[ovs-dev] [PATCH] ofp-parse: Do not exit() upon a parse error.

Ben Pfaff blp at nicira.com
Fri Jun 28 00:10:33 UTC 2013


Until now, failure to parse a flow in the ofp-parse module has caused the
program to abort immediately with a fatal error.  This makes it hard to
use these functions from any long-lived program.  This commit fixes the
problem.

Signed-off-by: Ben Pfaff <blp at nicira.com>
---
 lib/bundle.c               |   58 ++-
 lib/bundle.h               |    8 +-
 lib/dynamic-string.c       |    9 +-
 lib/dynamic-string.h       |    2 +-
 lib/learn.c                |  121 ++++---
 lib/learn.h                |    5 +-
 lib/meta-flow.c            |   13 +-
 lib/meta-flow.h            |    6 +-
 lib/multipath.c            |   47 ++-
 lib/multipath.h            |    6 +-
 lib/nx-match.c             |   69 +++-
 lib/nx-match.h             |   12 +-
 lib/ofp-parse.c            |  943 ++++++++++++++++++++++++++++++--------------
 lib/ofp-parse.h            |   36 +-
 tests/learn.at             |    2 +
 tests/ofproto-dpif.at      |    6 +-
 tests/test-bundle.c        |    9 +-
 tests/test-multipath.c     |    9 +-
 utilities/ovs-controller.c |    8 +-
 utilities/ovs-ofctl.c      |   71 +++-
 20 files changed, 988 insertions(+), 452 deletions(-)

diff --git a/lib/bundle.c b/lib/bundle.c
index d1834d0..288f17b 100644
--- a/lib/bundle.c
+++ b/lib/bundle.c
@@ -1,4 +1,4 @@
-/* Copyright (c) 2011, 2012 Nicira, Inc.
+/* Copyright (c) 2011, 2012, 2013 Nicira, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -251,8 +251,11 @@ bundle_to_nxast(const struct ofpact_bundle *bundle, struct ofpbuf *openflow)
     }
 }
 
-/* Helper for bundle_parse and bundle_parse_load. */
-static void
+/* Helper for bundle_parse and bundle_parse_load.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string.*/
+static char * WARN_UNUSED_RESULT
 bundle_parse__(const char *s, char **save_ptr,
                const char *fields, const char *basis, const char *algorithm,
                const char *slave_type, const char *dst,
@@ -261,12 +264,12 @@ bundle_parse__(const char *s, char **save_ptr,
     struct ofpact_bundle *bundle;
 
     if (!slave_delim) {
-        ovs_fatal(0, "%s: not enough arguments to bundle action", s);
+        return xasprintf("%s: not enough arguments to bundle action", s);
     }
 
     if (strcasecmp(slave_delim, "slaves")) {
-        ovs_fatal(0, "%s: missing slave delimiter, expected `slaves' got `%s'",
-                   s, slave_delim);
+        return xasprintf("%s: missing slave delimiter, expected `slaves' "
+                         "got `%s'", s, slave_delim);
     }
 
     bundle = ofpact_put_BUNDLE(ofpacts);
@@ -281,7 +284,7 @@ bundle_parse__(const char *s, char **save_ptr,
         }
 
         if (!ofputil_port_from_string(slave, &slave_port)) {
-            ovs_fatal(0, "%s: bad port number", slave);
+            return xasprintf("%s: bad port number", slave);
         }
         ofpbuf_put(ofpacts, &slave_port, sizeof slave_port);
 
@@ -297,7 +300,7 @@ bundle_parse__(const char *s, char **save_ptr,
     } else if (!strcasecmp(fields, "symmetric_l4")) {
         bundle->fields = NX_HASH_FIELDS_SYMMETRIC_L4;
     } else {
-        ovs_fatal(0, "%s: unknown fields `%s'", s, fields);
+        return xasprintf("%s: unknown fields `%s'", s, fields);
     }
 
     if (!strcasecmp(algorithm, "active_backup")) {
@@ -305,25 +308,34 @@ bundle_parse__(const char *s, char **save_ptr,
     } else if (!strcasecmp(algorithm, "hrw")) {
         bundle->algorithm = NX_BD_ALG_HRW;
     } else {
-        ovs_fatal(0, "%s: unknown algorithm `%s'", s, algorithm);
+        return xasprintf("%s: unknown algorithm `%s'", s, algorithm);
     }
 
     if (strcasecmp(slave_type, "ofport")) {
-        ovs_fatal(0, "%s: unknown slave_type `%s'", s, slave_type);
+        return xasprintf("%s: unknown slave_type `%s'", s, slave_type);
     }
 
     if (dst) {
-        mf_parse_subfield(&bundle->dst, dst);
+        char *error = mf_parse_subfield(&bundle->dst, dst);
+        if (error) {
+            return error;
+        }
     }
+
+    return NULL;
 }
 
 /* Converts a bundle action string contained in 's' to an nx_action_bundle and
- * stores it in 'b'.  Sets 'b''s l2 pointer to NULL. */
-void
+ * stores it in 'b'.  Sets 'b''s l2 pointer to NULL.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+char * WARN_UNUSED_RESULT
 bundle_parse(const char *s, struct ofpbuf *ofpacts)
 {
     char *fields, *basis, *algorithm, *slave_type, *slave_delim;
     char *tokstr, *save_ptr;
+    char *error;
 
     save_ptr = NULL;
     tokstr = xstrdup(s);
@@ -333,18 +345,24 @@ bundle_parse(const char *s, struct ofpbuf *ofpacts)
     slave_type = strtok_r(NULL, ", ", &save_ptr);
     slave_delim = strtok_r(NULL, ": ", &save_ptr);
 
-    bundle_parse__(s, &save_ptr, fields, basis, algorithm, slave_type, NULL,
-                   slave_delim, ofpacts);
+    error = bundle_parse__(s, &save_ptr, fields, basis, algorithm, slave_type,
+                           NULL, slave_delim, ofpacts);
     free(tokstr);
+
+    return error;
 }
 
 /* Converts a bundle_load action string contained in 's' to an nx_action_bundle
- * and stores it in 'b'.  Sets 'b''s l2 pointer to NULL. */
-void
+ * and stores it in 'b'.  Sets 'b''s l2 pointer to NULL.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string.*/
+char * WARN_UNUSED_RESULT
 bundle_parse_load(const char *s, struct ofpbuf *ofpacts)
 {
     char *fields, *basis, *algorithm, *slave_type, *dst, *slave_delim;
     char *tokstr, *save_ptr;
+    char *error;
 
     save_ptr = NULL;
     tokstr = xstrdup(s);
@@ -355,10 +373,12 @@ bundle_parse_load(const char *s, struct ofpbuf *ofpacts)
     dst = strtok_r(NULL, ", ", &save_ptr);
     slave_delim = strtok_r(NULL, ": ", &save_ptr);
 
-    bundle_parse__(s, &save_ptr, fields, basis, algorithm, slave_type, dst,
-                   slave_delim, ofpacts);
+    error = bundle_parse__(s, &save_ptr, fields, basis, algorithm, slave_type,
+                           dst, slave_delim, ofpacts);
 
     free(tokstr);
+
+    return error;
 }
 
 /* Appends a human-readable representation of 'nab' to 's'. */
diff --git a/lib/bundle.h b/lib/bundle.h
index 3e92374..dceb6e5 100644
--- a/lib/bundle.h
+++ b/lib/bundle.h
@@ -1,4 +1,4 @@
-/* Copyright (c) 2011, 2012 Nicira, Inc.
+/* Copyright (c) 2011, 2012, 2013 Nicira, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,6 +21,7 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#include "compiler.h"
 #include "ofp-errors.h"
 #include "openflow/nicira-ext.h"
 #include "openvswitch/types.h"
@@ -44,8 +45,9 @@ enum ofperr bundle_from_openflow(const struct nx_action_bundle *,
 enum ofperr bundle_check(const struct ofpact_bundle *, ofp_port_t max_ports,
                          const struct flow *);
 void bundle_to_nxast(const struct ofpact_bundle *, struct ofpbuf *of10);
-void bundle_parse(const char *, struct ofpbuf *ofpacts);
-void bundle_parse_load(const char *, struct ofpbuf *ofpacts);
+char *bundle_parse(const char *, struct ofpbuf *ofpacts) WARN_UNUSED_RESULT;
+char *bundle_parse_load(const char *, struct ofpbuf *ofpacts)
+    WARN_UNUSED_RESULT;
 void bundle_format(const struct ofpact_bundle *, struct ds *);
 
 #endif /* bundle.h */
diff --git a/lib/dynamic-string.c b/lib/dynamic-string.c
index 3cccb5c..9b3e7ba 100644
--- a/lib/dynamic-string.c
+++ b/lib/dynamic-string.c
@@ -238,14 +238,21 @@ ds_get_line(struct ds *ds, FILE *file)
  * Deletes comments introduced by "#" and skips lines that contains only white
  * space (after deleting comments).
  *
+ * If 'line_numberp' is nonnull, increments '*line_numberp' by the number of
+ * lines read from 'file'.
+ *
  * Returns 0 if successful, EOF if no non-blank line was found. */
 int
-ds_get_preprocessed_line(struct ds *ds, FILE *file)
+ds_get_preprocessed_line(struct ds *ds, FILE *file, int *line_numberp)
 {
     while (!ds_get_line(ds, file)) {
         char *line = ds_cstr(ds);
         char *comment;
 
+        if (line_numberp) {
+            ++*line_numberp;
+        }
+
         /* Delete comments. */
         comment = strchr(line, '#');
         if (comment) {
diff --git a/lib/dynamic-string.h b/lib/dynamic-string.h
index b988e1f..c069586 100644
--- a/lib/dynamic-string.h
+++ b/lib/dynamic-string.h
@@ -58,7 +58,7 @@ void ds_put_printable(struct ds *, const char *, size_t);
 void ds_put_hex_dump(struct ds *ds, const void *buf_, size_t size,
                      uintptr_t ofs, bool ascii);
 int ds_get_line(struct ds *, FILE *);
-int ds_get_preprocessed_line(struct ds *, FILE *);
+int ds_get_preprocessed_line(struct ds *, FILE *, int *line_number);
 int ds_get_test_line(struct ds *, FILE *);
 
 void ds_put_strftime(struct ds *, const char *template, time_t when, bool utc)
diff --git a/lib/learn.c b/lib/learn.c
index 0cc562d..d0a4796 100644
--- a/lib/learn.c
+++ b/lib/learn.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011, 2012 Nicira, Inc.
+ * Copyright (c) 2011, 2012, 2013 Nicira, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -390,13 +390,16 @@ learn_mask(const struct ofpact_learn *learn, struct flow_wildcards *wc)
     }
 }
 
-static void
+/* Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
 learn_parse_load_immediate(const char *s, struct ofpact_learn_spec *spec)
 {
     const char *full_s = s;
     const char *arrow = strstr(s, "->");
     struct mf_subfield dst;
     union mf_subvalue imm;
+    char *error;
 
     memset(&imm, 0, sizeof imm);
     if (s[0] == '0' && (s[1] == 'x' || s[1] == 'X') && arrow) {
@@ -408,7 +411,7 @@ learn_parse_load_immediate(const char *s, struct ofpact_learn_spec *spec)
         for (i = 0; i < n; i++) {
             int hexit = hexit_value(in[-i]);
             if (hexit < 0) {
-                ovs_fatal(0, "%s: bad hex digit in value", full_s);
+                return xasprintf("%s: bad hex digit in value", full_s);
             }
             out[-(i / 2)] |= i % 2 ? hexit << 4 : hexit;
         }
@@ -418,19 +421,19 @@ learn_parse_load_immediate(const char *s, struct ofpact_learn_spec *spec)
     }
 
     if (strncmp(s, "->", 2)) {
-        ovs_fatal(0, "%s: missing `->' following value", full_s);
+        return xasprintf("%s: missing `->' following value", full_s);
     }
     s += 2;
 
-    s = mf_parse_subfield(&dst, s);
-    if (*s != '\0') {
-        ovs_fatal(0, "%s: trailing garbage following destination", full_s);
+    error = mf_parse_subfield(&dst, s);
+    if (error) {
+        return error;
     }
 
     if (!bitwise_is_all_zeros(&imm, sizeof imm, dst.n_bits,
                               (8 * sizeof imm) - dst.n_bits)) {
-        ovs_fatal(0, "%s: value does not fit into %u bits",
-                  full_s, dst.n_bits);
+        return xasprintf("%s: value does not fit into %u bits",
+                         full_s, dst.n_bits);
     }
 
     spec->n_bits = dst.n_bits;
@@ -438,9 +441,12 @@ learn_parse_load_immediate(const char *s, struct ofpact_learn_spec *spec)
     spec->src_imm = imm;
     spec->dst_type = NX_LEARN_DST_LOAD;
     spec->dst = dst;
+    return NULL;
 }
 
-static void
+/* Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
 learn_parse_spec(const char *orig, char *name, char *value,
                  struct ofpact_learn_spec *spec)
 {
@@ -451,7 +457,7 @@ learn_parse_spec(const char *orig, char *name, char *value,
 
         error = mf_parse_value(dst, value, &imm);
         if (error) {
-            ovs_fatal(0, "%s", error);
+            return error;
         }
 
         spec->n_bits = dst->n_bits;
@@ -465,21 +471,23 @@ learn_parse_spec(const char *orig, char *name, char *value,
         spec->dst.n_bits = dst->n_bits;
     } else if (strchr(name, '[')) {
         /* Parse destination and check prerequisites. */
-        if (mf_parse_subfield(&spec->dst, name)[0] != '\0') {
-            ovs_fatal(0, "%s: syntax error after NXM field name `%s'",
-                      orig, name);
+        char *error;
+
+        error = mf_parse_subfield(&spec->dst, name);
+        if (error) {
+            return error;
         }
 
