uses first_coding_index for erasure meta obtained from coding shreds (#23974)

Now that nodes correctly populate position field in coding shreds, and
first_coding_index in erasure meta, the old code to maintain backward
compatibility can be removed.
The commit is working towards changing erasure coding schema to 32:64.

ledger/src/blockstore.rs

@@ -1108,10 +1108,9 @@ impl Blockstore {
     }
 
     fn erasure_mismatch(shred1: &Shred, shred2: &Shred) -> bool {
-        // TODO should also compare first-coding-index once position field is
-        // populated across cluster.
         shred1.coding_header.num_coding_shreds != shred2.coding_header.num_coding_shreds
             || shred1.coding_header.num_data_shreds != shred2.coding_header.num_data_shreds
+            || shred1.first_coding_index() != shred2.first_coding_index()
     }
 
     #[allow(clippy::too_many_arguments)]
@@ -6094,7 +6093,7 @@ pub mod tests {
             );
             coding_shred.common_header.fec_set_index = std::u32::MAX - 1;
             coding_shred.coding_header.num_data_shreds = 2;
-            coding_shred.coding_header.num_coding_shreds = 3;
+            coding_shred.coding_header.num_coding_shreds = 4;
             coding_shred.coding_header.position = 1;
             coding_shred.common_header.index = std::u32::MAX - 1;
             assert!(!Blockstore::should_insert_coding_shred(

ledger/src/blockstore_meta.rs

@@ -257,10 +257,6 @@ impl ErasureMeta {
             None => return false,
         };
         other.__unused_size = self.__unused_size;
-        // Ignore first_coding_index field for now to be backward compatible.
-        // TODO remove this once cluster is upgraded to always populate
-        // first_coding_index field.
-        other.first_coding_index = self.first_coding_index;
         self == &other
     }
 
@@ -275,16 +271,7 @@ impl ErasureMeta {
 
     pub(crate) fn coding_shreds_indices(&self) -> Range<u64> {
         let num_coding = self.config.num_coding() as u64;
-        // first_coding_index == 0 may imply that the field is not populated.
-        // self.set_index to be backward compatible.
-        // TODO remove this once cluster is upgraded to always populate
-        // first_coding_index field.
-        let first_coding_index = if self.first_coding_index == 0 {
-            self.set_index
-        } else {
-            self.first_coding_index
-        };
-        first_coding_index..first_coding_index + num_coding
+        self.first_coding_index..self.first_coding_index + num_coding
     }
 
     pub(crate) fn status(&self, index: &Index) -> ErasureMetaStatus {

ledger/src/shred.rs

@@ -504,9 +504,10 @@ impl Shred {
     pub(crate) fn first_coding_index(&self) -> Option<u32> {
         match self.shred_type() {
             ShredType::Data => None,
-            // TODO should be: self.index() - self.coding_header.position
-            // once position field is populated.
-            ShredType::Code => Some(self.fec_set_index()),
+            ShredType::Code => {
+                let position = u32::from(self.coding_header.position);
+                self.index().checked_sub(position)
+            }
         }
     }
 
@@ -536,25 +537,25 @@ impl Shred {
 
     // Returns the block index within the erasure coding set.
     fn erasure_block_index(&self) -> Option<usize> {
-        let index = self.index().checked_sub(self.fec_set_index())?;
-        let index = usize::try_from(index).ok()?;
         match self.shred_type() {
-            ShredType::Data => Some(index),
+            ShredType::Data => {
+                let index = self.index().checked_sub(self.fec_set_index())?;
+                usize::try_from(index).ok()
+            }
             ShredType::Code => {
-                // TODO should use first_coding_index once position field is
-                // populated.
                 // Assert that the last shred index in the erasure set does not
                 // overshoot u32.
                 self.fec_set_index().checked_add(u32::from(
-                    self.coding_header
-                        .num_data_shreds
-                        .max(self.coding_header.num_coding_shreds)
-                        .checked_sub(1)?,
+                    self.coding_header.num_data_shreds.checked_sub(1)?,
+                ))?;
+                self.first_coding_index()?.checked_add(u32::from(
+                    self.coding_header.num_coding_shreds.checked_sub(1)?,
                 ))?;
                 let num_data_shreds = usize::from(self.coding_header.num_data_shreds);
                 let num_coding_shreds = usize::from(self.coding_header.num_coding_shreds);
+                let position = usize::from(self.coding_header.position);
                 let fec_set_size = num_data_shreds.checked_add(num_coding_shreds)?;
-                let index = index.checked_add(num_data_shreds)?;
+                let index = position.checked_add(num_data_shreds)?;
                 (index < fec_set_size).then(|| index)
             }
         }