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bh=KzL2NYi8DOqKR+7PCpNLJLmX6lm5yOIfQT3MyS83lTM=; b=hCXBpdKL2aGt3IqPGRCR/jqaCxDYfESXSK2cFuSH4CrFy7MIAvtXA8d0UkG3CfosXErgC8 40hihW+DdaurHNNoZEICE9vKp39tsed69/Y9666XaWe+KTQ3HwfEFq0akdhtryLpyW4Qw6 PTcXZFM95LifF4Gg0bGHpQ0/lgoVZus= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-470-tOnnJekUPj-Iz-560pL32g-1; Mon, 22 Mar 2021 07:36:45 -0400 X-MC-Unique: tOnnJekUPj-Iz-560pL32g-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 3FC4B10082E0 for ; Mon, 22 Mar 2021 11:36:44 +0000 (UTC) Received: from localhost (ovpn-114-89.ams2.redhat.com [10.36.114.89]) by smtp.corp.redhat.com (Postfix) with ESMTP id DD05160C0F; Mon, 22 Mar 2021 11:36:40 +0000 (UTC) Date: Mon, 22 Mar 2021 11:36:39 +0000 From: Stefan Hajnoczi To: Gerd Hoffmann Subject: Re: [PATCH v3 0/8] [RfC] fix tracing for modules Message-ID: References: <20210121125028.3247190-1-kraxel@redhat.com> <20210203163202.GF241524@stefanha-x1.localdomain> <20210222151332.vea6cszd4pwtkeno@sirius.home.kraxel.org> MIME-Version: 1.0 In-Reply-To: <20210222151332.vea6cszd4pwtkeno@sirius.home.kraxel.org> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=stefanha@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="PDqJfmEiFVFq6jYr" Content-Disposition: inline Received-SPF: pass client-ip=63.128.21.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 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_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: Markus Armbruster , qemu-devel@nongnu.org, "Dr. David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --PDqJfmEiFVFq6jYr Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Feb 22, 2021 at 04:13:32PM +0100, Gerd Hoffmann wrote: > Hi, >=20 > > > TODO: > > > Enabling modular tracepoints via -trace cmd line doesn't work yet. > > > Guess we need to store the list somewhere for later re-processing. > > > Error handling is tricky, specifically the "tracepoint doesn't exist" > > > error. Suggestions / ideas are welcome. > >=20 > > Two ideas: > >=20 > > Global trace event name list > > ---------------------------- > > Build *some* global information about all trace events, including > > modules, into the main QEMU binary. For example, generate an array of > > all trace event names so QEMU can always print an error if a > > non-existent trace event name is used. (This is similar to the > > trace-events-all file, which is a global list of all trace events.) > >=20 > > Module name prefixes > > -------------------- > > Allow an optional module/group prefix like qxl:my_trace_event. When the > > user says: > >=20 > > --trace qxl:my_trace_event > >=20 > > QEMU knows that this trace event belongs to the "qxl" module/group. It > > will not attempt to load it until the qxl module registers itself. > >=20 > > If "my_trace_event" doesn't exist in the qxl module: > > 1. If the qxl module is not loaded we don't hit an error. Nevermind. > > 2. When the qxl module is loaded pending events are resolved and an > > error is printed. >=20 > Finally found the time to look at this again...=20 >=20 > So, we already have a "group". Which is basically the sub-directory of > the trace-events file right now, and it seems to be mostly a build system > thing. We get many small lists instead of one huge, but there seems to > be no other effect. We could change that though, by giving each group > an (optional?) prefix. Yes. This reminds me of an idea that was mentioned at the beginning of this effort: maybe QEMU modules should always have their own directory in the source tree instead of being alongside other source files that are built into the main binary. > There also is a probe prefix, apparently used by dtrace only. Not sure > how to deal with that. It prefix is qemu--. > Giving qemu modules its own dtrace prefix looks sensible to me. That > would probably something like "qemu-module-". I think the DTrace prefix needs to be the same as the executable name, but I'm not sure. I also don't know how that extends to shared libraries like QEMU modules. I'm afraid you would need to investigate the DTrace prefix. Stefan --PDqJfmEiFVFq6jYr Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmBYgUcACgkQnKSrs4Gr c8jYSwf9E7Wpj2cZG//PXIrCFAV3I8ESLDRqqjeyzwv0PgmSSJlya6CusEQoyB17 AzF0bTWvglNndm+lQe4ByMqHXAAdwyQSTCXJOmSUY5wCmQMgQZUbYxfDBI4qW8el LqMh+W8814Lh7e5etKsqmOT8f8nVkyVN4pbQK+secs8omZRgBYeUzCGy5rgZXPqp KytvdP1rW+i1Ih0JMtdzUP9XEj2/M7QrliwHS5rWh1TWFauGpYytZzkReGtEJWf3 ur5U6Pj79MKD+ZWqgru4Ff/AgWah9uE1FvDTfNZsTHcxysYQXfBGoUnvjEytBdmV x5jiXysemKTRsHBNiYsD1qGZuG9qqw== =nMVc -----END PGP SIGNATURE----- --PDqJfmEiFVFq6jYr--