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Overview
Comment:Reformat WAL code for clearer presentation. Update comments for correctness. Add checks to ensure that corruption in shared-memory does not result in an infinite loop.
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SHA1: 40eaada7ec45e70bdf64d060051f24c5c5e3faf3
User & Date: drh 2010-07-09 03:19:07.000
Context
2010-07-09
12:57
Fix warning under MSVC. (check-in: 0c32c4bbdd user: shaneh tags: trunk)
03:19
Reformat WAL code for clearer presentation. Update comments for correctness. Add checks to ensure that corruption in shared-memory does not result in an infinite loop. (check-in: 40eaada7ec user: drh tags: trunk)
2010-07-08
19:19
Replace code that became unreachable due to the journal_mode simplification with an assert(). (check-in: bcdddba4f0 user: drh tags: trunk)
Changes
Unified Diff Ignore Whitespace Patch
Changes to src/wal.c.
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** then an SQLite error code is returned and *ppPage is set to 0.
*/
static int walIndexPage(Wal *pWal, int iPage, volatile u32 **ppPage){
  int rc = SQLITE_OK;

  /* Enlarge the pWal->apWiData[] array if required */
  if( pWal->nWiData<=iPage ){
    int nByte = sizeof(u32 *)*(iPage+1);
    volatile u32 **apNew;
    apNew = (volatile u32 **)sqlite3_realloc((void *)pWal->apWiData, nByte);
    if( !apNew ){
      *ppPage = 0;
      return SQLITE_NOMEM;
    }

    memset((void *)&apNew[pWal->nWiData], 0, sizeof(u32 *)*(iPage+1-pWal->nWiData));
    pWal->apWiData = apNew;
    pWal->nWiData = iPage+1;
  }

  /* Request a pointer to the required page from the VFS */
  if( pWal->apWiData[iPage]==0 ){
    rc = sqlite3OsShmMap(pWal->pDbFd, iPage, WALINDEX_PGSZ, 







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** then an SQLite error code is returned and *ppPage is set to 0.
*/
static int walIndexPage(Wal *pWal, int iPage, volatile u32 **ppPage){
  int rc = SQLITE_OK;

  /* Enlarge the pWal->apWiData[] array if required */
  if( pWal->nWiData<=iPage ){
    int nByte = sizeof(u32*)*(iPage+1);
    volatile u32 **apNew;
    apNew = (volatile u32 **)sqlite3_realloc((void *)pWal->apWiData, nByte);
    if( !apNew ){
      *ppPage = 0;
      return SQLITE_NOMEM;
    }
    memset((void*)&apNew[pWal->nWiData], 0,
           sizeof(u32*)*(iPage+1-pWal->nWiData));
    pWal->apWiData = apNew;
    pWal->nWiData = iPage+1;
  }

  /* Request a pointer to the required page from the VFS */
  if( pWal->apWiData[iPage]==0 ){
    rc = sqlite3OsShmMap(pWal->pDbFd, iPage, WALINDEX_PGSZ, 
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  /* A frame is only valid if the page number is creater than zero.
  */
  pgno = sqlite3Get4byte(&aFrame[0]);
  if( pgno==0 ){
    return 0;
  }

  /* A frame is only valid if a checksum of the first 16 bytes

  ** of the frame-header, and the frame-data matches
  ** the checksum in the last 8 bytes of the frame-header.
  */
  nativeCksum = (pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN);
  walChecksumBytes(nativeCksum, aFrame, 8, aCksum, aCksum);
  walChecksumBytes(nativeCksum, aData, pWal->szPage, aCksum, aCksum);
  if( aCksum[0]!=sqlite3Get4byte(&aFrame[16]) 
   || aCksum[1]!=sqlite3Get4byte(&aFrame[20]) 
  ){







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  /* A frame is only valid if the page number is creater than zero.
  */
  pgno = sqlite3Get4byte(&aFrame[0]);
  if( pgno==0 ){
    return 0;
  }

  /* A frame is only valid if a checksum of the WAL header,
  ** all prior frams, the first 16 bytes of this frame-header, 
  ** and the frame-data matches the checksum in the last 8 
  ** bytes of this frame-header.
  */
  nativeCksum = (pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN);
  walChecksumBytes(nativeCksum, aFrame, 8, aCksum, aCksum);
  walChecksumBytes(nativeCksum, aData, pWal->szPage, aCksum, aCksum);
  if( aCksum[0]!=sqlite3Get4byte(&aFrame[16]) 
   || aCksum[1]!=sqlite3Get4byte(&aFrame[20]) 
  ){
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  /* Assuming the wal-index file was successfully mapped, populate the
  ** page number array and hash table entry.
  */
  if( rc==SQLITE_OK ){
    int iKey;                     /* Hash table key */
    int idx;                      /* Value to write to hash-table slot */
    TESTONLY( int nCollide = 0;   /* Number of hash collisions */ )

    idx = iFrame - iZero;
    assert( idx <= HASHTABLE_NSLOT/2 + 1 );
    
    /* If this is the first entry to be added to this hash-table, zero the
    ** entire hash table and aPgno[] array before proceding. 
    */







