Re: [Qemu-devel] [PATCHv4] net: delay freeing peer host device

[Michael S. Tsirkin]

On Wed, Oct 06, 2010 at 12:13:35PM -0500, Anthony Liguori wrote:
> On 10/06/2010 11:58 AM, Michael S. Tsirkin wrote:
> >On Wed, Oct 06, 2010 at 11:35:08AM -0500, Anthony Liguori wrote:
> >>On 10/06/2010 11:04 AM, Michael S. Tsirkin wrote:
> >>>With -netdev, virtio devices present offload
> >>>features to guest, depending on the backend used.
> >>>Thus, removing host netdev peer while guest is
> >>>active leads to guest-visible inconsistency and/or crashes.
> >>>
> >>>As a solution, while guest (NIC) peer device exists,
> >>>we prevent the host peer from being deleted.
> >>>This patch does this by adding peer_deleted flag in nic state:
> >>>if host device is going away while guest device
> >>>is around, set this flag and keep a shell of
> >>>the host device around for as long as guest device exists.
> >>>
> >>>The link is put down so all packets will get discarded.
> >>>
> >>>At the moment, management can detect that device deletion
> >>>is delayed by doing info net. As a next step, we shall add
> >>>commands that control hotplug/unplug without
> >>>removing the device, and an event to report that
> >>>guest has responded to the hotplug event.
> >>>
> >>>Signed-off-by: Michael S. Tsirkin<address@hidden>
> >>I don't think this is a very good idea.  Making netdev_del
> >>conditionally succeed is going to break management tools and is very
> >>non-intuitive.
> >>
> >>Regards,
> >>
> >>Anthony Liguori
> >But this is not what this does. With this patch netdev_del always
> >succeeds, and clears the device state leaving just an empty shell around.
> >The shell goes away together with the NIC.
> 
> Sorry, I confused myself.  I'm a little confused by the statement:
> 
> "At the moment, management can detect that device deletion is delayed by 
> doing info net."
> 
> Is this still the case since you remove the netdev from the list?
> 
> Regards,
> 
> Anthony Liguori

The device in question here is the PCI device removed with device_del.
The unplug there is asynchronous and I did not change this.

> 
> >>>---
> >>>
> >>>  Changes from v3:
> >>>    make sure ->cleanup is called for NICs
> >>>  Changes from v2:
> >>>    fix crash on repeated netdev_del
> >>>
> >>>  net.c |   49 ++++++++++++++++++++++++++++++++++++++++++-------
> >>>  net.h |    1 +
> >>>  2 files changed, 43 insertions(+), 7 deletions(-)
> >>>
> >>>diff --git a/net.c b/net.c
> >>>index 3d0fde7..ed74c7f 100644
> >>>--- a/net.c
> >>>+++ b/net.c
> >>>@@ -281,29 +281,64 @@ NICState *qemu_new_nic(NetClientInfo *info,
> >>>      return nic;
> >>>  }
> >>>
> >>>-void qemu_del_vlan_client(VLANClientState *vc)
> >>>+static void qemu_cleanup_vlan_client(VLANClientState *vc)
> >>>  {
> >>>      if (vc->vlan) {
> >>>          QTAILQ_REMOVE(&vc->vlan->clients, vc, next);
> >>>      } else {
> >>>-        if (vc->send_queue) {
> >>>-            qemu_del_net_queue(vc->send_queue);
> >>>-        }
> >>>          QTAILQ_REMOVE(&non_vlan_clients, vc, next);
> >>>-        if (vc->peer) {
> >>>-            vc->peer->peer = NULL;
> >>>-        }
> >>>      }
> >>>
> >>>      if (vc->info->cleanup) {
> >>>          vc->info->cleanup(vc);
> >>>      }
> >>>+}
> >>>
> >>>+static void qemu_free_vlan_client(VLANClientState *vc)
> >>>+{
> >>>+    if (!vc->vlan) {
> >>>+        if (vc->send_queue) {
> >>>+            qemu_del_net_queue(vc->send_queue);
> >>>+        }
> >>>+        if (vc->peer) {
> >>>+            vc->peer->peer = NULL;
> >>>+        }
> >>>+    }
> >>>      qemu_free(vc->name);
> >>>      qemu_free(vc->model);
> >>>      qemu_free(vc);
> >>>  }
> >>>
> >>>+void qemu_del_vlan_client(VLANClientState *vc)
> >>>+{
> >>>+    /* If there is a peer NIC, delete and cleanup client, but do not 
> >>>free. */
> >>>+    if (!vc->vlan&&   vc->peer&&   vc->peer->info->type == 
> >>>NET_CLIENT_TYPE_NIC) {
> >>>+        NICState *nic = DO_UPCAST(NICState, nc, vc->peer);
> >>>+        if (nic->peer_deleted) {
> >>>+            return;
> >>>+        }
> >>>+        nic->peer_deleted = true;
> >>>+        /* Let NIC know peer is gone. */
> >>>+        vc->peer->link_down = true;
> >>>+        if (vc->peer->info->link_status_changed) {
> >>>+            vc->peer->info->link_status_changed(vc->peer);
> >>>+        }
> >>>+        qemu_cleanup_vlan_client(vc);
> >>>+        return;
> >>>+    }
> >>>+
> >>>+    /* If this is a peer NIC and peer has already been deleted, free it 
> >>>now. */
> >>>+    if (!vc->vlan&&   vc->peer&&   vc->info->type == NET_CLIENT_TYPE_NIC) 
> >>>{
> >>>+        NICState *nic = DO_UPCAST(NICState, nc, vc);
> >>>+        if (nic->peer_deleted) {
> >>>+            qemu_free_vlan_client(vc->peer);
> >>>+        }
> >>>+    }
> >>>+
> >>>+    qemu_cleanup_vlan_client(vc);
> >>>+    qemu_free_vlan_client(vc);
> >>>+}
> >>>+
> >>>  VLANClientState *
> >>>  qemu_find_vlan_client_by_name(Monitor *mon, int vlan_id,
> >>>                                const char *client_str)
> >>>diff --git a/net.h b/net.h
> >>>index 518cf9c..44c31a9 100644
> >>>--- a/net.h
> >>>+++ b/net.h
> >>>@@ -72,6 +72,7 @@ typedef struct NICState {
> >>>      VLANClientState nc;
> >>>      NICConf *conf;
> >>>      void *opaque;
> >>>+    bool peer_deleted;
> >>>  } NICState;
> >>>
> >>>  struct VLANState {