Re: [PATCH] pnfs: do not reset to mds if wb_offset != wb_pgbase

[Benny Halevy <bhalevy@tonian.com>]

On 2013-03-19 22:28, Fred Isaman wrote:
> On Tue, Mar 19, 2013 at 3:35 PM, Benny Halevy <bhalevy@tonian.com> wrote:
>> On 2013-03-18 19:04, Fred Isaman wrote:
>>> A problem case is if the layout ends within the page request, which
>>> can happen due to the misalignment.
>>
>> First, the file layout currently supports only whole file layouts so I don't see
>> how that's a problem.
>> Regardless, I'd rather trim the layout segment to PAGE_SIZE boundaries
>> and get a new layout from the page aligned offset and on with minlength = PAGE_SIZE
>> (as we do today).
>>
>> Benny
>>
> 
> Yes, but consider....
> 
> let P = PAGE_SIZE
> 
> assume you have a layout from 0 to 4P, and you try to do a WRITE from
> 2P to 6P.  Now if the buffer is not page aligned, one of the nfs_page
> requests will contain the file's logical 4P offset at a random
> location within the nfs_page.  What happens then?

Fred,  Can you please provide a test that reproduces this concern
so we can verify the system behavior with and without my patch?

Benny

> 
> Fred
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