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Re: [Qemu-devel] [PATCHv2 10/11] iscsi: ignore aio_discard if unsupporte


From: Peter Lieven
Subject: Re: [Qemu-devel] [PATCHv2 10/11] iscsi: ignore aio_discard if unsupported
Date: Wed, 10 Jul 2013 22:31:34 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120827 Thunderbird/15.0

Am 10.07.2013 16:58, schrieb Kevin Wolf:
> Am 10.07.2013 um 16:49 hat Peter Lieven geschrieben:
>> Am 10.07.2013 16:28, schrieb Kevin Wolf:
>>> Am 10.07.2013 um 16:04 hat Peter Lieven geschrieben:
>>>> Am 10.07.2013 13:33, schrieb Kevin Wolf:
>>>>> Am 27.06.2013 um 15:11 hat Peter Lieven geschrieben:
>>>>>> if the target does not support UNMAP or the request
>>>>>> is too big silently ignore the discard request.
>>>>>>
>>>>>> Signed-off-by: Peter Lieven <address@hidden>
>>>>> Why not loop for the "too big" case? You can probably use the same logic
>>>>> for unmapping the whole device in .bdrv_create and here.
>>>> right, but looping in an aio function seemed not so trivial to me.
>>>> it seems more and more obvious to me that the best would be to change
>>>> all the remaining aio routines to co routines.
>>> The pattern for AIO functions is that the real work of submitting
>>> requests is done in the AIO callback, and it submits new AIO requests
>>> calling back into the same callback as long as acb->remaining_secs > 0
>>> (or something like that).
>>>
>>> You can still see that kind of thing alive in qed_aio_next_io(), (most
>>> of?) the rest is converted to coroutines because it makes the code look
>>> nicer.
>> would you agree if I leave the easy version in just to fix the potential
>> problems if iscsi_aio_discard is called with too high nb_sectors or
>> on a storage where UNMAP is unsupported.
>>
>> I will add a TODO with the comment that the limit of iscsi->max_unmap should
>> be replaced by a loop once the routine is replaced by a coroutine?
> Meh, another pony I don't get... ;-)
>
> Leaving a TODO comment for now is okay with me.
forget about the TODO. Looking at what I have already got, implementing
iscsi_co_discard is low hanging fruit. I will implement it directly. With the
too big loop and all the benefits of the co routines.

Peter




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