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List:       cifs-protocol
Subject:    Re: [cifs-protocol] SMB1 -- proper client behavior when it does not hold an oplock
From:       Sreekanth Nadendla <srenaden () microsoft ! com>
Date:       2012-04-27 22:13:15
Message-ID: CBF50ACE323A6B40BB09B300F02A60495AADD289 () TK5EX14MBXC130 ! redmond ! corp ! microsoft ! com
[Download RAW message or body]

Hello Jeff,
                Thank you for your inquiry about File sharing protocols. One of the \
Open specifications team member will contact you soon.

Regards,
Sreekanth Nadendla
Microsoft Windows Open Specifications


-----Original Message-----
From: Jeff Layton [mailto:jlayton@poochiereds.net] On Behalf Of Jeff Layton
Sent: Friday, April 27, 2012 2:34 PM
To: pfif@tridgell.net; cifs-protocol@samba.org; Interoperability Documentation Help
Cc: smfrench@gmail.com; crh@samba.org
Subject: SMB1 -- proper client behavior when it does not hold an oplock

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Sorry for the duplicate emails, but I sent this to the wrong dochelp address before. \
Let me try again...

Hi Dochelp!

I'm hoping you can help clarify some points about proper SMB1 (and maybe SMB2?) \
client behavior when it does not hold an oplock (at least one that allows write \
caching).

My understanding has always been that when a client does not have an oplock that \
                allows write caching, then it should not cache any writes
- -- full stop. If an application does a write then the kernel should not return \
until it has been sent to the server and the reply has come back. That behavior is at \
least suggested in MS-CIFS, though it does not come out and state that explicitly.

OTOH, Steve French suggested that that's not required by the protocol and that \
clients are allowed to buffer up writes "briefly" in order to allow the redirector to \
batch up small writes into a single request as long as it flushes them out in a \
timely fashion. That seems a little crazy to me, but I guess it's not the craziest \
thing in SMB1 if so...

So I guess my questions are:

1) What does the protocol actually mandate? Are you allowed to briefly buffer up \
writes before returning to an application when the client holds no oplock?

2) What does Windows actually do in this regard? If you are not allowed to do that by \
the protocol, then does it follow this strictly or does it do as Steve suggests and \
batch up small writes until it can fill a write request?

Thanks for any info you can provide!
- --
Jeff Layton <jlayton@samba.org>
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