adds rollout path to for chained Merkle shreds

The commit adds should_chain_merkle_shreds to incrementally roll out
chained Merkle shreds to clusters.

ledger/src/shred.rs

@@ -692,7 +692,7 @@ pub mod layout {
         Ok(flags & ShredFlags::SHRED_TICK_REFERENCE_MASK.bits())
     }
 
-    pub(crate) fn get_merkle_root(shred: &[u8]) -> Option<Hash> {
+    pub fn get_merkle_root(shred: &[u8]) -> Option<Hash> {
         match get_shred_variant(shred).ok()? {
             ShredVariant::LegacyCode | ShredVariant::LegacyData => None,
             ShredVariant::MerkleCode(proof_size, chained) => {

ledger/src/shred/stats.rs

@@ -23,6 +23,8 @@ pub struct ProcessShredsStats {
     num_data_shreds_hist: [usize; 5],
     // If the blockstore already has shreds for the broadcast slot.
     pub num_extant_slots: u64,
+    // When looking up chained merkle root from parent slot fails.
+    pub err_unknown_chained_merkle_root: u64,
     pub(crate) data_buffer_residual: usize,
     pub num_merkle_data_shreds: usize,
     pub num_merkle_coding_shreds: usize,
@@ -89,6 +91,11 @@ impl ProcessShredsStats {
             ("sign_coding_time", self.sign_coding_elapsed, i64),
             ("coding_send_time", self.coding_send_elapsed, i64),
             ("num_extant_slots", self.num_extant_slots, i64),
+            (
+                "err_unknown_chained_merkle_root",
+                self.err_unknown_chained_merkle_root,
+                i64
+            ),
             ("data_buffer_residual", self.data_buffer_residual, i64),
             ("num_data_shreds_07", self.num_data_shreds_hist[0], i64),
             ("num_data_shreds_15", self.num_data_shreds_hist[1], i64),
@@ -161,6 +168,7 @@ impl AddAssign<ProcessShredsStats> for ProcessShredsStats {
             coalesce_elapsed,
             num_data_shreds_hist,
             num_extant_slots,
+            err_unknown_chained_merkle_root,
             data_buffer_residual,
             num_merkle_data_shreds,
             num_merkle_coding_shreds,
@@ -175,6 +183,7 @@ impl AddAssign<ProcessShredsStats> for ProcessShredsStats {
         self.get_leader_schedule_elapsed += get_leader_schedule_elapsed;
         self.coalesce_elapsed += coalesce_elapsed;
         self.num_extant_slots += num_extant_slots;
+        self.err_unknown_chained_merkle_root += err_unknown_chained_merkle_root;
         self.data_buffer_residual += data_buffer_residual;
         self.num_merkle_data_shreds += num_merkle_data_shreds;
         self.num_merkle_coding_shreds += num_merkle_coding_shreds;

turbine/src/broadcast_stage.rs

@@ -66,6 +66,8 @@ pub enum Error {
     Blockstore(#[from] solana_ledger::blockstore::BlockstoreError),
     #[error(transparent)]
     ClusterInfo(#[from] solana_gossip::cluster_info::ClusterInfoError),
+    #[error("Invalid Merkle root, slot: {slot}, index: {index}")]
+    InvalidMerkleRoot { slot: Slot, index: u64 },
     #[error(transparent)]
     Io(#[from] std::io::Error),
     #[error(transparent)]
@@ -76,8 +78,14 @@ pub enum Error {
     Send,
     #[error(transparent)]
     Serialize(#[from] std::boxed::Box<bincode::ErrorKind>),
+    #[error("Shred not found, slot: {slot}, index: {index}")]
+    ShredNotFound { slot: Slot, index: u64 },
     #[error(transparent)]
     TransportError(#[from] solana_sdk::transport::TransportError),
+    #[error("Unknown last index, slot: {0}")]
+    UnknownLastIndex(Slot),
+    #[error("Unknown slot meta, slot: {0}")]
+    UnknownSlotMeta(Slot),
 }
 
 type Result<T> = std::result::Result<T, Error>;

turbine/src/broadcast_stage/broadcast_utils.rs

@@ -1,12 +1,15 @@
 use {
-    super::Result,
+    super::{Error, Result},
     bincode::serialized_size,
     crossbeam_channel::Receiver,
     solana_entry::entry::Entry,
-    solana_ledger::shred::ShredData,
+    solana_ledger::{
+        blockstore::Blockstore,
+        shred::{self, ShredData},
+    },
     solana_poh::poh_recorder::WorkingBankEntry,
     solana_runtime::bank::Bank,
-    solana_sdk::clock::Slot,
+    solana_sdk::{clock::Slot, hash::Hash},
     std::{
         sync::Arc,
         time::{Duration, Instant},
@@ -25,6 +28,7 @@ pub(super) struct ReceiveResults {
 
 #[derive(Clone)]
 pub struct UnfinishedSlotInfo {
+    pub(super) chained_merkle_root: Hash,
     pub next_shred_index: u32,
     pub(crate) next_code_index: u32,
     pub slot: Slot,
@@ -96,6 +100,34 @@ pub(super) fn recv_slot_entries(receiver: &Receiver<WorkingBankEntry>) -> Result
     })
 }
 
+// Returns the Merkle root of the last erasure batch of the parent slot.
+pub(super) fn get_chained_merkle_root_from_parent(
+    slot: Slot,
+    parent: Slot,
+    blockstore: &Blockstore,
+) -> Result<Hash> {
+    if slot == parent {
+        debug_assert_eq!(slot, 0u64);
+        return Ok(Hash::default());
+    }
+    debug_assert!(parent < slot, "parent: {parent} >= slot: {slot}");
+    let index = blockstore
+        .meta(parent)?
+        .ok_or_else(|| Error::UnknownSlotMeta(parent))?
+        .last_index
+        .ok_or_else(|| Error::UnknownLastIndex(parent))?;
+    let shred = blockstore
+        .get_data_shred(parent, index)?
+        .ok_or(Error::ShredNotFound {
+            slot: parent,
+            index,
+        })?;
+    shred::layout::get_merkle_root(&shred).ok_or(Error::InvalidMerkleRoot {
+        slot: parent,
+        index,
+    })
+}
+
 #[cfg(test)]
 mod tests {
     use {