From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 065C19866EA for ; Fri, 18 Mar 2022 11:02:35 +0000 (UTC) From: Christian Schoenebeck Date: Fri, 18 Mar 2022 12:02:31 +0100 Message-ID: <11686863.Z9n2BMzBuM@silver> In-Reply-To: <87cziksm5h.fsf@redhat.com> References: <4735344.EBYxvr1mta@silver> <3040881.qp741xram0@silver> <87cziksm5h.fsf@redhat.com> MIME-Version: 1.0 Subject: [virtio-comment] Re: [PATCH v3 4/4] Add CCW configuration field "indirect_num" Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="iso-8859-1" To: Cornelia Huck Cc: virtio-comment@lists.oasis-open.org, Stefan Hajnoczi , Greg Kurz , Dominique Martinet , Halil Pasic List-ID: On Donnerstag, 17. M=E4rz 2022 15:12:42 CET Cornelia Huck wrote: > On Wed, Mar 16 2022, Christian Schoenebeck wrote= : > > This new CCW configuration field allows to negotiate a more fine > > graded maximum lenght of indirect descriptor chains. > >=20 > > Bump CCW virtio revision to 3 and make the existence of this new > > field "indirect_num" dependant on revision 3. > >=20 > > Fixes: https://github.com/oasis-tcs/virtio-spec/issues/122 > > Signed-off-by: Christian Schoenebeck > > --- > >=20 > > content.tex | 14 +++++++++++++- > > 1 file changed, 13 insertions(+), 1 deletion(-) >=20 > (...) >=20 > > @@ -2581,12 +2583,17 @@ \subsubsection{Configuring a > > Virtqueue}\label{sec:Virtio Transport Options / Vir>=20 > > struct vq_config_block { > > =20 > > be16 index; > > be16 max_num; > >=20 > > + be32 indirect_num; /* since virtio-ccw rev. 3 */ >=20 > Maybe make it max_indirect_num (to mirror max_num?) Right, that name appears indeed more appropriate here. > > }; > > \end{lstlisting} > > =20 > > The requested number of buffers for queue \field{index} is returned in > > \field{max_num}. > >=20 > > +Since revision 3, \field{indirect_num} exists, which is supposed to > > reflect the +Queue Indirect Size (i.e. the maximum length of indirect > > descriptor tables) +supported by device for this queue. >=20 > It still depends on the feature flag, though. >=20 > Maybe >=20 > "If revision 2 or lower is set, struct vq_config_block extends up to > \field{max_num}. >=20 > If revision 3 or higher is set, struct vq_config_block extends to > \field{max_indirect_num}. If VIRTIO_RING_F_INDIRECT_SIZE is negotiated, > \field{indirect_max_num} contains the maximum Queue Indirect Size > (i.e. the maximum length of indirect descriptor tables) supported by the > device for this queue; otherwise, its contents are unpredictable." Maybe rather something like this instead: "Actual size of struct vq_config_block depends on the virtio-ccw revision. If revision 2 or lower is set, struct vq_config_block extends up to *including* \field{max_num}. If revision 3 or higher is set, struct vq_config_block extends up to *including* \field{max_indirect_num}. If VIRTIO_RING_F_INDIRECT_SIZE is=20 negotiated, \field{indirect_max_num} contains the maximum Queue Indirect Si= ze (i.e. the maximum length of indirect descriptor tables) supported by the device for this queue; otherwise, its contents are *undefined*." =20 > > + > >=20 > > Afterwards, CCW_CMD_SET_VQ is issued by the driver to inform the > > device about the location used for its queue. The transmitted > > structure is > >=20 > > @@ -2599,6 +2606,7 @@ \subsubsection{Configuring a > > Virtqueue}\label{sec:Virtio Transport Options / Vir>=20 > > be16 num; > > be64 driver; > > be64 device; > >=20 > > + be32 indirect_num; /* since virtio-ccw rev. 3 */ > >=20 > > }; > > \end{lstlisting} > >=20 > > @@ -2607,6 +2615,10 @@ \subsubsection{Configuring a > > Virtqueue}\label{sec:Virtio Transport Options / Vir>=20 > > available area and used area for queue \field{index}, respectively. Th= e > > actual virtqueue size (number of allocated buffers) is transmitted in > > \field{num}.>=20 > > +Since revision 3, \field{indirect_num} exists, which is supposed to > > reflect the +Queue Indirect Size (i.e. the maximum length of indirect > > descriptor tables) +supported by driver for this queue. >=20 > Similar to above: >=20 > "If revision 2 or lower is set, struct vq_info_block extends up to > \field{device}. >=20 > If revision 3 or higher is set, struct vq_info_block extends to > \field{indirect_num}. If VIRTIO_RING_F_INDIRECT_SIZE is negotiated, > the Queue Indirect Size (i.e. the maximum length of indirect descriptor > tables) supported by the driver for this queue is transmitted in > \field{indirect_num}." Ditto. > > + > >=20 > > \devicenormative{\paragraph}{Configuring a Virtqueue}{Virtio Transport > > Options / Virtio over channel I/O / Device Initialization / Configurin= g > > a Virtqueue} > > =20 > > \field{res0} is reserved and MUST be ignored by the device. >=20 > We should include a device normative statement: >=20 > "The device MUST NOT offer VIRTIO_RING_F_INDIRECT_SIZE, unless at least > revision 3 is set, and therefore \field{max_indirect_num} respectively > \field{indirect_num} are available." Oh, you are suggesting two different names for those two fields?=20 "max_indirect_num" vs. "indirect_num". If yes, why? Otherwise about adding that normative statement in general here: sure, make= s=20 sense. Best regards, Christian Schoenebeck This publicly archived list offers a means to provide input to the=0D OASIS Virtual I/O Device (VIRTIO) TC.=0D =0D In order to verify user consent to the Feedback License terms and=0D to minimize spam in the list archive, subscription is required=0D before posting.=0D =0D Subscribe: virtio-comment-subscribe@lists.oasis-open.org=0D Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org=0D List help: virtio-comment-help@lists.oasis-open.org=0D List archive: https://lists.oasis-open.org/archives/virtio-comment/=0D Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf= =0D List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lis= ts=0D Committee: https://www.oasis-open.org/committees/virtio/=0D Join OASIS: https://www.oasis-open.org/join/