[Qemu-devel] [PATCH 2/3] virtio-blk: disable write cache if not negotiated

[Paolo Bonzini <pbonzini@redhat.com>]

If the guest does not support flushes, we should run in writethrough mode.
The setting is temporary until the next reset, so that for example the
BIOS will run in writethrough mode while Linux will run with a writeback
cache.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/virtio-blk.c | 14 ++++++++++++++
 1 file modificato, 14 inserzioni(+)

diff --git a/hw/virtio-blk.c b/hw/virtio-blk.c
index 9c12b61..36bfb12 100644
--- a/hw/virtio-blk.c
+++ b/hw/virtio-blk.c
@@ -542,6 +542,19 @@ static uint32_t virtio_blk_get_features(VirtIODevice *vdev, uint32_t features)
     return features;
 }
 
+static void virtio_blk_set_status(VirtIODevice *vdev, uint8_t status)
+{
+    VirtIOBlock *s = to_virtio_blk(vdev);
+    uint32_t features;
+
+    if (!(status & VIRTIO_CONFIG_S_DRIVER_OK)) {
+        return;
+    }
+
+    features = vdev->guest_features;
+    bdrv_set_enable_write_cache(s->bs, !!(features & (1 << VIRTIO_BLK_F_WCE)));
+}
+
 static void virtio_blk_save(QEMUFile *f, void *opaque)
 {
     VirtIOBlock *s = opaque;
@@ -622,6 +635,7 @@ VirtIODevice *virtio_blk_init(DeviceState *dev, VirtIOBlkConf *blk)
     s->vdev.get_config = virtio_blk_update_config;
     s->vdev.set_config = virtio_blk_set_config;
     s->vdev.get_features = virtio_blk_get_features;
+    s->vdev.set_status = virtio_blk_set_status;
     s->vdev.reset = virtio_blk_reset;
     s->bs = blk->conf.bs;
     s->conf = &blk->conf;
-- 
1.7.11.2