X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;ds=sidebyside;f=lib%2Fnx-match.c;h=9d3b2be1bfba46d0ffac83c86b315d5fd9168573;hb=816fd533f85923c03cf8d9d6450bd9a0845d5160;hp=9b3c1e0539f6600116cdfc49337deb4ff6505fcf;hpb=28da1f8f725fc2a797174df18a7b3e31ef49ede0;p=openvswitch

diff --git a/lib/nx-match.c b/lib/nx-match.c
index 9b3c1e05..9d3b2be1 100644
--- a/lib/nx-match.c
+++ b/lib/nx-match.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2010, 2011 Nicira Networks.
+ * Copyright (c) 2010, 2011, 2012 Nicira Networks.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -23,11 +23,13 @@
 #include "classifier.h"
 #include "dynamic-string.h"
 #include "meta-flow.h"
+#include "ofp-errors.h"
 #include "ofp-util.h"
 #include "ofpbuf.h"
 #include "openflow/nicira-ext.h"
 #include "packets.h"
 #include "unaligned.h"
+#include "util.h"
 #include "vlog.h"
 
 VLOG_DEFINE_THIS_MODULE(nx_match);
@@ -36,16 +38,6 @@ VLOG_DEFINE_THIS_MODULE(nx_match);
  * 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);
 
-enum {
-    NXM_INVALID = OFP_MKERR_NICIRA(OFPET_BAD_REQUEST, NXBRC_NXM_INVALID),
-    NXM_BAD_TYPE = OFP_MKERR_NICIRA(OFPET_BAD_REQUEST, NXBRC_NXM_BAD_TYPE),
-    NXM_BAD_VALUE = OFP_MKERR_NICIRA(OFPET_BAD_REQUEST, NXBRC_NXM_BAD_VALUE),
-    NXM_BAD_MASK = OFP_MKERR_NICIRA(OFPET_BAD_REQUEST, NXBRC_NXM_BAD_MASK),
-    NXM_BAD_PREREQ = OFP_MKERR_NICIRA(OFPET_BAD_REQUEST, NXBRC_NXM_BAD_PREREQ),
-    NXM_DUP_TYPE = OFP_MKERR_NICIRA(OFPET_BAD_REQUEST, NXBRC_NXM_DUP_TYPE),
-    BAD_ARGUMENT = OFP_MKERR(OFPET_BAD_ACTION, OFPBAC_BAD_ARGUMENT)
-};
-
 /* Returns the width of the data for a field with the given 'header', in
  * bytes. */
 int
@@ -96,41 +88,52 @@ nx_entry_ok(const void *p, unsigned int match_len)
     return header;
 }
 
-int
-nx_pull_match(struct ofpbuf *b, unsigned int match_len, uint16_t priority,
-              struct cls_rule *rule)
+static enum ofperr
+nx_pull_match__(struct ofpbuf *b, unsigned int match_len, bool strict,
+                uint16_t priority, struct cls_rule *rule,
+                ovs_be64 *cookie, ovs_be64 *cookie_mask)
 {
     uint32_t header;
     uint8_t *p;
 
+    assert((cookie != NULL) == (cookie_mask != NULL));
+
     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 %zu)", match_len, b->size);
-        return ofp_mkerr(OFPET_BAD_REQUEST, OFPBRC_BAD_LEN);
+        return OFPERR_OFPBRC_BAD_LEN;
     }
 
     cls_rule_init_catchall(rule, priority);
-    while ((header = nx_entry_ok(p, match_len)) != 0) {
-        unsigned length = NXM_LENGTH(header);
+    if (cookie) {
+        *cookie = *cookie_mask = htonll(0);
+    }
+    for (;
+         (header = nx_entry_ok(p, match_len)) != 0;
+         p += 4 + NXM_LENGTH(header), match_len -= 4 + NXM_LENGTH(header)) {
         const struct mf_field *mf;
-        int error;
+        enum ofperr error;
 
         mf = mf_from_nxm_header(header);
         if (!mf) {
-            error = NXM_BAD_TYPE;
+            if (strict) {
+                error = OFPERR_NXBRC_NXM_BAD_TYPE;
+            } else {
+                continue;
+            }
         } else if (!mf_are_prereqs_ok(mf, &rule->flow)) {
-            error = NXM_BAD_PREREQ;
+            error = OFPERR_NXBRC_NXM_BAD_PREREQ;
         } else if (!mf_is_all_wild(mf, &rule->wc)) {
-            error = NXM_DUP_TYPE;
+            error = OFPERR_NXBRC_NXM_DUP_TYPE;
         } else {
             unsigned int width = mf->n_bytes;
             union mf_value value;
 
