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
--
