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Thu, 19 Sep 2019 08:24:13 +0000 (UTC) Received: from [10.36.117.104] (ovpn-117-104.ams2.redhat.com [10.36.117.104]) by smtp.corp.redhat.com (Postfix) with ESMTP id AE6F760C18; Thu, 19 Sep 2019 08:23:51 +0000 (UTC) To: Vladimir Sementsov-Ogievskiy , "qemu-devel@nongnu.org" References: <20190918130244.24257-1-vsementsov@virtuozzo.com> <9d7ae167-c77c-4d8a-bbbc-c33a03a115e5@virtuozzo.com> <0764e9fc-b0ff-12c7-fffb-adf68706383b@redhat.com> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwX4EEwECACgFAljj9eoCGwMFCQlmAYAGCwkI BwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEE3eEPcA/4Na5IIP/3T/FIQMxIfNzZshIq687qgG 8UbspuE/YSUDdv7r5szYTK6KPTlqN8NAcSfheywbuYD9A4ZeSBWD3/NAVUdrCaRP2IvFyELj xoMvfJccbq45BxzgEspg/bVahNbyuBpLBVjVWwRtFCUEXkyazksSv8pdTMAs9IucChvFmmq3 jJ2vlaz9lYt/lxN246fIVceckPMiUveimngvXZw21VOAhfQ+/sofXF8JCFv2mFcBDoa7eYob s0FLpmqFaeNRHAlzMWgSsP80qx5nWWEvRLdKWi533N2vC/EyunN3HcBwVrXH4hxRBMco3jvM m8VKLKao9wKj82qSivUnkPIwsAGNPdFoPbgghCQiBjBe6A75Z2xHFrzo7t1jg7nQfIyNC7ez MZBJ59sqA9EDMEJPlLNIeJmqslXPjmMFnE7Mby/+335WJYDulsRybN+W5rLT5aMvhC6x6POK z55fMNKrMASCzBJum2Fwjf/VnuGRYkhKCqqZ8gJ3OvmR50tInDV2jZ1DQgc3i550T5JDpToh dPBxZocIhzg+MBSRDXcJmHOx/7nQm3iQ6iLuwmXsRC6f5FbFefk9EjuTKcLMvBsEx+2DEx0E UnmJ4hVg7u1PQ+2Oy+Lh/opK/BDiqlQ8Pz2jiXv5xkECvr/3Sv59hlOCZMOaiLTTjtOIU7Tq 7ut6OL64oAq+zsFNBFXLn5EBEADn1959INH2cwYJv0tsxf5MUCghCj/CA/lc/LMthqQ773ga uB9mN+F1rE9cyyXb6jyOGn+GUjMbnq1o121Vm0+neKHUCBtHyseBfDXHA6m4B3mUTWo13nid 0e4AM71r0DS8+KYh6zvweLX/LL5kQS9GQeT+QNroXcC1NzWbitts6TZ+IrPOwT1hfB4WNC+X 2n4AzDqp3+ILiVST2DT4VBc11Gz6jijpC/KI5Al8ZDhRwG47LUiuQmt3yqrmN63V9wzaPhC+ xbwIsNZlLUvuRnmBPkTJwwrFRZvwu5GPHNndBjVpAfaSTOfppyKBTccu2AXJXWAE1Xjh6GOC 8mlFjZwLxWFqdPHR1n2aPVgoiTLk34LR/bXO+e0GpzFXT7enwyvFFFyAS0Nk1q/7EChPcbRb hJqEBpRNZemxmg55zC3GLvgLKd5A09MOM2BrMea+l0FUR+PuTenh2YmnmLRTro6eZ/qYwWkC u8FFIw4pT0OUDMyLgi+GI1aMpVogTZJ70FgV0pUAlpmrzk/bLbRkF3TwgucpyPtcpmQtTkWS gDS50QG9DR/1As3LLLcNkwJBZzBG6PWbvcOyrwMQUF1nl4SSPV0LLH63+BrrHasfJzxKXzqg rW28CTAE2x8qi7e/6M/+XXhrsMYG+uaViM7n2je3qKe7ofum3s4vq7oFCPsOgwARAQABwsFl BBgBAgAPBQJVy5+RAhsMBQkJZgGAAAoJEE3eEPcA/4NagOsP/jPoIBb/iXVbM+fmSHOjEshl KMwEl/m5iLj3iHnHPVLBUWrXPdS7iQijJA/VLxjnFknhaS60hkUNWexDMxVVP/6lbOrs4bDZ NEWDMktAeqJaFtxackPszlcpRVkAs6Msn9tu8hlvB517pyUgvuD7ZS9gGOMmYwFQDyytpepo YApVV00P0u3AaE0Cj/o71STqGJKZxcVhPaZ+LR+UCBZOyKfEyq+ZN311VpOJZ1IvTExf+S/5 lqnciDtbO3I4Wq0ArLX1gs1q1XlXLaVaA3yVqeC8E7kOchDNinD3hJS4OX0e1gdsx/e6COvy qNg5aL5n0Kl4fcVqM0LdIhsubVs4eiNCa5XMSYpXmVi3HAuFyg9dN+x8thSwI836FoMASwOl C7tHsTjnSGufB+D7F7ZBT61BffNBBIm1KdMxcxqLUVXpBQHHlGkbwI+3Ye+nE6HmZH7IwLwV W+Ajl7oYF+jeKaH4DZFtgLYGLtZ1LDwKPjX7VAsa4Yx7S5+EBAaZGxK510MjIx6SGrZWBrrV TEvdV00F2MnQoeXKzD7O4WFbL55hhyGgfWTHwZ457iN9SgYi1JLPqWkZB0JRXIEtjd4JEQcx +8Umfre0Xt4713VxMygW0PnQt5aSQdMD58jHFxTk092mU+yIHj5LeYgvwSgZN4airXk5yRXl SE+xAvmumFBY Organization: Red Hat GmbH Message-ID: <68c69aa9-5ea3-8a43-2ba0-40c959e30b22@redhat.com> Date: