Use incremental locking when use_cvdalloc.

The existing locking scheme examines the number of preexisting tap
interfaces on the system as created by cuttlefish-host-resources, then
acquires the number of locks as there are tap interfaces. This scheme
won't work when we want to incrementally create tap interfaces. Instead,
acquire as many instance locks as requested when we use_cvdalloc.

The case where instance numbers can be explicitly requested is slightly
interesting; here we just use TryAcquireLocks.

Author: 3405691582

base/cvd/cuttlefish/host/commands/cvd/cli/selector/creation_analyzer.cpp

@@ -157,8 +157,11 @@ CreationAnalyzer::AnalyzeInstanceIdsInternal(
     }
     return instance_info;
   }
+
+  std::set<int> requested(requested_instance_ids.begin(),
+                          requested_instance_ids.end());
   auto acquired_all_file_locks =
-      CF_EXPECT(instance_lock_file_manager_.LockAllAvailable());
+      CF_EXPECT(instance_lock_file_manager_.TryAcquireLocks(requested));
   auto id_to_lockfile_map =
       ConstructIdLockFileMap(std::move(acquired_all_file_locks));
   for (const auto& [id, instance_name] : id_name_pairs) {
@@ -177,10 +180,13 @@ CreationAnalyzer::AnalyzeInstanceIdsInternal(bool acquire_file_locks) {
             "For now, cvd server always acquire the file locks "
                 << "when IDs are automatically allocated.");
 
+  const auto incremental = selector_options_parser_.UseCvdalloc();
   // As this test was done earlier, this line must not fail
   const auto n_instances = selector_options_parser_.RequestedNumInstances();
   auto acquired_all_file_locks =
-      CF_EXPECT(instance_lock_file_manager_.LockAllAvailable());
+      incremental ? CF_EXPECT(instance_lock_file_manager_.AcquireUnusedLocks(
+                        n_instances))
+                  : CF_EXPECT(instance_lock_file_manager_.LockAllAvailable());
   auto id_to_lockfile_map =
       ConstructIdLockFileMap(std::move(acquired_all_file_locks));
 

base/cvd/cuttlefish/host/commands/cvd/cli/selector/start_selector_parser.cpp

@@ -248,6 +248,10 @@ bool StartSelectorParser::CalcMayBeDefaultGroup() {
 Result<void> StartSelectorParser::ParseOptions() {
   may_be_default_group_ = CalcMayBeDefaultGroup();
 
+  std::optional<bool> use_cvdalloc;
+  CF_EXPECT(FilterSelectorFlag(cmd_args_, "use_cvdalloc", use_cvdalloc));
+  use_cvdalloc_ = use_cvdalloc.value_or(false);
+
   std::optional<std::string> num_instances;
   std::optional<std::string> instance_nums;
   std::optional<std::string> base_instance_num;

base/cvd/cuttlefish/host/commands/cvd/cli/selector/start_selector_parser.h

@@ -54,6 +54,7 @@ class StartSelectorParser {
   }
   unsigned RequestedNumInstances() const { return requested_num_instances_; }
   bool IsMaybeDefaultGroup() const { return may_be_default_group_; }
+  bool UseCvdalloc() const { return use_cvdalloc_; }
 
  private:
   StartSelectorParser(const std::string& system_wide_user_home,
@@ -138,6 +139,7 @@ class StartSelectorParser {
   std::optional<std::vector<unsigned>> instance_ids_;
   unsigned requested_num_instances_;
   bool may_be_default_group_;
+  bool use_cvdalloc_;
 
   // temporarily keeps the leftover of the input cmd_args
   const std::string client_user_home_;