[Qemu-devel] Re: [PATCH master/0.14 2/2] virtio-serial: Add older machine compat property for flow control

[Michael S. Tsirkin]

On Mon, Feb 07, 2011 at 08:47:11AM -0700, Alex Williamson wrote:
> On Thu, 2011-02-03 at 11:47 +0530, Amit Shah wrote:
> > Add a compat property for older machine types.  When this is used (via
> > -M pc-0.13, for example), the new flow control mechanisms will not be
> > used.  This is done to keep migration from a machine started with older
> > type on a pc-0.14+ qemu to an older machine working.
> > 
> > The property is named 'flow_control' and defaults to on.
> > 
> > Reported-by: Alex Williamson <address@hidden>
> > Signed-off-by: Amit Shah <address@hidden>
> > ---
> >  hw/pc_piix.c           |   16 ++++++++++
> >  hw/virtio-pci.c        |    2 +
> >  hw/virtio-serial-bus.c |   77 
> > +++++++++++++++++++++++++++++++++++++++++-------
> >  hw/virtio-serial.h     |   12 +++++++
> >  4 files changed, 96 insertions(+), 11 deletions(-)
> 
> Acked-by: Alex Williamson <address@hidden>

Before merging this, I think we need to have a discussion on
cross version migration. Started a separate thread for that.

