validation: add ChainstateRole

src/kernel/chain.cpp

@@ -4,6 +4,7 @@
 
 #include <chain.h>
 #include <interfaces/chain.h>
+#include <kernel/chain.h>
 #include <sync.h>
 #include <uint256.h>
 
@@ -25,3 +26,13 @@ interfaces::BlockInfo MakeBlockInfo(const CBlockIndex* index, const CBlock* data
     return info;
 }
 } // namespace kernel
+
+std::ostream& operator<<(std::ostream& os, const ChainstateRole& role) {
+    switch(role) {
+        case ChainstateRole::NORMAL: os << "normal"; break;
+        case ChainstateRole::ASSUMEDVALID: os << "assumedvalid"; break;
+        case ChainstateRole::BACKGROUND: os << "background"; break;
+        default: os.setstate(std::ios_base::failbit);
+    }
+    return os;
+}

src/kernel/chain.h

@@ -5,6 +5,8 @@
 #ifndef BITCOIN_KERNEL_CHAIN_H
 #define BITCOIN_KERNEL_CHAIN_H
 
+#include<iostream>
+
 class CBlock;
 class CBlockIndex;
 namespace interfaces {
@@ -14,6 +16,24 @@ struct BlockInfo;
 namespace kernel {
 //! Return data from block index.
 interfaces::BlockInfo MakeBlockInfo(const CBlockIndex* block_index, const CBlock* data = nullptr);
+
 } // namespace kernel
 
+//! This enum describes the various roles a specific Chainstate instance can take.
+//! Other parts of the system sometimes need to vary in behavior depending on the
+//! existence of a background validation chainstate, e.g. when building indexes.
+enum class ChainstateRole {
+    // Single chainstate in use, "normal" IBD mode.
+    NORMAL,
+
+    // Doing IBD-style validation in the background. Implies use of an assumed-valid
+    // chainstate.
+    BACKGROUND,
+
+    // Active assumed-valid chainstate. Implies use of a background IBD chainstate.
+    ASSUMEDVALID,
+};
+
+std::ostream& operator<<(std::ostream& os, const ChainstateRole& role);
+
 #endif // BITCOIN_KERNEL_CHAIN_H

src/validation.cpp

@@ -5813,6 +5813,16 @@ bool ChainstateManager::DeleteSnapshotChainstate()
     return true;
 }
 
+ChainstateRole Chainstate::GetRole() const
+{
+    if (m_chainman.GetAll().size() <= 1) {
+        return ChainstateRole::NORMAL;
+    }
+    return (this != &m_chainman.ActiveChainstate()) ?
+               ChainstateRole::BACKGROUND :
+               ChainstateRole::ASSUMEDVALID;
+}
+
 const CBlockIndex* ChainstateManager::GetSnapshotBaseBlock() const
 {
     return m_active_chainstate ? m_active_chainstate->SnapshotBase() : nullptr;

src/validation.h

@@ -13,6 +13,7 @@
 #include <arith_uint256.h>
 #include <attributes.h>
 #include <chain.h>
+#include <kernel/chain.h>
 #include <consensus/amount.h>
 #include <deploymentstatus.h>
 #include <kernel/chainparams.h>
@@ -511,6 +512,12 @@ public:
         ChainstateManager& chainman,
         std::optional<uint256> from_snapshot_blockhash = std::nullopt);
 
+    //! Return the current role of the chainstate. See `ChainstateManager`
+    //! documentation for a description of the different types of chainstates.
+    //!
+    //! @sa ChainstateRole
+    ChainstateRole GetRole() const EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
+
     /**
      * Initialize the CoinsViews UTXO set database management data structures. The in-memory
      * cache is initialized separately.