[Qemu-devel] [PATCH v2 10/15] qbus_find_recursive(): push Error and make it terminate a recursive search

[Laszlo Ersek]

Push error handling to callers.

When a bus is found by name and it has no free slots, that's a fatal error
for the recursive search. Clarify the interface contract, and use error
propagation to unwind the recursion quickly.

Conversion status (call chains covered or substituted by error propagation
marked with square brackets):

do_device_add -> [qemu_find_opts -> error_report]
do_device_add -> qdev_device_add -> qerror_report
do_device_add -> qdev_device_add -> qbus_find -> [qbus_find_recursive
  -> qerror_report]
do_device_add -> qdev_device_add -> qbus_find -> qerror_report
do_device_add -> qdev_device_add -> [set_property -> qdev_prop_parse
  -> qerror_report_err]

Signed-off-by: Laszlo Ersek <address@hidden>
---
 hw/qdev-monitor.c |   55 ++++++++++++++++++++++++++++++++++++++++++++++------
 1 files changed, 48 insertions(+), 7 deletions(-)

diff --git a/hw/qdev-monitor.c b/hw/qdev-monitor.c
index 0a0bced..4fa64c9 100644
--- a/hw/qdev-monitor.c
+++ b/hw/qdev-monitor.c
@@ -288,6 +288,40 @@ static DeviceState *qbus_find_dev(BusState *bus, char 
*elem)
     return NULL;
 }
 
+/*
+ * qbus_find_recursive() -- locate a bus by name and/or type in a subtree
+ *
+ * Search the bus subtree rooted in @bus for a bus matching the optionally
+ * specified @name and the optionally specified @type attributes. Matching
+ * candidates are examined for a free bus slot.
+ *
+ * The following return configurations are possible:
+ *
+ * - @retval != NULL   Matching bus with a free slot found.
+ *
+ * - @retval == NULL   No matching bus with a free slot was found.
+ *                     For (@name != NULL) calls, a further distinction is
+ *                     made for this case:
+ *
+ *   - address@hidden == NULL  Bus not found by requested name. For recursive 
calls,
+ *                     the search should continue with siblings of @bus.
+ *
+ *   - address@hidden != NULL  Bus found by name, but it has no free slot. For
+ *                     recursive calls, this is an abort condition; names are
+ *                     unique.
+ *
+ *  Parameters:
+ *
+ *  - @bus   root of subtree to search
+ *
+ *  - @name  if non-NULL, restrict search by this bus name
+ *
+ *  - @type  if non-NULL, restrict search by this bus type
+ *
+ *  - @errp  Returns the error if bus is found by name but it has no free slot.
+ *           (@errp != NULL && address@hidden == NULL) must hold on input for 
all
+ *           calls.
+ */
 static BusState *qbus_find_recursive(BusState *bus, const char *name,
                                      const char *type, Error **errp)
 {
@@ -304,8 +338,7 @@ static BusState *qbus_find_recursive(BusState *bus, const 
char *name,
 
         /* bus is full -- fatal error for search by name */
         if (name != NULL) {
-            qerror_report(ERROR_CLASS_GENERIC_ERROR, "Bus '%s' is full",
-                          bus->name);
+            error_setg(errp, "Bus '%s' is full", bus->name);
             return NULL;
         }
     }
@@ -317,8 +350,8 @@ static BusState *qbus_find_recursive(BusState *bus, const 
char *name,
         QLIST_FOREACH(child, &dev->child_bus, sibling) {
             BusState *ret;
 
-            ret = qbus_find_recursive(child, name, type, NULL);
-            if (ret) {
+            ret = qbus_find_recursive(child, name, type, errp);
+            if (ret || error_is_set(errp)) {
                 return ret;
             }
         }
@@ -338,13 +371,20 @@ static BusState *qbus_find(const char *path)
         bus = sysbus_get_default();
         pos = 0;
     } else {
+        Error *err = NULL;
+
         if (sscanf(path, "%127[^/]%n", elem, &len) != 1) {
             assert(!path[0]);
             elem[0] = len = 0;
         }
-        bus = qbus_find_recursive(sysbus_get_default(), elem, NULL, NULL);
+        bus = qbus_find_recursive(sysbus_get_default(), elem, NULL, &err);
         if (!bus) {
-            qerror_report(QERR_BUS_NOT_FOUND, elem);
+            if (error_is_set(&err)) {
+                qerror_report_err(err);
+                error_free(err);
+            } else {
+                qerror_report(QERR_BUS_NOT_FOUND, elem);
+            }
             return NULL;
         }
         pos = len;
@@ -460,8 +500,9 @@ DeviceState *qdev_device_add(QemuOpts *opts)
         }
     } else {
         bus = qbus_find_recursive(sysbus_get_default(), NULL, k->bus_type,
-                                  NULL);
+                                  &local_err);
         if (!bus) {
+            assert(!error_is_set(&local_err));
             qerror_report(QERR_NO_BUS_FOR_DEVICE,
                           k->bus_type, driver);
             return NULL;
-- 
1.7.1