tool/pagesig.c

   1 /*
   2 ** 2013-10-01
   3 **
   4 ** The author disclaims copyright to this source code.  In place of
   5 ** a legal notice, here is a blessing:
   6 **
   7 **    May you do good and not evil.
   8 **    May you find forgiveness for yourself and forgive others.
   9 **    May you share freely, never taking more than you give.
  10 **
  11 ******************************************************************************
  12 **
  13 ** Compute hash signatures for every page of a database file.  This utility
  14 ** program is useful for analyzing the output logs generated by the
  15 ** ext/misc/vfslog.c extension.
  16 */
  17 #include <stdio.h>
  18 #include <string.h>
  19 #include <assert.h>
  20 #include <stdlib.h>
  21
  22 /*
  23 ** Compute signature for a block of content.
  24 **
  25 ** For blocks of 16 or fewer bytes, the signature is just a hex dump of
  26 ** the entire block.
  27 **
  28 ** For blocks of more than 16 bytes, the signature is a hex dump of the
  29 ** first 8 bytes followed by a 64-bit has of the entire block.
  30 */
  31 static void vlogSignature(unsigned char *p, int n, char *zCksum){
  32   unsigned int s0 = 0, s1 = 0;
  33   unsigned int *pI;
  34   int i;
  35   if( n<=16 ){
  36     for(i=0; i<n; i++) sprintf(zCksum+i*2, "%02x", p[i]);
  37   }else{
  38     pI = (unsigned int*)p;
  39     for(i=0; i<n-7; i+=8){
  40       s0 += pI[0] + s1;
  41       s1 += pI[1] + s0;
  42       pI += 2;
  43     }
  44     for(i=0; i<8; i++) sprintf(zCksum+i*2, "%02x", p[i]);
  45     sprintf(zCksum+i*2, "-%08x%08x", s0, s1);
  46   }
  47 }
  48
  49 /*
  50 ** Open a file.  Find its page size.  Read each page, and compute and
  51 ** display the page signature.
  52 */
  53 static void computeSigs(const char *zFilename){
  54   FILE *in = fopen(zFilename, "rb");
  55   unsigned pgsz;
  56   size_t got;
  57   unsigned n;
  58   unsigned char aBuf[50];
  59   unsigned char aPage[65536];
  60
  61   if( in==0 ){
  62     fprintf(stderr, "cannot open \"%s\"\n", zFilename);
  63     return;
  64   }
  65   got = fread(aBuf, 1, sizeof(aBuf), in);
  66   if( got!=sizeof(aBuf) ){
  67     goto endComputeSigs;
  68   }
  69   pgsz = aBuf[16]*256 + aBuf[17];
  70   if( pgsz==1 ) pgsz = 65536;
  71   if( (pgsz & (pgsz-1))!=0 ){
  72     fprintf(stderr, "invalid page size: %02x%02x\n", aBuf[16], aBuf[17]);
  73     goto endComputeSigs;
  74   }
  75   rewind(in);
  76   for(n=1; (got=fread(aPage, 1, pgsz, in))==pgsz; n++){
  77     vlogSignature(aPage, pgsz, aBuf);
  78     printf("%4d: %s\n", n, aBuf);
  79   }
  80
  81 endComputeSigs:
  82   fclose(in);
  83 }
  84
  85 /*
  86 ** Find page signatures for all named files.
  87 */
  88 int main(int argc, char **argv){
  89   int i;
  90   for(i=1; i<argc; i++) computeSigs(argv[i]);
  91   return 0;
  92 }