From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from list by lists.gnu.org with archive (Exim 4.90_1) id 1k1ADA-0002Zj-R0 for mharc-qemu-trivial@gnu.org; Thu, 30 Jul 2020 11:11:12 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:41240) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1k1AD9-0002YU-QZ for qemu-trivial@nongnu.org; Thu, 30 Jul 2020 11:11:11 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:25275 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1k1AD7-0005FP-FB for qemu-trivial@nongnu.org; Thu, 30 Jul 2020 11:11:11 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1596121868; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=hCK/tBx/pEN3xVJ+/dFaojg6ii0gFp7E1boM0G1oYiU=; b=HFF6XIgY+QYq+j/CHsWx0KWmgddI25WNoVLvOcZqRyeDUcyPTals/NTS2TyUH4bTuQ2sXb Fkj7u0fKGD2OFz5njxFq1lajejb30cP5VbE3XfwRUrn1Wi3Gz7oiqxUorrw/nLldYvto/d em1wBrP8F2gggytuqzYEggTO5d3DHAk= 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-288-goXgiGSHPqK3HbrFcJwjYA-1; Thu, 30 Jul 2020 11:11:01 -0400 X-MC-Unique: goXgiGSHPqK3HbrFcJwjYA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0B6DF102C7E9; Thu, 30 Jul 2020 15:11:00 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-112-143.ams2.redhat.com [10.36.112.143]) by smtp.corp.redhat.com (Postfix) with ESMTPS id CF9391992D; Thu, 30 Jul 2020 15:10:59 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 6CC101132FD2; Thu, 30 Jul 2020 17:10:58 +0200 (CEST) From: Markus Armbruster To: Peter Maydell Cc: Eric Blake , QEMU Trivial , Daniel P. =?utf-8?Q?Berrang=C3=A9?= , QEMU Developers Subject: Re: [PATCH] osdep.h: Add doc comment for qemu_get_thread_id() References: <20200716154114.10838-1-peter.maydell@linaro.org> <0f8b8fea-2bd0-7616-292b-8fb0f87cec75@redhat.com> Date: Thu, 30 Jul 2020 17:10:58 +0200 In-Reply-To: (Peter Maydell's message of "Tue, 28 Jul 2020 16:25:04 +0100") Message-ID: <87k0ylvy0t.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=205.139.110.61; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/30 03:41:52 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-trivial@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 30 Jul 2020 15:11:12 -0000 Peter Maydell writes: > On Tue, 28 Jul 2020 at 16:17, Eric Blake wrote: >> >> On 7/16/20 10:41 AM, Peter Maydell wrote: >> > Add a documentation comment for qemu_get_thread_id(): since this >> > is rather host-OS-specific it's useful if people writing the >> > implementation and people thinking of using the function know >> > what the purpose and limitations are. >> > >> > Signed-off-by: Peter Maydell >> > --- >> > Based on conversation with Dan on IRC, and prompted by the recent >> > patch to add OpenBSD support. >> > >> > Q: should we document exactly what the thread-id value is for >> > each host platform in the QMP documentation ? Somebody writing >> > a management layer app should ideally not have to grovel through >> > the application to figure out what they should do with the >> > integer value they get back from query-cpus... >> > >> > include/qemu/osdep.h | 14 ++++++++++++++ >> > 1 file changed, 14 insertions(+) >> >> Do we need a counterpart change... >> >> > >> > diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h >> > index 4841b5c6b5f..8279f72e5ed 100644 >> > --- a/include/qemu/osdep.h >> > +++ b/include/qemu/osdep.h >> > @@ -515,6 +515,20 @@ bool qemu_has_ofd_lock(void); >> > >> > bool qemu_write_pidfile(const char *pidfile, Error **errp); >> > >> > +/** >> > + * qemu_get_thread_id: Return OS-specific ID of current thread >> > + * >> > + * This function returns an OS-specific identifier of the >> > + * current thread. This will be used for the "thread-id" field in >> > + * the response to the QMP query-cpus and query-iothreads commands. >> >> ...to the qapi definition of query-cpus and query-iothreads? > > Well, that was my question above. Currently the QAPI documentation > says absolutely nothing about what the thread-id values mean > for any host OS (beyond "ID of the underlying host thread"), which > means that any management layer application needs to look in the > implementation to find out what they actually are... ... which they will have to do to actually use it for the purpose we have in mind, namely: >> > + * The intention is that a VM management layer application can then >> > + * use it to tie specific QEMU vCPU and IO threads to specific host >> > + * CPUs using whatever the host OS's CPU affinity setting API is. >> > + * New implementations of this function for new host OSes should >> > + * return the most sensible integer ID that works for that purpose. >> > + * >> > + * This function should not be used for anything else inside QEMU. >> > + */ Do they? > Improving the QAPI docs would probably be something like: > * add a list of host OSes and semantics to the doc comment > for CpuInfoFast > * add cross-references to that definition from everywhere > else in QAPI that uses a thread-id/thread_id > * add a comment in the C file to say "if you're adding another > OS ifdef here please update the QAPI doc comment" If they do, then this sounds like a plan. By the way, the #else case smells: #else return getpid(); #endif The PID is quite unlikely to be "an OS-specific identifier of the current thread". Shouldn't we fail instead of lie when we don't know how to compute the truth? 