[Qemu-devel] [PATCH 0/6 v3] introduce qbus reset callback and pci bus reset clean up

[Qemu-devel] [PATCH 0/6 v3] introduce qbus reset callback and pci bus reset clean up

[Isaku Yamahata]

I recreated the patch series based on your qbus walker of
git://repo.or.cz/qemu/aliguori.git

Anthony, can you please review the first three patches and merge them
if okay?
BTW what's the merge plan of the repo? Any chance to merge the walker part
first?

Patch description:
Introduce bus reset callback at qbus layer and clean up pci bus reset
by utilizing it. At last implement pci secondary bus reset which is
my motivation.
But I suppose scsi bus and ide bus also can take advantage of
this patch series.

Changes v2 -> v3:
- rebased to Anthony's qdev clean up tree.
- utilize qbus walker.

Changes v1 -> v2:
- addressed personal feed back from Gerd.
- reset signal are triggered by bus and propagated down into device.
- Only 5/8 is modified. Other patches remains same.

Isaku Yamahata (6):
  qdev: Make qbus_walk_children() call busfn for root bus.
  qdev: introduce reset call back for qbus level.
  qdev: introduce a helper function which triggers reset from a given
    device.
  pci: make pci reset use qdev reset frame work.
  pci: teach pci devices that have reset callback how to reset common
    registers.
  pci bridge: implement secondary bus reset.

 hw/e1000.c      |    1 +
 hw/lsi53c895a.c |    2 +
 hw/pci.c        |   45 +++++++++++++++++++++++++++++++++----
 hw/pci.h        |    2 +
 hw/pcnet.c      |    1 +
 hw/qdev-core.h  |    6 +++++
 hw/qdev.c       |   66 ++++++++++++++++++++++++++++++++++++------------------
 hw/rtl8139.c    |    2 +
 hw/virtio-pci.c |    1 +
 9 files changed, 99 insertions(+), 27 deletions(-)

[Qemu-devel] [PATCH 1/6] qdev: Make qbus_walk_children() call busfn for root bus.

[Isaku Yamahata]

Make qbus_walk_children() call busfn for root bus.
and it fixes qbus_realize_all().

The current qbus_walk_children() doesn't call busfn for root bus.
It cause qbus_relialize_all() to fail to call realize the system bus.
This patch also refactor qbus_walk_children() a bit.
Another only user of busfn, qbus_find_child_bus(), isn't affected by this.

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
---
 hw/qdev-core.h |    2 ++
 hw/qdev.c      |   51 ++++++++++++++++++++++++++++++---------------------
 2 files changed, 32 insertions(+), 21 deletions(-)

diff --git a/hw/qdev-core.h b/hw/qdev-core.h
index 5fdee3a..a9b7692 100644
--- a/hw/qdev-core.h
+++ b/hw/qdev-core.h
@@ -186,6 +186,8 @@ BusState *qbus_create(BusInfo *info, DeviceState *parent, const char *name);
 /* Returns > 0 if either devfn or busfn terminate walk, 0 otherwise. */
 int qbus_walk_children(BusState *bus, qdev_walkerfn *devfn, 
                        qbus_walkerfn *busfn, void *opaque);
+int qdev_walk_children(DeviceState *dev, qdev_walkerfn *devfn,
+                       qbus_walkerfn *busfn, void *opaque);
 
 DeviceState *qbus_find_child_dev(BusState *bus, const char *id);
 BusState *qbus_find_child_bus(BusState *bus, const char *id);
diff --git a/hw/qdev.c b/hw/qdev.c
index a981e05..c1ba6b8 100644
--- a/hw/qdev.c
+++ b/hw/qdev.c
@@ -296,33 +296,42 @@ int qbus_walk_children(BusState *bus, qdev_walkerfn *devfn,
                        qbus_walkerfn *busfn, void *opaque)
 {
     DeviceState *dev;
+    int err;
+
+    if (busfn) {
+        err = busfn(bus, opaque);
+        if (err) {
+            return err;
+        }
+    }
 
     QLIST_FOREACH(dev, &bus->children, sibling) {
-        BusState *child;
-        int err = 0;
+        err = qdev_walk_children(dev, devfn, busfn, opaque);
+        if (err < 0) {
+            return err;
+        }
+    }
 