         /* Parse source and check prerequisites. */
         if (value[0] != '\0') {
-            if (mf_parse_subfield(&spec->src, value)[0] != '\0') {
-                ovs_fatal(0, "%s: syntax error after NXM field name `%s'",
-                          orig, value);
+            error = mf_parse_subfield(&spec->src, value);
+            if (error) {
+                return error;
             }
             if (spec->src.n_bits != spec->dst.n_bits) {
-                ovs_fatal(0, "%s: bit widths of %s (%u) and %s (%u) differ",
-                          orig, name, spec->src.n_bits, value,
-                          spec->dst.n_bits);
+                return xasprintf("%s: bit widths of %s (%u) and %s (%u) "
+                                 "differ", orig, name, spec->src.n_bits, value,
+                                 spec->dst.n_bits);
             }
         } else {
             spec->src = spec->dst;
@@ -490,11 +498,18 @@ learn_parse_spec(const char *orig, char *name, char *value,
         spec->dst_type = NX_LEARN_DST_MATCH;
     } else if (!strcmp(name, "load")) {
         if (value[strcspn(value, "[-")] == '-') {
-            learn_parse_load_immediate(value, spec);
+            char *error = learn_parse_load_immediate(value, spec);
+            if (error) {
+                return error;
+            }
         } else {
             struct ofpact_reg_move move;
+            char *error;
 
-            nxm_parse_reg_move(&move, value);
+            error = nxm_parse_reg_move(&move, value);
+            if (error) {
+                return error;
+            }
 
             spec->n_bits = move.src.n_bits;
             spec->src_type = NX_LEARN_SRC_FIELD;
@@ -503,38 +518,29 @@ learn_parse_spec(const char *orig, char *name, char *value,
             spec->dst = move.dst;
         }
     } else if (!strcmp(name, "output")) {
-        if (mf_parse_subfield(&spec->src, value)[0] != '\0') {
-            ovs_fatal(0, "%s: syntax error after NXM field name `%s'",
-                      orig, name);
+        char *error = mf_parse_subfield(&spec->src, value);
+        if (error) {
+            return error;
         }
 
         spec->n_bits = spec->src.n_bits;
         spec->src_type = NX_LEARN_SRC_FIELD;
         spec->dst_type = NX_LEARN_DST_OUTPUT;
     } else {
-        ovs_fatal(0, "%s: unknown keyword %s", orig, name);
+        return xasprintf("%s: unknown keyword %s", orig, name);
     }
+
+    return NULL;
 }
 
-/* Parses 'arg' as a set of arguments to the "learn" action and appends a
- * matching OFPACT_LEARN action to 'ofpacts'.  ovs-ofctl(8) describes the
- * format parsed.
- *
- * Prints an error on stderr and aborts the program if 'arg' syntax is invalid.
- *
- * If 'flow' is nonnull, then it should be the flow from a struct match that is
- * the matching rule for the learning action.  This helps to better validate
- * the action's arguments.
- *
- * Modifies 'arg'. */
-void
-learn_parse(char *arg, struct ofpbuf *ofpacts)
+/* Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
+learn_parse__(char *orig, char *arg, struct ofpbuf *ofpacts)
 {
-    char *orig = xstrdup(arg);
-    char *name, *value;
-
     struct ofpact_learn *learn;
     struct match match;
+    char *name, *value;
 
     learn = ofpact_put_LEARN(ofpacts);
     learn->idle_timeout = OFP_FLOW_PERMANENT;
@@ -547,8 +553,8 @@ learn_parse(char *arg, struct ofpbuf *ofpacts)
         if (!strcmp(name, "table")) {
             learn->table_id = atoi(value);
             if (learn->table_id == 255) {
-                ovs_fatal(0, "%s: table id 255 not valid for `learn' action",
-                          orig);
+                return xasprintf("%s: table id 255 not valid for `learn' "
+                                 "action", orig);
             }
         } else if (!strcmp(name, "priority")) {
             learn->priority = atoi(value);
@@ -564,12 +570,16 @@ learn_parse(char *arg, struct ofpbuf *ofpacts)
             learn->cookie = strtoull(value, NULL, 0);
         } else {
             struct ofpact_learn_spec *spec;
+            char *error;
 
             spec = ofpbuf_put_zeros(ofpacts, sizeof *spec);
             learn = ofpacts->l2;
             learn->n_specs++;
 
-            learn_parse_spec(orig, name, value, spec);
+            error = learn_parse_spec(orig, name, value, spec);
+            if (error) {
+                return error;
+            }
 
             /* Update 'match' to allow for satisfying destination
              * prerequisites. */
@@ -581,7 +591,28 @@ learn_parse(char *arg, struct ofpbuf *ofpacts)
     }
     ofpact_update_len(ofpacts, &learn->ofpact);
 
+    return NULL;
+}
+
+/* Parses 'arg' as a set of arguments to the "learn" action and appends a
+ * matching OFPACT_LEARN action to 'ofpacts'.  ovs-ofctl(8) describes the
+ * format parsed.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string.
+ *
+ * If 'flow' is nonnull, then it should be the flow from a struct match that is
+ * the matching rule for the learning action.  This helps to better validate
+ * the action's arguments.
+ *
+ * Modifies 'arg'. */
+char * WARN_UNUSED_RESULT
+learn_parse(char *arg, struct ofpbuf *ofpacts)
+{
+    char *orig = xstrdup(arg);
+    char *error = learn_parse__(orig, arg, ofpacts);
     free(orig);
+    return error;
 }
 
 /* Appends a description of 'learn' to 's', in the format that ovs-ofctl(8)
diff --git a/lib/learn.h b/lib/learn.h
index 5bceb6e..0e676fe 100644
--- a/lib/learn.h
+++ b/lib/learn.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011, 2012 Nicira, Inc.
+ * Copyright (c) 2011, 2012, 2013 Nicira, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,6 +17,7 @@
 #ifndef LEARN_H
 #define LEARN_H 1
 
+#include "compiler.h"
 #include "ofp-errors.h"
 
 struct ds;
@@ -41,7 +42,7 @@ void learn_execute(const struct ofpact_learn *, const struct flow *,
                    struct ofputil_flow_mod *, struct ofpbuf *ofpacts);
 void learn_mask(const struct ofpact_learn *, struct flow_wildcards *);
 
-void learn_parse(char *, struct ofpbuf *ofpacts);
+char *learn_parse(char *, struct ofpbuf *ofpacts) WARN_UNUSED_RESULT;
 void learn_format(const struct ofpact_learn *, struct ds *);
 
 #endif /* learn.h */
diff --git a/lib/meta-flow.c b/lib/meta-flow.c
index 0677202..e66987c 100644
--- a/lib/meta-flow.c
+++ b/lib/meta-flow.c
@@ -2699,21 +2699,22 @@ mf_parse_subfield__(struct mf_subfield *sf, const char **sp)
 /* 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.
+ * 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.  */
-const char *
+char * WARN_UNUSED_RESULT
 mf_parse_subfield(struct mf_subfield *sf, const char *s)
 {
-    char *msg = mf_parse_subfield__(sf, &s);
-    if (msg) {
-        ovs_fatal(0, "%s", msg);
+    char *error = mf_parse_subfield__(sf, &s);
+    if (!error && s[0]) {
+        error = xstrdup("unexpected input following field syntax");
     }
-    return s;
+    return error;
 }
 
 void
diff --git a/lib/meta-flow.h b/lib/meta-flow.h
index a85a193..bc402dc 100644
--- a/lib/meta-flow.h
+++ b/lib/meta-flow.h
@@ -360,8 +360,10 @@ uint64_t mf_get_subfield(const struct mf_subfield *, const struct flow *);
 
 
 void mf_format_subfield(const struct mf_subfield *, struct ds *);
-char *mf_parse_subfield__(struct mf_subfield *sf, const char **s);
-const char *mf_parse_subfield(struct mf_subfield *, const char *);
+char *mf_parse_subfield__(struct mf_subfield *sf, const char **s)
+    WARN_UNUSED_RESULT;
+char *mf_parse_subfield(struct mf_subfield *, const char *s)
+    WARN_UNUSED_RESULT;
 
 enum ofperr mf_check_src(const struct mf_subfield *, const struct flow *);
 enum ofperr mf_check_dst(const struct mf_subfield *, const struct flow *);
diff --git a/lib/multipath.c b/lib/multipath.c
index dbd5704..e0b6bff 100644
--- a/lib/multipath.c
+++ b/lib/multipath.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2010, 2011, 2012 Nicira, Inc.
+ * Copyright (c) 2010, 2011, 2012, 2013 Nicira, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -195,14 +195,14 @@ multipath_algorithm(uint32_t hash, enum nx_mp_algorithm algorithm,
 /* Parses 's_' as a set of arguments to the "multipath" action and initializes
  * 'mp' accordingly.  ovs-ofctl(8) describes the format parsed.
  *
- * Prints an error on stderr and aborts the program if 's_' syntax is
- * invalid. */
-void
-multipath_parse(struct ofpact_multipath *mp, const char *s_)
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string.*/
+static char * WARN_UNUSED_RESULT
+multipath_parse__(struct ofpact_multipath *mp, const char *s_, char *s)
 {
-    char *s = xstrdup(s_);
     char *save_ptr = NULL;
     char *fields, *basis, *algorithm, *n_links_str, *arg, *dst;
+    char *error;
     int n_links;
 
     fields = strtok_r(s, ", ", &save_ptr);
@@ -212,7 +212,7 @@ multipath_parse(struct ofpact_multipath *mp, const char *s_)
     arg = strtok_r(NULL, ", ", &save_ptr);
     dst = strtok_r(NULL, ", ", &save_ptr);
     if (!dst) {
-        ovs_fatal(0, "%s: not enough arguments to multipath action", s_);
+        return xasprintf("%s: not enough arguments to multipath action", s_);
     }
 
     ofpact_init_MULTIPATH(mp);
@@ -221,7 +221,7 @@ multipath_parse(struct ofpact_multipath *mp, const char *s_)
     } else if (!strcasecmp(fields, "symmetric_l4")) {
         mp->fields = NX_HASH_FIELDS_SYMMETRIC_L4;
     } else {
-        ovs_fatal(0, "%s: unknown fields `%s'", s_, fields);
+        return xasprintf("%s: unknown fields `%s'", s_, fields);
     }
     mp->basis = atoi(basis);
     if (!strcasecmp(algorithm, "modulo_n")) {
@@ -233,24 +233,41 @@ multipath_parse(struct ofpact_multipath *mp, const char *s_)
     } else if (!strcasecmp(algorithm, "iter_hash")) {
         mp->algorithm = NX_MP_ALG_ITER_HASH;
     } else {
-        ovs_fatal(0, "%s: unknown algorithm `%s'", s_, algorithm);
+        return xasprintf("%s: unknown algorithm `%s'", s_, algorithm);
     }
     n_links = atoi(n_links_str);
     if (n_links < 1 || n_links > 65536) {
-        ovs_fatal(0, "%s: n_links %d is not in valid range 1 to 65536",
-                  s_, n_links);
+        return xasprintf("%s: n_links %d is not in valid range 1 to 65536",
+                         s_, n_links);
     }
     mp->max_link = n_links - 1;
     mp->arg = atoi(arg);
 
-    mf_parse_subfield(&mp->dst, dst);
+    error = mf_parse_subfield(&mp->dst, dst);
+    if (error) {
+        return error;
+    }
     if (mp->dst.n_bits < 16 && n_links > (1u << mp->dst.n_bits)) {
-        ovs_fatal(0, "%s: %d-bit destination field has %u possible values, "
-                  "less than specified n_links %d",
-                  s_, mp->dst.n_bits, 1u << mp->dst.n_bits, n_links);
+        return xasprintf("%s: %d-bit destination field has %u possible "
+                         "values, less than specified n_links %d",
+                         s_, mp->dst.n_bits, 1u << mp->dst.n_bits, n_links);
     }
 
+    return NULL;
+}
+
+/* Parses 's_' as a set of arguments to the "multipath" action and initializes
+ * 'mp' accordingly.  ovs-ofctl(8) describes the format parsed.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+char * WARN_UNUSED_RESULT
+multipath_parse(struct ofpact_multipath *mp, const char *s_)
+{
+    char *s = xstrdup(s_);
+    char *error = multipath_parse__(mp, s_, s);
     free(s);
+    return error;
 }
 
 /* Appends a description of 'mp' to 's', in the format that ovs-ofctl(8)
diff --git a/lib/multipath.h b/lib/multipath.h
index 97b5161..0673050 100644
--- a/lib/multipath.h
+++ b/lib/multipath.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2010, 2011, 2012 Nicira, Inc.
+ * Copyright (c) 2010, 2011, 2012, 2013 Nicira, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,6 +18,7 @@
 #define MULTIPATH_H 1
 
 #include <stdint.h>
+#include "compiler.h"
 #include "ofp-errors.h"
 
 struct ds;
@@ -42,7 +43,8 @@ void multipath_to_nxast(const struct ofpact_multipath *,
 void multipath_execute(const struct ofpact_multipath *, struct flow *,
                        struct flow_wildcards *);
 
-void multipath_parse(struct ofpact_multipath *, const char *);
+char *multipath_parse(struct ofpact_multipath *, const char *)
+    WARN_UNUSED_RESULT;
 void multipath_format(const struct ofpact_multipath *, struct ds *);
 
 #endif /* multipath.h */
diff --git a/lib/nx-match.c b/lib/nx-match.c
index 8bdd8ec..3a6d7cc 100644
--- a/lib/nx-match.c
+++ b/lib/nx-match.c
@@ -1004,50 +1004,67 @@ oxm_match_from_string(const char *s, struct ofpbuf *b)
     return match_len;
 }
 
-void
+/* Parses 's' as a "move" action, in the form described in ovs-ofctl(8), into
+ * '*move'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+char * WARN_UNUSED_RESULT
 nxm_parse_reg_move(struct ofpact_reg_move *move, const char *s)
 {
     const char *full_s = s;
+    char *error;
 
-    s = mf_parse_subfield(&move->src, s);
+    error = mf_parse_subfield__(&move->src, &s);
+    if (error) {
+        return error;
+    }
     if (strncmp(s, "->", 2)) {
-        ovs_fatal(0, "%s: missing `->' following source", full_s);
+        return xasprintf("%s: missing `->' following source", full_s);
     }
     s += 2;
-    s = mf_parse_subfield(&move->dst, s);
-    if (*s != '\0') {
-        ovs_fatal(0, "%s: trailing garbage following destination", full_s);
+    error = mf_parse_subfield(&move->dst, s);
+    if (error) {
+        return error;
     }
 
     if (move->src.n_bits != move->dst.n_bits) {
-        ovs_fatal(0, "%s: source field is %d bits wide but destination is "
-                  "%d bits wide", full_s,
-                  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;
 }
 
