[RFC PATCH v4 02/20] virtio-net: Honor VIRTIO_CONFIG_S_DEVICE_STOPPED

["Eugenio Pérez" <eperezma@redhat.com>]

So the guest can stop and start net device. It freely implements the RFC
https://lists.oasis-open.org/archives/virtio-comment/202012/msg00027.html

To stop (as "pause") the device is required to migrate status and vring
addresses between device and SVQ. Once the device is stopped, the driver
can request avail_idx, so it can be assigned to SVQ.

This is a WIP commit: as with VIRTIO_F_QUEUE_STATE, is introduced in
virtio_config.h before of even proposing for the kernel, with no feature
flag, and, with no checking in the device. It also needs a modified
vp_vdpa driver that supports to set and retrieve status.

For virtio-net with qemu device there is no need to restore avail
state: Since every tx and rx operation is entirely done in BQL
regarding virtio, it would be enough with restore last_avail_idx with
used_idx. Doing this way test the vq state part of the rest of the
series.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 include/standard-headers/linux/virtio_config.h | 2 ++
 hw/net/virtio-net.c                            | 6 ++++--
 hw/virtio/virtio-pci.c                         | 7 +++++--
 3 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/include/standard-headers/linux/virtio_config.h b/include/standard-headers/linux/virtio_config.h
index 59fad3eb45..b3f6b1365d 100644
--- a/include/standard-headers/linux/virtio_config.h
+++ b/include/standard-headers/linux/virtio_config.h
@@ -40,6 +40,8 @@
 #define VIRTIO_CONFIG_S_DRIVER_OK	4
 /* Driver has finished configuring features */
 #define VIRTIO_CONFIG_S_FEATURES_OK	8
+/* Device is stopped */
+#define VIRTIO_CONFIG_S_DEVICE_STOPPED 32
 /* Device entered invalid state, driver must reset it */
 #define VIRTIO_CONFIG_S_NEEDS_RESET	0x40
 /* We've given up on this device. */
diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index bd7958b9f0..e8f55cdeba 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -198,6 +198,7 @@ static bool virtio_net_started(VirtIONet *n, uint8_t status)
 {
     VirtIODevice *vdev = VIRTIO_DEVICE(n);
     return (status & VIRTIO_CONFIG_S_DRIVER_OK) &&
+        (!(status & VIRTIO_CONFIG_S_DEVICE_STOPPED)) &&
         (n->status & VIRTIO_NET_S_LINK_UP) && vdev->vm_running;
 }
 
@@ -385,7 +386,7 @@ static void virtio_net_set_status(struct VirtIODevice *vdev, uint8_t status)
             qemu_flush_queued_packets(ncs);
         }
 
-        if (!q->tx_waiting) {
+        if (!q->tx_waiting && !(status & VIRTIO_CONFIG_S_DEVICE_STOPPED)) {
             continue;
         }
 
@@ -1503,7 +1504,8 @@ static bool virtio_net_can_receive(NetClientState *nc)
     }
 
     if (!virtio_queue_ready(q->rx_vq) ||
-        !(vdev->status & VIRTIO_CONFIG_S_DRIVER_OK)) {
+        !(vdev->status & VIRTIO_CONFIG_S_DRIVER_OK) ||
+        vdev->status == VIRTIO_CONFIG_S_DEVICE_STOPPED) {
         return false;
     }
 
diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index 6f30118c4e..9ed0f62222 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -326,13 +326,15 @@ static void virtio_ioport_write(void *opaque, uint32_t addr, uint32_t val)
         }
         break;
     case VIRTIO_PCI_STATUS:
-        if (!(val & VIRTIO_CONFIG_S_DRIVER_OK)) {
+        if (!(val & VIRTIO_CONFIG_S_DRIVER_OK) ||
+            val & VIRTIO_CONFIG_S_DEVICE_STOPPED) {
             virtio_pci_stop_ioeventfd(proxy);
         }
 
         virtio_set_status(vdev, val & 0xFF);
 
-        if (val & VIRTIO_CONFIG_S_DRIVER_OK) {
+        if (val & VIRTIO_CONFIG_S_DRIVER_OK &&
+            !(val & VIRTIO_CONFIG_S_DEVICE_STOPPED)) {
             virtio_pci_start_ioeventfd(proxy);
         }
 
@@ -1303,6 +1305,7 @@ static void virtio_pci_common_write(void *opaque, hwaddr addr,
                        proxy->vqs[vdev->queue_sel].used[0]);
             virtio_queue_set_last_avail_idx(vdev, vdev->queue_sel,
                         proxy->vqs[vdev->queue_sel].state);
+            virtio_queue_update_used_idx(vdev, vdev->queue_sel);
             proxy->vqs[vdev->queue_sel].enabled = 1;
         } else {
             virtio_error(vdev, "wrong value for queue_enable %"PRIx64, val);
-- 
2.27.0