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([2804:431:c7c6:e000:6f43:93dd:11a0:93a1]) by smtp.gmail.com with ESMTPSA id x7sm1963515qtp.10.2021.03.31.12.40.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 31 Mar 2021 12:40:19 -0700 (PDT) Subject: Re: [PATCH 0/4] DEVICE_NOT_DELETED/DEVICE_UNPLUG_ERROR QAPI events To: Igor Mammedov References: <20210312200740.815014-1-danielhb413@gmail.com> <20210330012831.2ce0514c@redhat.com> From: Daniel Henrique Barboza Message-ID: <85172cec-3634-14b6-9e7b-a3527c482abd@gmail.com> Date: Wed, 31 Mar 2021 16:40:16 -0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210330012831.2ce0514c@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::72c; envelope-from=danielhb413@gmail.com; helo=mail-qk1-x72c.google.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_ENVFROM_END_DIGIT=0.25, FREEMAIL_FROM=0.001, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org, groug@kaod.org, qemu-ppc@nongnu.org, armbru@redhat.com, David Gibson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 3/29/21 8:28 PM, Igor Mammedov wrote: > On Wed, 24 Mar 2021 16:09:59 -0300 > Daniel Henrique Barboza wrote: > >> On 3/23/21 10:40 PM, David Gibson wrote: >>> On Tue, Mar 23, 2021 at 02:10:22PM -0300, Daniel Henrique Barboza wrote: >>>> >>>> >>>> On 3/22/21 10:12 PM, David Gibson wrote: >>>>> On Fri, Mar 12, 2021 at 05:07:36PM -0300, Daniel Henrique Barboza wrote: >>>>>> Hi, >>>>>> >>>>>> This series adds 2 new QAPI events, DEVICE_NOT_DELETED and >>>>>> DEVICE_UNPLUG_ERROR. They were (and are still being) discussed in [1]. >>>>>> >>>>>> Patches 1 and 3 are independent of the ppc patches and can be applied >>>>>> separately. Patches 2 and 4 are based on David's ppc-for-6.0 branch and >>>>>> are dependent on the QAPI patches. >>>>> >>>>> Implementation looks fine, but I think there's a bit more to discuss >>>>> before we can apply. >>>>> >>>>> I think it would make sense to re-order this and put UNPLUG_ERROR >>>>> first. Its semantics are clearer, and I think there's a stronger case >>>>> for it. >>>> >>>> Alright >>>> >>>>> >>>>> I'm a bit less sold on DEVICE_NOT_DELETED, after consideration. Does >>>>> it really tell the user/management anything useful beyond what >>>>> receiving neither a DEVICE_DELETED nor a DEVICE_UNPLUG_ERROR does? >>>> >>>> >>>> It informs that the hotunplug operation exceed the timeout that QEMU >>>> internals considers adequate, but QEMU can't assert that it was caused >>>> by an error or an unexpected delay. The end result is that the device >>>> is not going to be deleted from QMP, so DEVICE_NOT_DELETED. >>> >>> Is it, though? I mean, it is with this implementation for papr: >>> because we clear the unplug_requested flag, even if the guest later >>> tries to complete the unplug, it will fail. >>> >>> But if I understand what Markus was saying correctly, that might not >>> be possible for all hotplug systems. I believe Markus was suggesting >>> that DEVICE_NOT_DELETED could just mean that we haven't deleted the >>> device yet, but it could still happen later. >>> >>> And in that case, I'm not yet sold on the value of a message that >>> essentially just means "Ayup, still dunno what's happening, sorry". >>> >>>> Perhaps we should just be straightforward and create a DEVICE_UNPLUG_TIMEOUT >>>> event. >>> >>> Hm... what if we added a "reason" field to UNPLUG_ERROR. That could >>> be "guest rejected hotplug", or something more specific, in the rare >>> case that the guest has a way of signalling something more specific, >>> or "timeout" - but the later *only* to be sent in cases where on the >>> timeout we're able to block any later completion of the unplug (as we >>> can on papr). > > Is canceling unplug on timeout documented somewhere (like some spec)? Nope. > > If not it might (theoretically) confuse guest when it tries to unplug > after timeout and leave guest in some unexpected state. I consider this a remote possibility due to the generous timeout we're using in the machine, but it is a possibility nevertheless. > >> >> I believe that's already covered by the existing API: >> >> >> +# @DEVICE_UNPLUG_ERROR: >> +# >> +# Emitted when a device hot unplug error occurs. >> +# >> +# @device: device name >> +# >> +# @msg: Informative message >> >> The 'informative message' would be the reason the event occurred. In patch >> 4/4, for the memory hotunplug refused by the guest, it is being set as: >> >> qapi_error = g_strdup_printf("Memory hotunplug rejected by the guest " >> "for device %s", dev->id); >> qapi_event_send_device_unplug_error(dev->id, qapi_error); >> >> >> >> We could use the same DEVICE_UNPLUG_ERROR event in the CPU hotunplug timeout >> case (currently on patch 2/4) by just changing 'msg', e.g.: >> >> >> qapi_error = g_strdup_printf("CPU hotunplug timeout for device %s", dev->id); >> qapi_event_send_device_unplug_error(dev->id, qapi_error); >> > > lets make everything support ACPI (just kidding). I would love to make PAPR more ACPI and less .... PAPR. > > maybe we can reuse already existing ACPI_DEVICE_OST instead of DEVICE_UNPLUG_ERROR > which sort of does the same thing (and more) but instead of strings uses status codes > defined by spec. > > Idea similar to DEVICE_UNPLUG_ERROR was considered back then, but instead of QEMU being > a poor translator of status codes to non machine-readable strings we went with > exposing well documented status codes to user. This way user can implement > specific reactions to particular errors just looking at JSON + spec. This is not a bad idea. Problem is that we don't have all ACPI_DEVICE_OST fields to fill in because, well, both the timeout and the cancell mechanism aren't specified there. Thanks, DHB > >> Thanks, >> >> DHB >> >> >>> >>> Thoughs, Markus? >>> >> >