[cifs-protocol] [REG:111051857287367] BranchCache and SMB2: Questions specific to BranchCache.

Edgar Olougouna edgaro at microsoft.com
Tue May 31 14:43:22 MDT 2011


Please find our answers as follows. 

BranchCache divides content into 32 megabyte segments and further subdivides these segments into 64 kilobyte blocks. The content information encodes:
(1) ullOffsetInContent - the offset within the content at which the first segment present in the content information begins and 
(2) dwOffsetInFirstSegment - the offset from ullOffsetInContent at which the first block of the first segment present in the content information begins.
Let's walk through this with an example.
Let's assume the client requests a content range starting at content offset 33554433 (a.k.a. 32 megabytes plus one byte) and extending for 10 bytes.
ullOffsetInContent will be 32 megabytes because that is where the first segment present in the content information begins.
dwOffsetInFirstSegment will be 1 because the first segment in the content information is the second segment in the actual content because the requested content range starts at 32 megabytes plus one.
dwReadBytesInLastSegment will be 10 because that is the length of the content range that lies within the final segment present in the content information.
Note that dwReadBytesInLastSegment may be zero if the client did not request a content range (i.e. the client asked for the entire content).
The scenarios in which dwReadBytesInLastSegment will be zero are Windows specific behavior. In Windows 7, this happens whenever the content information covers the entire content. In order to participate in the MS-PCCRC protocol, a client must be able to parse content information that contains a zero value for dwReadBytesInLastSegment. The client must react by treating the segment size for the final segment encoded in the content information as the amount of data in the final segment. If dwReadBytesInLastSegment is non-zero then the client must only attempt to read dwReadBytesInLastSegment from the final segment, regardless of the segment size of the final segment.
On Windows 7, if the content fits in one segment and the client issued a request for the entire content then, dwReadBytesInLastSegment should be zero and dwOffsetInFirstSegment should be zero.

The product team will be reflecting the above clarification in the protocol document. Let me know whether this answers your questions.


-----Original Message-----
From: Edgar Olougouna 
Sent: Tuesday, May 31, 2011 11:07 AM
To: 'Christopher R. Hertel'
Cc: cifs-protocol at samba.org
Subject: RE: [cifs-protocol] [REG:111051857287367] BranchCache and SMB2: Questions specific to BranchCache.


I am actively working on this with the product team to clarify a few more points. I will update you as soon as possible.


-----Original Message-----
From: Christopher R. Hertel [mailto:crh at ubiqx.com]
Sent: Sunday, May 29, 2011 5:57 PM
To: Edgar Olougouna
Cc: MSSolve Case Email; cifs-protocol at samba.org
Subject: Re: [cifs-protocol] [REG:111051857287367] BranchCache and SMB2: Questions specific to BranchCache.


I am just checking in on this ticket.  I understand that the resolution to these issues can take some time, but I want to test my implementation at the FileSharing Plugfest in a few weeks time.  Having the answers would help me complete my testing implementation.


Chris -)-----

Obaid Farooqi wrote:
> Hi Chris:
> Thank you for contacting Microsoft regarding your query on branch cache. A member of the protocol documentation team will be in touch soon.
> Regards,
> Obaid Farooqi
> Escalation Engineer | Microsoft
> Exceeding your expectations is my highest priority.  If you would like 
> to provide feedback on your case you may contact my manager at 
> allisong at microsoft.com
> -----Original Message-----
> From: Christopher R. Hertel [mailto:crh at ubiqx.com]
> Sent: Tuesday, May 17, 2011 9:12 PM
> To: Interoperability Documentation Help
> Subject: BranchCache and SMB2: Questions specific to BranchCache.
> I have a couple of questions regarding BranchCache and [MS-PCCRC].  As you know, BranchCache--particularly the Content Information format specified in [MS-PCCRC]--can be used as an extension to SMB2.
> 1) In the Content Information structure ([MS-PCCRC:2.3]), there is the
>    following field definition:
>    dwOffsetInFirstSegment (4 bytes): Number of bytes into the first
>      segment within the Content Information data structure at which
>      the content range begins.
>    I can't make heads nor tails of that description, and the captures I
>    have done on the wire typically show that field set to zero.
>    Similarly, the examples in section 3 of [MS-PCCRC] show the value of
>    this field to be zero.
>    The field is 4 bytes in length, so it cannot be an offset into the
>    content itself, since content offsets are (should be) 8 bytes (64-bit).
>    Please clarify:  What does dwOffsetInFirstSegment actually represent?
> 2) I am not getting what I expect in the dwReadBytesInLastSegment field.
>    This field is defined in [MS-PCCRC:2.3], as follows:
>    dwReadBytesInLastSegment (4 bytes): Total number of bytes of the
>      content range which lie within the final segment in the Content
>      Information data structure.
>    It seems to me that this value represents the number of bytes
>    of actual content included in the calculation of the final
>    Segment block of the Content Information.  That interpretation
>    is supported by the examples in section 3.
>    In actual captures, however, Windows IIS server returns zero
>    (0x00000000) in the dwReadBytesInLastSegment field.
>    Is this a documentation bug or is the IIS server returning the
>    wrong value?
>    This is IIS running on W2K8r2 with fairly up-to-date patches
>    applied.
> Looking forward to the replies.
> Thanks.
> Chris -)-----
> --
> "Implementing CIFS - the Common Internet FileSystem" ISBN: 013047116X
> Samba Team -- http://www.samba.org/     -)-----   Christopher R. Hertel
> jCIFS Team -- http://jcifs.samba.org/   -)-----   ubiqx development, uninq.
> ubiqx Team -- http://www.ubiqx.org/     -)-----   crh at ubiqx.mn.org
> OnLineBook -- http://ubiqx.org/cifs/    -)-----   crh at ubiqx.org

Christopher R. Hertel -)-----             Storage Architect & CIFS Geek
http://www.ubiqx.com/               Data Storage and Systems Consulting
"Implementing CIFS - the Common Internet FileSystem"   ISBN: 013047116X

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