[PATCH v3 1/2] virtio-blk: Add the control virtqueue

[Linlin Zhang <linlin.zhang@oss.qualcomm.com>]

From: linlzhan <linlin.zhang@oss.qualcomm.com>

Add VIRTIO_BLK_F_CTRL_VQ to advertise control virtqueue support.

Define the control virtqueue location, driver queue discovery,
and common control request buffer layout. This provides a
standard framework for block-device control commands.

Signed-off-by: linlzhan <linlin.zhang@oss.qualcomm.com>
---
 device-types/blk/description.tex | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/device-types/blk/description.tex b/device-types/blk/description.tex
index 3b3a4e7..9bfdc4a 100644
--- a/device-types/blk/description.tex
+++ b/device-types/blk/description.tex
@@ -13,11 +13,16 @@ \subsection{Virtqueues}\label{sec:Device Types / Block Device / Virtqueues}
 \item[0] requestq1
 \item[\ldots]
 \item[N-1] requestqN
+\item[N] controlq, if VIRTIO_BLK_F_CTRL_VQ is negotiated
 \end{description}
 
  N=1 if VIRTIO_BLK_F_MQ is not negotiated, otherwise N is set by
  \field{num_queues}.
 
+If VIRTIO_BLK_F_CTRL_VQ is negotiated, the control virtqueue is appended
+after the request virtqueues. The control virtqueue is reserved for control
+requests defined by this specification.
+
 \subsection{Feature bits}\label{sec:Device Types / Block Device / Feature bits}
 
 \begin{description}
@@ -73,6 +78,8 @@ \subsection{Feature bits}\label{sec:Device Types / Block Device / Feature bits}
     VIRTIO_BLK_REQ_FLAG_OUT_FUA flag in the \field{flags} bitfield of the
     \field{virtio_blk_req} structure for VIRTIO_BLK_T_OUT requests.
 
+\item[VIRTIO_BLK_F_CTRL_VQ (22)] Device supports a control virtqueue.
+
 \end{description}
 
 \subsubsection{Legacy Interface: Feature bits}\label{sec:Device Types / Block Device / Feature bits / Legacy Interface: Feature bits}
@@ -274,6 +281,9 @@ \subsection{Device Initialization}\label{sec:Device Types / Block Device / Devic
 \item If the VIRTIO_BLK_F_MQ feature is negotiated, \field{num_queues} field
     can be read to determine the number of queues.
 
+\item If the VIRTIO_BLK_F_CTRL_VQ feature is negotiated, the driver MUST
+    identify the control virtqueue as queue N, after all request virtqueues.
+
 \item If the VIRTIO_BLK_F_SECURE_ERASE feature is negotiated,
     \field{max_secure_erase_sectors} and \field{max_secure_erase_seg} can be read
     to determine the maximum secure erase sectors and maximum number of
@@ -327,6 +337,10 @@ \subsection{Device Initialization}\label{sec:Device Types / Block Device / Devic
 The driver MUST NOT negotiate VIRTIO_BLK_F_REQ_FLAGS_OUT_FUA without
 VIRTIO_BLK_F_REQ_FLAGS.
 
+If the VIRTIO_BLK_F_CTRL_VQ feature is negotiated, the driver MUST NOT submit
+any request to the control virtqueue unless the request is defined by this
+specification.
+
 \devicenormative{\subsubsection}{Device Initialization}{Device Types / Block Device / Device Initialization}
 
 Devices SHOULD always offer VIRTIO_BLK_F_FLUSH, and MUST offer it
@@ -454,6 +468,11 @@ \subsection{Device Operation}\label{sec:Device Types / Block Device / Device Ope
 };
 \end{lstlisting}
 
+Control virtqueue requests consist of a type field in an output buffer,
+followed by an optional command-specific output buffer, an optional
+command-specific input buffer, and a status byte in an input buffer. The
+type field and status byte MUST each be in their own buffer.
+
 The type of the request is either a read (VIRTIO_BLK_T_IN), a write
 (VIRTIO_BLK_T_OUT), a discard (VIRTIO_BLK_T_DISCARD), a write zeroes
 (VIRTIO_BLK_T_WRITE_ZEROES), a flush (VIRTIO_BLK_T_FLUSH), a get device ID
-- 
2.34.1