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[83.57.168.235]) by smtp.gmail.com with ESMTPSA id e16sm3005998wrw.49.2021.06.10.03.06.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 10 Jun 2021 03:06:51 -0700 (PDT) Subject: Re: [RFC PATCH v2 1/2] qapi: Inline qmp_marshal_output() functions To: Markus Armbruster , Eric Blake References: <20210609184955.1193081-1-philmd@redhat.com> <20210609184955.1193081-2-philmd@redhat.com> <20210609202952.r4nb2smrptyckvk2@redhat.com> <87eedadpxt.fsf@dusky.pond.sub.org> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: <4050a737-5539-c6a8-3d60-78fc9721a865@redhat.com> Date: Thu, 10 Jun 2021 12:06:50 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <87eedadpxt.fsf@dusky.pond.sub.org> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=philmd@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=philmd@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.199, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, 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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Michael Roth , Paolo Bonzini , qemu-devel@nongnu.org, "Dr. David Alan Gilbert" , Stefan Berger Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 6/10/21 11:33 AM, Markus Armbruster wrote: > Eric Blake writes: > >> On Wed, Jun 09, 2021 at 08:49:54PM +0200, Philippe Mathieu-Daudé wrote: >>> In case we need to use QAPI types but no QAPI command / QAPI event >>> actually use them, the generated qmp_marshal_output() function will >>> trigger the compiler 'unused-function' warnings. >>> To prevent that, emit these functions inlined: the compiler will >>> ignore such unused functions. >>> >>> Signed-off-by: Philippe Mathieu-Daudé >>> --- >>> RFC: No clue about QAPI... >>> Tested with GCC. If the compiler is picky we could use the 'unused' >>> function attribute. >> >> And I have no clue if clang will warn about an unused inline function. >> Going with the compiler attribute seems safer and just as easy to do >> in the same two-line change (remember, the "unused" attribute merely >> means "suppress warnings if I don't use this", and not "warn me if I >> use it in spite of calling it unused"). >> >>> --- >>> scripts/qapi/commands.py | 4 ++-- >>> 1 file changed, 2 insertions(+), 2 deletions(-) >>> >>> diff --git a/scripts/qapi/commands.py b/scripts/qapi/commands.py >>> index 0e13d510547..bbed776a909 100644 >>> --- a/scripts/qapi/commands.py >>> +++ b/scripts/qapi/commands.py >>> @@ -91,8 +91,8 @@ def gen_call(name: str, >>> def gen_marshal_output(ret_type: QAPISchemaType) -> str: >>> return mcgen(''' >>> >>> -static void qmp_marshal_output_%(c_name)s(%(c_type)s ret_in, >>> - QObject **ret_out, Error **errp) >>> +static inline void qmp_marshal_output_%(c_name)s(%(c_type)s ret_in, >>> + QObject **ret_out, Error **errp) >> >> On the other hand, the qapi generator is smart enough to only output >> introspection data for qapi types that were actually used by a command >> or event, so how is that working, and why is it not also being used to >> elide the generation of unused qmp_marshal_output_FOO functions? This >> is where I'll have to defer to Markus. > > This is a QAPI generator restriction. Let me explain. > > The qmp_marshal_output_T() are shared by all commands returning T. > > The commands may be conditional. The user is responsible for making T's > 'if' the conjunction of the commands'. See the FIXME in commands.py. Yes, I noticed the FIXME: # FIXME: If T is a user-defined type, the user is responsible # for making this work, i.e. to make T's condition the # conjunction of the T-returning commands' conditions. If T # is a built-in type, this isn't possible: the # qmp_marshal_output_T() will be generated unconditionally. Using inline / unused attributes don't invalidate this :) > If I do this for tpm.json (appended), then tpm.h misses TpmModel when > CONFIG_TPM is off, and tpm_backend.h misses TpmType and TpmInfo. I > suspect more TPM code needs to be guarded by CONFIG_TPM. Yes, this is what I did first, use the code below and add #ifdef'ry, but the code becomes ugly and harder to maintain because the enums are used in middle of a QOM interface structure: include/sysemu/tpm.h-37-struct TPMIfClass { include/sysemu/tpm.h-38- InterfaceClass parent_class; include/sysemu/tpm.h-39- include/sysemu/tpm.h:40: enum TpmModel model; include/sysemu/tpm.h-41- void (*request_completed)(TPMIf *obj, int ret); include/sysemu/tpm.h-42- enum TPMVersion (*get_version)(TPMIf *obj); include/sysemu/tpm.h-43-}; include/sysemu/tpm.h-44- If you think using inline / unused attributes is not an option for QAPI, then the #ifdef'ry isn't worth it and I'd prefer use v1 which doesn't use conditional QAPI suggested by Marc-André. > diff --git a/qapi/tpm.json b/qapi/tpm.json > index 09332e6f99..e74c881ea6 100644 > --- a/qapi/tpm.json > +++ b/qapi/tpm.json > @@ -17,7 +17,9 @@ > # > # Since: 1.5 > ## > -{ 'enum': 'TpmModel', 'data': [ 'tpm-tis', 'tpm-crb', 'tpm-spapr' ] } > +{ 'enum': 'TpmModel', 'data': [ 'tpm-tis', 'tpm-crb', 'tpm-spapr' ], > + 'if': 'defined(CONFIG_TPM)' } > + > ## > # @query-tpm-models: > # > @@ -47,7 +49,8 @@ > # > # Since: 1.5 > ## > -{ 'enum': 'TpmType', 'data': [ 'passthrough', 'emulator' ] } > +{ 'enum': 'TpmType', 'data': [ 'passthrough', 'emulator' ], > + 'if': 'defined(CONFIG_TPM)' } > > ## > # @query-tpm-types: > @@ -124,7 +127,8 @@ > { 'struct': 'TPMInfo', > 'data': {'id': 'str', > 'model': 'TpmModel', > - 'options': 'TpmTypeOptions' } } > + 'options': 'TpmTypeOptions' }, > + 'if': 'defined(CONFIG_TPM)' } > > ## > # @query-tpm: >