[PATCH 6/7] omfs: add checksumming routines

[PATCH 6/7] omfs: add checksumming routines

[Bob Copeland]

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

    Signed-off-by: Bob Copeland <me@bobcopeland.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

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

[Christoph Hellwig]

On Sat, Apr 12, 2008 at 06:58:40PM -0400, Bob Copeland wrote:
>     OMFS checksums the metadata of all filesystem objects.  This change adds
>     the necessary functions to do so.

Looks good, but do we really need a separate source file for this one
routine?

[PATCH 6/7] omfs: add checksumming routines

[Bob Copeland]

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

Signed-off-by: Bob Copeland <me@bobcopeland.com>
---
 fs/omfs/checksum.c |   48 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 48 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..d6f1023
--- /dev/null
+++ b/fs/omfs/checksum.c
@@ -0,0 +1,48 @@
+#include <linux/fs.h>
+#include <linux/buffer_head.h>
+#include "omfs.h"
+
+#define POLY 0x1021
+
+/*
+ * crc-ccitt with MSB first (i.e., backwards), so we can't use the
+ * kernel table as-is.
+ */
+static u16 omfs_crc(u16 crc, unsigned char *buf, int count)
+{
+	int i, j;
+	for (i = 0; i < count; i++) {
+		crc ^= buf[i] << 8;
+		for (j = 0; j < 8; j++)
+			crc = (crc << 1) ^ ((crc & 0x8000) ? POLY : 0);
+	}
+	return crc;
+}
+
+/*
+ * 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, struct super_block *sb,
+		ino_t ino)
+{
+	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 = omfs_crc(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

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

[Harvey Harrison]

On Wed, 2008-03-26 at 20:45 -0400, Bob Copeland wrote:
> OMFS checksums the metadata of all filesystem objects.  This change adds
> the necessary functions to do so.
> 
> Signed-off-by: Bob Copeland <me@bobcopeland.com>
> ---
>  fs/omfs/checksum.c |   48 ++++++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 48 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..d6f1023
> --- /dev/null
> +++ b/fs/omfs/checksum.c
> @@ -0,0 +1,48 @@
> +#include <linux/fs.h>
> +#include <linux/buffer_head.h>
> +#include "omfs.h"
> +
> +#define POLY 0x1021
> +
> +/*
> + * crc-ccitt with MSB first (i.e., backwards), so we can't use the
> + * kernel table as-is.
> + */

Why not just add a be-bitwise table, similar to the crc32_le and
crc32_be implementation.


Harvey

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

[Bob Copeland]

On Wed, Mar 26, 2008 at 06:22:01PM -0700, Harvey Harrison wrote:
> > +/*
> > + * crc-ccitt with MSB first (i.e., backwards), so we can't use the
> > + * kernel table as-is.
> > + */
> 
> Why not just add a be-bitwise table, similar to the crc32_le and
> crc32_be implementation.

Yeah, that is probably a better idea.  I didn't do it before since
this lived outside the tree and I didn't want to patch the kernel.

Will that add 1k for everyone?

-- 
Bob Copeland %% www.bobcopeland.com 

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

[Sergey Vlasov]

[-- Attachment #1: Type: text/plain, Size: 1125 bytes --]

On Wed, 26 Mar 2008 20:45:59 -0400 Bob Copeland wrote:

> OMFS checksums the metadata of all filesystem objects.  This change adds
> the necessary functions to do so.
>
> Signed-off-by: Bob Copeland <me@bobcopeland.com>
> ---
>  fs/omfs/checksum.c |   48 ++++++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 48 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..d6f1023
> --- /dev/null
> +++ b/fs/omfs/checksum.c
> @@ -0,0 +1,48 @@
> +#include <linux/fs.h>
> +#include <linux/buffer_head.h>
> +#include "omfs.h"
> +
> +#define POLY 0x1021
> +
> +/*
> + * crc-ccitt with MSB first (i.e., backwards), so we can't use the
> + * kernel table as-is.
> + */
> +static u16 omfs_crc(u16 crc, unsigned char *buf, int count)
> +{
> +	int i, j;
> +	for (i = 0; i < count; i++) {
> +		crc ^= buf[i] << 8;
> +		for (j = 0; j < 8; j++)
> +			crc = (crc << 1) ^ ((crc & 0x8000) ? POLY : 0);
> +	}
> +	return crc;
> +}

Is this the same as crc_itu_t() from lib/crc-itu-t.c (also duplicated
in fs/udf/crc.c)?

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

[Bob Copeland]

On Thu, Mar 27, 2008 at 9:41 AM, Sergey Vlasov <vsu@altlinux.ru> wrote:
> On Wed, 26 Mar 2008 20:45:59 -0400 Bob Copeland wrote:
>  > +static u16 omfs_crc(u16 crc, unsigned char *buf, int count)
>
>  Is this the same as crc_itu_t() from lib/crc-itu-t.c (also duplicated
>  in fs/udf/crc.c)?

Ah, thanks, that is the one.  I'll update the patch.

-Bob

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

[Bob Copeland]

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@bobcopeland.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@bobcopeland.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