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  /* Assuming the wal-index file was successfully mapped, populate the
  ** page number array and hash table entry.
  */
  if( rc==SQLITE_OK ){
    int iKey;                     /* Hash table key */
    int idx;                      /* Value to write to hash-table slot */
    int nCollide;                 /* Number of hash collisions */

    idx = iFrame - iZero;
    assert( idx <= HASHTABLE_NSLOT/2 + 1 );
    
    /* If this is the first entry to be added to this hash-table, zero the
    ** entire hash table and aPgno[] array before proceding. 
    */
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    */
    if( aPgno[idx] ){
      walCleanupHash(pWal);
      assert( !aPgno[idx] );
    }

    /* Write the aPgno[] array entry and the hash-table slot. */

    for(iKey=walHash(iPage); aHash[iKey]; iKey=walNextHash(iKey)){
      assert( nCollide++ < idx );
    }
    aPgno[idx] = iPage;
    aHash[iKey] = (ht_slot)idx;

#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
    /* Verify that the number of entries in the hash table exactly equals
    ** the number of entries in the mapping region.







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    */
    if( aPgno[idx] ){
      walCleanupHash(pWal);
      assert( !aPgno[idx] );
    }

    /* Write the aPgno[] array entry and the hash-table slot. */
    nCollide = idx;
    for(iKey=walHash(iPage); aHash[iKey]; iKey=walNextHash(iKey)){
      if( (nCollide--)==0 ) return SQLITE_CORRUPT_BKPT;
    }
    aPgno[idx] = iPage;
    aHash[iKey] = (ht_slot)idx;

#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
    /* Verify that the number of entries in the hash table exactly equals
    ** the number of entries in the mapping region.
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    rc = walHashGet(pWal, i, &aHash, &aPgno, &iZero);
    if( rc==SQLITE_OK ){
      int j;                      /* Counter variable */
      int nEntry;                 /* Number of entries in this segment */
      ht_slot *aIndex;            /* Sorted index for this segment */

      aPgno++;

      nEntry = (int)(((i+1)==nSegment)?(int)(iLast-iZero):(u32 *)aHash-(u32 *)aPgno);



      aIndex = &((ht_slot *)&p->aSegment[p->nSegment])[iZero];
      iZero++;
  
      for(j=0; j<nEntry; j++){
        aIndex[j] = (ht_slot)j;
      }
      walMergesort((u32 *)aPgno, aTmp, aIndex, &nEntry);







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    rc = walHashGet(pWal, i, &aHash, &aPgno, &iZero);
    if( rc==SQLITE_OK ){
      int j;                      /* Counter variable */
      int nEntry;                 /* Number of entries in this segment */
      ht_slot *aIndex;            /* Sorted index for this segment */

      aPgno++;
      if( (i+1)==nSegment ){
        nEntry = (int)(iLast - iZero);
      }else{
        nEntry = (u32*)aHash - (u32*)aPgno;
      }
      aIndex = &((ht_slot *)&p->aSegment[p->nSegment])[iZero];
      iZero++;
  
      for(j=0; j<nEntry; j++){
        aIndex[j] = (ht_slot)j;
      }
      walMergesort((u32 *)aPgno, aTmp, aIndex, &nEntry);
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  **     table after the current read-transaction had started.
  */
  for(iHash=walFramePage(iLast); iHash>=0 && iRead==0; iHash--){
    volatile ht_slot *aHash;      /* Pointer to hash table */
    volatile u32 *aPgno;          /* Pointer to array of page numbers */
    u32 iZero;                    /* Frame number corresponding to aPgno[0] */
    int iKey;                     /* Hash slot index */

    int rc;

    rc = walHashGet(pWal, iHash, &aHash, &aPgno, &iZero);
    if( rc!=SQLITE_OK ){
      return rc;
    }

    for(iKey=walHash(pgno); aHash[iKey]; iKey=walNextHash(iKey)){
      u32 iFrame = aHash[iKey] + iZero;
      if( iFrame<=iLast && aPgno[aHash[iKey]]==pgno ){
        assert( iFrame>iRead );
        iRead = iFrame;
      }



    }
  }

#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
  /* If expensive assert() statements are available, do a linear search
  ** of the wal-index file content. Make sure the results agree with the
  ** result obtained using the hash indexes above.  */







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  **     table after the current read-transaction had started.
  */
  for(iHash=walFramePage(iLast); iHash>=0 && iRead==0; iHash--){
    volatile ht_slot *aHash;      /* Pointer to hash table */
    volatile u32 *aPgno;          /* Pointer to array of page numbers */
    u32 iZero;                    /* Frame number corresponding to aPgno[0] */
    int iKey;                     /* Hash slot index */
    int nCollide;                 /* Number of hash collisions remaining */
    int rc;                       /* Error code */

    rc = walHashGet(pWal, iHash, &aHash, &aPgno, &iZero);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    nCollide = HASHTABLE_NSLOT;
    for(iKey=walHash(pgno); aHash[iKey]; iKey=walNextHash(iKey)){
      u32 iFrame = aHash[iKey] + iZero;
      if( iFrame<=iLast && aPgno[aHash[iKey]]==pgno ){
        assert( iFrame>iRead );
        iRead = iFrame;
      }
      if( (nCollide--)==0 ){
        return SQLITE_CORRUPT_BKPT;
      }
    }
  }

#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
  /* If expensive assert() statements are available, do a linear search
  ** of the wal-index file content. Make sure the results agree with the
  ** result obtained using the hash indexes above.  */