-void
+/* Parses 's' as a "load" action, in the form described in ovs-ofctl(8), into
+ * '*load'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+char * WARN_UNUSED_RESULT
 nxm_parse_reg_load(struct ofpact_reg_load *load, const char *s)
 {
     const char *full_s = s;
     uint64_t value = strtoull(s, (char **) &s, 0);
+    char *error;
 
     if (strncmp(s, "->", 2)) {
-        ovs_fatal(0, "%s: missing `->' following value", full_s);
+        return xasprintf("%s: missing `->' following value", full_s);
     }
     s += 2;
-    s = mf_parse_subfield(&load->dst, s);
-    if (*s != '\0') {
-        ovs_fatal(0, "%s: trailing garbage following destination", full_s);
+    error = mf_parse_subfield(&load->dst, s);
+    if (error) {
+        return error;
     }
 
     if (load->dst.n_bits < 64 && (value >> load->dst.n_bits) != 0) {
-        ovs_fatal(0, "%s: value %"PRIu64" does not fit into %d bits",
-                  full_s, value, load->dst.n_bits);
+        return xasprintf("%s: value %"PRIu64" does not fit into %d bits",
+                         full_s, value, load->dst.n_bits);
     }
 
     load->subvalue.be64[0] = htonll(0);
     load->subvalue.be64[1] = htonll(value);
+    return NULL;
 }
 
 /* nxm_format_reg_move(), nxm_format_reg_load(). */
@@ -1316,13 +1333,27 @@ nxm_reg_load(const struct mf_subfield *dst, uint64_t src_data,
 }
 
 /* nxm_parse_stack_action, works for both push() and pop(). */
-void
+
+/* Parses 's' as a "push" or "pop" action, in the form described in
+ * ovs-ofctl(8), 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 * WARN_UNUSED_RESULT
 nxm_parse_stack_action(struct ofpact_stack *stack_action, const char *s)
 {
-    s = mf_parse_subfield(&stack_action->subfield, s);
+    char *error;
+
+    error = mf_parse_subfield__(&stack_action->subfield, &s);
+    if (error) {
+        return error;
+    }
+
     if (*s != '\0') {
-        ovs_fatal(0, "%s: trailing garbage following push or pop", s);
+        return xasprintf("%s: trailing garbage following push or pop", s);
     }
+
+    return NULL;
 }
 
 void
diff --git a/lib/nx-match.h b/lib/nx-match.h
index bb63b90..b03688b 100644
--- a/lib/nx-match.h
+++ b/lib/nx-match.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2010, 2011, 2012 Nicira, Inc.
+ * Copyright (c) 2010, 2011, 2012, 2013 Nicira, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,6 +20,7 @@
 #include <stdint.h>
 #include <sys/types.h>
 #include <netinet/in.h>
+#include "compiler.h"
 #include "flow.h"
 #include "ofp-errors.h"
 #include "openvswitch/types.h"
@@ -57,8 +58,10 @@ char *oxm_match_to_string(const uint8_t *, unsigned int match_len);
 int nx_match_from_string(const char *, struct ofpbuf *);
 int oxm_match_from_string(const char *, struct ofpbuf *);
 
-void nxm_parse_reg_move(struct ofpact_reg_move *, const char *);
-void nxm_parse_reg_load(struct ofpact_reg_load *, const char *);
+char *nxm_parse_reg_move(struct ofpact_reg_move *, const char *)
+    WARN_UNUSED_RESULT;
+char *nxm_parse_reg_load(struct ofpact_reg_load *, const char *)
+    WARN_UNUSED_RESULT;
 
 void nxm_format_reg_move(const struct ofpact_reg_move *, struct ds *);
 void nxm_format_reg_load(const struct ofpact_reg_load *, struct ds *);
@@ -86,7 +89,8 @@ void nxm_execute_reg_load(const struct ofpact_reg_load *, struct flow *);
 void nxm_reg_load(const struct mf_subfield *, uint64_t src_data,
                   struct flow *);
 
-void nxm_parse_stack_action(struct ofpact_stack *, const char *);
+char *nxm_parse_stack_action(struct ofpact_stack *, const char *)
+    WARN_UNUSED_RESULT;
 
 void nxm_format_stack_push(const struct ofpact_stack *, struct ds *);
 void nxm_format_stack_pop(const struct ofpact_stack *, struct ds *);
diff --git a/lib/ofp-parse.c b/lib/ofp-parse.c
index da36f88..ced6bcd 100644
--- a/lib/ofp-parse.c
+++ b/lib/ofp-parse.c
@@ -41,123 +41,196 @@
 
 VLOG_DEFINE_THIS_MODULE(ofp_parse);
 
-static void ofp_fatal(const char *flow, bool verbose, const char *format, ...)
-    NO_RETURN;
-
-static uint8_t
-str_to_u8(const char *str, const char *name)
+/* Parses 'str' as a 16-bit unsigned integer into '*valuep'.
+ *
+ * 'name' describes the value parsed in an error message, if any.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
+str_to_u16(const char *str, const char *name, uint16_t *valuep)
 {
     int value;
 
-    if (!str_to_int(str, 10, &value) || value < 0 || value > 255) {
-        ovs_fatal(0, "invalid %s \"%s\"", name, str);
+    if (!str_to_int(str, 0, &value) || value < 0 || value > 65535) {
+        return xasprintf("invalid %s \"%s\"", name, str);
     }
-    return value;
+    *valuep = value;
+    return NULL;
 }
 
-static uint16_t
-str_to_u16(const char *str, const char *name)
+/* Parses 'str' as an 8-bit unsigned integer into '*valuep'.
+ *
+ * 'name' describes the value parsed in an error message, if any.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
+str_to_u8(const char *str, const char *name, uint8_t *valuep)
 {
     int value;
 
-    if (!str_to_int(str, 0, &value) || value < 0 || value > 65535) {
-        ovs_fatal(0, "invalid %s \"%s\"", name, str);
+    if (!str_to_int(str, 0, &value) || value < 0 || value > 255) {
+        return xasprintf("invalid %s \"%s\"", name, str);
     }
-    return value;
+    *valuep = value;
+    return NULL;
 }
 
-static uint32_t
-str_to_u32(const char *str)
+/* Parses 'str' as a 32-bit unsigned integer into '*valuep'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
+str_to_u32(const char *str, uint32_t *valuep)
 {
     char *tail;
     uint32_t value;
 
     if (!str[0]) {
-        ovs_fatal(0, "missing required numeric argument");
+        return xstrdup("missing required numeric argument");
     }
 
     errno = 0;
     value = strtoul(str, &tail, 0);
     if (errno == EINVAL || errno == ERANGE || *tail) {
-        ovs_fatal(0, "invalid numeric format %s", str);
+        return xasprintf("invalid numeric format %s", str);
     }
-    return value;
+    *valuep = value;
+    return NULL;
 }
 
-static uint64_t
-str_to_u64(const char *str)
+/* Parses 'str' as an 64-bit unsigned integer into '*valuep'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
+str_to_u64(const char *str, uint64_t *valuep)
 {
     char *tail;
     uint64_t value;
 
     if (!str[0]) {
-        ovs_fatal(0, "missing required numeric argument");
+        return xstrdup("missing required numeric argument");
     }
 
     errno = 0;
     value = strtoull(str, &tail, 0);
     if (errno == EINVAL || errno == ERANGE || *tail) {
-        ovs_fatal(0, "invalid numeric format %s", str);
+        return xasprintf("invalid numeric format %s", str);
     }
-    return value;
+    *valuep = value;
+    return NULL;
 }
 
-static void
+/* Parses 'str' as an 64-bit unsigned integer in network byte order into
+ * '*valuep'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
+str_to_be64(const char *str, ovs_be64 *valuep)
+{
+    uint64_t value;
+    char *error;
+
+    error = str_to_u64(str, &value);
+    if (!error) {
+        *valuep = htonll(value);
+    }
+    return error;
+}
+
+/* Parses 'str' as an Ethernet address into 'mac'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
 str_to_mac(const char *str, uint8_t mac[6])
 {
     if (sscanf(str, ETH_ADDR_SCAN_FMT, ETH_ADDR_SCAN_ARGS(mac))
         != ETH_ADDR_SCAN_COUNT) {
-        ovs_fatal(0, "invalid mac address %s", str);
+        return xasprintf("invalid mac address %s", str);
     }
+    return NULL;
 }
 
-static void
+/* Parses 'str' as an IP address into '*ip'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
 str_to_ip(const char *str, ovs_be32 *ip)
 {
     struct in_addr in_addr;
 
     if (lookup_ip(str, &in_addr)) {
-        ovs_fatal(0, "%s: could not convert to IP address", str);
+        return xasprintf("%s: could not convert to IP address", str);
     }
     *ip = in_addr.s_addr;
+    return NULL;
 }
 
-static void
+/* Parses 'arg' as the argument to an "enqueue" action, and appends such an
+ * action to 'ofpacts'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
 parse_enqueue(char *arg, struct ofpbuf *ofpacts)
 {
     char *sp = NULL;
     char *port = strtok_r(arg, ":q", &sp);
     char *queue = strtok_r(NULL, "", &sp);
     struct ofpact_enqueue *enqueue;
+    char *error;
 
     if (port == NULL || queue == NULL) {
-        ovs_fatal(0, "\"enqueue\" syntax is \"enqueue:PORT:QUEUE\"");
+        return xstrdup("\"enqueue\" syntax is \"enqueue:PORT:QUEUE\"");
     }
 
     enqueue = ofpact_put_ENQUEUE(ofpacts);
-    enqueue->port = u16_to_ofp(str_to_u32(port));
-    enqueue->queue = str_to_u32(queue);
+    if (!ofputil_port_from_string(port, &enqueue->port)) {
+        return xasprintf("%s: enqueue to unknown port", port);
+    }
+    if (!error) {
+        error = str_to_u32(queue, &enqueue->queue);
+    }
+    return error;
 }
 
-static void
-parse_output(char *arg, struct ofpbuf *ofpacts)
+/* Parses 'arg' as the argument to an "output" action, and appends such an
+ * action to 'ofpacts'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
+parse_output(const char *arg, struct ofpbuf *ofpacts)
 {
     if (strchr(arg, '[')) {
         struct ofpact_output_reg *output_reg;
 
         output_reg = ofpact_put_OUTPUT_REG(ofpacts);
-        mf_parse_subfield(&output_reg->src, arg);
         output_reg->max_len = UINT16_MAX;
+        return mf_parse_subfield(&output_reg->src, arg);
     } else {
         struct ofpact_output *output;
 
         output = ofpact_put_OUTPUT(ofpacts);
-        output->port = u16_to_ofp(str_to_u32(arg));
         output->max_len = output->port == OFPP_CONTROLLER ? UINT16_MAX : 0;
+        if (!ofputil_port_from_string(arg, &output->port)) {
+            return xasprintf("%s: output to unknown port", arg);
+        }
+        return NULL;
     }
 }
 
-static void
+/* Parses 'arg' as the argument to an "resubmit" action, and appends such an
+ * action to 'ofpacts'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
 parse_resubmit(char *arg, struct ofpbuf *ofpacts)
 {
     struct ofpact_resubmit *resubmit;
@@ -168,22 +241,39 @@ parse_resubmit(char *arg, struct ofpbuf *ofpacts)
     in_port_s = strsep(&arg, ",");
     if (in_port_s && in_port_s[0]) {
         if (!ofputil_port_from_string(in_port_s, &resubmit->in_port)) {
-            ovs_fatal(0, "%s: resubmit to unknown port", in_port_s);
+            return xasprintf("%s: resubmit to unknown port", in_port_s);
         }
     } else {
         resubmit->in_port = OFPP_IN_PORT;
     }
 
     table_s = strsep(&arg, ",");
-    resubmit->table_id = table_s && table_s[0] ? str_to_u32(table_s) : 255;
+    if (table_s && table_s[0]) {
+        uint32_t table_id;
+        char *error;
+
+        error = str_to_u32(table_s, &table_id);
+        if (error) {
+            return error;
+        }
+        resubmit->table_id = table_id;
+    } else {
+        resubmit->table_id = 255;
+    }
 
     if (resubmit->in_port == OFPP_IN_PORT && resubmit->table_id == 255) {
-        ovs_fatal(0, "at least one \"in_port\" or \"table\" must be specified "
-                  " on resubmit");
+        return xstrdup("at least one \"in_port\" or \"table\" must be "
+                       "specified  on resubmit");
     }
+    return NULL;
 }
 
-static void
+/* Parses 'arg' as the argument to a "note" action, and appends such an action
+ * to 'ofpacts'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
 parse_note(const char *arg, struct ofpbuf *ofpacts)
 {
     struct ofpact_note *note;
@@ -202,7 +292,7 @@ parse_note(const char *arg, struct ofpbuf *ofpacts)
 
         byte = hexits_value(arg, 2, &ok);
         if (!ok) {
-            ovs_fatal(0, "bad hex digit in `note' argument");
+            return xstrdup("bad hex digit in `note' argument");
         }
         ofpbuf_put(ofpacts, &byte, 1);
 
@@ -212,26 +302,45 @@ parse_note(const char *arg, struct ofpbuf *ofpacts)
         arg += 2;
     }
     ofpact_update_len(ofpacts, &note->ofpact);
+    return NULL;
 }
 
