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[Qemu-devel] [PATCH v2] virtio: ring sizes vs. reset


From: Cornelia Huck
Subject: [Qemu-devel] [PATCH v2] virtio: ring sizes vs. reset
Date: Thu, 10 Sep 2015 13:48:24 +0200

We allow guests to change the size of the virtqueue rings by supplying
a number of buffers that is different from the number of buffers the
device was initialized with. Current code has some problems, however,
since reset does not reset the ringsizes to the default values (as this
is not saved anywhere).

Let's extend the core code to keep track of the default ringsizes and
migrate them once the guest changed them for any of the virtqueues
for a device.

Signed-off-by: Cornelia Huck <address@hidden>
---

v1->v2: lose the changed ringsize tracking, calculate directly before
        migrating

---
 hw/virtio/virtio.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 788b556..458fcbe 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -60,6 +60,7 @@ typedef struct VRingUsed
 typedef struct VRing
 {
     unsigned int num;
+    unsigned int num_default;
     unsigned int align;
     hwaddr desc;
     hwaddr avail;
@@ -633,6 +634,7 @@ void virtio_reset(void *opaque)
         vdev->vq[i].signalled_used = 0;
         vdev->vq[i].signalled_used_valid = false;
         vdev->vq[i].notification = true;
+        vdev->vq[i].vring.num = vdev->vq[i].vring.num_default;
     }
 }
 
@@ -964,6 +966,7 @@ VirtQueue *virtio_add_queue(VirtIODevice *vdev, int 
queue_size,
         abort();
 
     vdev->vq[i].vring.num = queue_size;
+    vdev->vq[i].vring.num_default = queue_size;
     vdev->vq[i].vring.align = VIRTIO_PCI_VRING_ALIGN;
     vdev->vq[i].handle_output = handle_output;
 
@@ -977,6 +980,7 @@ void virtio_del_queue(VirtIODevice *vdev, int n)
     }
 
     vdev->vq[n].vring.num = 0;
+    vdev->vq[n].vring.num_default = 0;
 }
 
 void virtio_irq(VirtQueue *vq)
@@ -1056,6 +1060,19 @@ static bool virtio_virtqueue_needed(void *opaque)
     return virtio_host_has_feature(vdev, VIRTIO_F_VERSION_1);
 }
 
+static bool virtio_ringsize_needed(void *opaque)
+{
+    VirtIODevice *vdev = opaque;
+    int i;
+
+    for (i = 0; i < VIRTIO_QUEUE_MAX; i++) {
+        if (vdev->vq[i].vring.num != vdev->vq[i].vring.num_default) {
+            return true;
+        }
+    }
+    return false;
+}
+
 static void put_virtqueue_state(QEMUFile *f, void *pv, size_t size)
 {
     VirtIODevice *vdev = pv;
@@ -1104,6 +1121,52 @@ static const VMStateDescription 
vmstate_virtio_virtqueues = {
     }
 };
 
+static void put_ringsize_state(QEMUFile *f, void *pv, size_t size)
+{
+    VirtIODevice *vdev = pv;
+    int i;
+
+    for (i = 0; i < VIRTIO_QUEUE_MAX; i++) {
+        qemu_put_be32(f, vdev->vq[i].vring.num_default);
+    }
+}
+
+static int get_ringsize_state(QEMUFile *f, void *pv, size_t size)
+{
+    VirtIODevice *vdev = pv;
+    int i;
+
+    for (i = 0; i < VIRTIO_QUEUE_MAX; i++) {
+        vdev->vq[i].vring.num_default = qemu_get_be32(f);
+    }
+    return 0;
+}
+
+static VMStateInfo vmstate_info_ringsize = {
+    .name = "ringsize_state",
+    .get = get_ringsize_state,
+    .put = put_ringsize_state,
+};
+
+static const VMStateDescription vmstate_virtio_ringsize = {
+    .name = "virtio/ringsize",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .needed = &virtio_ringsize_needed,
+    .fields = (VMStateField[]) {
+        {
+            .name         = "ringsize",
+            .version_id   = 0,
+            .field_exists = NULL,
+            .size         = 0,
+            .info         = &vmstate_info_ringsize,
+            .flags        = VMS_SINGLE,
+            .offset       = 0,
+        },
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 static const VMStateDescription vmstate_virtio_device_endian = {
     .name = "virtio/device_endian",
     .version_id = 1,
@@ -1138,6 +1201,7 @@ static const VMStateDescription vmstate_virtio = {
         &vmstate_virtio_device_endian,
         &vmstate_virtio_64bit_features,
         &vmstate_virtio_virtqueues,
+        &vmstate_virtio_ringsize,
         NULL
     }
 };
-- 
2.3.8




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