[PATCH 04/31] vdpa: Add vhost_svq_set_svq_kick_fd

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

This function allows the vhost-vdpa backend to override kick_fd.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 hw/virtio/vhost-shadow-virtqueue.h |  1 +
 hw/virtio/vhost-shadow-virtqueue.c | 45 ++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+)

diff --git a/hw/virtio/vhost-shadow-virtqueue.h b/hw/virtio/vhost-shadow-virtqueue.h
index 400effd9f2..a56ecfc09d 100644
--- a/hw/virtio/vhost-shadow-virtqueue.h
+++ b/hw/virtio/vhost-shadow-virtqueue.h
@@ -15,6 +15,7 @@
 
 typedef struct VhostShadowVirtqueue VhostShadowVirtqueue;
 
+void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int svq_kick_fd);
 const EventNotifier *vhost_svq_get_dev_kick_notifier(
                                               const VhostShadowVirtqueue *svq);
 
diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index bd87110073..21534bc94d 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -11,6 +11,7 @@
 #include "hw/virtio/vhost-shadow-virtqueue.h"
 
 #include "qemu/error-report.h"
+#include "qemu/main-loop.h"
 
 /* Shadow virtqueue to relay notifications */
 typedef struct VhostShadowVirtqueue {
@@ -18,8 +19,20 @@ typedef struct VhostShadowVirtqueue {
     EventNotifier hdev_kick;
     /* Shadow call notifier, sent to vhost */
     EventNotifier hdev_call;
+
+    /*
+     * Borrowed virtqueue's guest to host notifier.
+     * To borrow it in this event notifier allows to register on the event
+     * loop and access the associated shadow virtqueue easily. If we use the
+     * VirtQueue, we don't have an easy way to retrieve it.
+     *
+     * So shadow virtqueue must not clean it, or we would lose VirtQueue one.
+     */
+    EventNotifier svq_kick;
 } VhostShadowVirtqueue;
 
+#define INVALID_SVQ_KICK_FD -1
+
 /**
  * The notifier that SVQ will use to notify the device.
  */
@@ -29,6 +42,35 @@ const EventNotifier *vhost_svq_get_dev_kick_notifier(
     return &svq->hdev_kick;
 }
 
+/**
+ * Set a new file descriptor for the guest to kick SVQ and notify for avail
+ *
+ * @svq          The svq
+ * @svq_kick_fd  The new svq kick fd
+ */
+void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int svq_kick_fd)
+{
+    EventNotifier tmp;
+    bool check_old = INVALID_SVQ_KICK_FD !=
+                     event_notifier_get_fd(&svq->svq_kick);
+
+    if (check_old) {
+        event_notifier_set_handler(&svq->svq_kick, NULL);
+        event_notifier_init_fd(&tmp, event_notifier_get_fd(&svq->svq_kick));
+    }
+
+    /*
+     * event_notifier_set_handler already checks for guest's notifications if
+     * they arrive to the new file descriptor in the switch, so there is no
+     * need to explicitely check for them.
+     */
+    event_notifier_init_fd(&svq->svq_kick, svq_kick_fd);
+
+    if (!check_old || event_notifier_test_and_clear(&tmp)) {
+        event_notifier_set(&svq->hdev_kick);
+    }
+}
+
 /**
  * Creates vhost shadow virtqueue, and instruct vhost device to use the shadow
  * methods and file descriptors.
@@ -52,6 +94,9 @@ VhostShadowVirtqueue *vhost_svq_new(void)
         goto err_init_hdev_call;
     }
 
+    /* Placeholder descriptor, it should be deleted at set_kick_fd */
+    event_notifier_init_fd(&svq->svq_kick, INVALID_SVQ_KICK_FD);
+
     return g_steal_pointer(&svq);
 
 err_init_hdev_call:
-- 
2.27.0