERSION
+               && (hdrs->type == OFPT10_STATS_REQUEST ||
+                   hdrs->type == OFPT10_STATS_REPLY)) {
+        struct ofp_stats_msg *osm = buf->l2;
+
+        osm->type = htons(hdrs->stat);
+        osm->flags = htons(0);
+
+        if (hdrs->stat == OFPST_VENDOR) {
+            struct ofp10_vendor_stats_msg *ovsm = buf->l2;
+
+            ovsm->vendor = htonl(hdrs->vendor);
+            if (hdrs->vendor == NX_VENDOR_ID) {
+                struct nicira10_stats_msg *nsm = buf->l2;
+
+                nsm->subtype = htonl(hdrs->subtype);
+                memset(nsm->pad, 0, sizeof nsm->pad);
+            } else {
+                NOT_REACHED();
+            }
+        }
+    } else if (version != OFP10_VERSION
+               && (hdrs->type == OFPT11_STATS_REQUEST ||
+                   hdrs->type == OFPT11_STATS_REPLY)) {
+        struct ofp11_stats_msg *osm = buf->l2;
+
+        osm->type = htons(hdrs->stat);
+        osm->flags = htons(0);
+        memset(osm->pad, 0, sizeof osm->pad);
+
+        if (hdrs->stat == OFPST_VENDOR) {
+            struct ofp11_vendor_stats_msg *ovsm = buf->l2;
+
+            ovsm->vendor = htonl(hdrs->vendor);
+            if (hdrs->vendor == NX_VENDOR_ID) {
+                struct nicira11_stats_msg *nsm = buf->l2;
+
+                nsm->subtype = htonl(hdrs->subtype);
+            } else {
+                NOT_REACHED();
+            }
+        }
+    }
+}
+
+/* Returns 'raw''s name.
+ *
+ * The name is the name used for 'raw' in the OpenFlow specification.  For
+ * example, ofpraw_get_name(OFPRAW_OFPT10_FEATURES_REPLY) is
+ * "OFPT_FEATURES_REPLY".
+ *
+ * The caller must not modify or free the returned string. */
+const char *
+ofpraw_get_name(enum ofpraw raw)
+{
+    return raw_info_get(raw)->name;
+}
+
+/* Returns the stats reply that corresponds to 'raw' in the given OpenFlow
+ * 'version'. */
+enum ofpraw
+ofpraw_stats_request_to_reply(enum ofpraw raw, uint8_t version)
+{
+    const struct raw_info *info = raw_info_get(raw);
+    const struct raw_instance *instance = raw_instance_get(info, version);
+    enum ofpraw reply_raw;
+    struct ofphdrs hdrs;
+    enum ofperr error;
+
+    hdrs = instance->hdrs;
+    if (hdrs.version == OFP10_VERSION) {
+        assert(hdrs.type == OFPT10_STATS_REQUEST);
+        hdrs.type = OFPT10_STATS_REPLY;
+    } else {
+        assert(hdrs.type == OFPT11_STATS_REQUEST);
+        hdrs.type = OFPT11_STATS_REPLY;
+    }
+
+    error = ofpraw_from_ofphdrs(&reply_raw, &hdrs);
+    assert(!error);
+
+    return reply_raw;
+}
+
+/* Determines the OFPTYPE_* type of the OpenFlow message at 'oh', which has
+ * length 'oh->length'.  (The caller must ensure that 'oh->length' bytes of
+ * data are readable at 'oh'.)  On success, returns 0 and stores the type into
+ * '*typep'.  On failure, returns an OFPERR_* error code and zeros '*typep'.
+ *
+ * This function checks that 'oh' is a valid length for its particular type of
+ * message, and returns an error if not. */
+enum ofperr
+ofptype_decode(enum ofptype *typep, const struct ofp_header *oh)
+{
+    enum ofperr error;
+    enum ofpraw raw;
+
+    error = ofpraw_decode(&raw, oh);
+    *typep = error ? 0 : ofptype_from_ofpraw(raw);
+    return error;
+}
+
+/* Determines the OFPTYPE_* type of the OpenFlow message in 'msg', which starts
+ * at 'msg->data' and has length 'msg->size' bytes.  On success, returns 0 and
+ * stores the type into '*typep'.  On failure, returns an OFPERR_* error code
+ * and zeros '*typep'.
+ *
+ * This function checks that the message has a valid length for its particular
+ * type of message, and returns an error if not.