-static void
+/* Parses 'arg' as the argument to a "fin_timeout" action, and appends such an
+ * action to 'ofpacts'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
 parse_fin_timeout(struct ofpbuf *b, char *arg)
 {
     struct ofpact_fin_timeout *oft = ofpact_put_FIN_TIMEOUT(b);
     char *key, *value;
 
     while (ofputil_parse_key_value(&arg, &key, &value)) {
+        char *error;
+
         if (!strcmp(key, "idle_timeout")) {
-            oft->fin_idle_timeout = str_to_u16(value, key);
+            error =  str_to_u16(value, key, &oft->fin_idle_timeout);
         } else if (!strcmp(key, "hard_timeout")) {
-            oft->fin_hard_timeout = str_to_u16(value, key);
+            error = str_to_u16(value, key, &oft->fin_hard_timeout);
         } else {
-            ovs_fatal(0, "invalid key '%s' in 'fin_timeout' argument", key);
+            error = xasprintf("invalid key '%s' in 'fin_timeout' argument",
+                              key);
+        }
+
+        if (error) {
+            return error;
         }
     }
+    return NULL;
 }
 
-static void
+/* Parses 'arg' as the argument to a "controller" action, and appends such an
+ * action to 'ofpacts'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
 parse_controller(struct ofpbuf *b, char *arg)
 {
     enum ofp_packet_in_reason reason = OFPR_ACTION;
@@ -241,22 +350,31 @@ parse_controller(struct ofpbuf *b, char *arg)
     if (!arg[0]) {
         /* Use defaults. */
     } else if (strspn(arg, "0123456789") == strlen(arg)) {
-        max_len = str_to_u16(arg, "max_len");
+        char *error = str_to_u16(arg, "max_len", &max_len);
+        if (error) {
+            return error;
+        }
     } else {
         char *name, *value;
 
         while (ofputil_parse_key_value(&arg, &name, &value)) {
             if (!strcmp(name, "reason")) {
                 if (!ofputil_packet_in_reason_from_string(value, &reason)) {
-                    ovs_fatal(0, "unknown reason \"%s\"", value);
+                    return xasprintf("unknown reason \"%s\"", value);
                 }
             } else if (!strcmp(name, "max_len")) {
-                max_len = str_to_u16(value, "max_len");
+                char *error = str_to_u16(value, "max_len", &max_len);
+                if (error) {
+                    return error;
+                }
             } else if (!strcmp(name, "id")) {
-                controller_id = str_to_u16(value, "id");
+                char *error = str_to_u16(value, "id", &controller_id);
+                if (error) {
+                    return error;
+                }
             } else {
-                ovs_fatal(0, "unknown key \"%s\" parsing controller action",
-                          name);
+                return xasprintf("unknown key \"%s\" parsing controller "
+                                 "action", name);
             }
         }
     }
@@ -275,6 +393,8 @@ parse_controller(struct ofpbuf *b, char *arg)
         controller->reason = reason;
         controller->controller_id = controller_id;
     }
+
+    return NULL;
 }
 
 static void
@@ -290,7 +410,12 @@ parse_noargs_dec_ttl(struct ofpbuf *b)
     ofpact_update_len(b, &ids->ofpact);
 }
 
-static void
+/* Parses 'arg' as the argument to a "dec_ttl" action, and appends such an
+ * action to 'ofpacts'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
 parse_dec_ttl(struct ofpbuf *b, char *arg)
 {
     if (*arg == '\0') {
@@ -310,68 +435,99 @@ parse_dec_ttl(struct ofpbuf *b, char *arg)
             ids->n_controllers++;
         }
         if (!ids->n_controllers) {
-            ovs_fatal(0, "dec_ttl_cnt_ids: expected at least one controller "
-                      "id.");
+            return xstrdup("dec_ttl_cnt_ids: expected at least one controller "
+                           "id.");
         }
         ofpact_update_len(b, &ids->ofpact);
     }
+    return NULL;
 }
 
-static void
+/* Parses 'arg' as the argument to a "set_mpls_ttl" action, and appends such an
+ * action to 'ofpacts'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
 parse_set_mpls_ttl(struct ofpbuf *b, const char *arg)
 {
     struct ofpact_mpls_ttl *mpls_ttl = ofpact_put_SET_MPLS_TTL(b);
 
     if (*arg == '\0') {
-        ovs_fatal(0, "parse_set_mpls_ttl: expected ttl.");
+        return xstrdup("parse_set_mpls_ttl: expected ttl.");
     }
 
     mpls_ttl->ttl = atoi(arg);
+    return NULL;
 }
 
-static void
-set_field_parse(const char *arg, struct ofpbuf *ofpacts)
+/* Parses a "set_field" action with argument 'arg', appending the parsed
+ * action to 'ofpacts'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
+set_field_parse__(char *arg, struct ofpbuf *ofpacts)
 {
-    char *orig = xstrdup(arg);
     struct ofpact_reg_load *load = ofpact_put_REG_LOAD(ofpacts);
     char *value;
     char *delim;
     char *key;
     const struct mf_field *mf;
-    const char *error;
+    char *error;
     union mf_value mf_value;
 
-    value = orig;
-    delim = strstr(orig, "->");
+    value = arg;
+    delim = strstr(arg, "->");
     if (!delim) {
-        ovs_fatal(0, "%s: missing `->'", orig);
+        return xasprintf("%s: missing `->'", arg);
     }
     if (strlen(delim) <= strlen("->")) {
-        ovs_fatal(0, "%s: missing field name following `->'", orig);
+        return xasprintf("%s: missing field name following `->'", arg);
     }
 
     key = delim + strlen("->");
     mf = mf_from_name(key);
     if (!mf) {
-        ovs_fatal(0, "%s is not valid oxm field name", key);
+        return xasprintf("%s is not a valid OXM field name", key);
     }
     if (!mf->writable) {
-        ovs_fatal(0, "%s is not allowed to set", key);
+        return xasprintf("%s is read-only", key);
     }
 
     delim[0] = '\0';
     error = mf_parse_value(mf, value, &mf_value);
     if (error) {
-        ovs_fatal(0, "%s", error);
+        return error;
     }
     if (!mf_is_value_valid(mf, &mf_value)) {
-        ovs_fatal(0, "%s is not valid valid for field %s", value, key);
+        return xasprintf("%s is not a valid value for field %s", value, key);
     }
     ofpact_set_field_init(load, mf, &mf_value);
-    free(orig);
+
+    return NULL;
 }
 
-static void
+/* Parses 'arg' as the argument to a "set_field" action, and appends such an
+ * action to 'ofpacts'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
+set_field_parse(const char *arg, struct ofpbuf *ofpacts)
+{
+    char *copy = xstrdup(arg);
+    char *error = set_field_parse__(copy, ofpacts);
+    free(copy);
+    return error;
+}
+
+/* Parses 'arg' as the argument to a "write_metadata" instruction, and appends
+ * such an action to 'ofpacts'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
 parse_metadata(struct ofpbuf *b, char *arg)
 {
     struct ofpact_metadata *om;
@@ -380,51 +536,73 @@ parse_metadata(struct ofpbuf *b, char *arg)
     om = ofpact_put_WRITE_METADATA(b);
 
     if (mask) {
+        char *error;
+
         *mask = '\0';
-        om->mask = htonll(str_to_u64(mask + 1));
+        error = str_to_be64(mask + 1, &om->mask);
+        if (error) {
+            return error;
+        }
     } else {
         om->mask = htonll(UINT64_MAX);
     }
 
-    om->metadata = htonll(str_to_u64(arg));
+    return str_to_be64(arg, &om->metadata);
 }
 
-static void
+/* Parses 'arg' as the argument to a "sample" action, and appends such an
+ * action to 'ofpacts'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
 parse_sample(struct ofpbuf *b, char *arg)
 {
     struct ofpact_sample *os = ofpact_put_SAMPLE(b);
     char *key, *value;
 
     while (ofputil_parse_key_value(&arg, &key, &value)) {
+        char *error = NULL;
+
         if (!strcmp(key, "probability")) {
-            os->probability = str_to_u16(value, "probability");
-            if (os->probability == 0) {
-                ovs_fatal(0, "invalid probability value \"%s\"", value);
+            error = str_to_u16(value, "probability", &os->probability);
+            if (!error && os->probability == 0) {
+                error = xasprintf("invalid probability value \"%s\"", value);
             }
         } else if (!strcmp(key, "collector_set_id")) {
-            os->collector_set_id = str_to_u32(value);
+            error = str_to_u32(value, &os->collector_set_id);
         } else if (!strcmp(key, "obs_domain_id")) {
-            os->obs_domain_id = str_to_u32(value);
+            error = str_to_u32(value, &os->obs_domain_id);
         } else if (!strcmp(key, "obs_point_id")) {
-            os->obs_point_id = str_to_u32(value);
+            error = str_to_u32(value, &os->obs_point_id);
         } else {
-            ovs_fatal(0, "invalid key \"%s\" in \"sample\" argument",
-                      key);
+            error = xasprintf("invalid key \"%s\" in \"sample\" argument",
+                              key);
+        }
+        if (error) {
+            return error;
         }
     }
     if (os->probability == 0) {
-        ovs_fatal(0, "non-zero \"probability\" must be specified on sample");
+        return xstrdup("non-zero \"probability\" must be specified on sample");
     }
+    return NULL;
 }
 
-static void
+/* Parses 'arg' as the argument to action 'code', and appends such an action to
+ * 'ofpacts'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
 parse_named_action(enum ofputil_action_code code,
                    char *arg, struct ofpbuf *ofpacts)
 {
+    size_t orig_size = ofpacts->size;
     struct ofpact_tunnel *tunnel;
-    uint16_t vid;
+    char *error = NULL;
     uint16_t ethertype;
-    ovs_be32 ip;
+    uint16_t vid;
     uint8_t pcp;
     uint8_t tos;
 
@@ -434,30 +612,37 @@ parse_named_action(enum ofputil_action_code code,
 
     case OFPUTIL_OFPAT10_OUTPUT:
     case OFPUTIL_OFPAT11_OUTPUT:
-        parse_output(arg, ofpacts);
+        error = parse_output(arg, ofpacts);
         break;
 
     case OFPUTIL_OFPAT10_SET_VLAN_VID:
     case OFPUTIL_OFPAT11_SET_VLAN_VID:
-        vid = str_to_u32(arg);
+        error = str_to_u16(arg, "VLAN VID", &vid);
+        if (error) {
+            return error;
+        }
+
         if (vid & ~VLAN_VID_MASK) {
-            ovs_fatal(0, "%s: not a valid VLAN VID", arg);
+            return xasprintf("%s: not a valid VLAN VID", arg);
         }
         ofpact_put_SET_VLAN_VID(ofpacts)->vlan_vid = vid;
         break;
 
     case OFPUTIL_OFPAT10_SET_VLAN_PCP:
     case OFPUTIL_OFPAT11_SET_VLAN_PCP:
-        pcp = str_to_u32(arg);
+        error = str_to_u8(arg, "VLAN PCP", &pcp);
+        if (error) {
+            return error;
+        }
+
         if (pcp & ~7) {
-            ovs_fatal(0, "%s: not a valid VLAN PCP", arg);
+            return xasprintf("%s: not a valid VLAN PCP", arg);
         }
         ofpact_put_SET_VLAN_PCP(ofpacts)->vlan_pcp = pcp;
         break;
 
     case OFPUTIL_OFPAT12_SET_FIELD:
-        set_field_parse(arg, ofpacts);
-        break;
+        return set_field_parse(arg, ofpacts);
 
     case OFPUTIL_OFPAT10_STRIP_VLAN:
     case OFPUTIL_OFPAT11_POP_VLAN:
@@ -465,46 +650,52 @@ parse_named_action(enum ofputil_action_code code,
         break;
 
     case OFPUTIL_OFPAT11_PUSH_VLAN:
-        ethertype = str_to_u16(arg, "ethertype");
+        error = str_to_u16(arg, "ethertype", &ethertype);
+        if (error) {
+            return error;
+        }
+
         if (ethertype != ETH_TYPE_VLAN_8021Q) {
             /* XXX ETH_TYPE_VLAN_8021AD case isn't supported */
-            ovs_fatal(0, "%s: not a valid VLAN ethertype", arg);
+            return xasprintf("%s: not a valid VLAN ethertype", arg);
         }
+
         ofpact_put_PUSH_VLAN(ofpacts);
         break;
 
     case OFPUTIL_OFPAT11_SET_QUEUE:
-        ofpact_put_SET_QUEUE(ofpacts)->queue_id = str_to_u32(arg);
+        error = str_to_u32(arg, &ofpact_put_SET_QUEUE(ofpacts)->queue_id);
         break;
 
