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(p200300cbc70e9200ce93b5e68aa965d4.dip0.t-ipconnect.de. [2003:cb:c70e:9200:ce93:b5e6:8aa9:65d4]) by smtp.gmail.com with ESMTPSA id k1-20020adfe3c1000000b0031c6e1ea4c7sm1760667wrm.90.2023.08.25.03.10.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 25 Aug 2023 03:10:39 -0700 (PDT) Message-ID: <78fd367f-740a-4b37-0faf-dd0cabae4bd6@redhat.com> Date: Fri, 25 Aug 2023 12:10:38 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH v3 11/11] machine: Improve error message when using default RAM backend id Content-Language: en-US From: David Hildenbrand To: Markus Armbruster Cc: ThinerLogoer , qemu-devel@nongnu.org, qemu-ppc@nongnu.org, Paolo Bonzini , Peter Xu , Igor Mammedov , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , =?UTF-8?Q?Daniel_P=2eBerrang=c3=a9?= , Stefan Hajnoczi , Elena Ufimtseva , Jagannathan Raman , "Michael S. Tsirkin" , Ani Sinha , Xiao Guangrong , Daniel Henrique Barboza , Greg Kurz , Eric Blake , Eduardo Habkost References: <20230823153412.832081-1-david@redhat.com> <20230823153412.832081-12-david@redhat.com> <209b4b8c.54bc.18a2b7b6f53.Coremail.logoerthiner1@163.com> <87msyfo5b0.fsf@pond.sub.org> <87sf87momv.fsf@pond.sub.org> Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -49 X-Spam_score: -5.0 X-Spam_bar: ----- X-Spam_report: (-5.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-2.919, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 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-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 25.08.23 11:59, David Hildenbrand wrote: > On 25.08.23 11:56, Markus Armbruster wrote: >> David Hildenbrand writes: >> >>> On 25.08.23 11:10, Markus Armbruster wrote: >>>> David Hildenbrand writes: >>>> >>>>> On 25.08.23 08:57, ThinerLogoer wrote: >>>>>> Hello, >>>>>> >>>>>> At 2023-08-23 23:34:11, "David Hildenbrand" wrote: >>>>>>> For migration purposes, users might want to reuse the default RAM >>>>>>> backend id, but specify a different memory backend. >>>>>>> >>>>>>> For example, to reuse "pc.ram" on q35, one has to set >>>>>>> -machine q35,memory-backend=pc.ram >>>>>>> Only then, can a memory backend with the id "pc.ram" be created >>>>>>> manually. >>>>>>> >>>>>>> Let's improve the error message. >>>>>>> >>>>>>> Unfortuantely, we cannot use error_append_hint(), because the caller >>>>>>> passes &error_fatal. >>>>>>> >>>>>>> Suggested-by: ThinerLogoer >>>>>>> Signed-off-by: David Hildenbrand >>>>>>> --- >>>>>>> hw/core/machine.c | 4 +++- >>>>>>> 1 file changed, 3 insertions(+), 1 deletion(-) >>>>>>> >>>>>>> diff --git a/hw/core/machine.c b/hw/core/machine.c >>>>>>> index f0d35c6401..dbcd124d45 100644 >>>>>>> --- a/hw/core/machine.c >>>>>>> +++ b/hw/core/machine.c >>>>>>> @@ -1382,7 +1382,9 @@ void machine_run_board_init(MachineState *machine, const char *mem_path, Error * >>>>>>> machine_class->default_ram_id)) { >>>>>>> error_setg(errp, "object name '%s' is reserved for the default" >>>>>>> " RAM backend, it can't be used for any other purposes." >>>>>>> - " Change the object's 'id' to something else", >>>>>>> + " Change the object's 'id' to something else or disable" >>>>>>> + " automatic creation of the default RAM backend by setting" >>>>>>> + " the 'memory-backend' machine property", >>>>>>> machine_class->default_ram_id); >>>>>>> return; >>>>>>> } >>>>>> >>>>>> I'd suggest a more explicit version: >>>>>> >>>>>> " Change the object's 'id' to something else or disable" >>>>>> " automatic creation of the default RAM backend by appending" >>>>>> " 'memory-backend={machine_class->default_ram_id}' in '-machine' arguments", >>>>> >>>>> >>>>> Thanks, I'll do: >>>>> >>>>> diff --git a/hw/core/machine.c b/hw/core/machine.c >>>>> index f0d35c6401..cd0fd6cdd1 100644 >>>>> --- a/hw/core/machine.c >>>>> +++ b/hw/core/machine.c >>>>> @@ -1382,8 +1382,10 @@ void machine_run_board_init(MachineState *machine, const char *mem_path, Error * >>>>> machine_class->default_ram_id)) { >>>>> error_setg(errp, "object name '%s' is reserved for the default" >>>>> " RAM backend, it can't be used for any other purposes." >>>>> - " Change the object's 'id' to something else", >>>>> - machine_class->default_ram_id); >>>>> + " Change the object's 