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Tsirkin" , Ani Sinha , Xiao Guangrong , Daniel Henrique Barboza , Greg Kurz , Eric Blake , Eduardo Habkost Subject: Re: [PATCH v3 11/11] machine: Improve error message when using default RAM backend id 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> Date: Fri, 25 Aug 2023 11:56:24 +0200 In-Reply-To: (David Hildenbrand's message of "Fri, 25 Aug 2023 11:13:02 +0200") Message-ID: <87sf87momv.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 Received-SPF: pass client-ip=170.10.129.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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, 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 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? >> error_setg(errp, "object name '%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 appending" >> " 'memory-backend=%s' in '-machine' arguments\n", >> machine_class->default_ram_id); >> Moreover: >> * "object name" feels off, we're talking about IDs, aren't we? > > Yes, I think so. > >> * "appending X in Y" should be "appending X to Y". Consider "setting >> 'memory-backend=%s' with -machine". >> > > Can do, thanks.