             memcpy(&value, p + 4, width);
             if (!mf_is_value_valid(mf, &value)) {
-                error = NXM_BAD_VALUE;
+                error = OFPERR_NXBRC_NXM_BAD_VALUE;
             } else if (!NXM_HASMASK(header)) {
                 error = 0;
                 mf_set_value(mf, &value, rule);
@@ -139,7 +142,7 @@ nx_pull_match(struct ofpbuf *b, unsigned int match_len, uint16_t priority,
 
                 memcpy(&mask, p + 4 + width, width);
                 if (!mf_is_mask_valid(mf, &mask)) {
-                    error = NXM_BAD_MASK;
+                    error = OFPERR_NXBRC_NXM_BAD_MASK;
                 } else {
                     error = 0;
                     mf_set(mf, &value, &mask, rule);
@@ -147,24 +150,64 @@ nx_pull_match(struct ofpbuf *b, unsigned int match_len, uint16_t priority,
             }
         }
 
+        /* Check if the match is for a cookie rather than a classifier rule. */
+        if ((header == NXM_NX_COOKIE || header == NXM_NX_COOKIE_W) && cookie) {
+            if (*cookie_mask) {
+                error = OFPERR_NXBRC_NXM_DUP_TYPE;
+            } else {
+                unsigned int width = sizeof *cookie;
+
+                memcpy(cookie, p + 4, width);
+                if (NXM_HASMASK(header)) {
+                    memcpy(cookie_mask, p + 4 + width, width);
+                } else {
+                    *cookie_mask = htonll(UINT64_MAX);
+                }
+                error = 0;
+            }
+        }
+
         if (error) {
-            char *msg = ofputil_error_to_string(error);
             VLOG_DBG_RL(&rl, "bad nxm_entry %#08"PRIx32" (vendor=%"PRIu32", "
                         "field=%"PRIu32", hasmask=%"PRIu32", len=%"PRIu32"), "
                         "(%s)", header,
                         NXM_VENDOR(header), NXM_FIELD(header),
                         NXM_HASMASK(header), NXM_LENGTH(header),
-                        msg);
-            free(msg);
-
+                        ofperr_to_string(error));
             return error;
         }
-
-        p += 4 + length;
-        match_len -= 4 + length;
     }
 
-    return match_len ? NXM_INVALID : 0;
+    return match_len ? OFPERR_NXBRC_NXM_INVALID : 0;
+}
+
+/* Parses the nx_match formatted match description in 'b' with length
+ * 'match_len'.  The results are stored in 'rule', which is initialized with
+ * 'priority'.  If 'cookie' and 'cookie_mask' contain valid pointers, then the
+ * cookie and mask will be stored in them if a "NXM_NX_COOKIE*" match is
+ * defined.  Otherwise, 0 is stored in both.
+ *
+ * Fails with an error when encountering unknown NXM headers.
+ *
+ * Returns 0 if successful, otherwise an OpenFlow error code. */
+enum ofperr
+nx_pull_match(struct ofpbuf *b, unsigned int match_len,
+              uint16_t priority, struct cls_rule *rule,
+              ovs_be64 *cookie, ovs_be64 *cookie_mask)
+{
+    return nx_pull_match__(b, match_len, true, priority, rule, cookie,
+                           cookie_mask);
+}
+
+/* Behaves the same as nx_pull_match() with one exception.  Skips over unknown
+ * NXM headers instead of failing with an error when they are encountered. */
+enum ofperr
+nx_pull_match_loose(struct ofpbuf *b, unsigned int match_len,
+                    uint16_t priority, struct cls_rule *rule,
+                    ovs_be64 *cookie, ovs_be64 *cookie_mask)
+{
+    return nx_pull_match__(b, match_len, false, priority, rule, cookie,
+                           cookie_mask);
 }
 
 /* nx_put_match() and helpers.
@@ -367,7 +410,9 @@ nxm_put_frag(struct ofpbuf *b, const struct cls_rule *cr)
 
