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 C81A49866E6 for ; Thu, 17 Mar 2022 14:12:51 +0000 (UTC) From: Cornelia Huck In-Reply-To: <3040881.qp741xram0@silver> References: <4735344.EBYxvr1mta@silver> <3040881.qp741xram0@silver> Date: Thu, 17 Mar 2022 15:12:42 +0100 Message-ID: <87cziksm5h.fsf@redhat.com> MIME-Version: 1.0 Subject: [virtio-comment] Re: [PATCH v3 4/4] Add CCW configuration field "indirect_num" Content-Type: text/plain To: Christian Schoenebeck , virtio-comment@lists.oasis-open.org Cc: Stefan Hajnoczi , Greg Kurz , Dominique Martinet , Halil Pasic List-ID: 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. > > Bump CCW virtio revision to 3 and make the existence of this new > field "indirect_num" dependant on revision 3. > > Fixes: https://github.com/oasis-tcs/virtio-spec/issues/122 > Signed-off-by: Christian Schoenebeck > --- > content.tex | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > (...) > @@ -2581,12 +2583,17 @@ \subsubsection{Configuring a Virtqueue}\label{sec:Virtio Transport Options / Vir > struct vq_config_block { > be16 index; > be16 max_num; > + be32 indirect_num; /* since virtio-ccw rev. 3 */ Maybe make it max_indirect_num (to mirror max_num?) > }; > \end{lstlisting} > > The requested number of buffers for queue \field{index} is returned in > \field{max_num}. > > +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. It still depends on the feature flag, though. Maybe "If revision 2 or lower is set, struct vq_config_block extends up to \field{max_num}. 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." > + > 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 > @@ -2599,6 +2606,7 @@ \subsubsection{Configuring a Virtqueue}\label{sec:Virtio Transport Options / Vir > be16 num; > be64 driver; > be64 device; > + be32 indirect_num; /* since virtio-ccw rev. 3 */ > }; > \end{lstlisting} > > @@ -2607,6 +2615,10 @@ \subsubsection{Configuring a Virtqueue}\label{sec:Virtio Transport Options / Vir > available area and used area for queue \field{index}, respectively. The actual > virtqueue size (number of allocated buffers) is transmitted in \field{num}. > > +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. Similar to above: "If revision 2 or lower is set, struct vq_info_block extends up to \field{device}. 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}." > + > \devicenormative{\paragraph}{Configuring a Virtqueue}{Virtio Transport Options / Virtio over channel I/O / Device Initialization / Configuring a Virtqueue} > > \field{res0} is reserved and MUST be ignored by the device. We should include a device normative statement: "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." This publicly archived list offers a means to provide input to the OASIS Virtual I/O Device (VIRTIO) TC. In order to verify user consent to the Feedback License terms and to minimize spam in the list archive, subscription is required before posting. Subscribe: virtio-comment-subscribe@lists.oasis-open.org Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org List help: virtio-comment-help@lists.oasis-open.org List archive: https://lists.oasis-open.org/archives/virtio-comment/ Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lists Committee: https://www.oasis-open.org/committees/virtio/ Join OASIS: https://www.oasis-open.org/join/