OpLocks and file sizes.

[J. Bruce Fields]

On Mon, Mar 26, 2012 at 07:21:13PM -0700, 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.

It also means you're waiting for a round trip on every write.  If you're
going to do that, wouldn't you be better off sending more than a byte of
data while you're at it?

(Sorry, it's a digression, I know.)

--b.