[AFS3-std] Re: [OpenAFS-devel] convergence of RxOSD, Extended Call Backs, Byte Range Locking, etc.

[Hartmut Reuter]

Jeffrey Hutzelman wrote:
> --On Friday, July 24, 2009 10:31:27 AM -0400 "Matt W. Benjamin"
> <matt@linuxbox.com> wrote:
> 
>> Hi Hartmut, Felix,
>>
>> I see the point, it's not useful if it's only for decoration.  It does
>> feel intuitively right to have txid, if it could be used by a family of
>> RPCs.  Might make for cleaner interfaces for cancellation, abandonment,
>> (not to mention futures--reversibility, delegation, ...)?
> 
> Also note that multiple _reads_ can be going on at once, and you want to
> be able to track those, too, so you can avoid letting anyone write while
> there's a read in progress.
> 
> The fileserver simply assumes that anyone who tries to extend or release
> a lock is the caller that actually holds the lock, instead of using a
> transaction ID.  Let's not make the same mistake here.

I can't use the vnode->lock for this kind of locking, anyway, because
the End-of-I/O-rpc wouldn't run in the same thread. So I have planned a
counter for ongoing reads (write can only start if that came down to 0)
a counter for waiters (to know whether End-of-I/O-rpc has to wake
someone or just can free the struct) and, of course a writer field which
contains the ip-address of the writing client or 0 if there is no write
in progress.

But all these are implementation details which have nothing to do with
the AFS3 protocol and can be changed later if it seems appropriate.

-Hartmut
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Hartmut Reuter                  e-mail 		reuter@rzg.mpg.de
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