versionbits.cpp raw
1 // Copyright (c) 2016-present The Bitcoin Core developers
2 // Distributed under the MIT software license, see the accompanying
3 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
4
5 #include <consensus/params.h>
6 #include <deploymentinfo.h>
7 #include <kernel/chainparams.h>
8 #include <util/check.h>
9 #include <versionbits.h>
10 #include <versionbits_impl.h>
11
12 using enum ThresholdState;
13
14 std::string StateName(ThresholdState state)
15 {
16 switch (state) {
17 case DEFINED: return "defined";
18 case STARTED: return "started";
19 case LOCKED_IN: return "locked_in";
20 case ACTIVE: return "active";
21 case FAILED: return "failed";
22 }
23 return "invalid";
24 }
25
26 ThresholdState AbstractThresholdConditionChecker::GetStateFor(const CBlockIndex* pindexPrev, ThresholdConditionCache& cache) const
27 {
28 int nPeriod = Period();
29 int nThreshold = Threshold();
30 int min_activation_height = MinActivationHeight();
31 int64_t nTimeStart = BeginTime();
32 int64_t nTimeTimeout = EndTime();
33
34 // Check if this deployment is always active.
35 if (nTimeStart == Consensus::BIP9Deployment::ALWAYS_ACTIVE) {
36 return ThresholdState::ACTIVE;
37 }
38
39 // Check if this deployment is never active.
40 if (nTimeStart == Consensus::BIP9Deployment::NEVER_ACTIVE) {
41 return ThresholdState::FAILED;
42 }
43
44 // A block's state is always the same as that of the first of its period, so it is computed based on a pindexPrev whose height equals a multiple of nPeriod - 1.
45 if (pindexPrev != nullptr) {
46 pindexPrev = pindexPrev->GetAncestor(pindexPrev->nHeight - ((pindexPrev->nHeight + 1) % nPeriod));
47 }
48
49 // Walk backwards in steps of nPeriod to find a pindexPrev whose information is known
50 std::vector<const CBlockIndex*> vToCompute;
51 while (!cache.contains(pindexPrev)) {
52 if (pindexPrev == nullptr) {
53 // The genesis block is by definition defined.
54 cache[pindexPrev] = ThresholdState::DEFINED;
55 break;
56 }
57 if (pindexPrev->GetMedianTimePast() < nTimeStart) {
58 // Optimization: don't recompute down further, as we know every earlier block will be before the start time
59 cache[pindexPrev] = ThresholdState::DEFINED;
60 break;
61 }
62 vToCompute.push_back(pindexPrev);
63 pindexPrev = pindexPrev->GetAncestor(pindexPrev->nHeight - nPeriod);
64 }
65
66 // At this point, cache[pindexPrev] is known
67 assert(cache.contains(pindexPrev));
68 ThresholdState state = cache[pindexPrev];
69
70 // Now walk forward and compute the state of descendants of pindexPrev
71 while (!vToCompute.empty()) {
72 ThresholdState stateNext = state;
73 pindexPrev = vToCompute.back();
74 vToCompute.pop_back();
75
76 switch (state) {
77 case ThresholdState::DEFINED: {
78 if (pindexPrev->GetMedianTimePast() >= nTimeStart) {
79 stateNext = ThresholdState::STARTED;
80 }
81 break;
82 }
83 case ThresholdState::STARTED: {
84 // We need to count
85 const CBlockIndex* pindexCount = pindexPrev;
86 int count = 0;
87 for (int i = 0; i < nPeriod; i++) {
88 if (Condition(pindexCount)) {
89 count++;
90 }
91 pindexCount = pindexCount->pprev;
92 }
93 if (count >= nThreshold) {
94 stateNext = ThresholdState::LOCKED_IN;
95 } else if (pindexPrev->GetMedianTimePast() >= nTimeTimeout) {
96 stateNext = ThresholdState::FAILED;
97 }
98 break;
99 }
100 case ThresholdState::LOCKED_IN: {
101 // Progresses into ACTIVE provided activation height will have been reached.
102 if (pindexPrev->nHeight + 1 >= min_activation_height) {
103 stateNext = ThresholdState::ACTIVE;
104 }
105 break;
106 }
107 case ThresholdState::FAILED:
108 case ThresholdState::ACTIVE: {
109 // Nothing happens, these are terminal states.
