From ac4981160e790368cbb49b469937bee83edd26fb Mon Sep 17 00:00:00 2001
From: Xuehan Xu <xuxuehan@qianxin.com>
Date: Thu, 16 May 2024 14:56:20 +0800
Subject: [PATCH] crimson/os/seastore: add comments to highlight necessary
 invariants

Signed-off-by: Xuehan Xu <xuxuehan@qianxin.com>
---
 src/crimson/os/seastore/btree/fixed_kv_btree.h | 6 ++++++
 src/crimson/os/seastore/transaction_manager.h  | 4 ++++
 2 files changed, 10 insertions(+)

diff --git a/src/crimson/os/seastore/btree/fixed_kv_btree.h b/src/crimson/os/seastore/btree/fixed_kv_btree.h
index b0901213716..9a8dd52c361 100644
--- a/src/crimson/os/seastore/btree/fixed_kv_btree.h
+++ b/src/crimson/os/seastore/btree/fixed_kv_btree.h
@@ -1515,6 +1515,8 @@ private:
     };
 
     auto v = parent->template get_child<internal_node_t>(c, node_iter);
+    // checking the lba child must be atomic with creating
+    // and linking the absent child
     if (v.has_child()) {
       return v.get_child_fut().safe_then(
         [on_found=std::move(on_found), node_iter, c,
@@ -1583,6 +1585,8 @@ private:
     };
 
     auto v = parent->template get_child<leaf_node_t>(c, node_iter);
+    // checking the lba child must be atomic with creating
+    // and linking the absent child
     if (v.has_child()) {
       return v.get_child_fut().safe_then(
         [on_found=std::move(on_found), node_iter, c,
@@ -2136,6 +2140,8 @@ private:
     };
 
     auto v = parent_pos.node->template get_child<NodeType>(c, donor_iter);
+    // checking the lba child must be atomic with creating
+    // and linking the absent child
     if (v.has_child()) {
       return v.get_child_fut().safe_then(
         [do_merge=std::move(do_merge), &pos,
diff --git a/src/crimson/os/seastore/transaction_manager.h b/src/crimson/os/seastore/transaction_manager.h
index a6ee603866b..66574cc4225 100644
--- a/src/crimson/os/seastore/transaction_manager.h
+++ b/src/crimson/os/seastore/transaction_manager.h
@@ -176,6 +176,8 @@ public:
     Transaction &t,
     LBAMappingRef pin)
   {
+    // checking the lba child must be atomic with creating
+    // and linking the absent child
     auto ret = get_extent_if_linked<T>(t, std::move(pin));
     if (ret.index() == 1) {
       return std::move(std::get<1>(ret));
@@ -214,6 +216,8 @@ public:
     extent_types_t type)
   {
     auto v = pin->get_logical_extent(t);
+    // checking the lba child must be atomic with creating
+    // and linking the absent child
     if (v.has_child()) {
       return std::move(v.get_child_fut());
     } else {
-- 
2.39.5