-        if (devfn) {
-            err = devfn(dev, opaque);
+    return 0;
+}
+
+int qdev_walk_children(DeviceState *dev, qdev_walkerfn *devfn,
+                       qbus_walkerfn *busfn, void *opaque)
+{
+    BusState *bus;
+    int err;
+
+    if (devfn) {
+        err = devfn(dev, opaque);
+        if (err) {
+            return err;
         }
+    }
 
-        if (err > 0) {
+    QLIST_FOREACH(bus, &dev->child_bus, sibling) {
+        err = qbus_walk_children(bus, devfn, busfn, opaque);
+        if (err < 0) {
             return err;
-        } else if (err == 0) {
-            QLIST_FOREACH(child, &dev->child_bus, sibling) {
-                if (busfn) {
-                    err = busfn(child, opaque);
-                    if (err > 0) {
-                        return err;
-                    }
-                }
-
-                if (err == 0) {
-                    err = qbus_walk_children(child, devfn, busfn, opaque);
-                    if (err > 0) {
-                        return err;
-                    }
-                }
-            }
         }
     }
 
-- 
1.7.1.1

[Qemu-devel] [PATCH 2/6] qdev: introduce reset call back for qbus level.

[Isaku Yamahata]

and make it called via qbus_reset_all().
The qbus reset callback will be used by pci bus reset.

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
---
 hw/qdev-core.h |    3 +++
 hw/qdev.c      |   10 +++++++++-
 2 files changed, 12 insertions(+), 1 deletions(-)

diff --git a/hw/qdev-core.h b/hw/qdev-core.h
index a9b7692..49ac87a 100644
--- a/hw/qdev-core.h
+++ b/hw/qdev-core.h
@@ -58,12 +58,15 @@ typedef int (qbus_del_devfn)(BusState *bus, DeviceState *dev);
 
 typedef void (qbus_realizefn)(BusState *bus);
 
+typedef int (qbus_resetfn)(BusState *bus);
+
 struct BusInfo {
     const char *name;
     size_t size;
     qbus_add_devfn *add_dev;
     qbus_del_devfn *del_dev;
     qbus_realizefn *realize;
+    qbus_resetfn *reset;
     bus_get_dev_path get_dev_path;
     Property *props;
 };
diff --git a/hw/qdev.c b/hw/qdev.c
index c1ba6b8..9300d7f 100644
--- a/hw/qdev.c
+++ b/hw/qdev.c
@@ -166,9 +166,17 @@ static int qdev_reset_one(DeviceState *dev, void *opaque)
     return 0;
 }
 
+static int qbus_reset_one(BusState *bus, void *opaque)
+{
+    if (bus->info->reset) {
+        return bus->info->reset(bus);
+    }
+    return 0;
+}
+
 void qbus_reset_all(BusState *bus)
 {
-    qbus_walk_children(bus, qdev_reset_one, NULL, NULL);
+    qbus_walk_children(bus, qdev_reset_one, qbus_reset_one, NULL);
 }
 
 static int qdev_realize_one(DeviceState *dev, void *opaque)
-- 
1.7.1.1

[Qemu-devel] [PATCH 3/6] qdev: introduce a helper function which triggers reset from a given device.

[Isaku Yamahata]

introduce a helper function which triggers reset on device tree
from a given device.

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
---
 hw/qdev-core.h |    1 +
 hw/qdev.c      |    5 +++++
 2 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/hw/qdev-core.h b/hw/qdev-core.h
index 49ac87a..20ebe1f 100644
--- a/hw/qdev-core.h
+++ b/hw/qdev-core.h
@@ -195,6 +195,7 @@ int qdev_walk_children(DeviceState *dev, qdev_walkerfn *devfn,
 DeviceState *qbus_find_child_dev(BusState *bus, const char *id);
 BusState *qbus_find_child_bus(BusState *bus, const char *id);
 
+void qdev_reset_all(DeviceState *dev);
 void qbus_reset_all(BusState *bus);
 void qbus_realize_all(BusState *bus);
 
diff --git a/hw/qdev.c b/hw/qdev.c
index 9300d7f..191dfac 100644
--- a/hw/qdev.c
+++ b/hw/qdev.c
@@ -174,6 +174,11 @@ static int qbus_reset_one(BusState *bus, void *opaque)
     return 0;
 }
 
+void qdev_reset_all(DeviceState *dev)
+{
+    qdev_walk_children(dev, qdev_reset_one, qbus_reset_one, NULL);
+}
+
 void qbus_reset_all(BusState *bus)
 {
     qbus_walk_children(bus, qdev_reset_one, qbus_reset_one, NULL);
-- 
1.7.1.1

[Qemu-devel] [PATCH 4/6] pci: make pci reset use qdev reset frame work.