+ *
+ * In addition to setting '*typep', this function pulls off the OpenFlow header
+ * (including the stats headers, vendor header, and any subtype header) with
+ * ofpbuf_pull().  It also sets 'msg->l2' to the start of the OpenFlow header
+ * and 'msg->l3' just beyond the headers (that is, to the final value of
+ * msg->data). */
+enum ofperr
+ofptype_pull(enum ofptype *typep, struct ofpbuf *buf)
+{
+    enum ofperr error;
+    enum ofpraw raw;
+
+    error = ofpraw_pull(&raw, buf);
+    *typep = error ? 0 : ofptype_from_ofpraw(raw);
+    return error;
+}
+
+/* Returns the OFPTYPE_* type that corresponds to 'raw'.
+ *
+ * (This is a one-way trip, because the mapping from ofpraw to ofptype is
+ * many-to-one.)  */
+enum ofptype
+ofptype_from_ofpraw(enum ofpraw raw)
+{
+    return raw_info_get(raw)->type;
+}
+
+/* Updates the 'length' field of the OpenFlow message in 'buf' to
+ * 'buf->size'. */
+void
+ofpmsg_update_length(struct ofpbuf *buf)
+{
+    struct ofp_header *oh = ofpbuf_at_assert(buf, 0, sizeof *oh);
+    oh->length = htons(buf->size);
+}
+
+/* Returns just past the Openflow header (including the stats headers, vendor
+ * header, and any subtype header) in 'oh'. */
+const void *
+ofpmsg_body(const struct ofp_header *oh)
+{
+    struct ofphdrs hdrs;
+
+    ofphdrs_decode_assert(&hdrs, oh, ntohs(oh->length));
+    return (const uint8_t *) oh + ofphdrs_len(&hdrs);
+}
+
+/* Initializes 'replies' as a new list of stats messages that reply to
+ * 'request', which must be a stats request message.  Initially the list will
+ * consist of only a single reply part without any body.  The caller should
+ * use calls to the other ofpmp_*() functions to add to the body and split the
+ * message into multiple parts, if necessary. */
+void
+ofpmp_init(struct list *replies, const struct ofp_header *request)
+{
+    struct ofpbuf *msg;
+
+    list_init(replies);
+
+    msg = ofpraw_alloc_stats_reply(request, 1000);
+    list_push_back(replies, &msg->list_node);
+}
+
+/* Prepares to append up to 'len' bytes to the series of statistics replies in
+ * 'replies', which should have been initialized with ofpmp_init(), if
+ * necessary adding a new reply to the list.
+ *
+ * Returns an ofpbuf with at least 'len' bytes of tailroom.  The 'len' bytes
+ * have not actually been allocated, so the caller must do so with
+ * e.g. ofpbuf_put_uninit(). */
+struct ofpbuf *
+ofpmp_reserve(struct list *replies, size_t len)
+{
+    struct ofpbuf *msg = ofpbuf_from_list(list_back(replies));
+
+    if (msg->size + len <= UINT16_MAX) {
+        ofpbuf_prealloc_tailroom(msg, len);
+        return msg;
+    } else {
+        unsigned int hdrs_len;
+        struct ofpbuf *next;
+        struct ofphdrs hdrs;
+
+        ofphdrs_decode_assert(&hdrs, msg->data, msg->size);
+        hdrs_len = ofphdrs_len(&hdrs);
+
+        next = ofpbuf_new(MAX(1024, hdrs_len + len));
+        ofpbuf_put(next, msg->data, hdrs_len);
+        list_push_back(replies, &next->list_node);
+
+        return next;
+    }
+}
+
+/* Appends 'len' bytes to the series of statistics replies in 'replies', and
+ * returns the first byte. */
+void *
+ofpmp_append(struct list *replies, size_t len)
+{
+    return ofpbuf_put_uninit(ofpmp_reserve(replies, len), len);
+}
+
+/* Sometimes, when composing stats replies, it's difficult to predict how long
+ * an individual reply chunk will be before actually encoding it into the reply
+ * buffer.  This function allows easy handling of this case: just encode the
+ * reply, then use this function to break the message into two pieces if it
+ * exceeds the OpenFlow message limit.
