Re: [Qemu-devel] [PATCH v2 5/5] virtio: add "use-started" property

[Yongji Xie]

On Wed, 5 Jun 2019 at 17:00, Greg Kurz <address@hidden> wrote:
>
> On Tue,  4 Jun 2019 15:34:59 +0800
> address@hidden wrote:
>
> > From: Xie Yongji <address@hidden>
> >
> > In order to avoid migration issues, we introduce a "use-started"
> > property to the base virtio device to indicate whether use
> > "started" flag or not. This property will be true by default and
> > set to false when machine type <= 4.0.1.
> >
> > Signed-off-by: Xie Yongji <address@hidden>
> > ---
> >  hw/block/vhost-user-blk.c  |  4 ++--
> >  hw/core/machine.c          |  4 +++-
> >  hw/virtio/virtio.c         | 21 ++++++++-------------
> >  include/hw/virtio/virtio.h | 21 +++++++++++++++++++++
> >  4 files changed, 34 insertions(+), 16 deletions(-)
> >
> > diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
> > index 9cb61336a6..85bc4017e7 100644
> > --- a/hw/block/vhost-user-blk.c
> > +++ b/hw/block/vhost-user-blk.c
> > @@ -191,7 +191,7 @@ static void vhost_user_blk_stop(VirtIODevice *vdev)
> >  static void vhost_user_blk_set_status(VirtIODevice *vdev, uint8_t status)
> >  {
> >      VHostUserBlk *s = VHOST_USER_BLK(vdev);
> > -    bool should_start = vdev->started;
> > +    bool should_start = virtio_device_started(vdev, status);
> >      int ret;
> >
> >      if (!vdev->vm_running) {
> > @@ -317,7 +317,7 @@ static int vhost_user_blk_connect(DeviceState *dev)
> >      }
> >
> >      /* restore vhost state */
> > -    if (vdev->started) {
> > +    if (virtio_device_started(vdev, vdev->status)) {
> >          ret = vhost_user_blk_start(vdev);
> >          if (ret < 0) {
> >              error_report("vhost-user-blk: vhost start failed: %s",
> > diff --git a/hw/core/machine.c b/hw/core/machine.c
> > index f1a0f45f9c..133c113ebf 100644
> > --- a/hw/core/machine.c
> > +++ b/hw/core/machine.c
> > @@ -24,7 +24,9 @@
> >  #include "hw/pci/pci.h"
> >  #include "hw/mem/nvdimm.h"
> >
> > -GlobalProperty hw_compat_4_0_1[] = {};
> > +GlobalProperty hw_compat_4_0_1[] = {
> > +    { "virtio-device", "use-started", "false" },
> > +};
> >  const size_t hw_compat_4_0_1_len = G_N_ELEMENTS(hw_compat_4_0_1);
>
> I'm discovering hw_compat_4_0_1, which seems to be only used by the
> pc-q35-4.0.1 machine type...
>

Oops, my mistake.

> >
> >  GlobalProperty hw_compat_4_0[] = {};
>
> Not sure if it's the way to go but the same line should at least be added
> here for all other machine types that use hw_compat_4_0[] eg. pseries-4.0
> and older, which are the ones I need this fix for.
>

I agree.

> Cc'ing core machine code maintainers for advice.
>
> > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> > index 3960619bd4..9af2e339af 100644
> > --- a/hw/virtio/virtio.c
> > +++ b/hw/virtio/virtio.c
> > @@ -1165,10 +1165,7 @@ int virtio_set_status(VirtIODevice *vdev, uint8_t 
> > val)
> >
> >      if ((vdev->status & VIRTIO_CONFIG_S_DRIVER_OK) !=
> >          (val & VIRTIO_CONFIG_S_DRIVER_OK)) {
> > -        vdev->started = val & VIRTIO_CONFIG_S_DRIVER_OK;
> > -        if (unlikely(vdev->start_on_kick && vdev->started)) {
> > -            vdev->start_on_kick = false;
> > -        }
> > +        virtio_set_started(vdev, val & VIRTIO_CONFIG_S_DRIVER_OK);
>
> virtio_set_started() takes a bool as second argument, so this should
> rather be !!(val & VIRTIO_CONFIG_S_DRIVER_OK) to avoid potential
> warnings from picky compilers.
>

Will fix it in v3.

> The rest looks good, but I'm wondering if this patch should be the first
> one in the series to narrow the range of commits where backward migration
> is broken.
>

It's OK to me.

Thanks,
Yongji