linux-kernel - Re: [PATCH v5 1/2] lib: add crc64 calculation routines

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Date:   Thu, 26 Jul 2018 13:02:10 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Coly Li <colyli@...e.de>
Cc:     linux-kernel@...r.kernel.org, linux-bcache@...r.kernel.org,
        linux-block@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Michael Lyle <mlyle@...e.org>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Eric Biggers <ebiggers3@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v5 1/2] lib: add crc64 calculation routines

On Thu, 26 Jul 2018 13:33:51 +0800 Coly Li <colyli@...e.de> wrote:

> This patch adds the re-write crc64 calculation routines for Linux kernel.
> The CRC64 polynomial arithmetic follows ECMA-182 specification, inspired
> by CRC paper of Dr. Ross N. Williams
> (see http://www.ross.net/crc/download/crc_v3.txt) and other public domain
> implementations.
> 
> All the changes work in this way,
> - When Linux kernel is built, host program lib/gen_crc64table.c will be
>   compiled to lib/gen_crc64table and executed.
> - The output of gen_crc64table execution is an array called as lookup
>   table (a.k.a POLY 0x42f0e1eba9ea369) which contain 256 64-bit long
>   numbers, this talbe is dumped into header file lib/crc64table.h.
> - Then the header file is included by lib/crc64.c for normal 64bit crc
>   calculation.
> - Function declaration of the crc64 calculation routines is placed in
>   include/linux/crc64.h
> 
> Currently bcache is the only user of crc64_be(), another potential user
> is bcachefs which is on the way to be in mainline kernel. Therefore it
> makes sense to move crc64 calculation into lib/crc64.c as public code.

delta from v4:

--- a/include/linux/crc64.h~lib-add-crc64-calculation-routines-v5
+++ a/include/linux/crc64.h
@@ -1,6 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /*
- * See lib/crc64.c for the related specification and polynomical arithmetic.
+ * See lib/crc64.c for the related specification and polynomial arithmetic.
  */
 #ifndef _LINUX_CRC64_H
 #define _LINUX_CRC64_H
--- a/lib/crc64.c~lib-add-crc64-calculation-routines-v5
+++ a/lib/crc64.c
@@ -12,7 +12,7 @@
  * from,
  * http://www.ross.net/crc/download/crc_v3.txt
  *
- * crc64table[256] is the lookup table of a table-driver 64-bit CRC
+ * crc64table[256] is the lookup table of a table-driven 64-bit CRC
  * calculation, which is generated by gen_crc64table.c in kernel build
  * time. The polynomial of crc64 arithmetic is from ECMA-182 specification
  * as well, which is defined as,
@@ -35,8 +35,8 @@ MODULE_LICENSE("GPL v2");
 
 /**
  * crc64_be - Calculate bitwise big-endian ECMA-182 CRC64
- * @crc: seed value for computation. 0 for a new CRC computing, or the
- *	previous crc64 value if computing incrementally.
+ * @crc: seed value for computation. 0 or (u64)~0 for a new CRC calculation,
+	or the previous crc64 value if computing incrementally.
  * @p: pointer to buffer over which CRC64 is run
  * @len: length of buffer @p
  */
--- a/lib/gen_crc64table.c~lib-add-crc64-calculation-routines-v5
+++ a/lib/gen_crc64table.c
@@ -1,13 +1,13 @@
 // SPDX-License-Identifier: GPL-2.0
 /*
- * Generate lookup table for the talbe-driven CRC64 calculation.
+ * Generate lookup table for the table-driven CRC64 calculation.
  *
  * gen_crc64table is executed in kernel build time and generates
  * lib/crc64table.h. This header is included by lib/crc64.c for
- * the table-driver CRC64 calculation.
+ * the table-driven CRC64 calculation.
  *
  * See lib/crc64.c for more information about which specification
- * and polynomical arithmetic that gen_crc64table.c follows to
+ * and polynomial arithmetic that gen_crc64table.c follows to
  * generate the lookup table.
  *
  * Copyright 2018 SUSE Linux.
@@ -20,7 +20,7 @@
 
 #define CRC64_ECMA182_POLY 0x42F0E1EBA9EA3693ULL
 
-static int64_t crc64_table[256] = {0};
+static uint64_t crc64_table[256] = {0};
 
 static void generate_crc64_table(void)
 {