On 09/19/2013 10:48 AM, Paolo Bonzini wrote: > The following sequence happens:
> Hence, whenever the guest is reset, the cache mode of the disk should
> be reset to whatever was specified in the "-drive" option. With this
> change, the Linux virtio-blk driver finds that writeback caching is
> enabled, and tells the block layer to send cache flush commands
> appropriately.
>
> Reported-by: Rusty Russell <ru...@au1.ibm.com
> Cc: qemu-sta...@nongnu.org
> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
> ---
> hw/block/virtio-blk.c | 8 ++++++--
> include/hw/virtio/virtio-blk.h | 1 +
> 2 files changed, 7 insertions(+), 2 deletions(-)
Reviewed-by: Eric Blake <ebl...@redhat.com>
>
> features = vdev->guest_features;
> - bdrv_set_enable_write_cache(s->bs, !!(features & (1 <<
> VIRTIO_BLK_F_WCE)));
> + if (!(features & (1 << VIRTIO_BLK_F_CONFIG_WCE))) {
> + bdrv_set_enable_write_cache(s->bs,
> + !!(features & (1 << VIRTIO_BLK_F_WCE)));
> + }
> }
>
> static void virtio_blk_save(QEMUFile *f, void *opaque)
> @@ -674,6 +678,7 @@ static int virtio_blk_device_init(VirtIODevice *vdev)
> }
>
> blkconf_serial(&blk->conf, &blk->serial);
> + s->original_wce = bdrv_enable_write_cache(blk->conf.bs);
At first, I was worried that this does 'bool = int', and whether that
was correct in all cases. But looking further, bdrv_enable_write_cache
merely returns bs->enable_write_cache (also an int), but that all
assignments to bs->enable_write_cache are careful to only assign 0 or 1.
A followup patch that changes the types to bool might be in order, but
doesn't invalidate this patch.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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