[Isaku Yamahata]

make pci reset use qdev reset frame work.

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
---
 hw/pci.c |   38 ++++++++++++++++++++++++++++++++++----
 hw/pci.h |    2 ++
 2 files changed, 36 insertions(+), 4 deletions(-)

diff --git a/hw/pci.c b/hw/pci.c
index 655fead..4c99390 100644
--- a/hw/pci.c
+++ b/hw/pci.c
@@ -62,6 +62,7 @@ struct PCIBus {
 static char *pcibus_get_dev_path(DeviceState *dev);
 static int pcibus_add_dev(BusState *qbus, DeviceState *qdev);
 static int pcibus_del_dev(BusState *qbus, DeviceState *qdev);
+static int pcibus_reset(BusState *qbus);
 
 static struct BusInfo pci_bus_info = {
     .name       = "PCI",
@@ -69,6 +70,7 @@ static struct BusInfo pci_bus_info = {
     .get_dev_path = pcibus_get_dev_path,
     .add_dev    = pcibus_add_dev,
     .del_dev    = pcibus_del_dev,
+    .reset      = pcibus_reset,
     .props      = (Property[]) {
         DEFINE_PROP_PCI_DEVFN("addr", PCIDevice, devfn, -1),
         DEFINE_PROP_STRING("romfile", PCIDevice, romfile),
@@ -153,7 +155,7 @@ static void pci_update_irq_status(PCIDevice *dev)
     }
 }
 
-static void pci_device_reset(PCIDevice *dev)
+void pci_device_reset_default(PCIDevice *dev)
 {
     int r;
 
@@ -181,9 +183,29 @@ static void pci_device_reset(PCIDevice *dev)
     pci_update_mappings(dev);
 }
 
-static void pci_bus_reset(void *opaque)
+static void pci_device_reset(PCIDevice *dev)
+{
+    if (!dev->qdev.info) {
+        /* not all pci devices haven't been qdev'fied yet
+           TODO: remove this when all pci devices are qdev'fied. */
+        pci_device_reset_default(dev);
+    } else {
+        /*
+         * TODO:
+         * each device should know what to do on RST#.
+         * move pci_device_reset_default() into each callback.
+         */
+        qdev_reset_all(&dev->qdev);
+        pci_device_reset_default(dev);
+    }
+}
+
+/*
+ * Trigger pci bus reset under a given bus.
+ * This functions emulates RST#.
+ */
+static void pci_bus_reset(PCIBus *bus)
 {
-    PCIBus *bus = opaque;
     int i;
 
     for (i = 0; i < bus->nirq; i++) {
@@ -196,6 +218,15 @@ static void pci_bus_reset(void *opaque)
     }
 }
 
+static int pcibus_reset(BusState *qbus)
+{
+    pci_bus_reset(DO_UPCAST(PCIBus, qbus, qbus));
+
+    /* topology traverse is done by pci_bus_reset().
+       Tell qbus/qdev walker not to traverse the tree */
+    return 1;
+}
+
 static void pci_host_bus_register(int domain, PCIBus *bus)
 {
     struct PCIHostBus *host;
@@ -250,7 +281,6 @@ void pci_bus_new_inplace(PCIBus *bus, DeviceState *parent,
     pci_host_bus_register(0, bus); /* for now only pci domain 0 is supported */
 
     vmstate_register(NULL, -1, &vmstate_pcibus, bus);
-    qemu_register_reset(pci_bus_reset, bus);
 }
 
 PCIBus *pci_bus_new(DeviceState *parent, const char *name, int devfn_min)
diff --git a/hw/pci.h b/hw/pci.h
index 51ba8b6..8e72d78 100644
--- a/hw/pci.h
+++ b/hw/pci.h
@@ -214,6 +214,8 @@ PCIBus *pci_register_bus(DeviceState *parent, const char *name,
                          pci_set_irq_fn set_irq, pci_map_irq_fn map_irq,
                          void *irq_opaque, int devfn_min, int nirq);
 
+void pci_device_reset_default(PCIDevice *dev);
+
 void pci_bus_set_mem_base(PCIBus *bus, target_phys_addr_t base);
 
 PCIDevice *pci_nic_init(NICInfo *nd, const char *default_model,
-- 
1.7.1.1

[Qemu-devel] [PATCH 5/6] pci: teach pci devices that have reset callback how to reset common registers.

