util: New ovs_retval_to_string() function.

Many OVS functions return 0, EOF, or errno. There are several places in the
codebase where a return value is converted to a string. All must decide whether
the return value is set, and if it is, whether it is an errno value, EOF, or
otherwise invalid. This commit consolidates that code.

Reviewed by Ben Pfaff.

6 files changed, 41 insertions, 14 deletions

diff --git a/lib/jsonrpc.c b/lib/jsonrpc.c
index 7c761ea0..fb20bc58 100644
--- a/lib/jsonrpc.c
+++ b/lib/jsonrpc.c
@@ -142,6 +142,12 @@ jsonrpc_wait(struct jsonrpc *rpc)
     }
 }
 
+/*
+ * Possible status values:
+ * - 0: no error yet
+ * - >0: errno value
+ * - EOF: end of file (remote end closed connection; not necessarily an error)
+ */
 int
 jsonrpc_get_status(const struct jsonrpc *rpc)
 {
diff --git a/lib/ovsdb-error.c b/lib/ovsdb-error.c
index db8019f3..d6b4576e 100644
--- a/lib/ovsdb-error.c
+++ b/lib/ovsdb-error.c
@@ -237,4 +237,3 @@ ovsdb_error_assert(struct ovsdb_error *error)
         ovsdb_error_destroy(error);
     }
 }
-
diff --git a/lib/pcap.c b/lib/pcap.c
index 8c52f483..afd41fa8 100644
--- a/lib/pcap.c
+++ b/lib/pcap.c
@@ -76,8 +76,7 @@ pcap_read_header(FILE *file)
     struct pcap_hdr ph;
     if (fread(&ph, sizeof ph, 1, file) != 1) {
         int error = ferror(file) ? errno : EOF;
-        VLOG_WARN("failed to read pcap header: %s",
-                  error > 0 ? strerror(error) : "end of file");
+        VLOG_WARN("failed to read pcap header: %s", ovs_retval_to_string(error));
         return error;
     }
     if (ph.magic_number != 0xa1b2c3d4 && ph.magic_number != 0xd4c3b2a1) {
@@ -118,7 +117,7 @@ pcap_read(FILE *file, struct ofpbuf **bufp)
     if (fread(&prh, sizeof prh, 1, file) != 1) {
         int error = ferror(file) ? errno : EOF;
         VLOG_WARN("failed to read pcap record header: %s",
-                  error > 0 ? strerror(error) : "end of file");
+                  ovs_retval_to_string(error));
         return error;
     }
 
@@ -144,7 +143,7 @@ pcap_read(FILE *file, struct ofpbuf **bufp)
     if (fread(data, len, 1, file) != 1) {
         int error = ferror(file) ? errno : EOF;
         VLOG_WARN("failed to read pcap packet: %s",
-                  error > 0 ? strerror(error) : "end of file");
+                  ovs_retval_to_string(error));
         ofpbuf_delete(buf);
         return error;
     }
diff --git a/lib/util.c b/lib/util.c
index d6e470c9..193efb92 100644
--- a/lib/util.c
+++ b/lib/util.c
@@ -158,8 +158,7 @@ ovs_fatal(int err_no, const char *format, ...)
     vfprintf(stderr, format, args);
     va_end(args);
     if (err_no != 0)
-        fprintf(stderr, " (%s)",
-                err_no == EOF ? "end of file" : strerror(err_no));
+        fprintf(stderr, " (%s)", ovs_retval_to_string(err_no));
     putc('\n', stderr);
 
     exit(EXIT_FAILURE);
@@ -176,14 +175,40 @@ ovs_error(int err_no, const char *format, ...)
     vfprintf(stderr, format, args);
     va_end(args);
     if (err_no != 0) {
-        fprintf(stderr, " (%s)",
-                err_no == EOF ? "end of file" : strerror(err_no));
+        fprintf(stderr, " (%s)", ovs_retval_to_string(err_no));
     }
     putc('\n', stderr);
 
     errno = save_errno;
 }
 
+/* Many OVS functions return an int which is one of:
+ * - 0: no error yet
+ * - >0: errno value
+ * - EOF: end of file (not necessarily an error; depends on the function called)
+ *
+ * Returns the appropriate human-readable string. The caller must copy the
+ * string if it wants to hold onto it, as the storage may be overwritten on
+ * subsequent function calls.
+ */
+const char *
+ovs_retval_to_string(int retval)
+{
+    static char unknown[48];
+
+    if (!retval) {
+        return "";
+    }
+    if (retval > 0) {
+        return strerror(retval);
+    }
+    if (retval == EOF) {
+        return "End of file";
+    }
+    snprintf(unknown, sizeof unknown, "***unknown return value: %d***", retval);
+    return unknown;
+}
+
 /* Sets program_name based on 'argv0'.  Should be called at the beginning of
  * main(), as "set_program_name(argv[0]);".  */
 void set_program_name(const char *argv0)
diff --git a/lib/util.h b/lib/util.h
index 49790490..f3bf80c6 100644
--- a/lib/util.h
+++ b/lib/util.h
@@ -137,6 +137,7 @@ void ovs_strlcpy(char *dst, const char *src, size_t size);
 void ovs_fatal(int err_no, const char *format, ...)
     PRINTF_FORMAT(2, 3) NO_RETURN;
 void ovs_error(int err_no, const char *format, ...) PRINTF_FORMAT(2, 3);
+const char *ovs_retval_to_string(int);
 void ovs_hex_dump(FILE *, const void *, size_t, uintptr_t offset, bool ascii);
 
 bool str_to_int(const char *, int base, int *);
diff --git a/ofproto/ofproto.c b/ofproto/ofproto.c
index 67ce714d..c980f693 100644
--- a/ofproto/ofproto.c
+++ b/ofproto/ofproto.c
@@ -1363,13 +1363,10 @@ ofproto_get_ofproto_controller_info(const struct ofproto * ofproto,
 
         cinfo->pairs.n = 0;
 
-        if (last_error == EOF) {
-            cinfo->pairs.keys[cinfo->pairs.n] = "last_error";
-            cinfo->pairs.values[cinfo->pairs.n++] = xstrdup("End of file");
-        } else if (last_error > 0) {
+        if (last_error) {
             cinfo->pairs.keys[cinfo->pairs.n] = "last_error";
             cinfo->pairs.values[cinfo->pairs.n++] =
-                xstrdup(strerror(last_error));
+                xstrdup(ovs_retval_to_string(last_error));
         }
 
         cinfo->pairs.keys[cinfo->pairs.n] = "state";