[RFC PATCH] smbd: resilient file handle support

[Uri Simchoni]

Bryan,

Sorry for not updating - I haven't had time to figure it out yet, but 
there's one thing I can already confirm, namely that the Win10 failure 
against our box has nothing to do with resilient file handles - the 
failure occurs before creating the .vhdx. I'll update with findings when 
I have them.

Thanks,
Uri.

On 02/19/2016 08:53 PM, Bryan Burgin wrote:
> Uri,
>
> An update, following up on your comment "I [Uri] will check. I [Uri] have reports that we fail Windows 10 backup too unless downgrading to SMB2.0.2, but I haven't studied it closely as with Win8":
>
> Regarding the Bugzilla report at https://bugzilla.samba.org/show_bug.cgi?id=10159 and the fix we created for Windows 8 via the on-demand (you have to pull down the fix) QFE patch https://support.microsoft.com/en-us/kb/2920193 and Windows 8.1 via the "important" Windows Update roll-up patch https://support.microsoft.com/en-us/kb/2919355 is also included in Windows 10.
>
> The end-user scenarios that were reported back in 2013 was that the feature Windows Server Backup did not work when the target SMB2 server was a dialect 2.1 and above and, as was discovered as the root-cause, the server did not support FSCTL_LMR_REQUEST_RESILIENCY.  Samba servers at the time returned STATUS_NOT_SUPPORTED.  An API that Windows Server Backup relied on, CreateVirtualDisk(), did not consider FSCTL_LMR_REQUEST_RESILIENCY as an optional feature when the dialect was 2.1 or greater.  If the request for resiliency was not supported, the API failed and so did the feature.  The fix was to continue to request if FSCTL_LMR_REQUEST_RESILIENCY is supported (when the negotiated dialect is 2.1 or greater), but NOT to consider a response of STATUS_NOT_SUPPORTED as a hard failure.  This also affected other callers of CreateVirtualDisk(), which included using the Hyper-V Manager to create a new hard disk on a remote share.
>
> I tested both Windows Server Backup on a Windows Server 2016 TP4 box and creating a VHDX from a Windows 10 box using the Hyper-V Manager against a server I modified to always return STATUS_NOT_SUPPORTED to FSCTL_LMR_REQUEST_RESILIENCY requests.  I am satisfied that the issue that was reported in 2013 and fixed soon thereafter continues to be fixed in Windows 10 and Server 2016.
>
> If you have reports of issues, we would be very interested if additional information becomes available.  But, if there is a failure, it is likely a different root-cause that would need to be investigated.
>
> Bryan
>