110 break;
111 }
112 }
113 cache[pindexPrev] = state = stateNext;
114 }
115
116 return state;
117 }
118
119 BIP9Stats AbstractThresholdConditionChecker::GetStateStatisticsFor(const CBlockIndex* pindex, std::vector<bool>* signalling_blocks) const
120 {
121 BIP9Stats stats = {};
122
123 stats.period = Period();
124 stats.threshold = Threshold();
125
126 if (pindex == nullptr) return stats;
127
128 // Find how many blocks are in the current period
129 int blocks_in_period = 1 + (pindex->nHeight % stats.period);
130
131 // Reset signalling_blocks
132 if (signalling_blocks) {
133 signalling_blocks->assign(blocks_in_period, false);
134 }
135
136 // Count from current block to beginning of period
137 int elapsed = 0;
138 int count = 0;
139 const CBlockIndex* currentIndex = pindex;
140 do {
141 ++elapsed;
142 --blocks_in_period;
143 if (Condition(currentIndex)) {
144 ++count;
145 if (signalling_blocks) signalling_blocks->at(blocks_in_period) = true;
146 }
147 currentIndex = currentIndex->pprev;
148 } while(blocks_in_period > 0);
149
150 stats.elapsed = elapsed;
151 stats.count = count;
152 stats.possible = (stats.period - stats.threshold ) >= (stats.elapsed - count);
153
154 return stats;
155 }
156
157 int AbstractThresholdConditionChecker::GetStateSinceHeightFor(const CBlockIndex* pindexPrev, ThresholdConditionCache& cache) const
158 {
159 int64_t start_time = BeginTime();
160 if (start_time == Consensus::BIP9Deployment::ALWAYS_ACTIVE || start_time == Consensus::BIP9Deployment::NEVER_ACTIVE) {
161 return 0;
162 }
163
164 const ThresholdState initialState = GetStateFor(pindexPrev, cache);
165
166 // BIP 9 about state DEFINED: "The genesis block is by definition in this state for each deployment."
167 if (initialState == ThresholdState::DEFINED) {
168 return 0;
169 }
170
171 const int nPeriod = Period();
172
173 // A block's state is always the same as that of the first of its period, so it is computed based on a pindexPrev whose height equals a multiple of nPeriod - 1.
174 // To ease understanding of the following height calculation, it helps to remember that
175 // right now pindexPrev points to the block prior to the block that we are computing for, thus:
176 // if we are computing for the last block of a period, then pindexPrev points to the second to last block of the period, and
177 // if we are computing for the first block of a period, then pindexPrev points to the last block of the previous period.
178 // The parent of the genesis block is represented by nullptr.
179 pindexPrev = Assert(pindexPrev->GetAncestor(pindexPrev->nHeight - ((pindexPrev->nHeight + 1) % nPeriod)));
180
181 const CBlockIndex* previousPeriodParent = pindexPrev->GetAncestor(pindexPrev->nHeight - nPeriod);
182
183 while (previousPeriodParent != nullptr && GetStateFor(previousPeriodParent, cache) == initialState) {
184 pindexPrev = previousPeriodParent;
185 previousPeriodParent = pindexPrev->GetAncestor(pindexPrev->nHeight - nPeriod);
186 }
187
188 // Adjust the result because right now we point to the parent block.
189 return pindexPrev->nHeight + 1;
190 }
191
192 BIP9Info VersionBitsCache::Info(const CBlockIndex& block_index, const Consensus::Params& params, Consensus::DeploymentPos id)
193 {
194 BIP9Info result;
195
196 VersionBitsConditionChecker checker(params, id);
197
198 ThresholdState current_state, next_state;
199
200 {
201 LOCK(m_mutex);
202 current_state = checker.GetStateFor(block_index.pprev, m_caches[id]);
203 next_state = checker.GetStateFor(&block_index, m_caches[id]);
204 result.since = checker.GetStateSinceHeightFor(block_index.pprev, m_caches[id]);
205 }
206
207 result.current_state = StateName(current_state);
208 result.next_state = StateName(next_state);
209
210 const bool has_signal = (STARTED == current_state || LOCKED_IN == current_state);
211 if (has_signal) {
212 result.stats.emplace(checker.GetStateStatisticsFor(&block_index, &result.signalling_blocks));
213 if (LOCKED_IN == current_state) {
214 result.stats->threshold = 0;
215 result.stats->possible = false;
216 }
217 }
218
219 if (current_state == ACTIVE) {
220 result.active_since = result.since;
221 } else if (next_state == ACTIVE) {
222 result.active_since = block_index.nHeight + 1;
223 }
224
225 return result;
226 }
227
228 BIP9GBTStatus VersionBitsCache::GBTStatus(const CBlockIndex& block_index, const Consensus::Params& params)
229 {