-
     case OFPUTIL_OFPAT10_SET_DL_SRC:
     case OFPUTIL_OFPAT11_SET_DL_SRC:
-        str_to_mac(arg, ofpact_put_SET_ETH_SRC(ofpacts)->mac);
+        error = str_to_mac(arg, ofpact_put_SET_ETH_SRC(ofpacts)->mac);
         break;
 
     case OFPUTIL_OFPAT10_SET_DL_DST:
     case OFPUTIL_OFPAT11_SET_DL_DST:
-        str_to_mac(arg, ofpact_put_SET_ETH_DST(ofpacts)->mac);
+        error = str_to_mac(arg, ofpact_put_SET_ETH_DST(ofpacts)->mac);
         break;
 
     case OFPUTIL_OFPAT10_SET_NW_SRC:
     case OFPUTIL_OFPAT11_SET_NW_SRC:
-        str_to_ip(arg, &ip);
-        ofpact_put_SET_IPV4_SRC(ofpacts)->ipv4 = ip;
+        error = str_to_ip(arg, &ofpact_put_SET_IPV4_SRC(ofpacts)->ipv4);
         break;
 
     case OFPUTIL_OFPAT10_SET_NW_DST:
     case OFPUTIL_OFPAT11_SET_NW_DST:
-        str_to_ip(arg, &ip);
-        ofpact_put_SET_IPV4_DST(ofpacts)->ipv4 = ip;
+        error = str_to_ip(arg, &ofpact_put_SET_IPV4_DST(ofpacts)->ipv4);
         break;
 
     case OFPUTIL_OFPAT10_SET_NW_TOS:
     case OFPUTIL_OFPAT11_SET_NW_TOS:
-        tos = str_to_u32(arg);
+        error = str_to_u8(arg, "TOS", &tos);
+        if (error) {
+            return error;
+        }
+
         if (tos & ~IP_DSCP_MASK) {
-            ovs_fatal(0, "%s: not a valid TOS", arg);
+            return xasprintf("%s: not a valid TOS", arg);
         }
         ofpact_put_SET_IPV4_DSCP(ofpacts)->dscp = tos;
         break;
@@ -514,35 +705,37 @@ parse_named_action(enum ofputil_action_code code,
 
     case OFPUTIL_OFPAT10_SET_TP_SRC:
     case OFPUTIL_OFPAT11_SET_TP_SRC:
-        ofpact_put_SET_L4_SRC_PORT(ofpacts)->port = str_to_u32(arg);
+        error = str_to_u16(arg, "source port",
+                           &ofpact_put_SET_L4_SRC_PORT(ofpacts)->port);
         break;
 
     case OFPUTIL_OFPAT10_SET_TP_DST:
     case OFPUTIL_OFPAT11_SET_TP_DST:
-        ofpact_put_SET_L4_DST_PORT(ofpacts)->port = str_to_u32(arg);
+        error = str_to_u16(arg, "destination port",
+                           &ofpact_put_SET_L4_DST_PORT(ofpacts)->port);
         break;
 
     case OFPUTIL_OFPAT10_ENQUEUE:
-        parse_enqueue(arg, ofpacts);
+        error = parse_enqueue(arg, ofpacts);
         break;
 
     case OFPUTIL_NXAST_RESUBMIT:
-        parse_resubmit(arg, ofpacts);
+        error = parse_resubmit(arg, ofpacts);
         break;
 
     case OFPUTIL_NXAST_SET_TUNNEL:
     case OFPUTIL_NXAST_SET_TUNNEL64:
         tunnel = ofpact_put_SET_TUNNEL(ofpacts);
         tunnel->ofpact.compat = code;
-        tunnel->tun_id = str_to_u64(arg);
+        error = str_to_u64(arg, &tunnel->tun_id);
         break;
 
     case OFPUTIL_NXAST_WRITE_METADATA:
-        parse_metadata(ofpacts, arg);
+        error = parse_metadata(ofpacts, arg);
         break;
 
     case OFPUTIL_NXAST_SET_QUEUE:
-        ofpact_put_SET_QUEUE(ofpacts)->queue_id = str_to_u32(arg);
+        error = str_to_u32(arg, &ofpact_put_SET_QUEUE(ofpacts)->queue_id);
         break;
 
     case OFPUTIL_NXAST_POP_QUEUE:
@@ -550,27 +743,27 @@ parse_named_action(enum ofputil_action_code code,
         break;
 
     case OFPUTIL_NXAST_REG_MOVE:
-        nxm_parse_reg_move(ofpact_put_REG_MOVE(ofpacts), arg);
+        error = nxm_parse_reg_move(ofpact_put_REG_MOVE(ofpacts), arg);
         break;
 
     case OFPUTIL_NXAST_REG_LOAD:
-        nxm_parse_reg_load(ofpact_put_REG_LOAD(ofpacts), arg);
+        error = nxm_parse_reg_load(ofpact_put_REG_LOAD(ofpacts), arg);
         break;
 
     case OFPUTIL_NXAST_NOTE:
-        parse_note(arg, ofpacts);
+        error = parse_note(arg, ofpacts);
         break;
 
     case OFPUTIL_NXAST_MULTIPATH:
-        multipath_parse(ofpact_put_MULTIPATH(ofpacts), arg);
+        error = multipath_parse(ofpact_put_MULTIPATH(ofpacts), arg);
         break;
 
     case OFPUTIL_NXAST_BUNDLE:
-        bundle_parse(arg, ofpacts);
+        error = bundle_parse(arg, ofpacts);
         break;
 
     case OFPUTIL_NXAST_BUNDLE_LOAD:
-        bundle_parse_load(arg, ofpacts);
+        error = bundle_parse_load(arg, ofpacts);
         break;
 
     case OFPUTIL_NXAST_RESUBMIT_TABLE:
@@ -579,7 +772,7 @@ parse_named_action(enum ofputil_action_code code,
         NOT_REACHED();
 
     case OFPUTIL_NXAST_LEARN:
-        learn_parse(arg, ofpacts);
+        error = learn_parse(arg, ofpacts);
         break;
 
     case OFPUTIL_NXAST_EXIT:
@@ -587,12 +780,12 @@ parse_named_action(enum ofputil_action_code code,
         break;
 
     case OFPUTIL_NXAST_DEC_TTL:
-        parse_dec_ttl(ofpacts, arg);
+        error = parse_dec_ttl(ofpacts, arg);
         break;
 
     case OFPUTIL_NXAST_SET_MPLS_TTL:
     case OFPUTIL_OFPAT11_SET_MPLS_TTL:
-        parse_set_mpls_ttl(ofpacts, arg);
+        error = parse_set_mpls_ttl(ofpacts, arg);
         break;
 
     case OFPUTIL_OFPAT11_DEC_MPLS_TTL:
@@ -601,69 +794,90 @@ parse_named_action(enum ofputil_action_code code,
         break;
 
     case OFPUTIL_NXAST_FIN_TIMEOUT:
-        parse_fin_timeout(ofpacts, arg);
+        error = parse_fin_timeout(ofpacts, arg);
         break;
 
     case OFPUTIL_NXAST_CONTROLLER:
-        parse_controller(ofpacts, arg);
+        error = parse_controller(ofpacts, arg);
         break;
 
     case OFPUTIL_OFPAT11_PUSH_MPLS:
     case OFPUTIL_NXAST_PUSH_MPLS:
-        ofpact_put_PUSH_MPLS(ofpacts)->ethertype =
-            htons(str_to_u16(arg, "push_mpls"));
+        error = str_to_u16(arg, "push_mpls", &ethertype);
+        if (!error) {
+            ofpact_put_PUSH_MPLS(ofpacts)->ethertype = htons(ethertype);
+        }
         break;
 
     case OFPUTIL_OFPAT11_POP_MPLS:
     case OFPUTIL_NXAST_POP_MPLS:
-        ofpact_put_POP_MPLS(ofpacts)->ethertype =
-            htons(str_to_u16(arg, "pop_mpls"));
+        error = str_to_u16(arg, "pop_mpls", &ethertype);
+        if (!error) {
+            ofpact_put_POP_MPLS(ofpacts)->ethertype = htons(ethertype);
+        }
         break;
 
     case OFPUTIL_NXAST_STACK_PUSH:
-        nxm_parse_stack_action(ofpact_put_STACK_PUSH(ofpacts), arg);
+        error = nxm_parse_stack_action(ofpact_put_STACK_PUSH(ofpacts), arg);
         break;
     case OFPUTIL_NXAST_STACK_POP:
-        nxm_parse_stack_action(ofpact_put_STACK_POP(ofpacts), arg);
+        error = nxm_parse_stack_action(ofpact_put_STACK_POP(ofpacts), arg);
         break;
 
     case OFPUTIL_NXAST_SAMPLE:
-        parse_sample(ofpacts, arg);
+        error = parse_sample(ofpacts, arg);
         break;
     }
+
+    if (error) {
+        ofpacts->size = orig_size;
+    }
+    return error;
 }
 
-static bool
+/* Parses action 'act', with argument 'arg', and appends a parsed version to
+ * 'ofpacts'.
+ *
+ * 'n_actions' specifies the number of actions already parsed (for proper
+ * handling of "drop" actions).
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
 str_to_ofpact__(char *pos, char *act, char *arg,
                 struct ofpbuf *ofpacts, int n_actions)
 {
     int code = ofputil_action_code_from_name(act);
     if (code >= 0) {
-        parse_named_action(code, arg, ofpacts);
+        return parse_named_action(code, arg, ofpacts);
     } else if (!strcasecmp(act, "drop")) {
         if (n_actions) {
-            ovs_fatal(0, "Drop actions must not be preceded by other "
-                      "actions");
+            return xstrdup("Drop actions must not be preceded by other "
+                           "actions");
         } else if (ofputil_parse_key_value(&pos, &act, &arg)) {
-            ovs_fatal(0, "Drop actions must not be followed by other "
-                      "actions");
+            return xstrdup("Drop actions must not be followed by other "
+                           "actions");
         }
-        return false;
     } else {
         ofp_port_t port;
         if (ofputil_port_from_string(act, &port)) {
             ofpact_put_OUTPUT(ofpacts)->port = port;
         } else {
-            ovs_fatal(0, "Unknown action: %s", act);
+            return xasprintf("Unknown action: %s", act);
         }
     }
 
-    return true;
+    return NULL;
 }
 
-static void
+/* Parses 'str' as a series of actions, and appends them to 'ofpacts'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
 str_to_ofpacts(char *str, struct ofpbuf *ofpacts)
 {
+    size_t orig_size = ofpacts->size;
     char *pos, *act, *arg;
     enum ofperr error;
     int n_actions;
@@ -671,25 +885,35 @@ str_to_ofpacts(char *str, struct ofpbuf *ofpacts)
     pos = str;
     n_actions = 0;
     while (ofputil_parse_key_value(&pos, &act, &arg)) {
-        if (!str_to_ofpact__(pos, act, arg, ofpacts, n_actions)) {
-            break;
+        char *error = str_to_ofpact__(pos, act, arg, ofpacts, n_actions);
+        if (error) {
+            ofpacts->size = orig_size;
+            return error;
         }
         n_actions++;
     }
 
     error = ofpacts_verify(ofpacts->data, ofpacts->size);
     if (error) {
-        ovs_fatal(0, "Incorrect action ordering");
+        ofpacts->size = orig_size;
+        return xstrdup("Incorrect action ordering");
     }
 
     ofpact_pad(ofpacts);
+    return NULL;
 }
 
-static void
+/* Parses 'arg' as the argument to instruction 'type', and appends such an
+ * instruction to 'ofpacts'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
 parse_named_instruction(enum ovs_instruction_type type,
                         char *arg, struct ofpbuf *ofpacts)
 {
     enum ofperr error;
+    char *error_s;
 
     switch (type) {
     case OVSINST_OFPIT11_APPLY_ACTIONS:
@@ -698,28 +922,33 @@ parse_named_instruction(enum ovs_instruction_type type,
 
     case OVSINST_OFPIT11_WRITE_ACTIONS:
         /* XXX */
-        ovs_fatal(0, "instruction write-actions is not supported yet");
-        break;
+        return xstrdup("instruction write-actions is not supported yet");
 
     case OVSINST_OFPIT11_CLEAR_ACTIONS:
         ofpact_put_CLEAR_ACTIONS(ofpacts);
         break;
 
     case OVSINST_OFPIT13_METER:
-        ofpact_put_METER(ofpacts)->meter_id = str_to_u32(arg);
+        error_s = str_to_u32(arg, &ofpact_put_METER(ofpacts)->meter_id);
         break;
 
     case OVSINST_OFPIT11_WRITE_METADATA:
-        parse_metadata(ofpacts, arg);
+        error_s = parse_metadata(ofpacts, arg);
+        if (error_s) {
+            return error_s;
+        }
         break;
 
     case OVSINST_OFPIT11_GOTO_TABLE: {
         struct ofpact_goto_table *ogt = ofpact_put_GOTO_TABLE(ofpacts);
         char *table_s = strsep(&arg, ",");
         if (!table_s || !table_s[0]) {
-            ovs_fatal(0, "instruction goto-table needs table id");
+            return xstrdup("instruction goto-table needs table id");
+        }
+        error_s = str_to_u8(table_s, "table", &ogt->table_id);
+        if (error_s) {
+            return error_s;
         }
-        ogt->table_id = str_to_u8(table_s, "table");
         break;
     }
     }
@@ -728,13 +957,19 @@ parse_named_instruction(enum ovs_instruction_type type,
        could be invalid. */
     error = ofpacts_verify(ofpacts->data, ofpacts->size);
     if (error) {
-        ovs_fatal(0, "Incorrect instruction ordering");
+        return xstrdup("Incorrect instruction ordering");
     }
+    return NULL;
 }
 
-static void
+/* Parses 'str' as a series of instructions, and appends them to 'ofpacts'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
 str_to_inst_ofpacts(char *str, struct ofpbuf *ofpacts)
 {
+    size_t orig_size = ofpacts->size;
     char *pos, *inst, *arg;
     int type;
     const char *prev_inst = NULL;
@@ -745,8 +980,10 @@ str_to_inst_ofpacts(char *str, struct ofpbuf *ofpacts)
     while (ofputil_parse_key_value(&pos, &inst, &arg)) {
         type = ofpact_instruction_type_from_name(inst);
         if (type < 0) {
-            if (!str_to_ofpact__(pos, inst, arg, ofpacts, n_actions)) {
-                break;
+            char *error = str_to_ofpact__(pos, inst, arg, ofpacts, n_actions);
+            if (error) {
+                ofpacts->size = orig_size;
+                return error;
             }
 
             type = OVSINST_OFPIT11_APPLY_ACTIONS;
@@ -755,19 +992,26 @@ str_to_inst_ofpacts(char *str, struct ofpbuf *ofpacts)
                 continue;
             }
         } else if (type == OVSINST_OFPIT11_APPLY_ACTIONS) {
-            ovs_fatal(0, "%s isn't supported. Just write actions then "
-                      "it is interpreted as apply_actions", inst);
+            ofpacts->size = orig_size;
+            return xasprintf("%s isn't supported. Just write actions then "
+                             "it is interpreted as apply_actions", inst);
         } else {
-            parse_named_instruction(type, arg, ofpacts);
+            char *error = parse_named_instruction(type, arg, ofpacts);
+            if (error) {
+                ofpacts->size = orig_size;
+                return error;
+            }
         }
 
-        if (type == prev_type) {
-            ovs_fatal(0, "instruction can be specified at most once: %s",
-                      inst);
-        }
         if (type <= prev_type) {
-            ovs_fatal(0, "Instruction %s must be specified before %s",
-                      inst, prev_inst);
+            ofpacts->size = orig_size;
+            if (type == prev_type) {
+                return xasprintf("instruction %s may be specified only once",
+                                 inst);
+            } else {
+                return xasprintf("instruction %s must be specified before %s",
+                                 inst, prev_inst);
+            }
         }
 
         prev_inst = inst;
@@ -775,6 +1019,8 @@ str_to_inst_ofpacts(char *str, struct ofpbuf *ofpacts)
         n_actions++;
     }
     ofpact_pad(ofpacts);
+
+    return NULL;
 }
 
 struct protocol {
@@ -813,44 +1059,26 @@ parse_protocol(const char *name, const struct protocol **p_out)
     return false;
 }
 
