SQLite

}

/*
** Return the device characteristics for the file. This is always 0 for unix.
*/
static int unixDeviceCharacteristics(sqlite3_file *NotUsed){
  UNUSED_PARAMETER(NotUsed);
  return SQLITE_IOCAP_ZERO_DAMAGE;
}

#ifndef SQLITE_OMIT_WAL


/*
** Object used to represent an shared memory buffer.  

}

/*
** Return a vector of device characteristics.
*/
static int winDeviceCharacteristics(sqlite3_file *id){
  UNUSED_PARAMETER(id);
  return SQLITE_IOCAP_UNDELETABLE_WHEN_OPEN |
         SQLITE_IOCAP_ZERO_DAMAGE;
}

#ifndef SQLITE_OMIT_WAL

/* 
** Windows will only let you create file view mappings
** on allocation size granularity boundaries.

**
** For temporary files the effective sector size is always 512 bytes.
**
** Otherwise, for non-temporary files, the effective sector size is
** the value returned by the xSectorSize() method rounded up to 32 if
** it is less than 32, or rounded down to MAX_SECTOR_SIZE if it
** is greater than MAX_SECTOR_SIZE.
**
** If the file has the SQLITE_IOCAP_ZERO_DAMAGE property, then set the
** effective sector size to its minimum value (512).  The purpose of
** pPager->sectorSize is to define the "blast radius" of bytes that
** might change if a crash occurs while writing to a single byte in
** that range.  But with ZERO_DAMAGE, the blast radius is zero, so
** we minimize the sector size.  For backwards compatibility of the
** rollback journal file format, we cannot reduce the effective sector
** size below 512.
*/
static void setSectorSize(Pager *pPager){
  assert( isOpen(pPager->fd) || pPager->tempFile );

  if( !pPager->tempFile
   && (sqlite3OsDeviceCharacteristics(pPager->fd)&SQLITE_IOCAP_ZERO_DAMAGE)==0
  ){
    /* Sector size doesn't matter for temporary files. Also, the file
    ** may not have been opened yet, in which case the OsSectorSize()
    ** call will segfault.
    */
    pPager->sectorSize = sqlite3OsSectorSize(pPager->fd);
  }
  if( pPager->sectorSize<32 ){

** mean that writes of blocks that are nnn bytes in size and
** are aligned to an address which is an integer multiple of
** nnn are atomic.  The SQLITE_IOCAP_SAFE_APPEND value means
** that when data is appended to a file, the data is appended
** first then the size of the file is extended, never the other
** way around.  The SQLITE_IOCAP_SEQUENTIAL property means that
** information is written to disk in the same order as calls
** to xWrite().  The SQLITE_IOCAP_ZERO_DAMAGE property means that
** after reboot following a crash or power loss, the value of
** each byte in a file is a value that was actually written
** into that byte at some point.  In other words, a crash will
** not introduce garbage or randomness into a file, and byte of
** a file that are never written will not change values due to
** writes to nearby bytes.
*/
#define SQLITE_IOCAP_ATOMIC                 0x00000001
#define SQLITE_IOCAP_ATOMIC512              0x00000002
#define SQLITE_IOCAP_ATOMIC1K               0x00000004
#define SQLITE_IOCAP_ATOMIC2K               0x00000008
#define SQLITE_IOCAP_ATOMIC4K               0x00000010
#define SQLITE_IOCAP_ATOMIC8K               0x00000020
#define SQLITE_IOCAP_ATOMIC16K              0x00000040
#define SQLITE_IOCAP_ATOMIC32K              0x00000080
#define SQLITE_IOCAP_ATOMIC64K              0x00000100
#define SQLITE_IOCAP_SAFE_APPEND            0x00000200
#define SQLITE_IOCAP_SEQUENTIAL             0x00000400
#define SQLITE_IOCAP_UNDELETABLE_WHEN_OPEN  0x00000800
#define SQLITE_IOCAP_ZERO_DAMAGE            0x00001000

/*
** CAPI3REF: File Locking Levels
**
** SQLite uses one of these integer values as the second
** argument to calls it makes to the xLock() and xUnlock() methods
** of an [sqlite3_io_methods] object.