 /* Appends to 'b' the nx_match format that expresses 'cr' (except for
  * 'cr->priority', because priority is not part of nx_match), plus enough
- * zero bytes to pad the nx_match out to a multiple of 8.
+ * 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.
  *
@@ -376,7 +421,8 @@ nxm_put_frag(struct ofpbuf *b, const struct cls_rule *cr)
  * If 'cr' is a catch-all rule that matches every packet, then this function
  * appends nothing to 'b' and returns 0. */
 int
-nx_put_match(struct ofpbuf *b, const struct cls_rule *cr)
+nx_put_match(struct ofpbuf *b, const struct cls_rule *cr,
+             ovs_be64 cookie, ovs_be64 cookie_mask)
 {
     const flow_wildcards_t wc = cr->wc.wildcards;
     const struct flow *flow = &cr->flow;
@@ -556,6 +602,9 @@ nx_put_match(struct ofpbuf *b, const struct cls_rule *cr)
                     htonl(flow->regs[i]), htonl(cr->wc.reg_masks[i]));
     }
 
+    /* Cookie. */
+    nxm_put_64m(b, NXM_NX_COOKIE, cookie, cookie_mask);
+
     match_len = b->size - start_len;
     ofpbuf_put_zeros(b, ROUND_UP(match_len, 8) - match_len);
     return match_len;
@@ -625,6 +674,10 @@ format_nxm_field_name(struct ds *s, uint32_t header)
         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_VENDOR(header), NXM_FIELD(header));
     }
@@ -641,6 +694,7 @@ parse_nxm_field_name(const char *name, int name_len)
     if (wild) {
         name_len -= 2;
     }
+
     for (i = 0; i < MFF_N_IDS; i++) {
         const struct mf_field *mf = mf_from_id(i);
 
@@ -655,6 +709,15 @@ parse_nxm_field_name(const char *name, int name_len)
         }
     }
 
+    if (!strncmp("NXM_NX_COOKIE", name, name_len)
+                && (name_len == strlen("NXM_NX_COOKIE"))) {
+        if (!wild) {
+            return NXM_NX_COOKIE;
+        } else {
+            return NXM_NX_COOKIE_W;
+        }
+    }
+
     /* Check whether it's a 32-bit field header value as hex.
      * (This isn't ordinarily useful except for testing error behavior.) */
     if (name_len == 8) {
@@ -731,97 +794,40 @@ nx_match_from_string(const char *s, struct ofpbuf *b)
     return match_len;
 }
 
-const char *
-nxm_parse_field_bits(const char *s, uint32_t *headerp, int *ofsp, int *n_bitsp)
-{
-    const char *full_s = s;
-    const char *name;
-    uint32_t header;
-    int start, end;
-    int name_len;
-    int width;
-
-    name = s;
-    name_len = strcspn(s, "[");
-    if (s[name_len] != '[') {
-        ovs_fatal(0, "%s: missing [ looking for field name", full_s);
-    }
-
-    header = parse_nxm_field_name(name, name_len);
-    if (!header) {
-        ovs_fatal(0, "%s: unknown field `%.*s'", full_s, name_len, s);
-    }
-    width = nxm_field_bits(header);
-
-    s += name_len;
-    if (sscanf(s, "[%d..%d]", &start, &end) == 2) {
-        /* Nothing to do. */
-    } else if (sscanf(s, "[%d]", &start) == 1) {
-        end = start;
-    } else if (!strncmp(s, "[]", 2)) {
-        start = 0;
-        end = width - 1;
-    } else {
-        ovs_fatal(0, "%s: syntax error expecting [] or [<bit>] or "
-                  "[<start>..<end>]", full_s);
-    }
-    s = strchr(s, ']') + 1;
-
-    if (start > end) {
-        ovs_fatal(0, "%s: starting bit %d is after ending bit %d",
-                  full_s, start, end);
-    } else if (start >= width) {
-        ovs_fatal(0, "%s: starting bit %d is not valid because field is only "
-                  "%d bits wide", full_s, start, width);
-    } else if (end >= width){
-        ovs_fatal(0, "%s: ending bit %d is not valid because field is only "
-                  "%d bits wide", full_s, end, width);
-    }
-
-    *headerp = header;
-    *ofsp = start;
-    *n_bitsp = end - start + 1;
-
-    return s;
-}
-
 void
 nxm_parse_reg_move(struct nx_action_reg_move *move, const char *s)
 {
     const char *full_s = s;
-    uint32_t src, dst;
-    int src_ofs, dst_ofs;
-    int src_n_bits, dst_n_bits;
+    struct mf_subfield src, dst;
 