-static void
-ofp_fatal(const char *flow, bool verbose, const char *format, ...)
-{
-    va_list args;
-
-    if (verbose) {
-        fprintf(stderr, "%s:\n", flow);
-    }
-
-    va_start(args, format);
-    ovs_fatal_valist(0, format, args);
-}
-
-static void
+/* Parses 's' as the (possibly masked) value of field 'mf', and updates
+ * 'match' appropriately.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+static char * WARN_UNUSED_RESULT
 parse_field(const struct mf_field *mf, const char *s, struct match *match)
 {
     union mf_value value, mask;
     char *error;
 
     error = mf_parse(mf, s, &value, &mask);
-    if (error) {
-        ovs_fatal(0, "%s", error);
+    if (!error) {
+        mf_set(mf, &value, &mask, match);
     }
-
-    mf_set(mf, &value, &mask, match);
+    return error;
 }
 
-/* Convert 'str_' (as described in the Flow Syntax section of the ovs-ofctl man
- * page) into 'fm' for sending the specified flow_mod 'command' to a switch.
- * If 'actions' is specified, an action must be in 'string' and may be expanded
- * or reallocated.
- *
- * To parse syntax for an OFPT_FLOW_MOD (or NXT_FLOW_MOD), use an OFPFC_*
- * constant for 'command'.  To parse syntax for an OFPST_FLOW or
- * OFPST_AGGREGATE (or NXST_FLOW or NXST_AGGREGATE), use -1 for 'command'. */
-void
-parse_ofp_str(struct ofputil_flow_mod *fm, int command, const char *str_,
-              bool verbose)
+static char * WARN_UNUSED_RESULT
+parse_ofp_str__(struct ofputil_flow_mod *fm, int command, char *string)
 {
     enum {
         F_OUT_PORT = 1 << 0,
@@ -859,7 +1087,6 @@ parse_ofp_str(struct ofputil_flow_mod *fm, int command, const char *str_,
         F_PRIORITY = 1 << 4,
         F_FLAGS = 1 << 5,
     } fields;
-    char *string = xstrdup(str_);
     char *save_ptr = NULL;
     char *act_str = NULL;
     char *name;
@@ -913,13 +1140,13 @@ parse_ofp_str(struct ofputil_flow_mod *fm, int command, const char *str_,
     if (fields & F_ACTIONS) {
         act_str = strstr(string, "action");
         if (!act_str) {
-            ofp_fatal(str_, verbose, "must specify an action");
+            return xasprintf("must specify an action");
         }
         *act_str = '\0';
 
         act_str = strchr(act_str + 1, '=');
         if (!act_str) {
-            ofp_fatal(str_, verbose, "must specify an action");
+            return xasprintf("must specify an action");
         }
 
         act_str++;
@@ -927,6 +1154,7 @@ parse_ofp_str(struct ofputil_flow_mod *fm, int command, const char *str_,
     for (name = strtok_r(string, "=, \t\r\n", &save_ptr); name;
          name = strtok_r(NULL, "=, \t\r\n", &save_ptr)) {
         const struct protocol *p;
+        char *error = NULL;
 
         if (parse_protocol(name, &p)) {
             match_set_dl_type(&fm->match, htons(p->dl_type));
@@ -948,44 +1176,50 @@ parse_ofp_str(struct ofputil_flow_mod *fm, int command, const char *str_,
 
             value = strtok_r(NULL, ", \t\r\n", &save_ptr);
             if (!value) {
-                ofp_fatal(str_, verbose, "field %s missing value", name);
+                return xasprintf("field %s missing value", name);
             }
 
             if (!strcmp(name, "table")) {
-                fm->table_id = str_to_u8(value, name);
+                error = str_to_u8(value, "table", &fm->table_id);
             } else if (!strcmp(name, "out_port")) {
                 if (!ofputil_port_from_string(value, &fm->out_port)) {
-                    ofp_fatal(str_, verbose, "%s is not a valid OpenFlow port",
-                              name);
+                    error = xasprintf("%s is not a valid OpenFlow port",
+                                      value);
                 }
             } else if (fields & F_PRIORITY && !strcmp(name, "priority")) {
-                fm->priority = str_to_u16(value, name);
+                uint16_t priority;
+
+                error = str_to_u16(value, name, &priority);
+                fm->priority = priority;
             } else if (fields & F_TIMEOUT && !strcmp(name, "idle_timeout")) {
-                fm->idle_timeout = str_to_u16(value, name);
+                error = str_to_u16(value, name, &fm->idle_timeout);
             } else if (fields & F_TIMEOUT && !strcmp(name, "hard_timeout")) {
-                fm->hard_timeout = str_to_u16(value, name);
+                error = str_to_u16(value, name, &fm->hard_timeout);
             } else if (!strcmp(name, "cookie")) {
                 char *mask = strchr(value, '/');
 
                 if (mask) {
                     /* A mask means we're searching for a cookie. */
                     if (command == OFPFC_ADD) {
-                        ofp_fatal(str_, verbose, "flow additions cannot use "
-                                  "a cookie mask");
+                        return xstrdup("flow additions cannot use "
+                                       "a cookie mask");
                     }
                     *mask = '\0';
-                    fm->cookie = htonll(str_to_u64(value));
-                    fm->cookie_mask = htonll(str_to_u64(mask+1));
+                    error = str_to_be64(value, &fm->cookie);
+                    if (error) {
+                        return error;
+                    }
+                    error = str_to_be64(mask + 1, &fm->cookie_mask);
                 } else {
                     /* No mask means that the cookie is being set. */
                     if (command != OFPFC_ADD && command != OFPFC_MODIFY
-                            && command != OFPFC_MODIFY_STRICT) {
-                        ofp_fatal(str_, verbose, "cannot set cookie");
+                        && command != OFPFC_MODIFY_STRICT) {
+                        return xstrdup("cannot set cookie");
                     }
-                    fm->new_cookie = htonll(str_to_u64(value));
+                    error = str_to_be64(value, &fm->new_cookie);
                 }
             } else if (mf_from_name(name)) {
-                parse_field(mf_from_name(name), value, &fm->match);
+                error = parse_field(mf_from_name(name), value, &fm->match);
             } else if (!strcmp(name, "duration")
                        || !strcmp(name, "n_packets")
                        || !strcmp(name, "n_bytes")
@@ -995,12 +1229,16 @@ parse_ofp_str(struct ofputil_flow_mod *fm, int command, const char *str_,
                  * "ovs-ofctl dump-flows" back into commands that parse
                  * flows. */
             } else {
-                ofp_fatal(str_, verbose, "unknown keyword %s", name);
+                error = xasprintf("unknown keyword %s", name);
+            }
+
+            if (error) {
+                return error;
             }
         }
     }
     if (!fm->cookie_mask && fm->new_cookie == htonll(UINT64_MAX)
-            && (command == OFPFC_MODIFY || command == OFPFC_MODIFY_STRICT)) {
+        && (command == OFPFC_MODIFY || command == OFPFC_MODIFY_STRICT)) {
         /* On modifies without a mask, we are supposed to add a flow if
          * one does not exist.  If a cookie wasn't been specified, use a
          * default of zero. */
@@ -1008,40 +1246,69 @@ parse_ofp_str(struct ofputil_flow_mod *fm, int command, const char *str_,
     }
     if (fields & F_ACTIONS) {
         struct ofpbuf ofpacts;
-        enum ofperr err;
+        char *error;
 
         ofpbuf_init(&ofpacts, 32);
-        str_to_inst_ofpacts(act_str, &ofpacts);
-        fm->ofpacts_len = ofpacts.size;
-        fm->ofpacts = ofpbuf_steal_data(&ofpacts);
-
-        err = ofpacts_check(fm->ofpacts, fm->ofpacts_len, &fm->match.flow,
-                            OFPP_MAX);
-        if (err) {
-            exit(EXIT_FAILURE);
+        error = str_to_inst_ofpacts(act_str, &ofpacts);
+        if (!error) {
+            enum ofperr err;
+
+            err = ofpacts_check(ofpacts.data, ofpacts.size, &fm->match.flow,
+                                OFPP_MAX);
+            if (err) {
+                error = xasprintf("actions are invalid with specified match "
+                                  "(%s)", ofperr_to_string(err));
+            }
+        }
+        if (error) {
+            ofpbuf_uninit(&ofpacts);
+            return error;
         }
 
+        fm->ofpacts_len = ofpacts.size;
+        fm->ofpacts = ofpbuf_steal_data(&ofpacts);
     } else {
         fm->ofpacts_len = 0;
         fm->ofpacts = NULL;
     }
 
-    free(string);
+    return NULL;
 }
 
 /* Convert 'str_' (as described in the Flow Syntax section of the ovs-ofctl man
- * page) into 'mm' for sending the specified meter_mod 'command' to a switch.
- */
-void
-parse_ofp_meter_mod_str(struct ofputil_meter_mod *mm, const char *str_,
-                        int command, bool verbose)
+ * page) into 'fm' for sending the specified flow_mod 'command' to a switch.
+ *
+ * To parse syntax for an OFPT_FLOW_MOD (or NXT_FLOW_MOD), use an OFPFC_*
+ * constant for 'command'.  To parse syntax for an OFPST_FLOW or
+ * OFPST_AGGREGATE (or NXST_FLOW or NXST_AGGREGATE), use -1 for 'command'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+char * WARN_UNUSED_RESULT
+parse_ofp_str(struct ofputil_flow_mod *fm, int command, const char *str_)
+{
+    char *string = xstrdup(str_);
+    char *error;
+
+    error = parse_ofp_str__(fm, command, string);
+    if (error) {
+        fm->ofpacts = NULL;
+        fm->ofpacts_len = 0;
+    }
+
+    free(string);
+    return error;
+}
+
+static char * WARN_UNUSED_RESULT
+parse_ofp_meter_mod_str__(struct ofputil_meter_mod *mm, char *string,
+                          struct ofpbuf *bands, int command)
 {
     enum {
         F_METER = 1 << 0,
         F_FLAGS = 1 << 1,
         F_BANDS = 1 << 2,
     } fields;
-    char *string = xstrdup(str_);
     char *save_ptr = NULL;
     char *band_str = NULL;
     char *name;
@@ -1073,13 +1340,13 @@ parse_ofp_meter_mod_str(struct ofputil_meter_mod *mm, const char *str_,
     if (fields & F_BANDS) {
         band_str = strstr(string, "band");
         if (!band_str) {
-            ofp_fatal(str_, verbose, "must specify bands");
+            return xstrdup("must specify bands");
         }
         *band_str = '\0';
 
         band_str = strchr(band_str + 1, '=');
         if (!band_str) {
-            ofp_fatal(str_, verbose, "must specify bands");
+            return xstrdup("must specify bands");
         }
 
         band_str++;
@@ -1100,7 +1367,7 @@ parse_ofp_meter_mod_str(struct ofputil_meter_mod *mm, const char *str_,
 
             value = strtok_r(NULL, ", \t\r\n", &save_ptr);
             if (!value) {
-                ofp_fatal(str_, verbose, "field %s missing value", name);
+                return xasprintf("field %s missing value", name);
             }
 
             if (!strcmp(name, "meter")) {
@@ -1111,32 +1378,31 @@ parse_ofp_meter_mod_str(struct ofputil_meter_mod *mm, const char *str_,
                 } else if (!strcmp(value, "slowpath")) {
                     mm->meter.meter_id = OFPM13_SLOWPATH;
                 } else {
-                    mm->meter.meter_id = str_to_u32(value);
+                    char *error = str_to_u32(value, &mm->meter.meter_id);
+                    if (error) {
+                        return error;
+                    }
                     if (mm->meter.meter_id > OFPM13_MAX) {
-                        ofp_fatal(str_, verbose, "invalid value for %s", name);
+                        return xasprintf("invalid value for %s", name);
                     }
                 }
             } else {
-                ofp_fatal(str_, verbose, "unknown keyword %s", name);
+                return xasprintf("unknown keyword %s", name);
             }
         }
     }
     if (fields & F_METER && !mm->meter.meter_id) {
-        ofp_fatal(str_, verbose, "must specify 'meter'");
+        return xstrdup("must specify 'meter'");
     }
     if (fields & F_FLAGS && !mm->meter.flags) {
-        ofp_fatal(str_, verbose,
-                  "meter must specify either 'kbps' or 'pktps'");
+        return xstrdup("meter must specify either 'kbps' or 'pktps'");
     }
 
     if (fields & F_BANDS) {
-        struct ofpbuf bands;
         uint16_t n_bands = 0;
         struct ofputil_meter_band *band = NULL;
         int i;
 
-        ofpbuf_init(&bands, 64);
-
         for (name = strtok_r(band_str, "=, \t\r\n", &save_ptr); name;
              name = strtok_r(NULL, "=, \t\r\n", &save_ptr)) {
 