[Isaku Yamahata]

teach pci devices that have reset callback how to reset common registers.

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
---
 hw/e1000.c      |    1 +
 hw/lsi53c895a.c |    2 ++
 hw/pci.c        |    6 ------
 hw/pcnet.c      |    1 +
 hw/rtl8139.c    |    2 ++
 hw/virtio-pci.c |    1 +
 6 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/hw/e1000.c b/hw/e1000.c
index 9972b48..1987ef6 100644
--- a/hw/e1000.c
+++ b/hw/e1000.c
@@ -1077,6 +1077,7 @@ static void e1000_reset(void *opaque)
     memmove(d->mac_reg, mac_reg_init, sizeof mac_reg_init);
     d->rxbuf_min_shift = 1;
     memset(&d->tx, 0, sizeof d->tx);
+    pci_device_reset_default(&d->dev);
 }
 
 static NetClientInfo net_e1000_info = {
diff --git a/hw/lsi53c895a.c b/hw/lsi53c895a.c
index ecff004..c1a920b 100644
--- a/hw/lsi53c895a.c
+++ b/hw/lsi53c895a.c
@@ -358,6 +358,8 @@ static void lsi_soft_reset(LSIState *s)
         qemu_free(s->current);
         s->current = NULL;
     }
+
+    pci_device_reset_default(&s->dev);
 }
 
 static int lsi_dma_40bit(LSIState *s)
diff --git a/hw/pci.c b/hw/pci.c
index 4c99390..e23ac1b 100644
--- a/hw/pci.c
+++ b/hw/pci.c
@@ -190,13 +190,7 @@ static void pci_device_reset(PCIDevice *dev)
            TODO: remove this when all pci devices are qdev'fied. */
         pci_device_reset_default(dev);
     } else {
-        /*
-         * TODO:
-         * each device should know what to do on RST#.
-         * move pci_device_reset_default() into each callback.
-         */
         qdev_reset_all(&dev->qdev);
-        pci_device_reset_default(dev);
     }
 }
 
diff --git a/hw/pcnet.c b/hw/pcnet.c
index c8291bb..2910221 100644
--- a/hw/pcnet.c
+++ b/hw/pcnet.c
@@ -2025,6 +2025,7 @@ static void pci_reset(DeviceState *dev)
     PCIPCNetState *d = DO_UPCAST(PCIPCNetState, pci_dev.qdev, dev);
 
     pcnet_h_reset(&d->state);
+    pci_device_reset_default(&d->pci_dev);
 }
 
 static PCIDeviceInfo pcnet_info = {
diff --git a/hw/rtl8139.c b/hw/rtl8139.c
index 690d07b..a26a33a 100644
--- a/hw/rtl8139.c
+++ b/hw/rtl8139.c
@@ -1261,6 +1261,8 @@ static void rtl8139_reset(DeviceState *d)
 
     /* reset tally counters */
     RTL8139TallyCounters_clear(&s->tally_counters);
+
+    pci_device_reset_default(&s->dev);
 }
 
 static void RTL8139TallyCounters_clear(RTL8139TallyCounters* counters)
diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
index 8fe6b3b..5a170a1 100644
--- a/hw/virtio-pci.c
+++ b/hw/virtio-pci.c
@@ -186,6 +186,7 @@ static void virtio_pci_reset(DeviceState *d)
     virtio_reset(proxy->vdev);
     msix_reset(&proxy->pci_dev);
     proxy->bugs = 0;
+    pci_device_reset_default(&proxy->pci_dev);
 }
 
 static void virtio_ioport_write(void *opaque, uint32_t addr, uint32_t val)
-- 
1.7.1.1

[Qemu-devel] [PATCH 6/6] pci bridge: implement secondary bus reset.

