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Wed, 24 Jun 2020 09:16:43 -0700 (PDT) Subject: Re: [PATCH v2 1/2] qom: Introduce object_property_try_add_child() To: Auger Eric , eric.auger.pro@gmail.com, qemu-devel@nongnu.org, berrange@redhat.com, ehabkost@redhat.com, armbru@redhat.com References: <20200624124301.7112-1-eric.auger@redhat.com> <20200624124301.7112-2-eric.auger@redhat.com> <1a144355-27bd-a26f-752e-00c2751d3a1f@redhat.com> <2bf606dd-4ed3-ec65-3dc2-72089bc7cef5@redhat.com> <430f6b32-8456-ac1d-72b3-85e0e59ae9b5@redhat.com> From: Paolo Bonzini Message-ID: <3f1aafa9-aedb-b067-7eb7-5d9bc7ce49d1@redhat.com> Date: Wed, 24 Jun 2020 18:16:42 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <430f6b32-8456-ac1d-72b3-85e0e59ae9b5@redhat.com> Content-Language: en-US X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=207.211.31.120; envelope-from=pbonzini@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/24 02:33:25 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 24/06/20 18:02, Auger Eric wrote: > Hi Paolo, > > On 6/24/20 4:17 PM, Auger Eric wrote: >> Hi Paolo, >> >> On 6/24/20 4:12 PM, Paolo Bonzini wrote: >>> On 24/06/20 14:43, Eric Auger wrote: >>>> + op = object_property_try_add(obj, name, type, object_get_child_property, >>>> + NULL, object_finalize_child_property, >>>> + child, errp); >>>> + if (!op) { >>>> + goto out; >>>> + } >>>> op->resolve = object_resolve_child_property; >>>> +out: >>>> object_ref(child); >>>> child->parent = obj; >>>> return op; >>> >>> I think if there's an error you need to return NULL without ref-ing >>> child, shouldn't you? >> hum yes you're fully right, the out label is badly placed. > Looks the unref is done in user_creatable_add_type() in case of error. There are two references involved: - a reference returned from object_new. user_creatable_add_type() passes it back to the caller. The object_unref() you found is done before returning NULL, because in that case nothing is being passed to the caller - a reference stored in child->parent. In case of error that reference is dropped with object_property_del before returning NULL. object_property_try_add_child must not store anything in child->parent in case of error, and therefore it need not add that reference either. I hope this is clearer. Thanks, Paolo > Isn't it the corresponding one? Anyway I think it is better to avoid > getting the ref here as you suggest (and also free type) and don't unref > in user_creatable_add_type. > > Thanks > > Eric >>> >>> You can then add another test that object_property_add_child succeeds >>> after object_property_try_add_child fails. >> OK >> >> Thanks >> >> Eric >>> >>> Paolo >>> >