[PATCH v5 13/18] pci: introduce pci_find_the_only_child()

[Vladimir Sementsov-Ogievskiy]

To be used in further patch to identify the device hot-plugged into
pcie-root-port.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Anton Kuchin <antonkuchin@yandex-team.ru>
---
 include/hw/pci/pci.h |  1 +
 hw/pci/pci.c         | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
index d5a40cd058..b6c9c44527 100644
--- a/include/hw/pci/pci.h
+++ b/include/hw/pci/pci.h
@@ -341,6 +341,7 @@ void pci_for_each_device_under_bus_reverse(PCIBus *bus,
 void pci_for_each_bus_depth_first(PCIBus *bus, pci_bus_ret_fn begin,
                                   pci_bus_fn end, void *parent_state);
 PCIDevice *pci_get_function_0(PCIDevice *pci_dev);
+PCIDevice *pci_find_the_only_child(PCIBus *bus, int bus_num, Error **errp);
 
 /* Use this wrapper when specific scan order is not required. */
 static inline
diff --git a/hw/pci/pci.c b/hw/pci/pci.c
index 208c16f450..34fd1fb5b8 100644
--- a/hw/pci/pci.c
+++ b/hw/pci/pci.c
@@ -1771,6 +1771,39 @@ void pci_for_each_device(PCIBus *bus, int bus_num,
     }
 }
 
+typedef struct TheOnlyChild {
+    PCIDevice *dev;
+    int count;
+} TheOnlyChild;
+
+static void the_only_child_fn(PCIBus *bus, PCIDevice *dev, void *opaque)
+{
+    TheOnlyChild *s = opaque;
+
+    s->dev = dev;
+    s->count++;
+}
+
+PCIDevice *pci_find_the_only_child(PCIBus *bus, int bus_num, Error **errp)
+{
+    TheOnlyChild res = {0};
+
+    pci_for_each_device(bus, bus_num, the_only_child_fn, &res);
+
+    if (!res.dev) {
+        assert(res.count == 0);
+        error_setg(errp, "No child devices found");
+        return NULL;
+    }
+
+    if (res.count > 1) {
+        error_setg(errp, "Several child devices found");
+        return NULL;
+    }
+
+    return res.dev;
+}
+
 const pci_class_desc *get_class_desc(int class)
 {
     const pci_class_desc *desc;
-- 
2.34.1