LdrUnregisterDllNotification - NtDoc

Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers
#ifndef _NTLDR_H
#if (PHNT_MODE != PHNT_MODE_KERNEL)
// begin_msdn:"DLL Load Notification"
#if (PHNT_VERSION >= PHNT_VISTA)

/**
 * Cancels DLL load notification previously registered by calling the LdrRegisterDllNotification function.
 *
 * @param Cookie A pointer to the callback identifier received from the LdrRegisterDllNotification call that registered for notification.
 * @return NTSTATUS Successful or errant status.
 * @remarks https://learn.microsoft.com/en-us/windows/win32/devnotes/ldrunregisterdllnotification
 */
NTSYSAPI
NTSTATUS
NTAPI
LdrUnregisterDllNotification(
    _In_ PVOID Cookie
    );

#endif
// end_msdn
#endif
#endif

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This function is documented in Windows SDK.