-    s = nxm_parse_field_bits(s, &src, &src_ofs, &src_n_bits);
+    s = mf_parse_subfield(&src, s);
     if (strncmp(s, "->", 2)) {
         ovs_fatal(0, "%s: missing `->' following source", full_s);
     }
     s += 2;
-    s = nxm_parse_field_bits(s, &dst, &dst_ofs, &dst_n_bits);
+    s = mf_parse_subfield(&dst, s);
     if (*s != '\0') {
         ovs_fatal(0, "%s: trailing garbage following destination", full_s);
     }
 
-    if (src_n_bits != dst_n_bits) {
+    if (src.n_bits != dst.n_bits) {
         ovs_fatal(0, "%s: source field is %d bits wide but destination is "
-                  "%d bits wide", full_s, src_n_bits, dst_n_bits);
+                  "%d bits wide", full_s, src.n_bits, dst.n_bits);
     }
 
     ofputil_init_NXAST_REG_MOVE(move);
-    move->n_bits = htons(src_n_bits);
-    move->src_ofs = htons(src_ofs);
-    move->dst_ofs = htons(dst_ofs);
-    move->src = htonl(src);
-    move->dst = htonl(dst);
+    move->n_bits = htons(src.n_bits);
+    move->src_ofs = htons(src.ofs);
+    move->dst_ofs = htons(dst.ofs);
+    move->src = htonl(src.field->nxm_header);
+    move->dst = htonl(dst.field->nxm_header);
 }
 
 void
 nxm_parse_reg_load(struct nx_action_reg_load *load, const char *s)
 {
     const char *full_s = s;
-    uint32_t dst;
-    int ofs, n_bits;
+    struct mf_subfield dst;
     uint64_t value;
 
     value = strtoull(s, (char **) &s, 0);
@@ -829,152 +835,86 @@ nxm_parse_reg_load(struct nx_action_reg_load *load, const char *s)
         ovs_fatal(0, "%s: missing `->' following value", full_s);
     }
     s += 2;
-    s = nxm_parse_field_bits(s, &dst, &ofs, &n_bits);
+    s = mf_parse_subfield(&dst, s);
     if (*s != '\0') {
         ovs_fatal(0, "%s: trailing garbage following destination", full_s);
     }
 
-    if (n_bits < 64 && (value >> n_bits) != 0) {
-        ovs_fatal(0, "%s: value %"PRIu64" does not fit into %d bits",
-                  full_s, value, n_bits);
+    if (dst.n_bits < 64 && (value >> dst.n_bits) != 0) {
+        ovs_fatal(0, "%s: value %"PRIu64" does not fit into %u bits",
+                  full_s, value, dst.n_bits);
     }
 
     ofputil_init_NXAST_REG_LOAD(load);
-    load->ofs_nbits = nxm_encode_ofs_nbits(ofs, n_bits);
-    load->dst = htonl(dst);
+    load->ofs_nbits = nxm_encode_ofs_nbits(dst.ofs, dst.n_bits);
+    load->dst = htonl(dst.field->nxm_header);
     load->value = htonll(value);
 }
 
 /* nxm_format_reg_move(), nxm_format_reg_load(). */
 
-void
-nxm_format_field_bits(struct ds *s, uint32_t header, int ofs, int n_bits)
-{
-    format_nxm_field_name(s, header);
-    if (ofs == 0 && n_bits == nxm_field_bits(header)) {
-        ds_put_cstr(s, "[]");
-    } else if (n_bits == 1) {
-        ds_put_format(s, "[%d]", ofs);
-    } else {
-        ds_put_format(s, "[%d..%d]", ofs, ofs + n_bits - 1);
-    }
-}
-
 void
 nxm_format_reg_move(const struct nx_action_reg_move *move, struct ds *s)
 {
-    int n_bits = ntohs(move->n_bits);
-    int src_ofs = ntohs(move->src_ofs);
-    int dst_ofs = ntohs(move->dst_ofs);
-    uint32_t src = ntohl(move->src);
-    uint32_t dst = ntohl(move->dst);
+    struct mf_subfield src, dst;
+
+    nxm_decode_discrete(&src, move->src, move->src_ofs, move->n_bits);
+    nxm_decode_discrete(&dst, move->dst, move->dst_ofs, move->n_bits);
 
