[#1806] engine: Allow to flush write-cache

Signed-off-by: Evgenii Stratonikov <evgeniy@morphbits.ru>

pkg/local_object_storage/engine/writecache.go

@@ -0,0 +1,33 @@
+package engine
+
+import (
+	"github.com/nspcc-dev/neofs-node/pkg/local_object_storage/shard"
+)
+
+// FlushWriteCachePrm groups the parameters of FlushWriteCache operation.
+type FlushWriteCachePrm struct {
+	shardID *shard.ID
+}
+
+// SetShardID is an option to set shard ID.
+//
+// Option is required.
+func (p *FlushWriteCachePrm) SetShardID(id *shard.ID) {
+	p.shardID = id
+}
+
+// FlushWriteCacheRes groups the resulting values of FlushWriteCache operation.
+type FlushWriteCacheRes struct{}
+
+// FlushWriteCache flushes write-cache on a single shard.
+func (e *StorageEngine) FlushWriteCache(p FlushWriteCachePrm) (FlushWriteCacheRes, error) {
+	e.mtx.RLock()
+	sh, ok := e.shards[p.shardID.String()]
+	e.mtx.RUnlock()
+
+	if !ok {
+		return FlushWriteCacheRes{}, errShardNotFound
+	}
+
+	return FlushWriteCacheRes{}, sh.FlushWriteCache()
+}

pkg/local_object_storage/shard/writecache.go

@@ -0,0 +1,36 @@
+package shard
+
+import (
+	"errors"
+
+	"github.com/nspcc-dev/neofs-node/pkg/local_object_storage/shard/mode"
+)
+
+// errWriteCacheDisabled is returned when an operation on write-cache is performed,
+// but write-cache is disabled.
+var errWriteCacheDisabled = errors.New("write-cache is disabled")
+
+// FlushWriteCache moves writecache in read-only mode and flushes all data from it.
+// After the operation writecache will remain read-only mode.
+func (s *Shard) FlushWriteCache() error {
+	if !s.hasWriteCache() {
+		return errWriteCacheDisabled
+	}
+
+	s.m.RLock()
+	defer s.m.RUnlock()
+
+	// To write data to the blobstor we need to write to the blobstor and the metabase.
+	if s.info.Mode.ReadOnly() {
+		return ErrReadOnlyMode
+	}
+	if s.info.Mode.NoMetabase() {
+		return ErrDegradedMode
+	}
+
+	if err := s.writeCache.SetMode(mode.ReadOnly); err != nil {
+		return err
+	}
+
+	return s.writeCache.Flush()
+}