qdev: provide a path resolution (v2)

There are two types of supported paths--absolute paths and partial paths.

Absolute paths are derived from the root device and can follow child<> or
link<> properties.  Since they can follow link<> properties, they can be
arbitrarily long.  Absolute paths look like absolute filenames and are prefixed
with a leading slash.

Partial paths are look like relative filenames.  They do not begin with a
prefix.  The matching rules for partial paths are subtle but designed to make
specifying devices easy.  At each level of the composition tree, the partial
path is matched as an absolute path.  The first match is not returned.  At
least two matches are searched for.  A successful result is only returned if
only one match is founded.  If more than one match is found, a flag is returned
to indicate that the match was ambiguous.

At the end of the day, partial path support means that if you create a device
called 'ide0', you can just say 'ide0' as the path name and it will Just Work.
If we internally create a device called 'i440fx', you can just say 'i440fx' and
it will Just Work and long as you don't do anything silly.

A management tool should probably always use absolute paths since then they
don't have to deal with the possibility of ambiguity.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

2 files changed, 131 insertions, 0 deletions

diff --git a/hw/qdev.c b/hw/qdev.c
index 79849c9..2519f00 100644
--- a/hw/qdev.c
+++ b/hw/qdev.c
@@ -1221,3 +1221,106 @@ gchar *qdev_get_canonical_path(DeviceState *dev)
 
     return newpath;
 }
+
+static DeviceState *qdev_resolve_abs_path(DeviceState *parent,
+                                          gchar **parts,
+                                          int index)
+{
+    DeviceProperty *prop;
+    DeviceState *child;
+
+    if (parts[index] == NULL) {
+        return parent;
+    }
+
+    if (strcmp(parts[index], "") == 0) {
+        return qdev_resolve_abs_path(parent, parts, index + 1);
+    }
+
+    prop = qdev_property_find(parent, parts[index]);
+    if (prop == NULL) {
+        return NULL;
+    }
+
+    child = NULL;
+    if (strstart(prop->type, "link<", NULL)) {
+        DeviceState **pchild = prop->opaque;
+        if (*pchild) {
+            child = *pchild;
+        }
+    } else if (strstart(prop->type, "child<", NULL)) {
+        child = prop->opaque;
+    }
+
+    if (!child) {
+        return NULL;
+    }
+
+    return qdev_resolve_abs_path(child, parts, index + 1);
+}
+
+static DeviceState *qdev_resolve_partial_path(DeviceState *parent,
+                                              gchar **parts,
+                                              bool *ambiguous)
+{
+    DeviceState *dev;
+    DeviceProperty *prop;
+
+    dev = qdev_resolve_abs_path(parent, parts, 0);
+
+    QTAILQ_FOREACH(prop, &parent->properties, node) {
+        DeviceState *found;
+
+        if (!strstart(prop->type, "child<", NULL)) {
+            continue;
+        }
+
+        found = qdev_resolve_partial_path(prop->opaque, parts, ambiguous);
+        if (found) {
+            if (dev) {
+                if (ambiguous) {
+                    *ambiguous = true;
+                }
+                return NULL;
+            }
+            dev = found;
+        }
+
+        if (ambiguous && *ambiguous) {
+            return NULL;
+        }
+    }
+
+    return dev;
+}
+
+DeviceState *qdev_resolve_path(const char *path, bool *ambiguous)
+{
+    bool partial_path = true;
+    DeviceState *dev;
+    gchar **parts;
+
+    parts = g_strsplit(path, "/", 0);
+    if (parts == NULL || parts[0] == NULL) {
+        g_strfreev(parts);
+        return qdev_get_root();
+    }
+
+    if (strcmp(parts[0], "") == 0) {
+        partial_path = false;
+    }
+
+    if (partial_path) {
+        if (ambiguous) {
+            *ambiguous = false;
+        }
+        dev = qdev_resolve_partial_path(qdev_get_root(), parts, ambiguous);
+    } else {
+        dev = qdev_resolve_abs_path(qdev_get_root(), parts, 1);
+    }
+
+    g_strfreev(parts);
+
+    return dev;
+}
+
diff --git a/hw/qdev.h b/hw/qdev.h
index 0f00497..641d134 100644
--- a/hw/qdev.h
+++ b/hw/qdev.h
@@ -499,4 +499,32 @@ DeviceState *qdev_get_root(void);
  */
 gchar *qdev_get_canonical_path(DeviceState *dev);
 
+/**
+ * @qdev_resolve_path - resolves a path returning a device
+ *
+ * There are two types of supported paths--absolute paths and partial paths.
+ * 
+ * Absolute paths are derived from the root device and can follow child<> or
+ * link<> properties.  Since they can follow link<> properties, they can be
+ * arbitrarily long.  Absolute paths look like absolute filenames and are
+ * prefixed with a leading slash.
+ * 
+ * Partial paths look like relative filenames.  They do not begin with a
+ * prefix.  The matching rules for partial paths are subtle but designed to make
+ * specifying devices easy.  At each level of the composition tree, the partial
+ * path is matched as an absolute path.  The first match is not returned.  At
+ * least two matches are searched for.  A successful result is only returned if
+ * only one match is founded.  If more than one match is found, a flag is
+ * return to indicate that the match was ambiguous.
+ *
+ * @path - the path to resolve
+ *
+ * @ambiguous - returns true if the path resolution failed because of an
+ *              ambiguous match
+ *
+ * Returns:
+ *   The matched device or NULL on path lookup failure.
+ */
+DeviceState *qdev_resolve_path(const char *path, bool *ambiguous);
+
 #endif