config: Refactor configuration file parsing

Split the function parse_config() into smaller parts by introducing
the parse_statement(), and add more descriptive comments to improve
readability. In addition, make sure that the last element of the array
of strings 'configuration' is initialised to NULL, which is necessary
to properly count the number of elements after parsing.
Signed-off-by: Radostin Stoyanov <rstoyanov1@gmail.com>
Signed-off-by: Andrei Vagin <avagin@gmail.com>

criu/config.c

@@ -40,70 +40,37 @@ static int count_elements(char **to_count)
 	return count;
 }
 
-static char ** parse_config(char *filepath)
+/* Parse one statement in configuration file */
+int parse_statement(int i, char *line, char **configuration)
 {
-#define DEFAULT_CONFIG_SIZE	10
-	FILE* configfile = fopen(filepath, "r");
-	int config_size = DEFAULT_CONFIG_SIZE;
-	int i = 1, len = 0, offset;
-	size_t limit = 0;
-	bool was_newline;
-	char *tmp_string, *line = NULL, *quoted, *quotedptr;
-	char **configuration, **tmp_conf;
+	int offset = 0, len = 0;
+	bool was_newline = true;
+	char *tmp_string, *quoted, *quotedptr;
 
-	if (!configfile) {
-		return NULL;
-	}
-	configuration = xmalloc(config_size * sizeof(char *));
-	if (configuration == NULL) {
-		fclose(configfile);
-		exit(1);
-	}
-	/*
-	 * Initialize first element, getopt ignores it.
-	 */
-	configuration[0] = "criu";
-
-	while ((len = getline(&line, &limit, configfile)) != -1) {
-		offset = 0;
-		was_newline = true;
-		if (i >= config_size - 1) {
-			config_size *= 2;
-			tmp_conf = xrealloc(configuration, config_size * sizeof(char *));
-			if (tmp_conf == NULL) {
-				fclose(configfile);
-				exit(1);
-			}
-			configuration = tmp_conf;
-		}
 	while (1) {
+		/* Ignore white-space */
 		while ((isspace(*(line + offset)) && (*(line + offset) != '\n'))) offset++;
 
+		/* Read a single word. A word is everything
+		 * that doesn't contain white-space characters. */
 		if (sscanf(line + offset, "%m[^ \t\n]s", &configuration[i]) != 1) {
 			configuration[i] = NULL;
 			break;
 		}
 
+		/* Ignore comments - everything between '#' and '\n' */
 		if (configuration[i][0] == '#') {
-				if (sscanf(line, "%*[^\n]") != 0) {
-					pr_err("Error while reading configuration file %s\n", filepath);
-					fclose(configfile);
-					exit(1);
-				}
 			configuration[i] = NULL;
 			break;
 		}
+
 		if ((configuration[i][0] == '\"') && (strchr(line + offset + 1, '"'))) {
-				/*
-				 * Handle empty strings which strtok ignores
-				 */
+			/* Handle empty strings which strtok ignores */
 			if (!strcmp(configuration[i], "\"\"")) {
 				configuration[i] = "";
 				offset += strlen("\"\"");
 			} else if ((configuration[i] = strtok_r(line + offset, "\"", &quotedptr))) {
-					/*
-					 * Handle escaping of quotes in quoted string
-					 */
+				/* Handle escaping of quotes in quoted string */
 				while (configuration[i][strlen(configuration[i]) - 1] == '\\') {
 					offset++;
 					len = strlen(configuration[i]);
@@ -114,10 +81,9 @@ static char ** parse_config(char *filepath)
 					}
 					quoted = strtok_r(NULL, "\"", &quotedptr);
 					tmp_string = xmalloc(len + strlen(quoted) + 1);
-						if (tmp_string == NULL) {
-							fclose(configfile);
-							exit(1);
-						}
+					if (tmp_string == NULL)
+						return -1;
+
 					memmove(tmp_string, configuration[i], len);
 					memmove(tmp_string + len, quoted, strlen(quoted) + 1);
 					configuration[i] = tmp_string;
@@ -125,24 +91,72 @@ static char ** parse_config(char *filepath)
 				offset += 2;
 			}
 		}
+
 		offset += strlen(configuration[i]);
+
 		if (was_newline) {
 			was_newline = false;
 			len = strlen(configuration[i]);
 			tmp_string = xrealloc(configuration[i], len + strlen("--") + 1);
-				if (tmp_string == NULL) {
-					fclose(configfile);
-					exit(1);
-				}
+			if (tmp_string == NULL)
+				return -1;
+
 			memmove(tmp_string + strlen("--"), tmp_string, len + 1);
 			memmove(tmp_string, "--", strlen("--"));
 			configuration[i] = tmp_string;
 		}
 		i++;
 	}
+
+	return i;
+}
+
+/* Parse a configuration file */
+static char ** parse_config(char *filepath)
+{
+#define DEFAULT_CONFIG_SIZE	10
+	FILE* configfile = fopen(filepath, "r");
+	int config_size = DEFAULT_CONFIG_SIZE;
+	int i = 1;
+	size_t line_size = 0;
+	char *line = NULL;
+	char **configuration;
+
+	if (!configfile)
+		return NULL;
+
+	configuration = xmalloc(config_size * sizeof(char *));
+	if (configuration == NULL) {
+		fclose(configfile);
+		exit(1);
+	}
+	/*
+	 * Initialize first element, getopt ignores it.
+	 */
+	configuration[0] = "criu";
+
+	while (getline(&line, &line_size, configfile) != -1) {
+		/* Extend configuration buffer if necessary */
+		if (i >= config_size - 1) {
+			config_size *= 2;
+			configuration = xrealloc(configuration, config_size * sizeof(char *));
+			if (configuration == NULL) {
+				fclose(configfile);
+				exit(1);
+			}
+		}
+
+		i = parse_statement(i, line, configuration);
+		if (i < 0) {
+			fclose(configfile);
+			exit(1);
+		}
+
 		free(line);
 		line = NULL;
 	}
+	/* Initialize the last element */
+	configuration[i] = NULL;
 
 	free(line);
 	fclose(configfile);