'id' to something else or disable" >>>>> + " automatic creation of the default RAM backend by appending" >>>>> + " 'memory-backend=%s' in '-machine' arguments", >>>>> + machine_class->default_ram_id, machine_class->default_ram_id); >>>>> return; >>>>> } >>>>> if (!create_default_memdev(current_machine, mem_path, errp)) { >>>> >>> >>> Hi Markus, >>> >>>> error_setg()'s function comment specifies: >>>> * The resulting message should be a single phrase, with no newline or >>>> * trailing punctuation. >>>> Please use error_append_hint(), like so >>> >>> Please see the patch description: "Unfortunately, we cannot use error_append_hint(), because the caller passes &error_fatal." >>> >>> How should I deal with that? >> >> qapi/error.h tells you :) >> >> * = Creating errors = >> [...] >> * Create an error and add additional explanation: >> * error_setg(errp, "invalid quark"); >> * error_append_hint(errp, "Valid quarks are up, down, strange, " >> * "charm, top, bottom.\n"); >> * This may require use of ERRP_GUARD(); more on that below. >> [...] >> * = Why, when and how to use ERRP_GUARD() = >> * >> * Without ERRP_GUARD(), use of the @errp parameter is restricted: >> * - It must not be dereferenced, because it may be null. >> * - It should not be passed to error_prepend() or >> * error_append_hint(), because that doesn't work with &error_fatal. >> * ERRP_GUARD() lifts these restrictions. >> * >> * To use ERRP_GUARD(), add it right at the beginning of the function. >> * @errp can then be used without worrying about the argument being >> * NULL or &error_fatal. >> * >> * Using it when it's not needed is safe, but please avoid cluttering >> * the source with useless code. >> * >> * = Converting to ERRP_GUARD() = >> * >> * To convert a function to use ERRP_GUARD(): >> * >> * 0. If the Error ** parameter is not named @errp, rename it to >> * @errp. >> * >> * 1. Add an ERRP_GUARD() invocation, by convention right at the >> * beginning of the function. This makes @errp safe to use. >> * >> * 2. Replace &err by errp, and err by *errp. Delete local variable >> * @err. >> * >> * 3. Delete error_propagate(errp, *errp), replace >> * error_propagate_prepend(errp, *errp, ...) by error_prepend(errp, ...) >> * >> * 4. Ensure @errp is valid at return: when you destroy *errp, set >> * *errp = NULL. >> * >> * Example: >> * >> * bool fn(..., Error **errp) >> * { >> * Error *err = NULL; >> * >> * foo(arg, &err); >> * if (err) { >> * handle the error... >> * error_propagate(errp, err); >> * return false; >> * } >> * ... >> * } >> * >> * becomes >> * >> * bool fn(..., Error **errp) >> * { >> * ERRP_GUARD(); >> * >> * foo(arg, errp); >> * if (*errp) { >> * handle the error... >> * return false; >> * } >> * ... >> * } >> * >> * For mass-conversion, use scripts/coccinelle/errp-guard.cocci. >> >> Questions? > > Thanks for the pointer! > > ... hopefully I'm done with that error-handling pain in QEMU soon and > can continue focusing on things that make me feel more productive :P > ... hoping it's as simple as this: diff --git a/hw/core/machine.c b/hw/core/machine.c index f0d35c6401..09f40c7f07 100644 --- a/hw/core/machine.c +++ b/hw/core/machine.c @@ -1352,6 +1352,7 @@ out: void machine_run_board_init(MachineState *machine, const char *mem_path, Error **errp) { + ERRP_GUARD(); MachineClass *machine_class = MACHINE_GET_CLASS(machine); ObjectClass *oc = object_class_by_name(machine->cpu_type); CPUClass *cc; @@ -1380,9 +1381,13 @@ void machine_run_board_init(MachineState *machine, const char *mem_path, Error * numa_uses_legacy_mem()) { if (object_property_find(object_get_objects_root(), machine_class->default_ram_id)) { - error_setg(errp, "object name '%s' is reserved for the default" - " RAM backend, it can't be used for any other purposes." - " Change the object's 'id' to something else", + error_setg(errp, "object's id '%s' is reserved for the default" + " RAM backend, it can't be used for any other purposes", + machine_class->default_ram_id); + error_append_hint(errp, + "Change the object's 'id' to something else or disable" + " automatic creation of the default RAM backend by setting" + " 'memory-backend=%s' with '-machine'.\n", machine_class->default_ram_id); return; } -- Cheers, David / dhildenb