Re: librbd discard bug problems -> i got it

[Josh Durgin <josh.durgin@inktank.com>]

On 11/19/2012 03:42 PM, Stefan Priebe wrote:
> Am 20.11.2012 00:33, schrieb Josh Durgin:
>> On 11/19/2012 03:16 PM, Stefan Priebe wrote:
>>> mhm qemu rbd block driver. Get's always these errors back. As
>>> rbd_aio_bh_cb is directly called from librbd the problem must be there.
>>> Strangely i can't find where rbd_aio_bh_cb get's called with -512.
>>>
>>> ANy further ideas?
>>
>> Two ideas:
>>
>> 1) Is rbd_finish_aiocb getting this same return value?
> Will check this tomorrow.
>
>
>> 2) Perhaps it's an issue with the return value wrapping around with
>> very large discards. Adding some logging of the return values of each
>> rados operation in AioCompletion::complete_request() might give us a
>> clue. These large negative return values are suspicious.
>
> Good idea. As r and rval is int it is limited. But
> AioCompletion::complete_request is adding more and more stuff to rval.
> What could be a solution? Bump rval to int64? Or wrap to around to start
> at 0 again?

The final return value is limited to int at a few levels. Probably it's
best to make discard alway return 0 on success. aio_discard should
already be doing this, but perhaps it's not in this case.

Josh