Kernel, libc: Implement O_DIRECTORY and use that in dirent.h

kernel/src/sys/stdio.cpp

@@ -16,6 +16,7 @@
 #define OPEN_WRITE 2
 #define OPEN_NONBLOCK 4
 #define OPEN_CLOEXEC 8
+#define OPEN_DIRECTORY 16
 
 #define SEEK_SET 0
 #define SEEK_CUR 1
@@ -184,6 +185,15 @@ void sys_open(Context* context, const char* filename, int flags)
     bool able_to_block = (flags & OPEN_NONBLOCK) == 0;
     bool close_on_exec = (flags & OPEN_CLOEXEC) > 0;
 
+    bool only_directory = (flags & OPEN_DIRECTORY) > 0;
+
+    if (only_directory && node->type != VFS_DIRECTORY)
+    {
+        kfree(kfilename);
+        context->rax = -ENOTDIR;
+        return;
+    }
+
     kdbgln("open(): opening %s %s, allocated file descriptor %d", kfilename,
            (can_read && can_write) ? "rw"
            : can_read              ? "r-"

libs/libc/include/fcntl.h

@@ -11,6 +11,8 @@
 #define O_NONBLOCK 4
 /* Close the opened file descriptor on a call to execve(). */
 #define O_CLOEXEC 8
+/* Refuse to open the file if it is not a directory. */
+#define O_DIRECTORY 16
 
 /* Duplicate a file descriptor. */
 #define F_DUPFD 0

libs/libc/src/dirent.cpp

@@ -10,7 +10,7 @@ extern "C"
 {
     DIR* opendir(const char* path)
     {
-        int dirfd = open(path, O_RDONLY); // FIXME: Implement O_DIRECTORY and use that.
+        int dirfd = open(path, O_RDONLY | O_DIRECTORY);
         if (dirfd < 0) return NULL;
         return fdopendir(dirfd);
     }