    { "atomic4k",    SQLITE_IOCAP_ATOMIC4K    },
    { "atomic8k",    SQLITE_IOCAP_ATOMIC8K    },
    { "atomic16k",   SQLITE_IOCAP_ATOMIC16K   },
    { "atomic32k",   SQLITE_IOCAP_ATOMIC32K   },
    { "atomic64k",   SQLITE_IOCAP_ATOMIC64K   },
    { "sequential",  SQLITE_IOCAP_SEQUENTIAL  },
    { "safe_append", SQLITE_IOCAP_SAFE_APPEND },
    { "zero_damage", SQLITE_IOCAP_ZERO_DAMAGE },
    { 0, 0 }
  };

  int i;
  int iDc = 0;
  int iSectorSize = 0;
  int setSectorsize = 0;

        { "atomic8k",              SQLITE_IOCAP_ATOMIC8K    },
        { "atomic16k",             SQLITE_IOCAP_ATOMIC16K   },
        { "atomic32k",             SQLITE_IOCAP_ATOMIC32K   },
        { "atomic64k",             SQLITE_IOCAP_ATOMIC64K   },
        { "sequential",            SQLITE_IOCAP_SEQUENTIAL  },
        { "safe_append",           SQLITE_IOCAP_SAFE_APPEND },
        { "undeletable_when_open", SQLITE_IOCAP_UNDELETABLE_WHEN_OPEN },
        { "zero_damage",           SQLITE_IOCAP_ZERO_DAMAGE },
        { 0, 0 }
      };
      Tcl_Obj *pRet;
      int iFlag;

      if( objc>3 ){
        Tcl_WrongNumArgs(interp, 2, objv, "?ATTR-LIST?");

  u8 syncFlags;              /* Flags to use to sync header writes */
  u8 exclusiveMode;          /* Non-zero if connection is in exclusive mode */
  u8 writeLock;              /* True if in a write transaction */
  u8 ckptLock;               /* True if holding a checkpoint lock */
  u8 readOnly;               /* WAL_RDWR, WAL_RDONLY, or WAL_SHM_RDONLY */
  u8 truncateOnCommit;       /* True to truncate WAL file on commit */
  u8 noSyncHeader;           /* Avoid WAL header fsyncs if true */
  u8 noPadding;              /* No need to pad transactions to sector size */
  WalIndexHdr hdr;           /* Wal-index header for current transaction */
  const char *zWalName;      /* Name of WAL file */
  u32 nCkpt;                 /* Checkpoint sequence counter in the wal-header */
#ifdef SQLITE_DEBUG
  u8 lockError;              /* True if a locking error has occurred */
#endif
};

  if( rc!=SQLITE_OK ){
    walIndexClose(pRet, 0);
    sqlite3OsClose(pRet->pWalFd);
    sqlite3_free(pRet);
  }else{
    int iDC = sqlite3OsDeviceCharacteristics(pRet->pWalFd);
    if( iDC & SQLITE_IOCAP_SEQUENTIAL ){ pRet->noSyncHeader = 1; }
    if( iDC & SQLITE_IOCAP_ZERO_DAMAGE ){ pRet->noPadding = 1; }
    *ppWal = pRet;
    WALTRACE(("WAL%d: opened\n", pRet));
  }
  return rc;
}

/*

      return rc;
    }
    pLast = p;
  }

  /* Sync the log file if the 'isSync' flag was specified. */
  if( isCommit && (sync_flags & WAL_SYNC_TRANSACTIONS)!=0 ){
    if( !pWal->noPadding ){
      i64 iSegment = sqlite3OsSectorSize(pWal->pWalFd);
      i64 iOffset = walFrameOffset(iFrame+1, szPage);
  
      assert( iSegment>0 );
  
      iSegment = (((iOffset+iSegment-1)/iSegment) * iSegment);
      while( iOffset<iSegment ){
        void *pData;
#if defined(SQLITE_HAS_CODEC)
        if( (pData = sqlite3PagerCodec(pLast))==0 ) return SQLITE_NOMEM;
#else
        pData = pLast->pData;
#endif
        walEncodeFrame(pWal, pLast->pgno, nTruncate, pData, aFrame);
        /* testcase( IS_BIG_INT(iOffset) ); // requires a 4GiB WAL */
        rc = walWriteToLog(pWal, aFrame, sizeof(aFrame), iOffset);
        if( rc!=SQLITE_OK ){
          return rc;
        }
        iOffset += WAL_FRAME_HDRSIZE;
        rc = walWriteToLog(pWal, pData, szPage, iOffset);
        if( rc!=SQLITE_OK ){
          return rc;
        }
        nLast++;
        iOffset += szPage;
      }
    }
  
    rc = sqlite3OsSync(pWal->pWalFd, sync_flags & SQLITE_SYNC_MASK);
  }

  if( isCommit && pWal->truncateOnCommit && pWal->mxWalSize>=0 ){
    i64 sz = pWal->mxWalSize;
    if( walFrameOffset(iFrame+nLast+1, szPage)>pWal->mxWalSize ){
      sz = walFrameOffset(iFrame+nLast+1, szPage);