[PATCH] virtio-ccw: split descriptor/available/used rings (alternate)

Extend vq_info_block so that the addresses for descriptor table,
available ring and used ring may be transmitted independently.

Depending upon the selected revision, post a command reject instead
of a channel program check if the driver uses the legacy format
and length checks are suppressed.

VIRTIO-23

Signed-off-by: Cornelia Huck <>

---

This is an alternate approach, extending the exiting structure instead
of creating a different layout. I'm not 100% sure whether doing a
command reject instead of a channel program check in case of a short
buffer is the right approach, though. Doing a channel program check
would probably cover that error just as well, and we could resolve
VIRTIO-23 independently of VIRTIO-42.
---
 virtio-v1.0-wd01-part1-specification.txt |   32 +++++++++++++++++++++++++++---
 1 file changed, 29 insertions(+), 3 deletions(-)

diff --git a/virtio-v1.0-wd01-part1-specification.txt b/virtio-v1.0-wd01-part1-specification.txt
index ae646db..baff12f 100644
--- a/virtio-v1.0-wd01-part1-specification.txt
+++ b/virtio-v1.0-wd01-part1-specification.txt
@@ -1642,15 +1642,41 @@ host about the location used for its queue. The transmitted
 structure is
 
 struct vq_info_block {
+	__u64 desc;
+	__u32 res0;
+	__u16 index;
+	__u16 num;
+	__u64 avail;
+	__u64 used;
+} __attribute__ ((packed));
+
+desc, avail and used contain the guest addresses for the descriptor table,
+available ring and used ring for queue index, respectively. The actual
+virtqueue size (number of allocated buffers) is transmitted in num.
+res0 is reserved and must contain 0; otherwise, the device MUST post a
+unit check with command reject.
+
+If the revision selected by the driver is at least 1, the device MUST
+post a unit check with command reject if the transmitted data is between
+16 and 31 bytes if the driver suppressed incorrect length indication
+for the channel command. Otherwise, the normal conditions for handling
+incorrect data lenghts apply.
+
+2.3.3.2.2.1. Legacy Interface: A Note on Configuring a Virtqueue
+----------------------------------------------------------------
+
+For a legacy driver or for a driver that selected revision 0,
+CCW_CMD_SET_VQ uses the following communication block:
+
+struct vq_info_block_legacy {
 	__u64 queue;
 	__u32 align;
 	__u16 index;
 	__u16 num;
 } __attribute__ ((packed));
 
-queue contains the guest address for queue index. The actual
-number of allocated buffers is transmitted in num and their
-alignment in align.
+queue contains the guest address for queue index, num the number of buffers
+and align the alignment.
 
 100.3.3.2.2.  Virtqueue Layout
 ------------------------------
-- 
1.7.9.5