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(p200300cbc70e9200ce93b5e68aa965d4.dip0.t-ipconnect.de. [2003:cb:c70e:9200:ce93:b5e6:8aa9:65d4]) by smtp.gmail.com with ESMTPSA id r1-20020a05600c298100b003fe2b6d64c8sm4950634wmd.21.2023.08.25.02.59.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 25 Aug 2023 02:59:45 -0700 (PDT) Message-ID: Date: Fri, 25 Aug 2023 11:59:43 +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 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> From: David Hildenbrand Organization: Red Hat In-Reply-To: <87sf87momv.fsf@pond.sub.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.133.124; 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=ham 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 11:56, 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 -- Cheers, David / dhildenb