add interface to get blk alloc hints for chunks on same pg (#70)

* add interface to get blk alloc hints for chunks on same pg.
Specifically we bind PG to single PDEV,  the `chunk_to_hint` will check the pdev of pass-in chunk and fills the hint with pdev id of the pass-in chunk

src/lib/homestore/heap_chunk_selector.cpp

@@ -117,4 +117,16 @@ void HeapChunkSelector::build_per_dev_chunk_heap(const std::unordered_set< chunk
         if (excludingChunks.find(p.first) == excludingChunks.end()) { add_chunk_internal(p.first); }
     };
 }
-} // namespace homeobject
+
+homestore::blk_alloc_hints HeapChunkSelector::chunk_to_hints(chunk_num_t chunk_id) const {
+    auto iter = m_chunks.find(chunk_id);
+    if (iter == m_chunks.end()) {
+        LOGWARNMOD(homeobject, "No chunk found for chunk_id {}, will return default blk alloc hints", chunk_id);
+        return homestore::blk_alloc_hints();
+    }
+    homestore::blk_alloc_hints hints;
+    hints.pdev_id_hint = VChunk(iter->second).get_pdev_id();
+    return hints;
+}
+
+} // namespace homeobject

src/lib/homestore/heap_chunk_selector.h

@@ -1,5 +1,7 @@
 #pragma once
 
+#include "homeobject/common.hpp"
+
 #include <homestore/chunk_selector.h>
 #include <homestore/vchunk.h>
 #include <homestore/homestore_decl.hpp>
@@ -46,6 +48,8 @@ class HeapChunkSelector : public homestore::ChunkSelector {
     // this should be called after ShardManager is initialized and get all the open shards
     void build_per_dev_chunk_heap(const std::unordered_set< chunk_num_t >& excludingChunks);
 
+    homestore::blk_alloc_hints chunk_to_hints(chunk_num_t chunk_id) const;
+
 private:
     std::unordered_map< uint32_t, std::shared_ptr< PerDevHeap > > m_per_dev_heap;
 
@@ -54,4 +58,4 @@ class HeapChunkSelector : public homestore::ChunkSelector {
 
     void add_chunk_internal(const chunk_num_t);
 };
-} // namespace homeobject
+} // namespace homeobject