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([2804:431:c7c6:3fd7:65e0:e5c6:f4fc:733c]) by smtp.gmail.com with ESMTPSA id y9sm2388626qkm.19.2021.03.24.12.10.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 24 Mar 2021 12:10:02 -0700 (PDT) Subject: Re: [PATCH 0/4] DEVICE_NOT_DELETED/DEVICE_UNPLUG_ERROR QAPI events To: David Gibson References: <20210312200740.815014-1-danielhb413@gmail.com> From: Daniel Henrique Barboza Message-ID: Date: Wed, 24 Mar 2021 16:09:59 -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: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::830; envelope-from=danielhb413@gmail.com; helo=mail-qt1-x830.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: armbru@redhat.com, qemu-ppc@nongnu.org, qemu-devel@nongnu.org, groug@kaod.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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). 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); Thanks, DHB > > Thoughs, Markus? >