box: introduce tuple_chunk infrastructure

Introduced a new object tuple_chunk: a memory allocation is
associated with given tuple. tuple_format's vtab is extended
with few new methods to manage tuple_chunks lifecycle.
Implemented corresponding methid for memtx engine: a memory
chunks are allocated with memtx's smalloc allocator.

Needed for #1260

src/box/memtx_engine.c

@@ -1126,9 +1126,36 @@ memtx_tuple_delete(struct tuple_format *format, struct tuple *tuple)
 		smfree_delayed(&memtx->alloc, memtx_tuple, total);
 }
 
+void
+metmx_tuple_chunk_delete(struct tuple_format *format,
+			 struct tuple_chunk *tuple_chunk)
+{
+	struct memtx_engine *memtx = (struct memtx_engine *)format->engine;
+	uint32_t sz = tuple_chunk_sz(tuple_chunk->data_sz);
+	smfree(&memtx->alloc, tuple_chunk, sz);
+}
+
+struct tuple_chunk *
+memtx_tuple_chunk_new(struct tuple_format *format, struct tuple *tuple,
+		      uint32_t data_sz)
+{
+	struct memtx_engine *memtx = (struct memtx_engine *)format->engine;
+	uint32_t sz = tuple_chunk_sz(data_sz);
+	struct tuple_chunk *tuple_chunk =
+		(struct tuple_chunk *) smalloc(&memtx->alloc, sz);
+	if (tuple == NULL) {
+		diag_set(OutOfMemory, sz, "smalloc", "tuple");
+		return NULL;
+	}
+	tuple_chunk->data_sz = data_sz;
+	return tuple_chunk;
+}
+
 struct tuple_format_vtab memtx_tuple_format_vtab = {
 	memtx_tuple_delete,
 	memtx_tuple_new,
+	metmx_tuple_chunk_delete,
+	memtx_tuple_chunk_new,
 };
 
 /**

src/box/tuple.c

@@ -67,6 +67,8 @@ runtime_tuple_new(struct tuple_format *format, const char *data, const char *end
 static struct tuple_format_vtab tuple_format_runtime_vtab = {
 	runtime_tuple_delete,
 	runtime_tuple_new,
+	NULL,
+	NULL,
 };
 
 static struct tuple *
@@ -785,3 +787,9 @@ mp_str(const char *data)
 		return "<failed to format message pack>";
 	return buf;
 }
+
+uint32_t
+tuple_chunk_sz(uint32_t data_sz)
+{
+	return sizeof(struct tuple_chunk) + data_sz;
+}

src/box/tuple.h

@@ -447,6 +447,34 @@ tuple_delete(struct tuple *tuple)
 	format->vtab.tuple_delete(format, tuple);
 }
 
+/** Tuple chunk memory object. */
+struct tuple_chunk {
+	/** The payload size. Needed to perform memory release.*/
+	uint32_t data_sz;
+	/** Metadata object payload. */
+	char data[0];
+};
+
+/** Calculate the size of tuple_chunk object by given data_sz. */
+uint32_t
+tuple_chunk_sz(uint32_t data_sz);
+
+/** Allocate a new tuple_chunk for given tuple. */
+static inline struct tuple_chunk *
+tuple_chunk_new(struct tuple *tuple, uint32_t data_sz)
+{
+	struct tuple_format *format = tuple_format(tuple);
+	return format->vtab.tuple_chunk_new(format, tuple, data_sz);
+}
+
+/** Free a tuple_chunk is allocated for given tuple. */
+static inline void
+tuple_chunk_delete(struct tuple *tuple, struct tuple_chunk *tuple_chunk)
+{
+	struct tuple_format *format = tuple_format(tuple);
+	format->vtab.tuple_chunk_delete(format, tuple_chunk);
+}
+
 /**
  * Check tuple data correspondence to space format.
  * Actually, checks everything that is checked by

src/box/tuple_format.h

@@ -64,6 +64,7 @@ enum { TUPLE_INDEX_BASE = 1 };
 enum { TUPLE_OFFSET_SLOT_NIL = INT32_MAX };
 
 struct tuple;
+struct tuple_chunk;
 struct tuple_format;
 struct coll;
 
@@ -82,6 +83,14 @@ struct tuple_format_vtab {
 	struct tuple*
 	(*tuple_new)(struct tuple_format *format, const char *data,
 	             const char *end);
+	/** Free a tuple_chunk allocated for given tuple. */
+	void
+	(*tuple_chunk_delete)(struct tuple_format *format,
+			      struct tuple_chunk *tuple_chunk);
+	/** Allocate a new tuple_chunk for given tuple. */
+	struct tuple_chunk *
+	(*tuple_chunk_new)(struct tuple_format *format, struct tuple *tuple,
+			   uint32_t data_sz);
 };
 
 /** Tuple field meta information for tuple_format. */

src/box/vy_stmt.c

@@ -118,6 +118,8 @@ vy_stmt_env_create(struct vy_stmt_env *env)
 {
 	env->tuple_format_vtab.tuple_new = vy_tuple_new;
 	env->tuple_format_vtab.tuple_delete = vy_tuple_delete;
+	env->tuple_format_vtab.tuple_chunk_new = NULL;
+	env->tuple_format_vtab.tuple_chunk_delete = NULL;
 	env->max_tuple_size = 1024 * 1024;
 	env->key_format = vy_stmt_format_new(env, NULL, 0, NULL, 0, 0, NULL);
 	if (env->key_format == NULL)