Re: [PATCH 10/14] rbd: rbd_obj_request_wait() should cancel the request if interrupted

[Alex Elder <elder@linaro.org>]

On 07/08/2014 06:18 AM, Ilya Dryomov wrote:
>> > The only question that leaves me with is, does
>> > ceph_osdc_cancel_request() need to include the
>> > call to complete_request() that's present in
>> > ceph_osdc_wait_request()?
> I don't think so - I mentioned it in the ceph_osdc_cancel_request()
> function comment.  ceph_osdc_cancel_request() is supposed to be used by
> higher layers - rbd, cephfs - and exactly because their completion
> logic is decoupled from libceph completions (as you have brilliantly
> explained above) it's the higher layers who should be taking care of
> it.  IOW higher layers are in charge and are supposed to know what and
> when they are cancelling.

I noticed that comment only after sending my message.

RBD doesn't use the safe completion, only the FS client
does, and I was pretty focused on RBD behavior while
looking at this.  I was trying to conceptualize how
(from the perspective of the upper layer) the safe
completion differs from the "normal" completion.

It's possible that an "I have your request" (normal
completion) *also* carries with it the "your request
has completed" (safe completion) indication, but
the higher layer caller has no way of knowing that.

Maybe I should flip my question around, and ask, why
should the ceph_osdc_cancel_request() include the call
to complete_request()?

The answer lies in details of the file system client,
and I'm not in a position right now to dive into that.
Whether it's called in ceph_osdc_cancel_request() or
not has no effect on RBD.

Anyway, your response is fine with me, thank you.

					-Alex