lsfd: (filter) give a name to a constant

Signed-off-by: Masatake YAMATO <yamato@redhat.com>

misc-utils/lsfd-filter.c

@@ -692,7 +692,7 @@ static struct node *dparser_compile1(struct parser *parser, struct node *last)
 	switch (t->type) {
 	case TOKEN_NAME: {
 		int col_id = parser->column_name_to_id(t->val.str, parser->data);
-		if (col_id == -1) {
+		if (col_id == LSFD_FILTER_UNKNOWN_COL_ID) {
 			snprintf(parser->errmsg, ERRMSG_LEN,
 				 _("error: no such column: %s"), t->val.str);
 			token_free(t);

misc-utils/lsfd-filter.h

@@ -14,8 +14,16 @@
 #include <stdio.h>
 #include <stdbool.h>
 
+#define LSFD_FILTER_UNKNOWN_COL_ID -1
+
 struct lsfd_filter;
 
+/*
+ * @column_name_to_id: a function converting a column name to its id.
+ *
+ * @column_name_to_id should return LSFD_FILTER_UNKNOWN_COL_ID if
+ * an unknown column name is given.
+ */
 struct lsfd_filter *lsfd_filter_new(const char *const expr, struct libscols_table *tb,
 				      int ncols,
 				      int (*column_name_to_id)(const char *, void *),

misc-utils/lsfd.c

@@ -203,7 +203,7 @@ static int column_name_to_id(const char *name, size_t namesz)
 	}
 	warnx(_("unknown column: %s"), name);
 
-	return -1;
+	return LSFD_FILTER_UNKNOWN_COL_ID;
 }
 
 static int column_name_to_id_cb(const char *name, void *data __attribute__((__unused__)))