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Thu, 30 Jul 2020 15:10:59 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 6CC101132FD2; Thu, 30 Jul 2020 17:10:58 +0200 (CEST) From: Markus Armbruster To: Peter Maydell Subject: Re: [PATCH] osdep.h: Add doc comment for qemu_get_thread_id() References: <20200716154114.10838-1-peter.maydell@linaro.org> <0f8b8fea-2bd0-7616-292b-8fb0f87cec75@redhat.com> Date: Thu, 30 Jul 2020 17:10:58 +0200 In-Reply-To: (Peter Maydell's message of "Tue, 28 Jul 2020 16:25:04 +0100") Message-ID: <87k0ylvy0t.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=205.139.110.61; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/30 03:41:52 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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_H2=-1, 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: QEMU Trivial , "Daniel P. =?utf-8?Q?Berrang=C3=A9?=" , QEMU Developers Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Peter Maydell writes: > On Tue, 28 Jul 2020 at 16:17, Eric Blake wrote: >> >> On 7/16/20 10:41 AM, Peter Maydell wrote: >> > Add a documentation comment for qemu_get_thread_id(): since this >> > is rather host-OS-specific it's useful if people writing the >> > implementation and people thinking of using the function know >> > what the purpose and limitations are. >> > >> > Signed-off-by: Peter Maydell >> > --- >> > Based on conversation with Dan on IRC, and prompted by the recent >> > patch to add OpenBSD support. >> > >> > Q: should we document exactly what the thread-id value is for >> > each host platform in the QMP documentation ? Somebody writing >> > a management layer app should ideally not have to grovel through >> > the application to figure out what they should do with the >> > integer value they get back from query-cpus... >> > >> > include/qemu/osdep.h | 14 ++++++++++++++ >> > 1 file changed, 14 insertions(+) >> >> Do we need a counterpart change... >> >> > >> > diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h >> > index 4841b5c6b5f..8279f72e5ed 100644 >> > --- a/include/qemu/osdep.h >> > +++ b/include/qemu/osdep.h >> > @@ -515,6 +515,20 @@ bool qemu_has_ofd_lock(void); >> > >> > bool qemu_write_pidfile(const char *pidfile, Error **errp); >> > >> > +/** >> > + * qemu_get_thread_id: Return OS-specific ID of current thread >> > + * >> > + * This function returns an OS-specific identifier of the >> > + * current thread. This will be used for the "thread-id" field in >> > + * the response to the QMP query-cpus and query-iothreads commands. >> >> ...to the qapi definition of query-cpus and query-iothreads? > > Well, that was my question above. Currently the QAPI documentation > says absolutely nothing about what the thread-id values mean > for any host OS (beyond "ID of the underlying host thread"), which > means that any management layer application needs to look in the > implementation to find out what they actually are... ... which they will have to do to actually use it for the purpose we have in mind, namely: >> > + * The intention is that a VM management layer application can then >> > + * use it to tie specific QEMU vCPU and IO threads to specific host >> > + * CPUs using whatever the host OS's CPU affinity setting API is. >> > + * New implementations of this function for new host OSes should >> > + * return the most sensible integer ID that works for that purpose. >> > + * >> > + * This function should not be used for anything else inside QEMU. >> > + */ Do they? > Improving the QAPI docs would probably be something like: > * add a list of host OSes and semantics to the doc comment > for CpuInfoFast > * add cross-references to that definition from everywhere > else in QAPI that uses a thread-id/thread_id > * add a comment in the C file to say "if you're adding another > OS ifdef here please update the QAPI doc comment" If they do, then this sounds like a plan. By the way, the #else case smells: #else return getpid(); #endif The PID is quite unlikely to be "an OS-specific identifier of the current thread". Shouldn't we fail instead of lie when we don't know how to compute the truth?