Re: [RFC PATCH 2/8] rqbased-dm: add block layer hook

[business1 <coreyu@bsgteamsite.com>]

Kiyoshi Ueda wrote:
> 
> Hi Jens,
> 
> Sorry for the less explanation.
> 
> On Wed, 20 Dec 2006 14:49:24 +0100, Jens Axboe <jens.axboe@oracle.com>
> wrote:
>> On Tue, Dec 19 2006, Kiyoshi Ueda wrote:
>> > This patch adds new "end_io_first" hook in __end_that_request_first()
>> > for request-based device-mapper.
>> 
>> What's this for, lack of stacking?
> 
> I don't understand the meaning of "lack of stacking" well but
> I guess that it means "Is the existing hook in end_that_request_last()
> not enough?"  If so, the answer is no.
> (If the geuss is wrong, please let me know.)
> 
> The new hook is needed for error handling in dm.
> For example, when an error occurred on a request, dm-multipath
> wants to try another path before returning EIO to application.
> Without the new hook, at the point of end_that_request_last(),
> the bios are already finished with error and can't be retried.
> 
> Thanks,
> Kiyoshi Ueda
> 
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