@@ -1144,12 +1410,12 @@ parse_ofp_meter_mod_str(struct ofputil_meter_mod *mm, const char *str_,
 
             value = strtok_r(NULL, ", \t\r\n", &save_ptr);
             if (!value) {
-                ofp_fatal(str_, verbose, "field %s missing value", name);
+                return xasprintf("field %s missing value", name);
             }
 
             if (!strcmp(name, "type")) {
                 /* Start a new band */
-                band = ofpbuf_put_zeros(&bands, sizeof *band);
+                band = ofpbuf_put_zeros(bands, sizeof *band);
                 n_bands++;
 
                 if (!strcmp(value, "drop")) {
@@ -1157,59 +1423,66 @@ parse_ofp_meter_mod_str(struct ofputil_meter_mod *mm, const char *str_,
                 } else if (!strcmp(value, "dscp_remark")) {
                     band->type = OFPMBT13_DSCP_REMARK;
                 } else {
-                    ofp_fatal(str_, verbose, "field %s unknown value %s", name,
-                              value);
+                    return xasprintf("field %s unknown value %s", name, value);
                 }
             } else if (!band || !band->type) {
-                ofp_fatal(str_, verbose,
-                          "band must start with the 'type' keyword");
+                return xstrdup("band must start with the 'type' keyword");
             } else if (!strcmp(name, "rate")) {
-                band->rate = str_to_u32(value);
+                char *error = str_to_u32(value, &band->rate);
+                if (error) {
+                    return error;
+                }
             } else if (!strcmp(name, "burst_size")) {
-                band->burst_size = str_to_u32(value);
+                char *error = str_to_u32(value, &band->burst_size);
+                if (error) {
+                    return error;
+                }
             } else if (!strcmp(name, "prec_level")) {
-                band->prec_level = str_to_u8(value, name);
+                char *error = str_to_u8(value, name, &band->prec_level);
+                if (error) {
+                    return error;
+                }
             } else {
-                ofp_fatal(str_, verbose, "unknown keyword %s", name);
+                return xasprintf("unknown keyword %s", name);
             }
         }
         /* validate bands */
         if (!n_bands) {
-            ofp_fatal(str_, verbose, "meter must have bands");
+            return xstrdup("meter must have bands");
         }
 
         mm->meter.n_bands = n_bands;
-        mm->meter.bands = ofpbuf_steal_data(&bands);
+        mm->meter.bands = ofpbuf_steal_data(bands);
 
         for (i = 0; i < n_bands; ++i) {
             band = &mm->meter.bands[i];
 
             if (!band->type) {
-                ofp_fatal(str_, verbose, "band must have 'type'");
+                return xstrdup("band must have 'type'");
             }
             if (band->type == OFPMBT13_DSCP_REMARK) {
                 if (!band->prec_level) {
-                    ofp_fatal(str_, verbose, "'dscp_remark' band must have"
-                              " 'prec_level'");
+                    return xstrdup("'dscp_remark' band must have"
+                                   " 'prec_level'");
                 }
             } else {
                 if (band->prec_level) {
-                    ofp_fatal(str_, verbose, "Only 'dscp_remark' band may have"
-                              " 'prec_level'");
+                    return xstrdup("Only 'dscp_remark' band may have"
+                                   " 'prec_level'");
                 }
             }
             if (!band->rate) {
-                ofp_fatal(str_, verbose, "band must have 'rate'");
+                return xstrdup("band must have 'rate'");
             }
             if (mm->meter.flags & OFPMF13_BURST) {
                 if (!band->burst_size) {
-                    ofp_fatal(str_, verbose, "band must have 'burst_size' "
-                              "when 'burst' flag is set");
+                    return xstrdup("band must have 'burst_size' "
+                                   "when 'burst' flag is set");
                 }
             } else {
                 if (band->burst_size) {
-                    ofp_fatal(str_, verbose, "band may have 'burst_size' only "
-                              "when 'burst' flag is set");
+                    return xstrdup("band may have 'burst_size' only "
+                                   "when 'burst' flag is set");
                 }
             }
         }
@@ -1218,18 +1491,39 @@ parse_ofp_meter_mod_str(struct ofputil_meter_mod *mm, const char *str_,
         mm->meter.bands = NULL;
     }
 
+    return NULL;
+}
+
+/* Convert 'str_' (as described in the Flow Syntax section of the ovs-ofctl man
+ * page) into 'mm' for sending the specified meter_mod 'command' to a switch.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+char * WARN_UNUSED_RESULT
+parse_ofp_meter_mod_str(struct ofputil_meter_mod *mm, const char *str_,
+                        int command)
+{
+    struct ofpbuf bands;
+    char *string;
+    char *error;
+
+    ofpbuf_init(&bands, 64);
+    string = xstrdup(str_);
+
+    error = parse_ofp_meter_mod_str__(mm, string, &bands, command);
+
     free(string);
+    ofpbuf_uninit(&bands);
+
+    return error;
 }
 
-/* Convert 'str_' (as described in the documentation for the "monitor" command
- * in the ovs-ofctl man page) into 'fmr'. */
-void
-parse_flow_monitor_request(struct ofputil_flow_monitor_request *fmr,
-                           const char *str_)
+static char * WARN_UNUSED_RESULT
+parse_flow_monitor_request__(struct ofputil_flow_monitor_request *fmr,
+                             const char *str_, char *string)
 {
     static uint32_t id;
 
-    char *string = xstrdup(str_);
     char *save_ptr = NULL;
     char *name;
 
@@ -1266,73 +1560,127 @@ parse_flow_monitor_request(struct ofputil_flow_monitor_request *fmr,
 
             value = strtok_r(NULL, ", \t\r\n", &save_ptr);
             if (!value) {
-                ovs_fatal(0, "%s: field %s missing value", str_, name);
+                return xasprintf("%s: field %s missing value", str_, name);
             }
 
             if (!strcmp(name, "table")) {
-                fmr->table_id = str_to_u8(value, name);
+                char *error = str_to_u8(value, "table", &fmr->table_id);
+                if (error) {
+                    return error;
+                }
             } else if (!strcmp(name, "out_port")) {
                 fmr->out_port = u16_to_ofp(atoi(value));
             } else if (mf_from_name(name)) {
-                parse_field(mf_from_name(name), value, &fmr->match);
+                char *error;
+
+                error = parse_field(mf_from_name(name), value, &fmr->match);
+                if (error) {
+                    return error;
+                }
             } else {
-                ovs_fatal(0, "%s: unknown keyword %s", str_, name);
+                return xasprintf("%s: unknown keyword %s", str_, name);
             }
         }
     }
+    return NULL;
+}
+
+/* Convert 'str_' (as described in the documentation for the "monitor" command
+ * in the ovs-ofctl man page) into 'fmr'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+char * WARN_UNUSED_RESULT
+parse_flow_monitor_request(struct ofputil_flow_monitor_request *fmr,
+                           const char *str_)
+{
+    char *string = xstrdup(str_);
+    char *error = parse_flow_monitor_request__(fmr, str_, string);
     free(string);
+    return error;
 }
 
 /* Parses 's' as a set of OpenFlow actions and appends the actions to
  * 'actions'.
  *
- * Prints an error on stderr and aborts the program if 's' syntax is
- * invalid. */
-void
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+char * WARN_UNUSED_RESULT
 parse_ofpacts(const char *s_, struct ofpbuf *ofpacts)
 {
     char *s = xstrdup(s_);
-    str_to_ofpacts(s, ofpacts);
+    char *error = str_to_ofpacts(s, ofpacts);
     free(s);
+
+    return error;
 }
 
 /* Parses 'string' as an OFPT_FLOW_MOD or NXT_FLOW_MOD with command 'command'
- * (one of OFPFC_*) into 'fm'. */
-void
+ * (one of OFPFC_*) into 'fm'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+char * WARN_UNUSED_RESULT
 parse_ofp_flow_mod_str(struct ofputil_flow_mod *fm, const char *string,
-                       uint16_t command, bool verbose)
+                       uint16_t command)
 {
-    struct match match_copy;
-
-    parse_ofp_str(fm, command, string, verbose);
+    char *error = parse_ofp_str(fm, command, string);
+    if (!error) {
+        /* Normalize a copy of the match.  This ensures that non-normalized
+         * flows get logged but doesn't affect what gets sent to the switch, so
+         * that the switch can do whatever it likes with the flow. */
+        struct match match_copy = fm->match;
+        ofputil_normalize_match(&match_copy);
+    }
 
-    /* Normalize a copy of the match.  This ensures that non-normalized flows
-     * get logged but doesn't affect what gets sent to the switch, so that the
-     * switch can do whatever it likes with the flow. */
-    match_copy = fm->match;
-    ofputil_normalize_match(&match_copy);
+    return error;
 }
 
-void
+/* Opens file 'file_name' and reads each line as a flow_mod of the specified
+ * type (one of OFPFC_*).  Stores each flow_mod in '*fm', an array allocated
+ * on the caller's behalf, and the number of flow_mods in '*n_fms'.
+ *
+ * Returns NULL if successful, otherwise a malloc()'d string describing the
+ * error.  The caller is responsible for freeing the returned string. */
+char * WARN_UNUSED_RESULT
 parse_ofp_flow_mod_file(const char *file_name, uint16_t command,
                         struct ofputil_flow_mod **fms, size_t *n_fms)
 {
     size_t allocated_fms;
+    int line_number;
     FILE *stream;
     struct ds s;
 
+    *fms = NULL;
+    *n_fms = 0;
+
     stream = !strcmp(file_name, "-") ? stdin : fopen(file_name, "r");
     if (stream == NULL) {
-        ovs_fatal(errno, "%s: open", file_name);
+        return xasprintf("%s: open failed (%s)", file_name, strerror(errno));
     }
 
     allocated_fms = *n_fms;
     ds_init(&s);
-    while (!ds_get_preprocessed_line(&s, stream)) {
+    line_number = 0;
+    while (!ds_get_preprocessed_line(&s, stream, &line_number)) {
+        char *error;
+
         if (*n_fms >= allocated_fms) {
             *fms = x2nrealloc(*fms, &allocated_fms, sizeof **fms);
         }
-        parse_ofp_flow_mod_str(&(*fms)[*n_fms], ds_cstr(&s), command, false);
+        error = parse_ofp_flow_mod_str(&(*fms)[*n_fms], ds_cstr(&s), command);
+        if (error) {
+            size_t i;
+
+            for (i = 0; i < *n_fms; i++) {
+                free((*fms)[i].ofpacts);
+            }
+            free(*fms);
+            *fms = NULL;
+            *n_fms = 0;
+
+            return xasprintf("%s:%d: %s", file_name, line_number, error);
+        }
         *n_fms += 1;
     }
     ds_destroy(&s);
@@ -1340,21 +1688,28 @@ parse_ofp_flow_mod_file(const char *file_name, uint16_t command,
     if (stream != stdin) {
         fclose(stream);
     }
+    return NULL;
 }
 
-void
+char * WARN_UNUSED_RESULT
 parse_ofp_flow_stats_request_str(struct ofputil_flow_stats_request *fsr,
                                  bool aggregate, const char *string)
 {
     struct ofputil_flow_mod fm;
+    char *error;
+
+    error = parse_ofp_str(&fm, -1, string);
+    if (error) {
+        return error;
+    }
 
-    parse_ofp_str(&fm, -1, string, false);
     fsr->aggregate = aggregate;
     fsr->cookie = fm.cookie;
     fsr->cookie_mask = fm.cookie_mask;
     fsr->match = fm.match;
     fsr->out_port = fm.out_port;
     fsr->table_id = fm.table_id;
+    return NULL;
 }
 
 /* Parses a specification of a flow from 's' into 'flow'.  's' must take the
diff --git a/lib/ofp-parse.h b/lib/ofp-parse.h
index 6ee25a4..707f5d8 100644
--- a/lib/ofp-parse.h
+++ b/lib/ofp-parse.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2010, 2011, 2012 Nicira, Inc.
+ * Copyright (c) 2010, 2011, 2012, 2013 Nicira, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -22,6 +22,7 @@
 #include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>
+#include "compiler.h"
 
 struct flow;
 struct ofpbuf;
@@ -30,26 +31,31 @@ struct ofputil_flow_monitor_request;
 struct ofputil_flow_stats_request;
 struct ofputil_meter_mod;
 
-void parse_ofp_str(struct ofputil_flow_mod *, int command, const char *str_,
-                   bool verbose);
+char *parse_ofp_str(struct ofputil_flow_mod *, int command, const char *str_)
+    WARN_UNUSED_RESULT;
 
-void parse_ofp_flow_mod_str(struct ofputil_flow_mod *, const char *string,
-                            uint16_t command, bool verbose);
-void parse_ofp_flow_mod_file(const char *file_name, uint16_t command,
-                             struct ofputil_flow_mod **fms, size_t *n_fms);
+char *parse_ofp_flow_mod_str(struct ofputil_flow_mod *, const char *string,
+                            uint16_t command)
+    WARN_UNUSED_RESULT;
+char *parse_ofp_flow_mod_file(const char *file_name, uint16_t command,
+                              struct ofputil_flow_mod **fms, size_t *n_fms)
+    WARN_UNUSED_RESULT;
 
-void parse_ofp_flow_stats_request_str(struct ofputil_flow_stats_request *,
-                                      bool aggregate, const char *string);
+char *parse_ofp_flow_stats_request_str(struct ofputil_flow_stats_request *,
+                                       bool aggregate, const char *string)
+    WARN_UNUSED_RESULT;
 
-
-void parse_ofpacts(const char *, struct ofpbuf *ofpacts);
+char *parse_ofpacts(const char *, struct ofpbuf *ofpacts)
+    WARN_UNUSED_RESULT;
 
 char *parse_ofp_exact_flow(struct flow *, const char *);
 
-void parse_ofp_meter_mod_str(struct ofputil_meter_mod *, const char *string,
-			      int command, bool verbose);
+char *parse_ofp_meter_mod_str(struct ofputil_meter_mod *, const char *string,
+			      int command)
+    WARN_UNUSED_RESULT;
 
-void parse_flow_monitor_request(struct ofputil_flow_monitor_request *,
-                                const char *);
+char *parse_flow_monitor_request(struct ofputil_flow_monitor_request *,
+                                const char *)
+    WARN_UNUSED_RESULT;
 
