Directory Leasing feature in Samba smbd

[Jeremy Allison]

On Wed, Sep 02, 2020 at 04:27:54PM -0400, Tom Talpey via samba-technical wrote:
> On 9/2/2020 3:20 PM, Jeremy Allison via samba-technical wrote:
> > On Wed, Sep 02, 2020 at 05:18:05PM +0000, Krishna Harathi wrote:
> > > Jeremy,
> > > 
> > > Thanks for the insightful response on how to start on directory leasing feature.
> > > 
> > > After reading more into Microsoft SMB2/3 directory leasing, in our customer case, looks like the windows client is taking advantage of the granted directory lease and maintaining a directory cache.
> > > 
> > > I am attempting to setup the following even before writing test cases.
> > > 
> > >    1. Using directory lease capable Windows Server 2012R2 (or later), setup a shared folder/directory with a set of files/folders in it.
> > >    2. On a Windows client capable of using directory lease , map the shared folder to a local drive letter.
> > >    3.  Start capturing tcpip packets on either client or server.
> > >    4. Browse the shared folder on the client multiple times.
> > >    5. The tcpip dump should show only a single directory scan set (SMB2_FIND_BOTH_DIRECTORY_INFO requests/responses)
> > > 
> > > Is my assumption and approach correct? Is there a better/direct way to monitor the directory lease and cache in the client?
> > > 
> > > Only information I found on Windows is the global configuration values of "DirectoryCacheEntriesMax" and "DirectoryCacheEntrySizeMax" shown with powershell "get-smbclientconfiguration". Are there any stats to monitor to determine that the directory cache is active with entries from the mapped drive that has the directory leased?
> > > 
> > > Once this setup is done and confirmed working, I will have a better understanding on what to expect and I will start adding test cases to smb torture.
> > 
> > Hi Krishna,
> > 
> > That would seem to be a good way to explore
> > how the Windows client behaves. I don't have
> > good insights into how the Windows client
> > manages its cache I'm afraid.
> 
> I think it's a very risky thing to assert that any particular caching
> occurs. There is no protocol requirement for caching, so the behavior
> of the client is purely an implementation choice.
> 
> It's great to explore but "adding test cases to smb torture" is my
> concern. What kind of test cases?

The same kind of test cases we used to determine the behavior
of leases on files.

a). Open a directory with lease, different varients of RWH etc.
b). Try opening a directory with an oplock (does that work?)
c). Try creating a file in the directory via a second connection,
watch for the break traffic on the handle etc.

We're not planning to test the client caching, as you say that's
a client policy decision.