FindFirst2 and DFS links

[Suresh Jayaraman]

On 03/04/2011 12:23 AM, George K Colley wrote:
> 
> On Mar 3, 2011, at 6:02 AM, Suresh Jayaraman wrote:
> 
>> Hi all,
>>
>> I'm looking into a CIFS client bug report where access to a DFS link
>> fails with -EREMOTE error intermittently. Later accesses to the DFS link
>> succeeds as dentry revalidation gets information about the DFS link.
>>
>> When the failure occurs, it appears that the Server (both Samba and
>> Windows 2k8 server) returned -EREMOTE (NT_STATUS_PATH_NOT_COVERED) in
>> response to the FindFirst2 call on the DFS link. Looking at the CIFS
>> Spec, PATH_NOT_COVERED is not listed as one of the possible errors for
>> FindFirst2. So it's not clear why the Server is sending the same.
>>
>> In order to handle this error, the CIFS client should find a way to
>> figure out from the Server's FindFirst2 response that it is a DFS link.
>> The only promising bit (in File attributes) is the "Reparse Point" which
>> is set in the response from a Windows Server. However, the Reparse point
>> could be something other than (symlinks or volume mountpoint etc) a DFS
>> junction. Is there a way to clearly distinguish a DFS junction?
>>
>> In short:
>>
>> * Is there a way to identify a DFS junction from the FindFirst2
>>  response?
>> * Is NT_STATUS_PATH_NOT_COVERED error expected for a DFS junction in the
>>  FindFirst2 response?
>>
>>
> From a Windows Server you can, not sure what Samba does:
> 
> /*
> * Confirmed from MS:
> * When the attribute has the Reparse Point bit set then the EASize
> * contains the reparse tag info. This behavior is consistent for 
> * Full, Both, FullId, or BothId query dir calls.  It will pack the 
> * reparse tag into the EaSize value if ATTRIBUTE_REPARSE_POINT is set.  
> * I verified with local MS Engineers, and they also checking to make 
> * sure the behavior is covered in MS-FSA. 

Yeah, seems plausible to obtain the reparse tag via Easize by setting
the info level to FIND_FILE_FULL_DIRECTORY_INFO (instead of
FIND_FILE_DIRECTORY_INFO). I'll need to look at the packet capture from
the Samba server too.

Thanks,

-- 
Suresh Jayaraman