OpLocks and file sizes.

Christopher R. Hertel crh at ubiqx.mn.org
Tue Mar 27 10:23:21 MDT 2012

On 03/27/2012 12:24 AM, Ira Cooper wrote:
> On Tue, Mar 27, 2012 at 12:37 AM, Christopher R. Hertel <crh at ubiqx.mn.org>wrote:
>> On 03/26/2012 09:21 PM, Richard Sharpe wrote:
>>> On Mon, 26 Mar 2012, Christopher R. Hertel wrote:
>>>> Some quick OpLock questions...
>>>> Say we've got a file with an exclusive OpLock, and the client is
>> appending
>>>> to the end of the file (making it a bigger file, of course).  In that
>> case,
>>>> the server won't know the new size of the file until the writes have
>> been
>>>> flushed to the server, which would happen on close or OpLock break.
>>> My experience is that Windows does a one-byte write to extend the actual
>>> size of the file to the end of each write that would extend the file,
>> even
>>> though the data goes into the local cache.
>>> This has the advantage that ENOSPC can be reported sooner than file
>> close time.
>> That's what I thought might happen, but I don't recall it being there in
>> [MS-CIFS].
>> Anyone else have any clues on this?
> No, but I have a good question: How would all this interact with platforms
> that use compression on their filesystems?  Any ZFS using platform would
> run into this issue if they enable compression.

Question on compression in ZFS:
  Does ZFS support quotas and compression within the same file systems?
  If so, does the real size or compressed size count against the quota?

On OpLocks:
  Clearly there are some semantic issues that need to be figured out.
  I will see what the docs have to say and post what I find.
  The semantics that NFSv4 requires may conflict with the semantics
  that SMB1/SMB2 require.  That's the issue we're trying to figure out.

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

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