 #endif /* ofp-parse.h */
diff --git a/tests/learn.at b/tests/learn.at
index ec1c347..ce810b4 100644
--- a/tests/learn.at
+++ b/tests/learn.at
@@ -75,11 +75,13 @@ AT_CHECK([[ovs-ofctl parse-flow 'actions=learn(load:5->NXM_OF_IP_DST[])']],
   [1], [], [stderr])
 AT_CHECK([sed -e 's/.*|meta_flow|WARN|//' < stderr], [0],
   [[destination field ip_dst lacks correct prerequisites
+ovs-ofctl: actions are invalid with specified match (OFPBAC_BAD_ARGUMENT)
 ]], [[]])
 AT_CHECK([[ovs-ofctl parse-flow 'actions=learn(load:NXM_OF_IP_DST[]->NXM_NX_REG1[])']],
   [1], [], [stderr])
 AT_CHECK([sed -e 's/.*|meta_flow|WARN|//' < stderr], [0],
   [[source field ip_dst lacks correct prerequisites
+ovs-ofctl: actions are invalid with specified match (OFPBAC_BAD_ARGUMENT)
 ]])
 AT_CLEANUP
 
diff --git a/tests/ofproto-dpif.at b/tests/ofproto-dpif.at
index 88492cf..5e2afb9 100644
--- a/tests/ofproto-dpif.at
+++ b/tests/ofproto-dpif.at
@@ -166,7 +166,7 @@ AT_SETUP([ofproto-dpif - DSCP])
 OVS_VSWITCHD_START([add-port br0 p1 -- set Interface p1 type=dummy])
 ADD_OF_PORTS([br0], [9])
 AT_DATA([flows.txt], [dnl
-actions=output:65534,enqueue:1:1,enqueue:1:2,enqueue:1:2,enqueue:1:1,output:1,mod_nw_tos:0,output:1,output:65534
+actions=output:LOCAL,enqueue:1:1,enqueue:1:2,enqueue:1:2,enqueue:1:1,output:1,mod_nw_tos:0,output:1,output:LOCAL
 ])
 AT_CHECK([ovs-ofctl add-flows br0 flows.txt])
 AT_CHECK([ovs-vsctl -- \
@@ -197,8 +197,8 @@ AT_DATA([flows.txt], [dnl
 in_port=local actions=local,flood
 in_port=1 actions=flood
 in_port=2 actions=all
-in_port=3 actions=output:65534,output:1,output:2,output:3,output:4,output:5,output:6,output:7
-in_port=4 actions=enqueue:65534:1,enqueue:1:1,enqueue:2:1,enqueue:3:2,enqueue:4:1,enqueue:5:1,enqueue:6:1,enqueue:7:1
+in_port=3 actions=output:LOCAL,output:1,output:2,output:3,output:4,output:5,output:6,output:7
+in_port=4 actions=enqueue:LOCAL:1,enqueue:1:1,enqueue:2:1,enqueue:3:2,enqueue:4:1,enqueue:5:1,enqueue:6:1,enqueue:7:1
 ])
 AT_CHECK([ovs-ofctl add-flows br0 flows.txt])
 AT_CHECK([ovs-ofctl mod-port br0 5 noforward])
diff --git a/tests/test-bundle.c b/tests/test-bundle.c
index 0e7525c..41e2e38 100644
--- a/tests/test-bundle.c
+++ b/tests/test-bundle.c
@@ -1,4 +1,4 @@
-/* Copyright (c) 2011, 2012 Nicira, Inc.
+/* Copyright (c) 2011, 2012, 2013 Nicira, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -71,9 +71,14 @@ parse_bundle_actions(char *actions)
     struct ofpact_bundle *bundle;
     struct ofpbuf ofpacts;
     struct ofpact *action;
+    char *error;
 
     ofpbuf_init(&ofpacts, 0);
-    bundle_parse_load(actions, &ofpacts);
+    error = bundle_parse_load(actions, &ofpacts);
+    if (error) {
+        ovs_fatal(0, "%s", error);
+    }
+
     action = ofpacts.data;
     bundle = ofpact_get_BUNDLE(xmemdup(action, action->len));
     ofpbuf_uninit(&ofpacts);
diff --git a/tests/test-multipath.c b/tests/test-multipath.c
index e8aacff..f1b12e2 100644
--- a/tests/test-multipath.c
+++ b/tests/test-multipath.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2010, 2012 Nicira, Inc.
+ * Copyright (c) 2010, 2012, 2013 Nicira, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -35,6 +35,7 @@ main(int argc, char *argv[])
     enum { MP_MAX_LINKS = 63 };
     struct ofpact_multipath mp;
     bool ok = true;
+    char *error;
     int n;
 
     set_program_name(argv[0]);
@@ -44,7 +45,11 @@ main(int argc, char *argv[])
         ovs_fatal(0, "usage: %s multipath_action", program_name);
     }
 
-    multipath_parse(&mp, argv[1]);
+    error = multipath_parse(&mp, argv[1]);
+    if (error) {
+        ovs_fatal(0, "%s", error);
+    }
+
     for (n = 1; n <= MP_MAX_LINKS; n++) {
         enum { N_FLOWS = 65536 };
         double disruption, perfect, distribution;
diff --git a/utilities/ovs-controller.c b/utilities/ovs-controller.c
index 70bc2e6..cca9c39 100644
--- a/utilities/ovs-controller.c
+++ b/utilities/ovs-controller.c
@@ -278,6 +278,7 @@ parse_options(int argc, char *argv[])
 
     for (;;) {
         int indexptr;
+        char *error;
         int c;
 
         c = getopt_long(argc, argv, short_options, long_options, &indexptr);
@@ -327,8 +328,11 @@ parse_options(int argc, char *argv[])
             break;
 
         case OPT_WITH_FLOWS:
-            parse_ofp_flow_mod_file(optarg, OFPFC_ADD, &default_flows,
-                                    &n_default_flows);
+            error = parse_ofp_flow_mod_file(optarg, OFPFC_ADD, &default_flows,
+                                            &n_default_flows);
+            if (error) {
+                ovs_fatal(0, "%s", error);
+            }
             break;
 
         case OPT_UNIXCTL:
diff --git a/utilities/ovs-ofctl.c b/utilities/ovs-ofctl.c
index b2470e6..42879b8 100644
--- a/utilities/ovs-ofctl.c
+++ b/utilities/ovs-ofctl.c
@@ -866,8 +866,14 @@ prepare_dump_flows(int argc, char *argv[], bool aggregate,
     enum ofputil_protocol usable_protocols, protocol;
     struct ofputil_flow_stats_request fsr;
     struct vconn *vconn;
+    char *error;
+
+    error = parse_ofp_flow_stats_request_str(&fsr, aggregate,
+                                             argc > 2 ? argv[2] : "");
+    if (error) {
+        ovs_fatal(0, "%s", error);
+    }
 
-    parse_ofp_flow_stats_request_str(&fsr, aggregate, argc > 2 ? argv[2] : "");
     usable_protocols = ofputil_flow_stats_request_usable_protocols(&fsr);
 
     protocol = open_vconn(argv[1], &vconn);
@@ -1087,8 +1093,12 @@ ofctl_flow_mod_file(int argc OVS_UNUSED, char *argv[], uint16_t command)
 {
     struct ofputil_flow_mod *fms = NULL;
     size_t n_fms = 0;
+    char *error;
 
-    parse_ofp_flow_mod_file(argv[2], command, &fms, &n_fms);
+    error = parse_ofp_flow_mod_file(argv[2], command, &fms, &n_fms);
+    if (error) {
+        ovs_fatal(0, "%s", error);
+    }
     ofctl_flow_mod__(argv[1], fms, n_fms);
     free(fms);
 }
@@ -1100,7 +1110,12 @@ ofctl_flow_mod(int argc, char *argv[], uint16_t command)
         ofctl_flow_mod_file(argc, argv, command);
     } else {
         struct ofputil_flow_mod fm;
-        parse_ofp_flow_mod_str(&fm, argc > 2 ? argv[2] : "", command, false);
+        char *error;
+
+        error = parse_ofp_flow_mod_str(&fm, argc > 2 ? argv[2] : "", command);
+        if (error) {
+            ovs_fatal(0, "%s", error);
+        }
         ofctl_flow_mod__(argv[1], &fm, 1);
     }
 }
@@ -1439,8 +1454,12 @@ ofctl_monitor(int argc, char *argv[])
         } else if (!strncmp(arg, "watch:", 6)) {
             struct ofputil_flow_monitor_request fmr;
             struct ofpbuf *msg;
+            char *error;
 
-            parse_flow_monitor_request(&fmr, arg + 6);
+            error = parse_flow_monitor_request(&fmr, arg + 6);
+            if (error) {
+                ovs_fatal(0, "%s", error);
+            }
 
             msg = ofpbuf_new(0);
             ofputil_append_flow_monitor_request(&fmr, msg);
@@ -1538,10 +1557,14 @@ ofctl_packet_out(int argc, char *argv[])
     struct ofputil_packet_out po;
     struct ofpbuf ofpacts;
     struct vconn *vconn;
+    char *error;
     int i;
 
     ofpbuf_init(&ofpacts, 64);
-    parse_ofpacts(argv[3], &ofpacts);
+    error = parse_ofpacts(argv[3], &ofpacts);
+    if (error) {
+        ovs_fatal(0, "%s", error);
+    }
 
     po.buffer_id = UINT32_MAX;
     po.in_port = str_to_port_no(argv[1], argv[2]);
@@ -1905,6 +1928,7 @@ static enum ofputil_protocol
 read_flows_from_file(const char *filename, struct classifier *cls, int index)
 {
     enum ofputil_protocol usable_protocols;
+    int line_number;
     struct ds s;
     FILE *file;
 
@@ -1915,11 +1939,16 @@ read_flows_from_file(const char *filename, struct classifier *cls, int index)
 
     ds_init(&s);
     usable_protocols = OFPUTIL_P_ANY;
-    while (!ds_get_preprocessed_line(&s, file)) {
+    line_number = 0;
+    while (!ds_get_preprocessed_line(&s, file, &line_number)) {
         struct fte_version *version;
         struct ofputil_flow_mod fm;
+        char *error;
 
-        parse_ofp_str(&fm, OFPFC_ADD, ds_cstr(&s), true);
+        error = parse_ofp_str(&fm, OFPFC_ADD, ds_cstr(&s));
+        if (error) {
+            ovs_fatal(0, "%s:%d: %s", filename, line_number, error);
+        }
 
         version = xmalloc(sizeof *version);
         version->cookie = fm.new_cookie;
@@ -2232,8 +2261,12 @@ static void
 ofctl_parse_flow(int argc OVS_UNUSED, char *argv[])
 {
     struct ofputil_flow_mod fm;
+    char *error;
 
-    parse_ofp_flow_mod_str(&fm, argv[1], OFPFC_ADD, false);
+    error = parse_ofp_flow_mod_str(&fm, argv[1], OFPFC_ADD);
+    if (error) {
+        ovs_fatal(0, "%s", error);
+    }
     ofctl_parse_flows__(&fm, 1);
 }
 
@@ -2244,8 +2277,12 @@ ofctl_parse_flows(int argc OVS_UNUSED, char *argv[])
 {
     struct ofputil_flow_mod *fms = NULL;
     size_t n_fms = 0;
+    char *error;
 
-    parse_ofp_flow_mod_file(argv[1], OFPFC_ADD, &fms, &n_fms);
+    error = parse_ofp_flow_mod_file(argv[1], OFPFC_ADD, &fms, &n_fms);
+    if (error) {
+        ovs_fatal(0, "%s", error);
+    }
     ofctl_parse_flows__(fms, n_fms);
     free(fms);
 }
@@ -2367,7 +2404,7 @@ ofctl_parse_ofp10_actions(int argc OVS_UNUSED, char *argv[] OVS_UNUSED)
     struct ds in;
 
     ds_init(&in);
-    while (!ds_get_preprocessed_line(&in, stdin)) {
+    while (!ds_get_preprocessed_line(&in, stdin, NULL)) {
         struct ofpbuf of10_out;
         struct ofpbuf of10_in;
         struct ofpbuf ofpacts;
@@ -2431,7 +2468,7 @@ ofctl_parse_ofp10_match(int argc OVS_UNUSED, char *argv[] OVS_UNUSED)
 
     ds_init(&in);
     ds_init(&expout);
-    while (!ds_get_preprocessed_line(&in, stdin)) {
+    while (!ds_get_preprocessed_line(&in, stdin, NULL)) {
         struct ofpbuf match_in, match_expout;
         struct ofp10_match match_out;
         struct ofp10_match match_normal;
@@ -2503,7 +2540,7 @@ ofctl_parse_ofp11_match(int argc OVS_UNUSED, char *argv[] OVS_UNUSED)
     struct ds in;
 
     ds_init(&in);
-    while (!ds_get_preprocessed_line(&in, stdin)) {
+    while (!ds_get_preprocessed_line(&in, stdin, NULL)) {
         struct ofpbuf match_in;
         struct ofp11_match match_out;
         struct match match;
@@ -2552,7 +2589,7 @@ ofctl_parse_ofp11_actions(int argc OVS_UNUSED, char *argv[] OVS_UNUSED)
     struct ds in;
 
     ds_init(&in);
-    while (!ds_get_preprocessed_line(&in, stdin)) {
+    while (!ds_get_preprocessed_line(&in, stdin, NULL)) {
         struct ofpbuf of11_out;
         struct ofpbuf of11_in;
         struct ofpbuf ofpacts;
@@ -2610,7 +2647,7 @@ ofctl_parse_ofp11_instructions(int argc OVS_UNUSED, char *argv[] OVS_UNUSED)
     struct ds in;
 
     ds_init(&in);
-    while (!ds_get_preprocessed_line(&in, stdin)) {
+    while (!ds_get_preprocessed_line(&in, stdin, NULL)) {
         struct ofpbuf of11_out;
         struct ofpbuf of11_in;
         struct ofpbuf ofpacts;
@@ -2693,6 +2730,7 @@ ofctl_check_vlan(int argc OVS_UNUSED, char *argv[])
     struct match of11_match;
 
     enum ofperr error;
+    char *error_s;
 
     match_init_catchall(&match);
     match.flow.vlan_tci = htons(strtoul(argv[1], NULL, 16));
@@ -2702,7 +2740,10 @@ ofctl_check_vlan(int argc OVS_UNUSED, char *argv[])
     string_s = match_to_string(&match, OFP_DEFAULT_PRIORITY);
     printf("%s -> ", string_s);
     fflush(stdout);
-    parse_ofp_str(&fm, -1, string_s, false);
+    error_s = parse_ofp_str(&fm, -1, string_s);
+    if (error_s) {
+        ovs_fatal(0, "%s", error_s);
+    }
     printf("%04"PRIx16"/%04"PRIx16"\n",
            ntohs(fm.match.flow.vlan_tci),
            ntohs(fm.match.wc.masks.vlan_tci));
-- 
1.7.2.5




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