platform: rework NMPlatformError codes

- rename "NONE" to "SUCCESS", what it really is.
- change the to-string result not to contain spaces
  and being closer the name of the enum value.
- add new error reasons "UNSPECIFIED" and "BUG".
- remove the code comments around the enum definition.
  They add no further description about why this error
  happens and only paraphrase the name of the enum.
- reserve negative integers for 'errno'. This is neat
  because if we get a system error we can pass on the
  underlying errno as cause.

(cherry picked from commit f7fb68755c)

src/platform/nm-platform.c

@@ -173,11 +173,46 @@ void nm_platform_set_error (NMPlatform *self, NMPlatformError error)
 NMPlatformError
 nm_platform_get_error (NMPlatform *self)
 {
-	_CHECK_SELF (self, klass, NM_PLATFORM_ERROR_NONE);
+	_CHECK_SELF (self, klass, NM_PLATFORM_ERROR_BUG);
 
 	return self->error;
 }
 
+/**
+ * nm_platform_error_to_string:
+ * @error_code: the error code to stringify.
+ *
+ * Returns: A string representation of the error.
+ * For negative numbers, this function interprets
+ * the code as -errno.
+ */
+const char *
+nm_platform_error_to_string (NMPlatformError error)
+{
+	switch (error) {
+	case NM_PLATFORM_ERROR_SUCCESS:
+		return "success";
+	case NM_PLATFORM_ERROR_BUG:
+		return "bug";
+	case NM_PLATFORM_ERROR_UNSPECIFIED:
+		return "unspecified";
+	case NM_PLATFORM_ERROR_NOT_FOUND:
+		return "not-found";
+	case NM_PLATFORM_ERROR_EXISTS:
+		return "exists";
+	case NM_PLATFORM_ERROR_WRONG_TYPE:
+		return "wrong-type";
+	case NM_PLATFORM_ERROR_NOT_SLAVE:
+		return "not-slave";
+	case NM_PLATFORM_ERROR_NO_FIRMWARE:
+		return "no-firmware";
+	default:
+		if (error < 0)
+			return g_strerror (- ((int) error));
+		return "unknown";
+	}
+}
+
 /**
  * nm_platform_get_error_message:
  * @self: platform instance
@@ -189,29 +224,14 @@ nm_platform_get_error_msg (NMPlatform *self)
 {
 	_CHECK_SELF (self, klass, NULL);
 
-	switch (self->error) {
-	case NM_PLATFORM_ERROR_NONE:
-		return "unknown error";
-	case NM_PLATFORM_ERROR_NOT_FOUND:
-		return "object not found";
-	case NM_PLATFORM_ERROR_EXISTS:
-		return "object already exists";
-	case NM_PLATFORM_ERROR_WRONG_TYPE:
-		return "object is wrong type";
-	case NM_PLATFORM_ERROR_NOT_SLAVE:
-		return "link not a slave";
-	case NM_PLATFORM_ERROR_NO_FIRMWARE:
-		return "firmware not found";
-	default:
-		return "invalid error number";
-	}
+	return nm_platform_error_to_string (self->error);
 }
 
 static void
 reset_error (NMPlatform *self)
 {
 	g_assert (self);
-	self->error = NM_PLATFORM_ERROR_NONE;
+	self->error = NM_PLATFORM_ERROR_SUCCESS;
 }
 
 #define IFA_F_MANAGETEMPADDR_STR "mngtmpaddr"

src/platform/nm-platform.h

@@ -55,18 +55,23 @@ typedef struct _NMPlatform NMPlatform;
 #endif
 
 typedef enum {
-	/* no error specified, sometimes this means the arguments were wrong */
-	NM_PLATFORM_ERROR_NONE,
-	/* object was not found */
+
+	/* dummy value, to enforce that the enum type is signed and has a size
+	 * to hold an integer. We want to encode errno from <errno.h> as negative
+	 * values. */
+	_NM_PLATFORM_ERROR_MININT = G_MININT,
+
+	NM_PLATFORM_ERROR_SUCCESS = 0,
+
+	NM_PLATFORM_ERROR_BUG,
+
+	NM_PLATFORM_ERROR_UNSPECIFIED,
+
 	NM_PLATFORM_ERROR_NOT_FOUND,
-	/* object already exists */
 	NM_PLATFORM_ERROR_EXISTS,
-	/* object is wrong type */
 	NM_PLATFORM_ERROR_WRONG_TYPE,
-	/* object is not a slave */
 	NM_PLATFORM_ERROR_NOT_SLAVE,
-	/* firmware is not found */
-	NM_PLATFORM_ERROR_NO_FIRMWARE
+	NM_PLATFORM_ERROR_NO_FIRMWARE,
 } NMPlatformError;
 
 typedef enum {
@@ -583,6 +588,7 @@ nm_platform_route_scope_inv (guint8 scope)
 
 const char *nm_link_type_to_string (NMLinkType link_type);
 
+const char *nm_platform_error_to_string (NMPlatformError error);
 void nm_platform_set_error (NMPlatform *self, NMPlatformError error);
 NMPlatformError nm_platform_get_error (NMPlatform *self);
 const char *nm_platform_get_error_msg (NMPlatform *self);

src/platform/tests/test-common.h

@@ -16,7 +16,7 @@
 #define debug(...) nm_log_dbg (LOGD_PLATFORM, __VA_ARGS__)
 
 #define error(err) g_assert (nm_platform_get_error (NM_PLATFORM_GET) == err)
-#define no_error() error (NM_PLATFORM_ERROR_NONE)
+#define no_error() error (NM_PLATFORM_ERROR_SUCCESS)
 
 typedef struct {
 	int handler_id;