+\f
+/* Makes a subfield starting at bit offset 'ofs' and continuing for 'n_bits' in
+ * 'rule''s field 'mf' exactly match the 'n_bits' least-significant bits of
+ * 'x'.
+ *
+ * Example: suppose that 'mf' is originally the following 2-byte field in
+ * 'rule':
+ *
+ * value == 0xe00a == 2#1110000000001010
+ * mask == 0xfc3f == 2#1111110000111111
+ *
+ * The call mf_set_subfield(mf, 0x55, 8, 7, rule) would have the following
+ * effect (note that 0x55 is 2#1010101):
+ *
+ * value == 0xd50a == 2#1101010100001010
+ * mask == 0xff3f == 2#1111111100111111
+ *
+ * The caller is responsible for ensuring that the result will be a valid
+ * wildcard pattern for 'mf'. The caller is responsible for ensuring that
+ * 'rule' meets 'mf''s prerequisites. */
+void
+mf_set_subfield(const struct mf_subfield *sf, uint64_t x,
+ struct cls_rule *rule)
+{
+ const struct mf_field *field = sf->field;
+ unsigned int n_bits = sf->n_bits;
+ unsigned int ofs = sf->ofs;
+
+ if (ofs == 0 && field->n_bytes * 8 == n_bits) {
+ union mf_value value;
+ int i;
+
+ for (i = field->n_bytes - 1; i >= 0; i--) {
+ ((uint8_t *) &value)[i] = x;
+ x >>= 8;
+ }
+ mf_set_value(field, &value, rule);
+ } else {
+ union mf_value value, mask;
+ uint8_t *vp = (uint8_t *) &value;
+ uint8_t *mp = (uint8_t *) &mask;
+
+ mf_get(field, rule, &value, &mask);
+ bitwise_put(x, vp, field->n_bytes, ofs, n_bits);
+ bitwise_put(UINT64_MAX, mp, field->n_bytes, ofs, n_bits);
+ mf_set(field, &value, &mask, rule);
+ }
+}
+
+/* Similar to mf_set_subfield() but modifies only a flow, not a cls_rule. */
+void
+mf_set_subfield_value(const struct mf_subfield *sf, uint64_t x,
+ struct flow *flow)
+{
+ const struct mf_field *field = sf->field;
+ unsigned int n_bits = sf->n_bits;
+ unsigned int ofs = sf->ofs;
+ union mf_value value;
+
+ if (ofs == 0 && field->n_bytes * 8 == n_bits) {
+ int i;
+
+ for (i = field->n_bytes - 1; i >= 0; i--) {
+ ((uint8_t *) &value)[i] = x;
+ x >>= 8;
+ }
+ mf_set_flow_value(field, &value, flow);
+ } else {
+ mf_get_value(field, flow, &value);
+ bitwise_put(x, &value, field->n_bytes, ofs, n_bits);
+ mf_set_flow_value(field, &value, flow);
+ }
+}
+
+/* Returns the value of 'sf' within 'flow'. 'sf' must be valid for reading
+ * 'flow', e.g. as checked by mf_check_src() and sf->n_bits must be 64 or
+ * less. */
+uint64_t
+mf_get_subfield(const struct mf_subfield *sf, const struct flow *flow)
+{
+ union mf_value value;
+
+ mf_get_value(sf->field, flow, &value);
+ return bitwise_get(&value, sf->field->n_bytes, sf->ofs, sf->n_bits);
+}
+
+/* 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 if (sf->field->nxm_name) {
+ ds_put_cstr(s, sf->field->nxm_name);
+ } else if (sf->field->nxm_header) {
+ uint32_t header = sf->field->nxm_header;
+ ds_put_format(s, "%d:%d", NXM_VENDOR(header), NXM_FIELD(header));
+ } else {
+ ds_put_cstr(s, 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 mf_field *
+mf_parse_subfield_name(const char *name, int name_len, bool *wild)
+{
+ int i;
+
+ *wild = name_len > 2 && !memcmp(&name[name_len - 2], "_W", 2);
+ if (*wild) {
+ name_len -= 2;
+ }
+
+ for (i = 0; i < MFF_N_IDS; i++) {
+ const struct mf_field *mf = mf_from_id(i);
+
+ if (mf->nxm_name
+ && !strncmp(mf->nxm_name, name, name_len)
+ && mf->nxm_name[name_len] == '\0') {
+ return mf;
+ }
+ }
+
+ return NULL;
+}
+
+/* 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 *
+mf_parse_subfield__(struct mf_subfield *sf, const char **sp)
+{
+ const struct mf_field *field;
+ const char *name;
+ int start, end;
+ const char *s;
+ int name_len;
+ bool wild;
+
+ s = *sp;
+ name = s;
+ name_len = strcspn(s, "[");
+ if (s[name_len] != '[') {
+ return xasprintf("%s: missing [ looking for field name", *sp);
+ }
+
+ field = mf_parse_subfield_name(name, name_len, &wild);
+ if (!field) {
+ return xasprintf("%s: unknown field `%.*s'", *sp, name_len, s);
+ }
+
+ 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 = field->n_bits - 1;
+ } 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 beginning of 's' into 'sf'. Returns the first
+ * byte in 's' following the parsed string.
+ *
+ * Exits with an error message if 's' has incorrect syntax.
+ *
+ * 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. */
+const char *
+mf_parse_subfield(struct mf_subfield *sf, const char *s)
+{
+ char *msg = mf_parse_subfield__(sf, &s);
+ if (msg) {
+ ovs_fatal(0, "%s", msg);
+ }
+ return s;
+}