validationcaches: Add and use ValidationCacheSizes

Also:

- Make DEFAULT_MAX_SIG_CACHE_SIZE into constexpr
  DEFAULT_MAX_SIG_CACHE_BYTES to utilize the compile-time integer
  arithmetic overflow checking available to constexpr.
- Fix comment (MiB instead of MB) for DEFAULT_MAX_SIG_CACHE_BYTES.
- Pass in max_size_bytes parameter to InitS*Cache(), modify log line to
  no longer allude to maxsigcachesize being split evenly between the two
  validation caches.
- Fix possible integer truncation and add a comment.

[META] I've kept the integer types as int64_t in order to not introduce
       unintended behaviour changes, in the next commit we will make
       them size_t.

2 files changed, 45 insertions, 0 deletions

diff --git a/src/node/validation_cache_args.cpp b/src/node/validation_cache_args.cpp
new file mode 100644
index 0000000000..ed183c24fe
--- /dev/null
+++ b/src/node/validation_cache_args.cpp
@@ -0,0 +1,28 @@
+// Copyright (c) 2022 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <node/validation_cache_args.h>
+
+#include <kernel/validation_cache_sizes.h>
+
+#include <util/system.h>
+
+#include <memory>
+#include <optional>
+
+using kernel::ValidationCacheSizes;
+
+namespace node {
+void ApplyArgsManOptions(const ArgsManager& argsman, ValidationCacheSizes& cache_sizes)
+{
+    if (auto max_size = argsman.GetIntArg("-maxsigcachesize")) {
+        // Multiply first, divide after to avoid integer truncation
+        int64_t size_each = *max_size * (1 << 20) / 2;
+        cache_sizes = {
+            .signature_cache_bytes = size_each,
+            .script_execution_cache_bytes = size_each,
+        };
+    }
+}
+} // namespace node
diff --git a/src/node/validation_cache_args.h b/src/node/validation_cache_args.h
new file mode 100644
index 0000000000..f447c13b49
--- /dev/null
+++ b/src/node/validation_cache_args.h
@@ -0,0 +1,17 @@
+// Copyright (c) 2022 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_NODE_VALIDATION_CACHE_ARGS_H
+#define BITCOIN_NODE_VALIDATION_CACHE_ARGS_H
+
+class ArgsManager;
+namespace kernel {
+struct ValidationCacheSizes;
+};
+
+namespace node {
+void ApplyArgsManOptions(const ArgsManager& argsman, kernel::ValidationCacheSizes& cache_sizes);
+} // namespace node
+
+#endif // BITCOIN_NODE_VALIDATION_CACHE_ARGS_H