xz: switch from public domain to BSD Zero Clause License (0BSD)

Remove the public domain notices and add SPDX license identifiers.

Change MODULE_LICENSE from "GPL" to "Dual BSD/GPL" because 0BSD should
count as a BSD license variant here.

The switch to 0BSD was done in the upstream XZ Embedded project because
public domain has (real or perceived) legal issues in some jurisdictions.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Lasse Collin <[e-mail]>
Reviewed-by: Sam James <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Albert Ou <[e-mail]>
Cc: Catalin Marinas <[e-mail]>
Cc: Emil Renner Berthing <[e-mail]>
Cc: Herbert Xu <[e-mail]>
Cc: Joel Stanley <[e-mail]>
Cc: Jonathan Corbet <[e-mail]>
Cc: Jubin Zhong <[e-mail]>
Cc: Jules Maselbas <[e-mail]>
Cc: Krzysztof Kozlowski <[e-mail]>
Cc: Michael Ellerman <[e-mail]>
Cc: Palmer Dabbelt <[e-mail]>
Cc: Paul Walmsley <[e-mail]>
Cc: Randy Dunlap <[e-mail]>
Cc: Rui Li <[e-mail]>
Cc: Simon Glass <[e-mail]>
Cc: Will Deacon <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

include/linux/decompress/unxz.h

···
+/* SPDX-License-Identifier: 0BSD */
+
 /*
  * Wrapper for decompressing XZ-compressed kernel, initramfs, and initrd
  *
  * Author: Lasse Collin <[e-mail]>
- *
- * This file has been put into the public domain.
- * You can do whatever you want with this file.
  */
 
 #ifndef DECOMPRESS_UNXZ_H

include/linux/xz.h

···
+/* SPDX-License-Identifier: 0BSD */
+
 /*
  * XZ decompressor
  *
  * Authors: Lasse Collin <[e-mail]>
  *          Igor Pavlov <https://7-zip.org/>
- *
- * This file has been put into the public domain.
- * You can do whatever you want with this file.
  */
 
 #ifndef XZ_H

lib/decompress_unxz.c

···
+// SPDX-License-Identifier: 0BSD
+
 /*
  * Wrapper for decompressing XZ-compressed kernel, initramfs, and initrd
  *
  * Author: Lasse Collin <[e-mail]>
- *
- * This file has been put into the public domain.
- * You can do whatever you want with this file.
  */
 
 /*

lib/xz/xz_crc32.c

···
+// SPDX-License-Identifier: 0BSD
+
 /*
  * CRC32 using the polynomial from IEEE-802.3
  *
  * Authors: Lasse Collin <[e-mail]>
  *          Igor Pavlov <https://7-zip.org/>
- *
- * This file has been put into the public domain.
- * You can do whatever you want with this file.
  */
 
 /*

lib/xz/xz_dec_bcj.c

···
+// SPDX-License-Identifier: 0BSD
+
 /*
  * Branch/Call/Jump (BCJ) filter decoders
  *
  * Authors: Lasse Collin <[e-mail]>
  *          Igor Pavlov <https://7-zip.org/>
- *
- * This file has been put into the public domain.
- * You can do whatever you want with this file.
  */
 
 #include "xz_private.h"

lib/xz/xz_dec_lzma2.c

···
+// SPDX-License-Identifier: 0BSD
+
 /*
  * LZMA2 decoder
  *
  * Authors: Lasse Collin <[e-mail]>
  *          Igor Pavlov <https://7-zip.org/>
- *
- * This file has been put into the public domain.
- * You can do whatever you want with this file.
  */
 
 #include "xz_private.h"

lib/xz/xz_dec_stream.c

···
+// SPDX-License-Identifier: 0BSD
+
 /*
  * .xz Stream decoder
  *
  * Author: Lasse Collin <[e-mail]>
- *
- * This file has been put into the public domain.
- * You can do whatever you want with this file.
  */
 
 #include "xz_private.h"

lib/xz/xz_dec_syms.c

···
+// SPDX-License-Identifier: 0BSD
+
 /*
  * XZ decoder module information
  *
  * Author: Lasse Collin <[e-mail]>
- *
- * This file has been put into the public domain.
- * You can do whatever you want with this file.
  */
 
 #include <linux/module.h>
···
 MODULE_DESCRIPTION("XZ decompressor");
 MODULE_VERSION("1.1");
 MODULE_AUTHOR("Lasse Collin <[e-mail]> and Igor Pavlov");
-
-/*
- * This code is in the public domain, but in Linux it's simplest to just
- * say it's GPL and consider the authors as the copyright holders.
- */
-MODULE_LICENSE("GPL");
+MODULE_LICENSE("Dual BSD/GPL");

lib/xz/xz_dec_test.c

···
+// SPDX-License-Identifier: 0BSD
+
 /*
  * XZ decoder tester
  *
  * Author: Lasse Collin <[e-mail]>
- *
- * This file has been put into the public domain.
- * You can do whatever you want with this file.
  */
 
 #include <linux/kernel.h>
···
 MODULE_DESCRIPTION("XZ decompressor tester");
 MODULE_VERSION("1.0");
 MODULE_AUTHOR("Lasse Collin <[e-mail]>");
-
-/*
- * This code is in the public domain, but in Linux it's simplest to just
- * say it's GPL and consider the authors as the copyright holders.
- */
-MODULE_LICENSE("GPL");
+MODULE_LICENSE("Dual BSD/GPL");

lib/xz/xz_lzma2.h

···
+/* SPDX-License-Identifier: 0BSD */
+
 /*
  * LZMA2 definitions
  *
  * Authors: Lasse Collin <[e-mail]>
  *          Igor Pavlov <https://7-zip.org/>
- *
- * This file has been put into the public domain.
- * You can do whatever you want with this file.
  */
 
 #ifndef XZ_LZMA2_H

lib/xz/xz_private.h

···
+/* SPDX-License-Identifier: 0BSD */
+
 /*
  * Private includes and definitions
  *
  * Author: Lasse Collin <[e-mail]>
- *
- * This file has been put into the public domain.
- * You can do whatever you want with this file.
  */
 
 #ifndef XZ_PRIVATE_H

lib/xz/xz_stream.h

···
+/* SPDX-License-Identifier: 0BSD */
+
 /*
  * Definitions for handling the .xz file format
  *
  * Author: Lasse Collin <[e-mail]>
- *
- * This file has been put into the public domain.
- * You can do whatever you want with this file.
  */
 
 #ifndef XZ_STREAM_H

scripts/xz_wrap.sh

···
 #!/bin/sh
+# SPDX-License-Identifier: 0BSD
 #
 # This is a wrapper for xz to compress the kernel image using appropriate
 # compression options depending on the architecture.
 #
 # Author: Lasse Collin <[e-mail]>
-#
-# This file has been put into the public domain.
-# You can do whatever you want with this file.
-#
 
 BCJ=
 LZMA2OPTS=