[contrib][linux] Add zstd_common module

The zstd_common module was added upstream in commit
torvalds/linux@637a642.

But the kernel specific code was inlined into the library. This commit
switches it to use the out of line method that we use for the other
modules.

contrib/linux-kernel/Makefile

@@ -59,6 +59,7 @@ libzstd:
 	mv linux/lib/zstd/zstd.h linux/include/linux/zstd_lib.h
 	mv linux/lib/zstd/zstd_errors.h linux/include/linux/
 	cp linux_zstd.h linux/include/linux/zstd.h
+	cp zstd_common_module.c linux/lib/zstd
 	cp zstd_compress_module.c linux/lib/zstd
 	cp zstd_decompress_module.c linux/lib/zstd
 	cp decompress_sources.h linux/lib/zstd

contrib/linux-kernel/linux.mk

@@ -10,16 +10,10 @@
 # ################################################################
 obj-$(CONFIG_ZSTD_COMPRESS) += zstd_compress.o
 obj-$(CONFIG_ZSTD_DECOMPRESS) += zstd_decompress.o
-
-ccflags-y += -Wno-error=deprecated-declarations
+obj-$(CONFIG_ZSTD_COMMON) += zstd_common.o
 
 zstd_compress-y := \
 		zstd_compress_module.o \
-		common/debug.o \
-		common/entropy_common.o \
-		common/error_private.o \
-		common/fse_decompress.o \
-		common/zstd_common.o \
 		compress/fse_compress.o \
 		compress/hist.o \
 		compress/huf_compress.o \
@@ -35,13 +29,16 @@ zstd_compress-y := \
 
 zstd_decompress-y := \
 		zstd_decompress_module.o \
+		decompress/huf_decompress_amd64.o \
+		decompress/huf_decompress.o \
+		decompress/zstd_ddict.o \
+		decompress/zstd_decompress.o \
+		decompress/zstd_decompress_block.o \
+
+zstd_common-y := \
+		zstd_common_module.o \
 		common/debug.o \
 		common/entropy_common.o \
 		common/error_private.o \
 		common/fse_decompress.o \
 		common/zstd_common.o \
-		decompress/huf_decompress.o \
-		decompress/huf_decompress_amd64.o \
-		decompress/zstd_ddict.o \
-		decompress/zstd_decompress.o \
-		decompress/zstd_decompress_block.o \

contrib/linux-kernel/zstd_common_module.c

@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0+ OR BSD-3-Clause
+/*
+ * Copyright (c) Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under both the BSD-style license (found in the
+ * LICENSE file in the root directory of this source tree) and the GPLv2 (found
+ * in the COPYING file in the root directory of this source tree).
+ * You may select, at your option, one of the above-listed licenses.
+ */
+
+#include <linux/module.h>
+
+#include "common/huf.h"
+#include "common/fse.h"
+#include "common/zstd_internal.h"
+
+// Export symbols shared by compress and decompress into a common module
+
+#undef ZSTD_isError   /* defined within zstd_internal.h */
+EXPORT_SYMBOL_GPL(FSE_readNCount);
+EXPORT_SYMBOL_GPL(HUF_readStats);
+EXPORT_SYMBOL_GPL(HUF_readStats_wksp);
+EXPORT_SYMBOL_GPL(ZSTD_isError);
+EXPORT_SYMBOL_GPL(ZSTD_getErrorName);
+EXPORT_SYMBOL_GPL(ZSTD_getErrorCode);
+EXPORT_SYMBOL_GPL(ZSTD_customMalloc);
+EXPORT_SYMBOL_GPL(ZSTD_customCalloc);
+EXPORT_SYMBOL_GPL(ZSTD_customFree);
+
+MODULE_LICENSE("Dual BSD/GPL");
+MODULE_DESCRIPTION("Zstd Common");