230 BIP9GBTStatus result;
231
232 LOCK(m_mutex);
233 for (int i = 0; i < (int)Consensus::MAX_VERSION_BITS_DEPLOYMENTS; i++) {
234 auto pos = static_cast<Consensus::DeploymentPos>(i);
235 VersionBitsConditionChecker checker(params, pos);
236 ThresholdState state = checker.GetStateFor(&block_index, m_caches[pos]);
237 const VBDeploymentInfo& vbdepinfo = VersionBitsDeploymentInfo[pos];
238 BIP9GBTStatus::Info gbtinfo{.bit=params.vDeployments[pos].bit, .mask=checker.Mask(), .gbt_optional_rule=vbdepinfo.gbt_optional_rule};
239
240 switch (state) {
241 case DEFINED:
242 case FAILED:
243 // Not exposed to GBT
244 break;
245 case STARTED:
246 result.signalling.try_emplace(vbdepinfo.name, gbtinfo);
247 break;
248 case LOCKED_IN:
249 result.locked_in.try_emplace(vbdepinfo.name, gbtinfo);
250 break;
251 case ACTIVE:
252 result.active.try_emplace(vbdepinfo.name, gbtinfo);
253 break;
254 }
255 }
256 return result;
257 }
258
259 bool VersionBitsCache::IsActiveAfter(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos)
260 {
261 LOCK(m_mutex);
262 return ThresholdState::ACTIVE == VersionBitsConditionChecker(params, pos).GetStateFor(pindexPrev, m_caches[pos]);
263 }
264
265 static int32_t ComputeBlockVersion(const CBlockIndex* pindexPrev, const Consensus::Params& params, std::array<ThresholdConditionCache, Consensus::MAX_VERSION_BITS_DEPLOYMENTS>& caches)
266 {
267 int32_t nVersion = VERSIONBITS_TOP_BITS;
268
269 for (int i = 0; i < (int)Consensus::MAX_VERSION_BITS_DEPLOYMENTS; i++) {
270 Consensus::DeploymentPos pos = static_cast<Consensus::DeploymentPos>(i);
271 VersionBitsConditionChecker checker(params, pos);
272 ThresholdState state = checker.GetStateFor(pindexPrev, caches[pos]);
273 if (state == ThresholdState::LOCKED_IN || state == ThresholdState::STARTED) {
274 nVersion |= checker.Mask();
275 }
276 }
277
278 return nVersion;
279 }
280
281 int32_t VersionBitsCache::ComputeBlockVersion(const CBlockIndex* pindexPrev, const Consensus::Params& params)
282 {
283 LOCK(m_mutex);
284 return ::ComputeBlockVersion(pindexPrev, params, m_caches);
285 }
286
287 void VersionBitsCache::Clear()
288 {
289 LOCK(m_mutex);
290 for (unsigned int d = 0; d < Consensus::MAX_VERSION_BITS_DEPLOYMENTS; d++) {
291 m_caches[d].clear();
292 }
293 }
294
295 namespace {
296 /**
297 * Threshold condition checker that triggers when unknown versionbits are seen on the network.
298 */
299 class WarningBitsConditionChecker : public AbstractThresholdConditionChecker
300 {
301 private:
302 const Consensus::Params& m_params;
303 std::array<ThresholdConditionCache, Consensus::MAX_VERSION_BITS_DEPLOYMENTS>& m_caches;
304 int m_bit;
305 int period{2016};
306 int threshold{1815}; // 90% threshold used in BIP 341
307
308 public:
309 explicit WarningBitsConditionChecker(const CChainParams& chainparams, std::array<ThresholdConditionCache, Consensus::MAX_VERSION_BITS_DEPLOYMENTS>& caches, int bit)
310 : m_params{chainparams.GetConsensus()}, m_caches{caches}, m_bit(bit)
311 {
312 if (chainparams.IsTestChain()) {
313 period = chainparams.GetConsensus().DifficultyAdjustmentInterval();
314 threshold = period * 3 / 4; // 75% for test nets per BIP9 suggestion
315 }
316 }
317
318 int64_t BeginTime() const override { return 0; }
319 int64_t EndTime() const override { return std::numeric_limits<int64_t>::max(); }
320 int Period() const override { return period; }
321 int Threshold() const override { return threshold; }
322
323 bool Condition(const CBlockIndex* pindex) const override
324 {
325 return pindex->nHeight >= m_params.MinBIP9WarningHeight &&
326 ((pindex->nVersion & VERSIONBITS_TOP_MASK) == VERSIONBITS_TOP_BITS) &&
327 ((pindex->nVersion >> m_bit) & 1) != 0 &&
328 ((::ComputeBlockVersion(pindex->pprev, m_params, m_caches) >> m_bit) & 1) == 0;
329 }
330 };
331 } // anonymous namespace
332
333 std::vector<std::pair<int, bool>> VersionBitsCache::CheckUnknownActivations(const CBlockIndex* pindex, const CChainParams& chainparams)
334 {
335 LOCK(m_mutex);
336 std::vector<std::pair<int, bool>> result;
337 for (int bit = 0; bit < VERSIONBITS_NUM_BITS; ++bit) {
338 WarningBitsConditionChecker checker(chainparams, m_caches, bit);
339 ThresholdState state = checker.GetStateFor(pindex, m_warning_caches.at(bit));
340 if (state == ACTIVE || state == LOCKED_IN) {
341 result.emplace_back(bit, state == ACTIVE);
342 }
343 }
344 return result;
345 }
346