     ds_put_format(s, "move:");
-    nxm_format_field_bits(s, src, src_ofs, n_bits);
+    mf_format_subfield(&src, s);
     ds_put_cstr(s, "->");
-    nxm_format_field_bits(s, dst, dst_ofs, n_bits);
+    mf_format_subfield(&dst, s);
 }
 
 void
 nxm_format_reg_load(const struct nx_action_reg_load *load, struct ds *s)
 {
-    int ofs = nxm_decode_ofs(load->ofs_nbits);
-    int n_bits = nxm_decode_n_bits(load->ofs_nbits);
-    uint32_t dst = ntohl(load->dst);
-    uint64_t value = ntohll(load->value);
+    struct mf_subfield dst;
 
-    ds_put_format(s, "load:%#"PRIx64"->", value);
-    nxm_format_field_bits(s, dst, ofs, n_bits);
+    ds_put_format(s, "load:%#"PRIx64"->", ntohll(load->value));
+
+    nxm_decode(&dst, load->dst, load->ofs_nbits);
+    mf_format_subfield(&dst, s);
 }
 
 /* nxm_check_reg_move(), nxm_check_reg_load(). */
 
-static bool
-field_ok(const struct mf_field *mf, const struct flow *flow, int size)
-{
-    return (mf
-            && mf_are_prereqs_ok(mf, flow)
-            && size <= nxm_field_bits(mf->nxm_header));
-}
-
-int
+enum ofperr
 nxm_check_reg_move(const struct nx_action_reg_move *action,
                    const struct flow *flow)
 {
-    int src_ofs, dst_ofs, n_bits;
+    struct mf_subfield src;
+    struct mf_subfield dst;
     int error;
 
-    n_bits = ntohs(action->n_bits);
-    src_ofs = ntohs(action->src_ofs);
-    dst_ofs = ntohs(action->dst_ofs);
-
-    error = nxm_src_check(action->src, src_ofs, n_bits, flow);
+    nxm_decode_discrete(&src, action->src, action->src_ofs, action->n_bits);
+    error = mf_check_src(&src, flow);
     if (error) {
         return error;
     }
 
-    return nxm_dst_check(action->dst, dst_ofs, n_bits, flow);
-}
-
-/* Given a flow, checks that the source field represented by 'src_header'
- * in the range ['ofs', 'ofs' + 'n_bits') is valid. */
-int
-nxm_src_check(ovs_be32 src_header_, unsigned int ofs, unsigned int n_bits,
-              const struct flow *flow)
-{
-    uint32_t src_header = ntohl(src_header_);
-    const struct mf_field *src = mf_from_nxm_header(src_header);
-
-    if (!n_bits) {
-        VLOG_WARN_RL(&rl, "zero bit source field");
-    } else if (NXM_HASMASK(src_header) || !field_ok(src, flow, ofs + n_bits)) {
-        VLOG_WARN_RL(&rl, "invalid source field");
-    } else {
-        return 0;
-    }
-
-    return BAD_ARGUMENT;
-}
-
-/* Given a flow, checks that the destination field represented by 'dst_header'
- * in the range ['ofs', 'ofs' + 'n_bits') is valid. */
-int
-nxm_dst_check(ovs_be32 dst_header_, unsigned int ofs, unsigned int n_bits,
-              const struct flow *flow)
-{
-    uint32_t dst_header = ntohl(dst_header_);
-    const struct mf_field *dst = mf_from_nxm_header(dst_header);
-
-    if (!n_bits) {
-        VLOG_WARN_RL(&rl, "zero bit destination field");
-    } else if (NXM_HASMASK(dst_header) || !field_ok(dst, flow, ofs + n_bits)) {
-        VLOG_WARN_RL(&rl, "invalid destination field");
-    } else if (!dst->writable) {
-        VLOG_WARN_RL(&rl, "destination field is not writable");
-    } else {
-        return 0;
-    }
-
-    return BAD_ARGUMENT;
+    nxm_decode_discrete(&dst, action->dst, action->dst_ofs, action->n_bits);
+    return mf_check_dst(&dst, flow);
 }
 
