From: Michael Vrable <mvrable@cs.ucsd.edu>
Date: Tue, 31 Aug 2010 20:02:38 +0000 (-0700)
Subject: Update CRC-32 implementation.
X-Git-Url: https://git.vrable.net/?a=commitdiff_plain;h=d27b934a06369794d21a3eeaf86c55f942518956;p=bluesky.git

Update CRC-32 implementation.

Invert the result of the CRC computation at the end.  This will catch extra
null bytes at the end of the buffer, but required updating the CRC
validation.
---

diff --git a/bluesky/bluesky-private.h b/bluesky/bluesky-private.h
index 837c6e5..01d8b88 100644
--- a/bluesky/bluesky-private.h
+++ b/bluesky/bluesky-private.h
@@ -246,6 +246,7 @@ void bluesky_cloudlog_flush(BlueSkyFS *fs);
 /* Logging infrastructure for ensuring operations are persistently recorded to
  * disk. */
 #define BLUESKY_CRC32C_SEED (~(uint32_t)0)
+#define BLUESKY_CRC32C_VALIDATOR ((uint32_t)0xb798b438UL)
 uint32_t crc32c(uint32_t crc, const char *buf, unsigned int length);
 uint32_t crc32c_finalize(uint32_t crc);
 
diff --git a/bluesky/crc32c.c b/bluesky/crc32c.c
index 8e11bbf..40ce983 100644
--- a/bluesky/crc32c.c
+++ b/bluesky/crc32c.c
@@ -17,6 +17,10 @@
 #include <stdint.h>
 #include "bluesky-private.h"
 
+/* Generator polynomial is 0x1edc6f41; input and output are reflected.  The
+ * recommended starting value for the accumulator is ~0, and the bits of the
+ * CRC are inverted at the end as well. */
+
 static const uint32_t crc32c_table[256] = {
     0x00000000L, 0xF26B8303L, 0xE13B70F7L, 0x1350F3F4L,
     0xC79A971FL, 0x35F1141CL, 0x26A1E7E8L, 0xD4CA64EBL,
@@ -101,5 +105,5 @@ uint32_t crc32c(uint32_t crc, const char *buf, unsigned int length)
 
 uint32_t crc32c_finalize(uint32_t crc)
 {
-    return GUINT32_TO_LE(crc);
+    return ~GUINT32_TO_LE(crc);
 }
diff --git a/bluesky/log.c b/bluesky/log.c
index e79b21b..a3acf10 100644
--- a/bluesky/log.c
+++ b/bluesky/log.c
@@ -616,8 +616,11 @@ static gboolean validate_journal_item(const char *buf, size_t len, off_t offset)
     uint32_t crc = crc32c(BLUESKY_CRC32C_SEED, buf + offset,
                           sizeof(struct log_header) + sizeof(struct log_footer)
                           + size);
-    if (crc != 0)
+    if (crc != BLUESKY_CRC32C_VALIDATOR) {
+        g_warning("Journal entry failed to validate: CRC %08x != %08x",
+                  crc, BLUESKY_CRC32C_VALIDATOR);
         return FALSE;
+    }
 
     return TRUE;
 }