Why is FILE_FLAG_BACKUP_SEMANTICS needed to open a directory with CreateFile()?

Question

The documentation for CreateFile() specifies that:

To open a directory using CreateFile, specify the FILE_FLAG_BACKUP_SEMANTICS flag as part of dwFlagsAndAttributes.

What I don't understand is why this flag is needed.

The documented meaning of the flag is:

The file is being opened or created for a backup or restore operation. The system ensures that the calling process overrides file security checks when the process has SE_BACKUP_NAME and SE_RESTORE_NAME privileges.

How is this related to directories?

I've been looking for an answer to this for a while now.

Answer 1

Look at the operations you can perform on a directory handle. They're all backup-related. This isn't Unix, you don't use a directory handle for readdir or openat It's used for BackupRead, BackupWrite, and change notification (which is also something a backup tool wants, to get a consistent snapshot).