-int
+enum ofperr
 nxm_check_reg_load(const struct nx_action_reg_load *action,
                    const struct flow *flow)
 {
-    unsigned int ofs = nxm_decode_ofs(action->ofs_nbits);
-    unsigned int n_bits = nxm_decode_n_bits(action->ofs_nbits);
-    int error;
+    struct mf_subfield dst;
+    enum ofperr error;
 
-    error = nxm_dst_check(action->dst, ofs, n_bits, flow);
+    nxm_decode(&dst, action->dst, action->ofs_nbits);
+    error = mf_check_dst(&dst, flow);
     if (error) {
         return error;
     }
 
     /* Reject 'action' if a bit numbered 'n_bits' or higher is set to 1 in
      * action->value. */
-    if (n_bits < 64 && ntohll(action->value) >> n_bits) {
-        return BAD_ARGUMENT;
+    if (dst.n_bits < 64 && ntohll(action->value) >> dst.n_bits) {
+        return OFPERR_OFPBAC_BAD_ARGUMENT;
     }
 
     return 0;
@@ -982,117 +922,72 @@ nxm_check_reg_load(const struct nx_action_reg_load *action,
 
 /* nxm_execute_reg_move(), nxm_execute_reg_load(). */
 
-static void
-bitwise_copy(const void *src_, unsigned int src_len, unsigned int src_ofs,
-             void *dst_, unsigned int dst_len, unsigned int dst_ofs,
-             unsigned int n_bits)
-{
-    const uint8_t *src = src_;
-    uint8_t *dst = dst_;
-
-    src += src_len - (src_ofs / 8 + 1);
-    src_ofs %= 8;
-
-    dst += dst_len - (dst_ofs / 8 + 1);
-    dst_ofs %= 8;
-
-    if (src_ofs == 0 && dst_ofs == 0) {
-        unsigned int n_bytes = n_bits / 8;
-        if (n_bytes) {
-            dst -= n_bytes - 1;
-            src -= n_bytes - 1;
-            memcpy(dst, src, n_bytes);
-
-            n_bits %= 8;
-            src--;
-            dst--;
-        }
-        if (n_bits) {
-            uint8_t mask = (1 << n_bits) - 1;
-            *dst = (*dst & ~mask) | (*src & mask);
-        }
-    } else {
-        while (n_bits > 0) {
-            unsigned int max_copy = 8 - MAX(src_ofs, dst_ofs);
-            unsigned int chunk = MIN(n_bits, max_copy);
-            uint8_t mask = ((1 << chunk) - 1) << dst_ofs;
-
-            *dst &= ~mask;
-            *dst |= ((*src >> src_ofs) << dst_ofs) & mask;
-
-            src_ofs += chunk;
-            if (src_ofs == 8) {
-                src--;
-                src_ofs = 0;
-            }
-            dst_ofs += chunk;
-            if (dst_ofs == 8) {
-                dst--;
-                dst_ofs = 0;
-            }
-            n_bits -= chunk;
-        }
-    }
-}
-
-/* Returns the value of the NXM field corresponding to 'header' at 'ofs_nbits'
- * in 'flow'. */
-uint64_t
-nxm_read_field_bits(ovs_be32 header, ovs_be16 ofs_nbits,
-                    const struct flow *flow)
-{
-    const struct mf_field *field = mf_from_nxm_header(ntohl(header));
-    union mf_value value;
-    union mf_value bits;
-
-    mf_get_value(field, flow, &value);
-    bits.be64 = htonll(0);
-    bitwise_copy(&value, field->n_bytes, nxm_decode_ofs(ofs_nbits),
-                 &bits, sizeof bits.be64, 0,
-                 nxm_decode_n_bits(ofs_nbits));
-    return ntohll(bits.be64);
-}
-
 void
 nxm_execute_reg_move(const struct nx_action_reg_move *action,
                      struct flow *flow)
 {
-    const struct mf_field *src = mf_from_nxm_header(ntohl(action->src));
-    const struct mf_field *dst = mf_from_nxm_header(ntohl(action->dst));
+    struct mf_subfield src, dst;
     union mf_value src_value;
     union mf_value dst_value;
 
