diff options
| -rw-r--r-- | virtio-v1.0-wd01-part1-specification.txt | 24 |
1 files changed, 23 insertions, 1 deletions
diff --git a/virtio-v1.0-wd01-part1-specification.txt b/virtio-v1.0-wd01-part1-specification.txt index a4e4223..dd0faea 100644 --- a/virtio-v1.0-wd01-part1-specification.txt +++ b/virtio-v1.0-wd01-part1-specification.txt @@ -1292,7 +1292,29 @@ For notifying the host of virtqueue buffers, the guest unfortunately can't use a channel command (the asynchronous characteristics of channel I/O interact badly with the host block I/O backend). Instead, it uses a diagnose 0x500 call with subcode -3 specifying the queue. +3 specifying the queue, as follows: + ++------+-------------------+--------------+ +| GPR | Input Value | Output Value | ++------+-------------------+--------------+ ++------+-------------------+--------------+ +| 1 | 0x3 | | ++------+-------------------+--------------+ +| 2 | Subchannel ID | Host Cookie | ++------+-------------------+--------------+ +| 3 | Virtqueue number | | ++------+-------------------+--------------+ +| 4 | Host Cookie | | ++------+-------------------+--------------+ + +Host cookie is an optional per-virtqueue 64 bit value that can be +used by the hypervisor to speed up the notification execution. +For each notification, the output value is returned in GPR2 and +should be passed in GPR4 for the next notification: + + info->cookie = do_notify(schid, + virtqueue_get_queue_index(vq), + info->cookie); 2.3.3.3.3. Early printk for Virtio Consoles ------------------------------------------- |