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([2804:431:c7c7:c152:6ea6:a44d:671e:88f]) by smtp.gmail.com with ESMTPSA id c33sm2251884qtk.40.2020.08.21.07.49.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 21 Aug 2020 07:49:36 -0700 (PDT) Subject: Re: [PATCH 1/1] spapr_vscsi: do not allow device hotplug To: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , qemu-devel@nongnu.org References: <20200820190635.379657-1-danielhb413@gmail.com> <7f6ab4e6-42b1-3de4-5893-2ef09fc9dd26@redhat.com> From: Daniel Henrique Barboza Message-ID: Date: Fri, 21 Aug 2020 11:49:33 -0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2607:f8b0:4864:20::843; envelope-from=danielhb413@gmail.com; helo=mail-qt1-x843.google.com X-detected-operating-system: by eggs.gnu.org: No matching host in p0f cache. That's all we know. X-Spam_score_int: -17 X-Spam_score: -1.8 X-Spam_bar: - X-Spam_report: (-1.8 / 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, 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-ppc@nongnu.org, Markus Armbruster , david@gibson.dropbear.id.au Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 8/21/20 11:12 AM, Philippe Mathieu-Daudé wrote: > On 8/21/20 4:08 PM, Daniel Henrique Barboza wrote: >> >> >> On 8/21/20 8:08 AM, Philippe Mathieu-Daudé wrote: >>> Cc'ing Markus >>> >>> On 8/20/20 9:06 PM, Daniel Henrique Barboza wrote: >>>> We do not implement hotplug in the vscsi bus, but we forgot to >>>> tell qdev about it. The result is that users are able to hotplug >>>> devices in the vscsi bus, the devices appear in qdev, but they >>>> aren't usable by the guest OS unless the user reboots it first. >>>> >>>> Setting qbus hotplug_handler to NULL will tell qdev-monitor, via >>>> qbus_is_hotpluggable(), that we do not support hotplug operations >>>> in spapr_vscsi. >>>> >>>> Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1862059 >>>> >>>> Signed-off-by: Daniel Henrique Barboza >>>> --- >>>>   hw/scsi/spapr_vscsi.c | 3 +++ >>>>   1 file changed, 3 insertions(+) >>>> >>>> diff --git a/hw/scsi/spapr_vscsi.c b/hw/scsi/spapr_vscsi.c >>>> index d17dc03c73..57f0a1336f 100644 >>>> --- a/hw/scsi/spapr_vscsi.c >>>> +++ b/hw/scsi/spapr_vscsi.c >>>> @@ -1219,6 +1219,9 @@ static void spapr_vscsi_realize(SpaprVioDevice >>>> *dev, Error **errp) >>>>         scsi_bus_new(&s->bus, sizeof(s->bus), DEVICE(dev), >>>>                    &vscsi_scsi_info, NULL); >>>> + >>>> +    /* ibmvscsi SCSI bus does not allow hotplug. */ >>>> +    qbus_set_hotplug_handler(BUS(&s->bus), NULL); >>> >>> Can't this be a problem later in DeviceClass::unrealize()? >> >> Not as far as I've tested. A call to qbus_set_hotplug_handler(bus,NULL) >> after setting it to NULL isn't breaking anything either (just tested). >> >> I verified before sending the patch that setting hotplug_handler to >> NULL is done in some unrealize() calls in buses, but not on devices. >> And I'm not sure which instance would cause an unrealize() in the >> device to fail if the hotplug_handler of the bus is NULL. As far as >> I'm concerned this shouldn't be happening in our case here, where we're >> not dealing with hotplug devices in the bus at all. >> >> Which potential problems are you referring to? > > I was wondering if qdev_unrealize() runs similar checks than > qdev_realize(). I have no idea. I would need to check/study the code to answer that. > >> >>> >>> I was expecting something like, overwriting the parent bus type: >>> >>> -- >8 -- >>> @@ -1271,6 +1271,7 @@ static void spapr_vscsi_class_init(ObjectClass >>> *klass, void *data) >>>       DeviceClass *dc = DEVICE_CLASS(klass); >>>       SpaprVioDeviceClass *k = VIO_SPAPR_DEVICE_CLASS(klass); >>> >>> +    k->bus_type = NULL; /* ibmvscsi SCSI bus does not allow hotplug. */ >>>       k->realize = spapr_vscsi_realize; >>>       k->reset = spapr_vscsi_reset; >>>       k->devnode = spapr_vscsi_devnode; >>> --- >> >> spapr_vscsi is not a bus, is an interface. Setting NULL to bus_type in >> spapr_vio >> breaks guest init: >> >> >> qemu-system-ppc64: /home/danielhb/qemu/hw/core/qdev.c:102: >> qdev_set_parent_bus: Assertion `dc->bus_type && >> object_dynamic_cast(OBJECT(bus), dc->bus_type)' failed. >> Aborted >> >> >> I'm not so sure this would be better than what I'm doing either. >> qdev_device_add() >> calls qbus_is_hotpluggable() to see if the chosen bus allows hotplug. This >> function verifies if bus->hotplug_handler is NULL. What I'm doing is simply >> setting hotplug_handler to NULL in the SCSI bus instance that belongs to >> spapr_vscsi. As far as I understand this is a valid use of the qdev API - I >> should be able to set hotplug_handler to NULL if I don't want devices being >> hotplugged in the bus I'm instantiating. Either that, or >> qbus_is_hotpluggable() >> must check for something else that I can safely turn off. > > I'm not saying I know the correct way to do that, this is why I added > Markus in the loop :) I'm wondering from an API point of view what is > the best way to achieve what you want. I'm glad this works this way. It's alright to question hehehe far too often we're remembered that 'works this way' is a looong way from 'this is the right way'. Let's see if Markus agrees with this approach or if there is a better way of doing it. I'll happily change for a safer approach that will not hit me in the back in the future. Thanks, DHB > >> >> >> Thanks, >> >> >> DHB >> >> >> >> >>> >>>>   } >>>>     void spapr_vscsi_create(SpaprVioBus *bus) >>>> >>> >> >