Thu, 19 Sep 2019 10:23:50 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.62]); Thu, 19 Sep 2019 08:24:13 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [RFC] error: auto propagated local_err 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: "fam@euphon.net" , "peter.maydell@linaro.org" , "mst@redhat.com" , "codyprime@gmail.com" , "mark.cave-ayland@ilande.co.uk" , "mdroth@linux.vnet.ibm.com" , "kraxel@redhat.com" , "mreitz@redhat.com" , "qemu-block@nongnu.org" , "quintela@redhat.com" , "armbru@redhat.com" , "pasic@linux.ibm.com" , "borntraeger@de.ibm.com" , "marcandre.lureau@redhat.com" , "rth@twiddle.net" , "farman@linux.ibm.com" , "groug@kaod.org" , "dgilbert@redhat.com" , "alex.williamson@redhat.com" , "qemu-arm@nongnu.org" , "stefanha@redhat.com" , "jsnow@redhat.com" , "david@gibson.dropbear.id.au" , "kwolf@redhat.com" , "berrange@redhat.com" , "cohuck@redhat.com" , "qemu-s390x@nongnu.org" , "sundeep.lkml@gmail.com" , "qemu-ppc@nongnu.org" , "pbonzini@redhat.com" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 19.09.19 10:20, Vladimir Sementsov-Ogievskiy wrote: > 19.09.2019 10:53, David Hildenbrand wrote: >> On 19.09.19 09:41, Vladimir Sementsov-Ogievskiy wrote: >>> 19.09.2019 10:32, David Hildenbrand wrote: >>>> On 18.09.19 15:02, Vladimir Sementsov-Ogievskiy wrote: >>>>> Hi all! >>>>> >>>>> Here is a proposal (three of them, actually) of auto propagation for >>>>> local_err, to not call error_propagate on every exit point, when we >>>>> deal with local_err. >>>>> >>>>> It also may help make Greg's series[1] about error_append_hint smaller. >>>>> >>>>> See definitions and examples below. >>>>> >>>>> I'm cc-ing to this RFC everyone from series[1] CC list, as if we like >>>>> it, the idea will touch same code (and may be more). >>>>> >>>>> [1]: https://lists.gnu.org/archive/html/qemu-devel/2019-09/msg03449.html >>>>> >>>>> Signed-off-by: Vladimir Sementsov-Ogievskiy >>>>> --- >>>>> include/qapi/error.h | 102 +++++++++++++++++++++++++++++++++++++++++++ >>>>> block.c | 63 ++++++++++++-------------- >>>>> block/backup.c | 8 +++- >>>>> block/gluster.c | 7 +++ >>>>> 4 files changed, 144 insertions(+), 36 deletions(-) >>>>> >>>>> diff --git a/include/qapi/error.h b/include/qapi/error.h >>>>> index 3f95141a01..083e061014 100644 >>>>> --- a/include/qapi/error.h >>>>> +++ b/include/qapi/error.h >>>>> @@ -322,6 +322,108 @@ void error_set_internal(Error **errp, >>>>> ErrorClass err_class, const char *fmt, ...) >>>>> GCC_FMT_ATTR(6, 7); >>>>> >>>>> +typedef struct ErrorPropagator { >>>>> + Error **errp; >>>>> + Error *local_err; >>>>> +} ErrorPropagator; >>>>> + >>>>> +static inline void error_propagator_cleanup(ErrorPropagator *prop) >>>>> +{ >>>>> + if (prop->local_err) { >>>>> + error_propagate(prop->errp, prop->local_err); >>>>> + } >>>>> +} >>>>> + >>>>> +G_DEFINE_AUTO_CLEANUP_CLEAR_FUNC(ErrorPropagator, error_propagator_cleanup); >>>>> + >>>>> +/* >>>>> + * ErrorPropagationPair >>>>> + * >>>>> + * [Error *local_err, Error **errp] >>>>> + * >>>>> + * First element is local_err, second is original errp, which is propagation >>>>> + * target. Yes, errp has a bit another type, so it should be converted. >>>>> + * >>>>> + * ErrorPropagationPair may be used as errp, which points to local_err, >>>>> + * as it's type is compatible. >>>>> + */ >>>>> +typedef Error *ErrorPropagationPair[2]; >>>>> + >>>>> +static inline void error_propagation_pair_cleanup(ErrorPropagationPair *arr) >>>>> +{ >>>>> + Error *local_err = (*arr)[0]; >>>>> + Error **errp = (Error **)(*arr)[1]; >>>>> + >>>>> + if (local_err) { >>>>> + error_propagate(errp, local_err); >>>>> + } >>>>> +} >>>>> + >>>>> +G_DEFINE_AUTO_CLEANUP_CLEAR_FUNC(ErrorPropagationPair, >>>>> + error_propagation_pair_cleanup); >>>>> + >>>>> +/* >>>>> + * DEF_AUTO_ERRP >>>>> + * >>>>> + * Define auto_errp variable, which may be used instead of errp, and >>>>> + * *auto_errp may be safely checked to be zero or not, and may be safely >>>>> + * used for error_append_hint(). auto_errp is automatically propagated >>>>> + * to errp at function exit. >>>>> + */ >>>>> +#define DEF_AUTO_ERRP(auto_errp, errp) \ >>>>> + g_auto(ErrorPropagationPair) (auto_errp) = {NULL, (Error *)(errp)} >>>>> + >>>>> + >>>>> +/* >>>>> + * Another variant: >>>>> + * Pros: >>>>> + * - normal structure instead of cheating with array >>>>> + * - we can directly use errp, if it's not NULL and don't point to >>>>> + * error_abort or error_fatal >>>>> + * Cons: >>>>> + * - we need to define two variables instead of one >>>>> + */ >>>>> +typedef struct ErrorPropagationStruct { >>>>> + Error *local_err; >>>>> + Error **errp; >>>>> +} ErrorPropagationStruct; >>>>> + >>>>> +static inline void error_propagation_struct_cleanup(ErrorPropagationStruct *prop) >>>>> +{ >>>>> + if (prop->local_err) { >>>>> + error_propagate(prop->errp, prop->local_err); >>>>> + } >>>>> +} >>>>> + >>>>> +G_DEFINE_AUTO_CLEANUP_CLEAR_FUNC(ErrorPropagationStruct, >>>>> + error_propagation_struct_cleanup); >>>>> + >>>>> +#define DEF_AUTO_ERRP_V2(auto_errp, errp) \ >>>>> + g_auto(ErrorPropagationStruct) (__auto_errp_prop) = {.errp = (errp)}; \ >>>>> + Error **auto_errp = \ >>>>> + ((errp) == NULL || *(errp) == error_abort || *(errp) == error_fatal) ? \ >>>>> + &__auto_errp_prop.local_err : \ >>>>> + (errp); >>>>> + >>>>> +/* >>>>> + * Third variant: >>>>> + * Pros: >>>>> + * - simpler movement for functions which don't have local_err yet >>>>> + * the only thing to do is to call one macro at function start. >>>>> + * This extremely simplifies Greg's series >>>>> + * Cons: >>>>> + * - looks like errp shadowing.. Still seems safe. >>>>> + * - must be after all definitions of local variables and before any >>>>> + * code. >>>>> + * - like v2, several statements in one