[Isaku Yamahata]

implement secondary bus reset.

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
---
 hw/pci.c |   13 ++++++++++++-
 1 files changed, 12 insertions(+), 1 deletions(-)

diff --git a/hw/pci.c b/hw/pci.c
index e23ac1b..183f595 100644
--- a/hw/pci.c
+++ b/hw/pci.c
@@ -1626,6 +1626,9 @@ static void pci_bridge_update_mappings(PCIBus *b)
 static void pci_bridge_write_config(PCIDevice *d,
                              uint32_t address, uint32_t val, int len)
 {
+    PCIBridge *s = container_of(d, PCIBridge, dev);
+    uint16_t bridge_control = pci_get_word(d->config + PCI_BRIDGE_CONTROL);
+
     pci_default_write_config(d, address, val, len);
 
     if (/* io base/limit */
@@ -1634,10 +1637,18 @@ static void pci_bridge_write_config(PCIDevice *d,
         /* memory base/limit, prefetchable base/limit and
            io base/limit upper 16 */
         ranges_overlap(address, len, PCI_MEMORY_BASE, 20)) {
-        PCIBridge *s = container_of(d, PCIBridge, dev);
         PCIBus *secondary_bus = &s->bus;
         pci_bridge_update_mappings(secondary_bus);
     }
+
+    if (ranges_overlap(address, len, PCI_BRIDGE_CONTROL, 2)) {
+        uint16_t new = pci_get_word(d->config + PCI_BRIDGE_CONTROL);
+        if (!(bridge_control & PCI_BRIDGE_CTL_BUS_RESET) &&
+            (new & PCI_BRIDGE_CTL_BUS_RESET)) {
+            /* 0 -> 1 */
+            pci_bus_reset(&s->bus);
+        }
+    }
 }
 
 PCIBus *pci_find_bus(PCIBus *bus, int bus_num)
-- 
1.7.1.1

[Qemu-devel] Re: [PATCH 0/6 v3] introduce qbus reset callback and pci bus reset clean up

[Anthony Liguori]

On 09/02/2010 04:25 AM, Isaku Yamahata wrote:
> I recreated the patch series based on your qbus walker of
> git://repo.or.cz/qemu/aliguori.git
>
> Anthony, can you please review the first three patches and merge them
> if okay?
>    

They look really nice, I'll merge them into my branch.

> BTW what's the merge plan of the repo? Any chance to merge the walker part
> first?
>    

I'm still working on vmsd refactoring but I can split out an initial 
series that doesn't contain that and includes your reset changes.

Regards,

Anthony LIguori

> Patch description:
> Introduce bus reset callback at qbus layer and clean up pci bus reset
> by utilizing it. At last implement pci secondary bus reset which is
> my motivation.
> But I suppose scsi bus and ide bus also can take advantage of
> this patch series.
>
> Changes v2 ->  v3:
> - rebased to Anthony's qdev clean up tree.
> - utilize qbus walker.
>
> Changes v1 ->  v2:
> - addressed personal feed back from Gerd.
> - reset signal are triggered by bus and propagated down into device.
> - Only 5/8 is modified. Other patches remains same.
>
> Isaku Yamahata (6):
>    qdev: Make qbus_walk_children() call busfn for root bus.
>    qdev: introduce reset call back for qbus level.
>    qdev: introduce a helper function which triggers reset from a given
>      device.
>    pci: make pci reset use qdev reset frame work.
>    pci: teach pci devices that have reset callback how to reset common
>      registers.
>    pci bridge: implement secondary bus reset.
>
>   hw/e1000.c      |    1 +
>   hw/lsi53c895a.c |    2 +
>   hw/pci.c        |   45 +++++++++++++++++++++++++++++++++----
>   hw/pci.h        |    2 +
>   hw/pcnet.c      |    1 +
>   hw/qdev-core.h  |    6 +++++
>   hw/qdev.c       |   66 ++++++++++++++++++++++++++++++++++++------------------
>   hw/rtl8139.c    |    2 +
>   hw/virtio-pci.c |    1 +
>   9 files changed, 99 insertions(+), 27 deletions(-)
>
>    

Re: [Qemu-devel] [PATCH 1/6] qdev: Make qbus_walk_children() call busfn for root bus.

