feat(dirent): directory iteration

src/dirent/fdopendir.c

@@ -0,0 +1,47 @@
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <dirent.h>
+
+#include <errno.h>
+
+#include <sys/stat.h>
+
+#include "../internal/malloc.h"
+#include "../internal/syscall.h"
+#include "dirent_impl.h"
+
+/*
+ * fdopendir (todo 24): validate the descriptor with SYS_fstat (POSIX
+ * requires the fd to name a directory), then allocate the stream state.
+ * On failure the descriptor is NOT closed — it stays owned by the caller,
+ * exactly as passed in.
+ */
+DIR *
+fdopendir(int fd)
+{
+    struct stat st;
+    DIR *d;
+
+    if (syscall_ret(__syscall2(SYS_fstat, fd, (long)&st)) < 0)
+    {
+        return NULL;
+    }
+    if (!S_ISDIR(st.st_mode))
+    {
+        errno = ENOTDIR;
+        return NULL;
+    }
+    d = __libc_malloc(sizeof *d);
+    if (d == NULL)
+    {
+        errno = ENOMEM;
+        return NULL;
+    }
+    d->fd = fd;
+    d->buf_pos = 0;
+    d->buf_end = 0;
+    d->de.d_off = 0;
+    return d;
+}