liblua: Emulate DIR, opendir, fdopendir, closedir

In a similar fashion to FILE, provide thin shims for the standard directory
manipulation functions.

Reviewed by:	imp
Sponsored by:	Dell EMC Isilon
Differential Revision:	https://reviews.freebsd.org/D14417

stand/liblua/lstd.c

@@ -127,6 +127,42 @@ getc(FILE *stream)
 	return EOF;
 }
 
+DIR *
+opendir(const char *name)
+{
+	DIR *dp;
+	int fd;
+
+	fd = open(name, O_RDONLY);
+	if (fd < 0)
+		return NULL;
+	dp = fdopendir(fd);
+	if (dp == NULL)
+		close(fd);
+	return dp;
+}
+
+DIR *
+fdopendir(int fd)
+{
+	DIR *dp;
+
+	dp = malloc(sizeof(*dp));
+	if (dp == NULL)
+		return NULL;
+	dp->fd = fd;
+	return dp;
+}
+
+int
+closedir(DIR *dp)
+{
+	close(dp->fd);
+	dp->fd = -1;
+	free(dp);
+	return 0;
+}
+
 void
 luai_writestring(const char *s, int i)
 {

stand/liblua/lstd.h

@@ -43,6 +43,11 @@ typedef struct FILE
 	size_t size;
 } FILE;
 
+typedef struct DIR
+{
+	int fd;
+} DIR;
+
 FILE *fopen(const char *filename, const char *mode);
 FILE *freopen( const char *filename, const char *mode, FILE *stream);
 size_t fread(void *ptr, size_t size, size_t count, FILE *stream);
@@ -50,6 +55,9 @@ int fclose(FILE *stream);
 int ferror(FILE *stream);
 int feof(FILE *stream);
 int getc(FILE * stream);
+DIR *opendir(const char *name);
+DIR *fdopendir(int fd);
+int closedir(DIR *);
 
 #ifndef EOF
 #define EOF (-1)