crimson/os/seastore: do "copy_on_write" if the to-be-modified object

needs it

At present, only clone objects may need COW, as HEAD objects won't be
sharing any direct lba mapping with other objects in non-recovery
scenarios.

Although the HEAD object may share its direct mappings with the temp
object that's going to be recovered and replace it, it won't be
accepting any modifications at that time.

Signed-off-by: Xuehan Xu <[email protected]>

Author: xxhdx1985126

src/crimson/os/seastore/object_data_handler.cc

@@ -1383,6 +1383,36 @@ ObjectDataHandler::clear_ret ObjectDataHandler::clear(
     });
 }
 
+ObjectDataHandler::clone_ret
+ObjectDataHandler::copy_on_write(
+  context_t ctx)
+{
+  return with_object_data(
+    ctx,
+    [ctx, this](auto &object_data) -> clone_iertr::future<> {
+    auto mapping = co_await ctx.tm.get_pin(
+      ctx.t, object_data.get_reserved_data_base()
+    ).handle_error_interruptible(
+      clone_iertr::pass_further{},
+      crimson::ct_error::assert_all{"unexpected enoent"}
+    );
+    object_data_t d_object_data = get_null_object_data();
+    co_await do_clone(ctx, object_data, d_object_data, mapping, false);
+    auto old_base = object_data.get_reserved_data_base();
+    auto old_len = object_data.get_reserved_data_len();
+    object_data.update_reserved(
+      d_object_data.get_reserved_data_base(),
+      d_object_data.get_reserved_data_len());
+    ctx.onode.unset_need_cow(ctx.t);
+    co_await ctx.tm.remove_mappings_in_range(
+      ctx.t, old_base, old_len, std::move(mapping), {false, true}
+    ).handle_error_interruptible(
+      clone_iertr::pass_further{},
+      crimson::ct_error::assert_all{"unexpected enoent"}
+    ).discard_result();
+  });
+}
+
 ObjectDataHandler::clone_ret
 ObjectDataHandler::do_clone(
   context_t ctx,

src/crimson/os/seastore/object_data_handler.h

@@ -331,6 +331,8 @@ class ObjectDataHandler {
   using clone_ret = clone_iertr::future<>;
   clone_ret clone(context_t ctx);
 
+  clone_ret copy_on_write(context_t ctx);
+
 private:
   /// Updates region [_offset, _offset + bl.length) to bl
   write_ret overwrite(

src/crimson/os/seastore/seastore.cc

@@ -1891,12 +1891,18 @@ SeaStore::Shard::_remove(
       ObjectDataHandler(max_object_size),
       [&onode, this, &ctx](auto &objhandler)
     {
-      return objhandler.clear(
-        ObjectDataHandler::context_t{
-          *transaction_manager,
-          *ctx.transaction,
-          *onode,
-        });
+      auto fut = ObjectDataHandler::clone_iertr::now();
+      auto objctx = ObjectDataHandler::context_t{
+	  *transaction_manager,
+	  *ctx.transaction,
+	  *onode,
+	};
+      if (onode->need_cow()) {
+	fut = objhandler.copy_on_write(objctx);
+      }
+      return fut.si_then([&objhandler, objctx] {
+	return objhandler.clear(objctx);
+      });
     });
   }).si_then([this, &ctx, &onode] {
     return onode_manager->erase_onode(*ctx.transaction, onode);
@@ -1934,14 +1940,18 @@ SeaStore::Shard::_write(
     std::move(_bl),
     ObjectDataHandler(max_object_size),
     [=, this, &ctx, &onode](auto &bl, auto &objhandler) {
-      return objhandler.write(
-        ObjectDataHandler::context_t{
-          *transaction_manager,
-          *ctx.transaction,
-          onode,
-        },
-        offset,
-        bl);
+      auto fut = ObjectDataHandler::clone_iertr::now();
+      auto objctx = ObjectDataHandler::context_t{
+	  *transaction_manager,
+	  *ctx.transaction,
+	  onode,
+	};
+      if (onode.need_cow()) {
+	fut = objhandler.copy_on_write(objctx);
+      }
+      return fut.si_then([&objhandler, objctx, offset, &bl] {
+	return objhandler.write(objctx, offset, bl);
+      });
     });
 }
 
@@ -2023,14 +2033,18 @@ SeaStore::Shard::_zero(
   return seastar::do_with(
     ObjectDataHandler(max_object_size),
     [=, this, &ctx, &onode](auto &objhandler) {
-      return objhandler.zero(
-        ObjectDataHandler::context_t{
-          *transaction_manager,
-          *ctx.transaction,
-          onode,
-        },
-        offset,
-        len);
+    auto fut = ObjectDataHandler::clone_iertr::now();
+    auto objctx = ObjectDataHandler::context_t{
+	*transaction_manager,
+	*ctx.transaction,
+	onode,
+      };
+    if (onode.need_cow()) {
+      fut = objhandler.copy_on_write(objctx);
+    }
+    return fut.si_then([&objhandler, objctx, offset, len] {
+      return objhandler.zero(objctx, offset, len);
+    });
   });
 }
 
@@ -2079,13 +2093,18 @@ SeaStore::Shard::_truncate(
   return seastar::do_with(
     ObjectDataHandler(max_object_size),
     [=, this, &ctx, &onode](auto &objhandler) {
-    return objhandler.truncate(
-      ObjectDataHandler::context_t{
-        *transaction_manager,
-        *ctx.transaction,
-        onode
-      },
-      size);
+    auto fut = ObjectDataHandler::clone_iertr::now();
+    auto objctx = ObjectDataHandler::context_t{
+	*transaction_manager,
+	*ctx.transaction,
+	onode,
+      };
+    if (onode.need_cow()) {
+      fut = objhandler.copy_on_write(objctx);
+    }
+    return fut.si_then([&objhandler, objctx, size] {
+      return objhandler.truncate(objctx, size);
+    });
   });
 }