Use binder-based iterator to retrieve FRROs

If for some reason there are a lot of fabricated overlays in the
resources cache, the binder limit of the list of fabricated overlay
infos could exceed the maximum binder transaction size. Rather than
return all of the frro infos in one transactions, register an iterator
with the native idmap2d service and use multiple binder transactions
to iterate through all of the frros.

Bug: 192948522
Test: Toggle device theme colors several times and observe frro cache
      Reboot device and observe old frros are deleted
Change-Id: I5e9cf3ae9d1d45eda683c24141a0cd4e4301e02f

1 files changed, 29 insertions, 6 deletions

diff --git a/cmds/idmap2/idmap2d/Idmap2Service.cpp b/cmds/idmap2/idmap2d/Idmap2Service.cpp
index 2cfbac3f2c26..a8d648917b08 100644
--- a/cmds/idmap2/idmap2d/Idmap2Service.cpp
+++ b/cmds/idmap2/idmap2d/Idmap2Service.cpp
@@ -297,17 +297,40 @@ Status Idmap2Service::createFabricatedOverlay(
   return ok();
 }
 
-Status Idmap2Service::getFabricatedOverlayInfos(
+Status Idmap2Service::acquireFabricatedOverlayIterator() {
+  if (frro_iter_.has_value()) {
+    LOG(WARNING) << "active ffro iterator was not previously released";
+  }
+  frro_iter_ = std::filesystem::directory_iterator(kIdmapCacheDir);
+  return ok();
+}
+
+Status Idmap2Service::releaseFabricatedOverlayIterator() {
+  if (!frro_iter_.has_value()) {
+    LOG(WARNING) << "no active ffro iterator to release";
+  }
+  return ok();
+}
+
+Status Idmap2Service::nextFabricatedOverlayInfos(
     std::vector<os::FabricatedOverlayInfo>* _aidl_return) {
-  for (const auto& entry : std::filesystem::directory_iterator(kIdmapCacheDir)) {
-    if (!android::IsFabricatedOverlay(entry.path())) {
+  constexpr size_t kMaxEntryCount = 100;
+  if (!frro_iter_.has_value()) {
+    return error("no active frro iterator");
+  }
+
+  size_t count = 0;
+  auto& entry_iter = *frro_iter_;
+  auto entry_iter_end = end(*frro_iter_);
+  for (; entry_iter != entry_iter_end && count < kMaxEntryCount; ++entry_iter) {
+    auto& entry = *entry_iter;
+    if (!entry.is_regular_file() || !android::IsFabricatedOverlay(entry.path())) {
       continue;
     }
 
     const auto overlay = FabricatedOverlayContainer::FromPath(entry.path());
     if (!overlay) {
-      // This is a sign something went wrong.
-      LOG(ERROR) << "Failed to open '" << entry.path() << "': " << overlay.GetErrorMessage();
+      LOG(WARNING) << "Failed to open '" << entry.path() << "': " << overlay.GetErrorMessage();
       continue;
     }
 
@@ -319,8 +342,8 @@ Status Idmap2Service::getFabricatedOverlayInfos(
     out_info.targetOverlayable = info.target_name;
     out_info.path = entry.path();
     _aidl_return->emplace_back(std::move(out_info));
+    count++;
   }
-
   return ok();
 }