is_locked optimization

[tridge at samba.org]

Jeremy,

 > I'll add in the test into Samba4, but you are probably right. Having said
 > that, I still think the optimization is probably useful for Windows
 > based clients. The Windows redirector almost certainly handles
 > such things locally, so no such locks will be seen on the wire.

Are you really sure about this? Maybe you could write a windows test
program that uses byte range locks and see if they are not sent on
oplocked files.

 > Probably I should add in a switch for this, so that it's an
 > optimization we can turn on (but probably not by default). The
 > code change is very simple, so it'll be easy to switch on or off.

Please determine first if the switch potentially causes data
corruption by writing a win32 test. If it does cause data corruption
then we should either not have the switch or document very clearly
that it can cause data corruption.

Cheers, Tridge