> > diff --git a/hw/pc_piix.c b/hw/pc_piix.c
> > index 7b74473..05b0449 100644
> > --- a/hw/pc_piix.c
> > +++ b/hw/pc_piix.c
> > @@ -243,6 +243,10 @@ static QEMUMachine pc_machine_v0_13 = {
> >              .driver   = "PCI",
> >              .property = "command_serr_enable",
> >              .value    = "off",
> > +        },{
> > +            .driver   = "virtio-serial-pci",
> > +            .property = "flow_control",
> > +            .value    = stringify(0),
> >          },
> >          { /* end of list */ }
> >      },
> > @@ -263,6 +267,10 @@ static QEMUMachine pc_machine_v0_12 = {
> >              .property = "vectors",
> >              .value    = stringify(0),
> >          },{
> > +            .driver   = "virtio-serial-pci",
> > +            .property = "flow_control",
> > +            .value    = stringify(0),
> > +        },{
> >              .driver   = "VGA",
> >              .property = "rombar",
> >              .value    = stringify(0),
> > @@ -298,6 +306,10 @@ static QEMUMachine pc_machine_v0_11 = {
> >              .property = "vectors",
> >              .value    = stringify(0),
> >          },{
> > +            .driver   = "virtio-serial-pci",
> > +            .property = "flow_control",
> > +            .value    = stringify(0),
> > +        },{
> >              .driver   = "ide-drive",
> >              .property = "ver",
> >              .value    = "0.11",
> > @@ -341,6 +353,10 @@ static QEMUMachine pc_machine_v0_10 = {
> >              .property = "vectors",
> >              .value    = stringify(0),
> >          },{
> > +            .driver   = "virtio-serial-pci",
> > +            .property = "flow_control",
> > +            .value    = stringify(0),
> > +        },{
> >              .driver   = "virtio-net-pci",
> >              .property = "vectors",
> >              .value    = stringify(0),
> > diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
> > index 952b5d2..530ce9d 100644
> > --- a/hw/virtio-pci.c
> > +++ b/hw/virtio-pci.c
> > @@ -904,6 +904,8 @@ static PCIDeviceInfo virtio_info[] = {
> >              DEFINE_VIRTIO_COMMON_FEATURES(VirtIOPCIProxy, host_features),
> >              DEFINE_PROP_UINT32("max_ports", VirtIOPCIProxy,
> >                                 serial.max_virtserial_ports, 31),
> > +            DEFINE_PROP_UINT32("flow_control", VirtIOPCIProxy,
> > +                               serial.flow_control, 1),
> >              DEFINE_PROP_END_OF_LIST(),
> >          },
> >          .qdev.reset = virtio_pci_reset,
> > diff --git a/hw/virtio-serial-bus.c b/hw/virtio-serial-bus.c
> > index 1753785..f681646 100644
> > --- a/hw/virtio-serial-bus.c
> > +++ b/hw/virtio-serial-bus.c
> > @@ -49,6 +49,8 @@ struct VirtIOSerial {
> >      uint32_t *ports_map;
> >  
> >      struct virtio_console_config config;
> > +
> > +    bool flow_control;
> >  };
> >  
> >  static VirtIOSerialPort *find_port_by_id(VirtIOSerial *vser, uint32_t id)
> > @@ -123,12 +125,46 @@ static void discard_vq_data(VirtQueue *vq, 
> > VirtIODevice *vdev)
> >      virtio_notify(vdev, vq);
> >  }
> >  
> > +static void do_flush_queued_data_no_flow_control(VirtIOSerialPort *port,
> > +                                                 VirtQueue *vq,
> > +                                                 VirtIODevice *vdev)
> > +{
> > +    VirtQueueElement elem;
> > +
> > +    while (!port->throttled && virtqueue_pop(vq, &elem)) {
> > +        uint8_t *buf;
> > +        size_t ret, buf_size;
> > +
> > +        buf_size = iov_size(elem.out_sg, elem.out_num);
> > +        buf = qemu_malloc(buf_size);
> > +        ret = iov_to_buf(elem.out_sg, elem.out_num, buf, 0, buf_size);
> > +
> > +        /*
> > +         * have_data has been modified to return the number of bytes
> > +         * successfully consumed.  We can't act upon that information
> > +         * in the no-flow-control implementation, so we'll discard it
> > +         * here.  No callers currently use flow control, but they
> > +         * should take this into account for backward compatibility.
> > +         */
> > +        port->info->have_data(port, buf, ret);
> > +        qemu_free(buf);
> > +
> > +        virtqueue_push(vq, &elem, 0);
> > +    }
> > +    virtio_notify(vdev, vq);
> > +}
> > +
> >  static void do_flush_queued_data(VirtIOSerialPort *port, VirtQueue *vq,
> >                                   VirtIODevice *vdev)
> >  {
> >      assert(port);
> >      assert(virtio_queue_ready(vq));
> >  
> > +    if (!virtio_serial_flow_control_enabled(port)) {
> > +        do_flush_queued_data_no_flow_control(port, vq, vdev);
> > +        return;
> > +    }
> > +
> >      while (!port->throttled) {
> >          unsigned int i;
> >  
> > @@ -296,6 +332,15 @@ void virtio_serial_throttle_port(VirtIOSerialPort 
> > *port, bool throttle)
> >      flush_queued_data(port);
> >  }
> >  
> > +bool virtio_serial_flow_control_enabled(VirtIOSerialPort *port)
> > +{
> > +    if (!port) {
> > +        return false;
> > +    }
> > +
> > +    return port->vser->flow_control;
> > +}
> > +
> >  /* Guest wants to notify us of some event */
> >  static void handle_control_message(VirtIOSerial *vser, void *buf, size_t 
> > len)
> >  {
> > @@ -533,17 +578,19 @@ static void virtio_serial_save(QEMUFile *f, void 
> > *opaque)
> >          qemu_put_byte(f, port->guest_connected);
> >          qemu_put_byte(f, port->host_connected);
> >  
> > -   elem_popped = 0;
> > -        if (port->elem.out_num) {
> > -            elem_popped = 1;
> > -        }
> > -        qemu_put_be32s(f, &elem_popped);
> > -        if (elem_popped) {
> > -            qemu_put_be32s(f, &port->iov_idx);
> > -            qemu_put_be64s(f, &port->iov_offset);
> > +        if (virtio_serial_flow_control_enabled(port)) {
> > +            elem_popped = 0;
> > +            if (port->elem.out_num) {
> > +                elem_popped = 1;
> > +            }
> > +            qemu_put_be32s(f, &elem_popped);
> > +            if (elem_popped) {
> > +                qemu_put_be32s(f, &port->iov_idx);
> > +                qemu_put_be64s(f, &port->iov_offset);
> >  
> > -            qemu_put_buffer(f, (unsigned char *)&port->elem,
> > -                            sizeof(port->elem));
> > +                qemu_put_buffer(f, (unsigned char *)&port->elem,
> > +                                sizeof(port->elem));
> > +            }
> >          }
> >      }
> >  }
> > @@ -816,6 +863,7 @@ VirtIODevice *virtio_serial_init(DeviceState *dev, 
> > virtio_serial_conf *conf)
> >      VirtIOSerial *vser;
> >      VirtIODevice *vdev;
> >      uint32_t i, max_supported_ports;
> > +    unsigned int savevm_ver;
> >  
> >      if (!conf->max_virtserial_ports)
> >          return NULL;
> > @@ -881,11 +929,18 @@ VirtIODevice *virtio_serial_init(DeviceState *dev, 
> > virtio_serial_conf *conf)
> >  
> >      vser->qdev = dev;
> >  
> > +    vser->flow_control = true;
> > +    savevm_ver = 3;
> > +    if (!conf->flow_control) {
> > +        vser->flow_control = false;
> > +        savevm_ver = 2;
> > +    }
> > +
> >      /*
> >       * Register for the savevm section with the virtio-console name
> >       * to preserve backward compat
> >       */
> > -    register_savevm(dev, "virtio-console", -1, 3, virtio_serial_save,
> > +    register_savevm(dev, "virtio-console", -1, savevm_ver, 
> > virtio_serial_save,
> >                      virtio_serial_load, vser);
> >  
> >      return vdev;
> > diff --git a/hw/virtio-serial.h b/hw/virtio-serial.h
> > index de624c3..57d2dee 100644
> > --- a/hw/virtio-serial.h
> > +++ b/hw/virtio-serial.h
> > @@ -48,6 +48,13 @@ struct virtio_console_control {
> >  struct virtio_serial_conf {
> >      /* Max. number of ports we can have for a the virtio-serial device */
> >      uint32_t max_virtserial_ports;
> > +
> > +    /*
> > +     * Should this device behave the way it did in prior to pc-0.14
> > +     * (ie. no flow control)?  This will be necessary to allow
> > +     * migrations from a pre-0.14-machine type to older qemu code
> > +     */
> > +    uint32_t flow_control;
> >  };
> >  
> >  /* Some events for the internal messages (control packets) */
> > @@ -204,4 +211,9 @@ size_t virtio_serial_guest_ready(VirtIOSerialPort 
> > *port);
> >   */
> >  void virtio_serial_throttle_port(VirtIOSerialPort *port, bool throttle);
> >  
> > +/*
> > + * Does this machine type disable the use of flow control?
> > + */
> > +bool virtio_serial_flow_control_enabled(VirtIOSerialPort *port);
> > +
> >  #endif
> 
>