open macro >>>>> + */ >>>>> +#define MAKE_ERRP_SAFE(errp) \ >>>>> +g_auto(ErrorPropagationStruct) (__auto_errp_prop) = {.errp = (errp)}; \ >>>>> +if ((errp) == NULL || *(errp) == error_abort || *(errp) == error_fatal) { \ >>>>> + (errp) = &__auto_errp_prop.local_err; \ >>>>> +} >>>> >>>> >>>> Using that idea, what about something like this: >>>> >>>> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c >>>> index 8bfb6684cb..043ad69f8b 100644 >>>> --- a/hw/s390x/s390-virtio-ccw.c >>>> +++ b/hw/s390x/s390-virtio-ccw.c >>>> @@ -58,22 +58,42 @@ S390CPU *s390_cpu_addr2state(uint16_t cpu_addr) >>>> return S390_CPU(ms->possible_cpus->cpus[cpu_addr].cpu); >>>> } >>>> >>>> +typedef struct ErrorPropagator { >>>> + Error **errp; >>>> + Error *local_err; >>>> +} ErrorPropagator; >>>> + >>>> +static inline void error_propagator_cleanup(ErrorPropagator *prop) >>>> +{ >>>> + if (prop->local_err) { >>>> + error_propagate(prop->errp, prop->local_err); >>>> + } >>>> +} >>>> + >>>> +G_DEFINE_AUTO_CLEANUP_CLEAR_FUNC(ErrorPropagator, error_propagator_cleanup); >>>> + >>>> +#define DEFINE_LOCAL_ERRP(_errp) \ >>>> +g_auto(ErrorPropagator) (__auto_errp_prop) = {.errp = (_errp)}; \ >>>> +Error **local_errp = &__auto_errp_prop.local_err >>>> + >>>> static S390CPU *s390x_new_cpu(const char *typename, uint32_t core_id, >>>> Error **errp) >>>> { >>>> + DEFINE_LOCAL_ERRP(errp); >>>> S390CPU *cpu = S390_CPU(object_new(typename)); >>>> - Error *err = NULL; >>>> >>>> - object_property_set_int(OBJECT(cpu), core_id, "core-id", &err); >>>> - if (err != NULL) { >>>> + object_property_set_int(OBJECT(cpu), core_id, "core-id", local_errp); >>>> + if (*local_errp != NULL) { >>>> goto out; >>>> } >>>> - object_property_set_bool(OBJECT(cpu), true, "realized", &err); >>>> + object_property_set_bool(OBJECT(cpu), true, "realized", local_errp); >>>> >>>> out: >>>> object_unref(OBJECT(cpu)); >>>> - if (err) { >>>> - error_propagate(errp, err); >>>> + if (*local_errp) { >>>> cpu = NULL; >>>> } >>>> return cpu; >>>> >>>> >>> >>> So it's DEF_AUTO_ERRP_V2 with first parameter hardcoded to be local_errp. >>> I still prefer MAKE_ERRP_SAFE(), to not introduce extra variables. >>> >> >> I lost track of the different approaches ;) >> >> The local variable will most probably optimized out by the compiler. I >> dislike MAKE_ERRP_SAFE(), as it mixes defining a new variable with code. >> > > But it makes Greg's series extremely simple: just add MAKE_ERRP_SAFE() to some > functions. And as Eric explains, mixing code and definitions is not a problem. I still dislike it ;) > > Still, we can do like this: > > #define MAKE_ERRP_SAFE() \ > g_auto(ErrorPropagator) (__auto_errp_prop) = {.errp = errp}; \ > Error **__local_errp_unused __attribute__ ((unused)) = (errp = &__auto_errp_prop.local_err) > > Which are two valid definitions. Yeah, I would prefer something like that! -- Thanks, David / dhildenb