+ *
+ * In detail, if the final stats message in 'replies' is too long for OpenFlow,
+ * this function breaks it into two separate stats replies, the first one with
+ * the first 'start_ofs' bytes, the second one containing the bytes from that
+ * offset onward. */
+void
+ofpmp_postappend(struct list *replies, size_t start_ofs)
+{
+    struct ofpbuf *msg = ofpbuf_from_list(list_back(replies));
+
+    assert(start_ofs <= UINT16_MAX);
+    if (msg->size > UINT16_MAX) {
+        size_t len = msg->size - start_ofs;
+        memcpy(ofpmp_append(replies, len),
+               (const uint8_t *) msg->data + start_ofs, len);
+        msg->size = start_ofs;
+    }
+}
+
+static ovs_be16 *
+ofpmp_flags__(const struct ofp_header *oh)
+{
+    return (oh->version == OFP10_VERSION
+            ? &((struct ofp_stats_msg *) oh)->flags
+            : &((struct ofp11_stats_msg *) oh)->flags);
+}
+
+/* Returns the OFPSF_* flags found in the OpenFlow stats header of 'oh', which
+ * must be an OpenFlow stats request or reply.
+ *
+ * (OFPSF_REPLY_MORE is the only defined flag.) */
+uint16_t
+ofpmp_flags(const struct ofp_header *oh)
+{
+    return ntohs(*ofpmp_flags__(oh));
+}
+
+/* Returns true if the OFPSF_REPLY_MORE flag is set in the OpenFlow stats
+ * header of 'oh', which must be an OpenFlow stats request or reply, false if
+ * it is not set. */
+bool
+ofpmp_more(const struct ofp_header *oh)
+{
+    return (ofpmp_flags(oh) & OFPSF_REPLY_MORE) != 0;
+}
+
+static void ofpmsgs_init(void);
+
+static const struct raw_info *
+raw_info_get(enum ofpraw raw)
+{
+    ofpmsgs_init();
+
+    assert(raw < ARRAY_SIZE(raw_infos));
+    return &raw_infos[raw];
+}
+
+static struct raw_instance *
+raw_instance_get(const struct raw_info *info, uint8_t version)
+{
+    assert(version >= info->min_version && version <= info->max_version);
+    return &info->instances[version - info->min_version];
+}
+
+static enum ofperr
+ofpraw_from_ofphdrs(enum ofpraw *raw, const struct ofphdrs *hdrs)
+{
+    static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 1);
+
+    struct raw_instance *raw_hdrs;
+    uint32_t hash;
+
+    ofpmsgs_init();
+
+    hash = ofphdrs_hash(hdrs);
+    HMAP_FOR_EACH_WITH_HASH (raw_hdrs, hmap_node, hash, &raw_instance_map) {
+        if (ofphdrs_equal(hdrs, &raw_hdrs->hdrs)) {
+            *raw = raw_hdrs->raw;
+            return 0;
+        }
+    }
+
+    if (!VLOG_DROP_WARN(&rl)) {
+        struct ds s;
+
+        ds_init(&s);
+        ds_put_format(&s, "version %"PRIu8", type %"PRIu8,
+                      hdrs->version, hdrs->type);
+        if (ofphdrs_is_stat(hdrs)) {
+            ds_put_format(&s, ", stat %"PRIu16, hdrs->stat);
+        }
+        if (hdrs->vendor) {
+            ds_put_format(&s, ", vendor 0x%"PRIx32", subtype %"PRIu32,
+                          hdrs->vendor, hdrs->subtype);
+        }
+        VLOG_WARN("unknown OpenFlow message (%s)", ds_cstr(&s));
+        ds_destroy(&s);
+    }
+
+    return (hdrs->vendor ? OFPERR_OFPBRC_BAD_SUBTYPE
+            : ofphdrs_is_stat(hdrs) ? OFPERR_OFPBRC_BAD_STAT
+            : OFPERR_OFPBRC_BAD_TYPE);
+}
+
+static void
+ofpmsgs_init(void)
+{
+    const struct raw_info *info;
+
+    if (raw_instance_map.buckets) {
+        return;
+    }
+
+    hmap_init(&raw_instance_map);
+    for (info = raw_infos; info < &raw_infos[ARRAY_SIZE(raw_infos)]; info++)
+    {
+        int n_instances = info->max_version - info->min_version + 1;
+        struct raw_instance *inst;
+
+        for (inst = info->instances;
+             inst < &info->instances[n_instances];
+             inst++) {
+            inst->hdrs_len = ofphdrs_len(&inst->hdrs);
+            hmap_insert(&raw_instance_map, &inst->hmap_node,
+                        ofphdrs_hash(&inst->hdrs));
+        }
+    }
+}