[Markus Armbruster]

Please excuse my late reply.  I'm so much behind in this list, it's not
funny anymore.

I agree with Anthony, this series looks nice.  A few remarks inline.


Isaku Yamahata <yamahata@valinux.co.jp> writes:

> Make qbus_walk_children() call busfn for root bus.

Please don't repeat the subject in the body.

While I'm nit-picking about commit messages: subject is a heading, and
as such it shouldn't end in a period.

> and it fixes qbus_realize_all().

Can't see qbus_realize_all() in master; I guess it's in Anthony's tree.

> The current qbus_walk_children() doesn't call busfn for root bus.
> It cause qbus_relialize_all() to fail to call realize the system bus.

Do you mean qbus_realize_all()?

> This patch also refactor qbus_walk_children() a bit.
> Another only user of busfn, qbus_find_child_bus(), isn't affected by this.
>
> Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
> ---
>  hw/qdev-core.h |    2 ++
>  hw/qdev.c      |   51 ++++++++++++++++++++++++++++++---------------------
>  2 files changed, 32 insertions(+), 21 deletions(-)
>
> diff --git a/hw/qdev-core.h b/hw/qdev-core.h
> index 5fdee3a..a9b7692 100644
> --- a/hw/qdev-core.h
> +++ b/hw/qdev-core.h
> @@ -186,6 +186,8 @@ BusState *qbus_create(BusInfo *info, DeviceState *parent, const char *name);
>  /* Returns > 0 if either devfn or busfn terminate walk, 0 otherwise. */
>  int qbus_walk_children(BusState *bus, qdev_walkerfn *devfn, 
>                         qbus_walkerfn *busfn, void *opaque);
> +int qdev_walk_children(DeviceState *dev, qdev_walkerfn *devfn,
> +                       qbus_walkerfn *busfn, void *opaque);
>  
>  DeviceState *qbus_find_child_dev(BusState *bus, const char *id);
>  BusState *qbus_find_child_bus(BusState *bus, const char *id);
> diff --git a/hw/qdev.c b/hw/qdev.c
> index a981e05..c1ba6b8 100644
> --- a/hw/qdev.c
> +++ b/hw/qdev.c
> @@ -296,33 +296,42 @@ int qbus_walk_children(BusState *bus, qdev_walkerfn *devfn,
>                         qbus_walkerfn *busfn, void *opaque)
>  {
>      DeviceState *dev;
> +    int err;
> +
> +    if (busfn) {
> +        err = busfn(bus, opaque);
> +        if (err) {
> +            return err;
> +        }
> +    }
>  
>      QLIST_FOREACH(dev, &bus->children, sibling) {
> -        BusState *child;
> -        int err = 0;
> +        err = qdev_walk_children(dev, devfn, busfn, opaque);
> +        if (err < 0) {
> +            return err;
> +        }
> +    }
>  
> -        if (devfn) {
> -            err = devfn(dev, opaque);
> +    return 0;
> +}
> +
> +int qdev_walk_children(DeviceState *dev, qdev_walkerfn *devfn,
> +                       qbus_walkerfn *busfn, void *opaque)
> +{
> +    BusState *bus;
> +    int err;
> +
> +    if (devfn) {
> +        err = devfn(dev, opaque);
> +        if (err) {
> +            return err;
>          }
> +    }
>  
> -        if (err > 0) {
> +    QLIST_FOREACH(bus, &dev->child_bus, sibling) {
> +        err = qbus_walk_children(bus, devfn, busfn, opaque);
> +        if (err < 0) {
>              return err;
> -        } else if (err == 0) {
> -            QLIST_FOREACH(child, &dev->child_bus, sibling) {
> -                if (busfn) {
> -                    err = busfn(child, opaque);
> -                    if (err > 0) {
> -                        return err;
> -                    }
> -                }
> -
> -                if (err == 0) {
> -                    err = qbus_walk_children(child, devfn, busfn, opaque);
> -                    if (err > 0) {
> -                        return err;
> -                    }
> -                }
> -            }
>          }
>      }

Isn't it funny that functions that work on a qdev sub-trees always come
in pairs?  qdev_foo() and qbus_foo().  That's because of the split
between device and bus nodes.