feat(repair): implement blk repair structure and API

Author: lidatong

src/ballet/bmtree/fd_bmtree.h

@@ -151,6 +151,8 @@ struct __attribute__((packed)) fd_bmtree_node {
 };
 typedef struct fd_bmtree_node fd_bmtree_node_t;
 
+FD_STATIC_ASSERT( sizeof(fd_bmtree_node_t) == 32, update FD_SHRED_MERKLE_ROOT_SZ );
+
 /* bmtree_hash_leaf computes `SHA-256(prefix|data), where prefix is the
    first prefix_sz bytes of fd_bmtree_leaf_prefix.  prefix_sz is
    typically FD_BMTREE_LONG_PREFIX_SZ or FD_BMTREE_SHORT_PREFIX_SZ.

src/disco/net/xdp/fd_xdp_tile.c

@@ -753,6 +753,8 @@ net_rx_packet( fd_net_ctx_t *      ctx,
   } else if( FD_UNLIKELY( udp_dstport==ctx->repair_intake_listen_port ) ) {
     proto = DST_PROTO_REPAIR;
     out = ctx->repair_out;
+    // if( FD_UNLIKELY( sz == REPAIR_PING_SZ ) ) out = ctx->repair_out; /* ping-pong */
+    // else                                      out = ctx->shred_out;
   } else if( FD_UNLIKELY( udp_dstport==ctx->repair_serve_listen_port ) ) {
     proto = DST_PROTO_REPAIR;
     out = ctx->repair_out;

src/discof/repair/fd_fec_repair.h

@@ -66,8 +66,8 @@ struct fd_fec_intra {
   ulong prev; /* internal use by dlist */
   ulong next; /* internal use by map_chain */
 
-  ulong  slot; /* slot of the block this fec set is part of  */
-  ushort parent_off;
+  ulong  slot;        /* slot of the block this fec set is part of  */
+  ushort parent_off;  /* parent slot's offset from slot */
   uint   fec_set_idx; /* index of the first data shred */
   long   ts;          /* timestamp upon receiving the first shred */
   ulong  recv_cnt;    /* count of shreds received so far data + coding */