-    mf_get_value(dst, flow, &dst_value);
-    mf_get_value(src, flow, &src_value);
-    bitwise_copy(&src_value, src->n_bytes, ntohs(action->src_ofs),
-                 &dst_value, dst->n_bytes, ntohs(action->dst_ofs),
-                 ntohs(action->n_bits));
-    mf_set_flow_value(dst, &dst_value, flow);
+    nxm_decode_discrete(&src, action->src, action->src_ofs, action->n_bits);
+    nxm_decode_discrete(&dst, action->dst, action->dst_ofs, action->n_bits);
+
+    mf_get_value(dst.field, flow, &dst_value);
+    mf_get_value(src.field, flow, &src_value);
+    bitwise_copy(&src_value, src.field->n_bytes, src.ofs,
+                 &dst_value, dst.field->n_bytes, dst.ofs,
+                 src.n_bits);
+    mf_set_flow_value(dst.field, &dst_value, flow);
 }
 
 void
 nxm_execute_reg_load(const struct nx_action_reg_load *action,
                      struct flow *flow)
 {
-    nxm_reg_load(action->dst, action->ofs_nbits, ntohll(action->value), flow);
+    struct mf_subfield dst;
+
+    nxm_decode(&dst, action->dst, action->ofs_nbits);
+    mf_set_subfield_value(&dst, ntohll(action->value), flow);
 }
 
-/* Calculates ofs and n_bits from the given 'ofs_nbits' parameter, and copies
- * 'src_data'[0:n_bits] to 'dst_header'[ofs:ofs+n_bits] in the given 'flow'. */
+/* Initializes 'sf->field' with the field corresponding to the given NXM
+ * 'header' and 'sf->ofs' and 'sf->n_bits' decoded from 'ofs_nbits' with
+ * nxm_decode_ofs() and nxm_decode_n_bits(), respectively.
+ *
+ * Afterward, 'sf' might be invalid in a few different ways:
+ *
+ *   - 'sf->field' will be NULL if 'header' is unknown.
+ *
+ *   - 'sf->ofs' and 'sf->n_bits' might exceed the width of sf->field.
+ *
+ * The caller should call mf_check_src() or mf_check_dst() to check for these
+ * problems. */
 void
-nxm_reg_load(ovs_be32 dst_header, ovs_be16 ofs_nbits, uint64_t src_data,
-             struct flow *flow)
+nxm_decode(struct mf_subfield *sf, ovs_be32 header, ovs_be16 ofs_nbits)
 {
-    const struct mf_field *dst = mf_from_nxm_header(ntohl(dst_header));
-    int n_bits = nxm_decode_n_bits(ofs_nbits);
-    int dst_ofs = nxm_decode_ofs(ofs_nbits);
-    union mf_value dst_value;
-    union mf_value src_value;
+    sf->field = mf_from_nxm_header(ntohl(header));
+    sf->ofs = nxm_decode_ofs(ofs_nbits);
+    sf->n_bits = nxm_decode_n_bits(ofs_nbits);
+}
 
-    mf_get_value(dst, flow, &dst_value);
-    src_value.be64 = htonll(src_data);
-    bitwise_copy(&src_value, sizeof src_value.be64, 0,
-                 &dst_value, dst->n_bytes, dst_ofs,
-                 n_bits);
-    mf_set_flow_value(dst, &dst_value, flow);
+/* Initializes 'sf->field' with the field corresponding to the given NXM
+ * 'header' and 'sf->ofs' and 'sf->n_bits' from 'ofs' and 'n_bits',
+ * respectively.
+ *
+ * Afterward, 'sf' might be invalid in a few different ways:
+ *
+ *   - 'sf->field' will be NULL if 'header' is unknown.
+ *
+ *   - 'sf->ofs' and 'sf->n_bits' might exceed the width of sf->field.
+ *
+ * The caller should call mf_check_src() or mf_check_dst() to check for these
+ * problems. */
+void
+nxm_decode_discrete(struct mf_subfield *sf, ovs_be32 header,
+                    ovs_be16 ofs, ovs_be16 n_bits)
+{
+    sf->field = mf_from_nxm_header(ntohl(header));
+    sf->ofs = ntohs(ofs);
+    sf->n_bits = ntohs(n_bits);
 }