linux-kernel - Re: [PATCH 6/7] omfs: add checksumming routines

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Date:	Sat, 29 Mar 2008 23:30:06 -0400
From:	Bob Copeland <me@...copeland.com>
To:	Sergey Vlasov <vsu@...linux.ru>,
	Harvey Harrison <harvey.harrison@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 6/7] omfs: add checksumming routines

Version 2 of this patch, with changes:
 - use lib/crc-itu-t.c instead of open-coded version

>From 6ce3bb9ce2faaf937df0ec8e64c39e1adc403b2e Mon Sep 17 00:00:00 2001
From: Bob Copeland <me@...copeland.com>
Date: Thu, 27 Mar 2008 17:23:12 -0400
Subject: [PATCH] omfs: add checksumming routines

OMFS checksums the metadata of all filesystem objects.  This change adds
the necessary functions to do so.

Signed-off-by: Bob Copeland <me@...copeland.com>
---
 fs/omfs/checksum.c |   31 +++++++++++++++++++++++++++++++
 1 files changed, 31 insertions(+), 0 deletions(-)
 create mode 100644 fs/omfs/checksum.c

diff --git a/fs/omfs/checksum.c b/fs/omfs/checksum.c
new file mode 100644
index 0000000..cbd0471
--- /dev/null
+++ b/fs/omfs/checksum.c
@@ -0,0 +1,31 @@
+#include <linux/fs.h>
+#include <linux/buffer_head.h>
+#include <linux/crc-itu-t.h>
+#include "omfs.h"
+
+/*
+ * Update the header checksums for a dirty inode based on its contents.
+ * Caller is expected to hold the buffer head underlying oi and mark it
+ * dirty.
+ */
+int omfs_update_checksums(struct omfs_inode *oi)
+{
+	int ret = 0;
+	int xor, i, ofs = 0, count;
+	u16 crc = 0;
+	unsigned char *ptr = (unsigned char *) oi;
+
+	count = be32_to_cpu(oi->i_head.h_body_size);
+	ofs = sizeof(struct omfs_header);
+
+	crc = crc_itu_t(crc, ptr + ofs, count);
+	oi->i_head.h_crc = cpu_to_be16(crc);
+
+	xor = ptr[0];
+	for (i = 1; i < OMFS_XOR_COUNT; i++)
+		xor ^= ptr[i];
+
+	oi->i_head.h_check_xor = xor;
+
+	return ret;
+}
-- 
1.5.4.2.182.gb3092


-- 
Bob Copeland %% www.bobcopeland.com 

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