kernel+libc: Add O_DIRECTORY and use it in opendir()

kernel/src/sys/open.cpp

@@ -44,6 +44,8 @@ Result<u64> sys_open(Registers*, SyscallArgs args)
         if ((flags & O_WRONLY) && (inode->mode() & S_IWUSR) == 0) return err(EACCES);
     }
 
+    if(inode->type() != VFS::InodeType::Directory && (flags & O_DIRECTORY)) return err(ENOTDIR);
+
     if ((flags & O_WRONLY) && (flags & O_TRUNC)) inode->truncate(0);
 
     int fd = TRY(current->allocate_fd(0));

libc/include/bits/open-flags.h

@@ -12,6 +12,7 @@
 #define O_TRUNC 32
 #define O_NONBLOCK 64
 #define O_CLOEXEC 128
+#define O_DIRECTORY 256
 
 #define O_ACCMODE O_RDWR
 

libc/src/dirent.cpp

@@ -13,8 +13,7 @@ extern "C"
         DIR* dp = (DIR*)malloc(sizeof(DIR));
         if (!dp) { return nullptr; }
 
-        // FIXME: Use O_DIRECTORY (validate that path is actually a directory)
-        int fd = open(path, O_RDONLY);
+        int fd = open(path, O_RDONLY | O_DIRECTORY);
         if (fd < 0)
         {
             free(dp);