Add getStrongRefCountForNodeByHandle to ProcessState

ServiceManager can use this function to query individual services for their ref counts.

Bug: 143108344
Test: Manual (printed ref counts from servicemanager and confirmed that they matched the data in /d/binder/state)
Change-Id: I8c84f4b10b1c2b7690b39d1c4f4f50abd7d715b0

1 files changed, 24 insertions, 0 deletions

diff --git a/libs/binder/ProcessState.cpp b/libs/binder/ProcessState.cpp
index 0336d3ebd4..ea61dc5aff 100644
--- a/libs/binder/ProcessState.cpp
+++ b/libs/binder/ProcessState.cpp
@@ -188,6 +188,30 @@ ssize_t ProcessState::getKernelReferences(size_t buf_count, uintptr_t* buf)
     return count;
 }
 
+// Queries the driver for the current strong reference count of the node
+// that the handle points to. Can only be used by the servicemanager.
+//
+// Returns -1 in case of failure, otherwise the strong reference count.
+ssize_t ProcessState::getStrongRefCountForNodeByHandle(int32_t handle) {
+    binder_node_info_for_ref info;
+    memset(&info, 0, sizeof(binder_node_info_for_ref));
+
+    info.handle = handle;
+
+    status_t result = ioctl(mDriverFD, BINDER_GET_NODE_INFO_FOR_REF, &info);
+
+    if (result != OK) {
+        static bool logged = false;
+        if (!logged) {
+          ALOGW("Kernel does not support BINDER_GET_NODE_INFO_FOR_REF.");
+          logged = true;
+        }
+        return -1;
+    }
+
+    return info.strong_count;
+}
+
 void ProcessState::setCallRestriction(CallRestriction restriction) {
     LOG_ALWAYS_FATAL_IF(IPCThreadState::selfOrNull() != nullptr,
         "Call restrictions must be set before the threadpool is started.");