"Backup" interface?

[Derrell.Lipman at UnwiredUniverse.com]

I am in search of a method of backing up open files on Windows machines, using
Samba or libsmbclient on a Linux machine.  I've heard rumors of a "Backup
Interface" in the network protocols, which allows backing up open files when a
normal open() would fail), but have not been able to find any information on
it.  Is there such an interface, and if so, does Samba provide access to it?

Thanks,

Derrell