struct unixOpenCnt *pOpen;       /* Info about all open fd's on this inode */
  struct unixLockInfo *pLock;      /* Info about locks on this inode */
  int h;                           /* The file descriptor */
  int dirfd;                       /* File descriptor for the directory */
  unsigned char locktype;          /* The type of lock held on this fd */
  int lastErrno;                   /* The unix errno from the last I/O error */
  void *lockingContext;            /* Locking style specific state */

#if SQLITE_ENABLE_LOCKING_STYLE
  int openFlags;                   /* The flags specified at open() */
#endif
#if SQLITE_THREADSAFE && defined(__linux__)
  pthread_t tid;                   /* The thread that "owns" this unixFile */
#endif
#if OS_VXWORKS
................................................................................
  ** occur if a file is updated without also updating the transaction
  ** counter.  This test is made to avoid new problems similar to the
  ** one described by ticket #3584. 
  */
  unsigned char transCntrChng;   /* True if the transaction counter changed */
  unsigned char dbUpdate;        /* True if any part of database file changed */
  unsigned char inNormalWrite;   /* True if in a normal write operation */

  /* If true, that means we are dealing with a database file that has
  ** a range of locking bytes from PENDING_BYTE through PENDING_BYTE+511
  ** which should never be read or written.  Asserts() will verify this */
  unsigned char isLockable;      /* True if file might be locked */
#endif
#ifdef SQLITE_TEST
  /* In test mode, increase the size of this structure a bit so that 
  ** it is larger than the struct CrashFile defined in test6.c.
  */
  char aPadding[32];
#endif
................................................................................
** using the file closes.
*/
struct unixOpenCnt {
  struct unixFileId fileId;   /* The lookup key */
  int nRef;                   /* Number of pointers to this structure */
  int nLock;                  /* Number of outstanding locks */
  int nPending;               /* Number of pending close() operations */



  int *aPending;              /* Malloced space holding fds awaiting close() */
#if OS_VXWORKS
  sem_t *pSem;                     /* Named POSIX semaphore */
  char aSemName[MAX_PATHNAME+1];   /* Name of that semaphore */
#endif
  struct unixOpenCnt *pNext, *pPrev;   /* List of all unixOpenCnt objects */
};

................................................................................

end_lock:
  unixLeaveMutex();
  OSTRACE4("LOCK    %d %s %s\n", pFile->h, locktypeName(locktype), 
      rc==SQLITE_OK ? "ok" : "failed");
  return rc;
}























































/*
** Lower the locking level on file descriptor pFile to locktype.  locktype
** must be either NO_LOCK or SHARED_LOCK.
**
** If the locking level of the file descriptor is already at or below
** the requested locking level, this routine is a no-op.
................................................................................
        pFile->lastErrno = tErrno;
      }
      goto end_unlock;
    }
  }
  if( locktype==NO_LOCK ){
    struct unixOpenCnt *pOpen;
    int rc2 = SQLITE_OK;

    /* Decrement the shared lock counter.  Release the lock using an
    ** OS call only when all threads in this same process have released
    ** the lock.
    */
    pLock->cnt--;
    if( pLock->cnt==0 ){
................................................................................
    ** count reaches zero, close any other file descriptors whose close
    ** was deferred because of outstanding locks.
    */
    pOpen = pFile->pOpen;
    pOpen->nLock--;
    assert( pOpen->nLock>=0 );
    if( pOpen->nLock==0 && pOpen->nPending>0 ){
      int i;
      for(i=0; i<pOpen->nPending; i++){
        /* close pending fds, but if closing fails don't free the array
        ** assign -1 to the successfully closed descriptors and record the
        ** error.  The next attempt to unlock will try again. */
        if( pOpen->aPending[i] < 0 ) continue;
        if( close(pOpen->aPending[i]) ){
          pFile->lastErrno = errno;
          rc2 = SQLITE_IOERR_CLOSE;
        }else{
          pOpen->aPending[i] = -1;
        }
      }
      if( rc2==SQLITE_OK ){
        sqlite3_free(pOpen->aPending);
        pOpen->nPending = 0;
        pOpen->aPending = 0;
      }
    }
    if( rc==SQLITE_OK ){
      rc = rc2;

    }
  }
	
end_unlock:
  unixLeaveMutex();
  if( rc==SQLITE_OK ) pFile->locktype = locktype;
  return rc;
................................................................................
    unixEnterMutex();
    if( pFile->pOpen && pFile->pOpen->nLock ){
      /* If there are outstanding locks, do not actually close the file just
      ** yet because that would clear those locks.  Instead, add the file
      ** descriptor to pOpen->aPending.  It will be automatically closed when
      ** the last lock is cleared.
      */
      int *aNew;
      struct unixOpenCnt *pOpen = pFile->pOpen;
      aNew = sqlite3_realloc(pOpen->aPending, (pOpen->nPending+1)*sizeof(int) );
      if( aNew==0 ){
        /* If a malloc fails, just leak the file descriptor */
      }else{
        pOpen->aPending = aNew;
        pOpen->aPending[pOpen->nPending] = pFile->h;
        pOpen->nPending++;
        pFile->h = -1;
      }
    }
    releaseLockInfo(pFile->pLock);
    releaseOpenCnt(pFile->pOpen);
    rc = closeUnixFile(id);
    unixLeaveMutex();
  }
  return rc;
................................................................................

  if( rc==SQLITE_OK ){
    if( locktype==NO_LOCK ){
      struct unixOpenCnt *pOpen = pFile->pOpen;
      pOpen->nLock--;
      assert( pOpen->nLock>=0 );
      if( pOpen->nLock==0 && pOpen->nPending>0 ){
        int i;
        for(i=0; i<pOpen->nPending; i++){
          if( pOpen->aPending[i] < 0 ) continue;
          if( close(pOpen->aPending[i]) ){
            pFile->lastErrno = errno;
            rc = SQLITE_IOERR_CLOSE;
          }else{
            pOpen->aPending[i] = -1;
          }
        }
        if( rc==SQLITE_OK ){
          sqlite3_free(pOpen->aPending);
          pOpen->nPending = 0;
          pOpen->aPending = 0;
        }
      }
    }
  }
  unixLeaveMutex();

  if( rc==SQLITE_OK ) pFile->locktype = locktype;

  return rc;
}

/*
** Close a file & cleanup AFP specific locking context 
*/
static int afpClose(sqlite3_file *id) {
................................................................................
    unixEnterMutex();
    if( pFile->pOpen && pFile->pOpen->nLock ){
      /* If there are outstanding locks, do not actually close the file just
      ** yet because that would clear those locks.  Instead, add the file
      ** descriptor to pOpen->aPending.  It will be automatically closed when
      ** the last lock is cleared.
      */
      int *aNew;
      struct unixOpenCnt *pOpen = pFile->pOpen;
      aNew = sqlite3_realloc(pOpen->aPending, (pOpen->nPending+1)*sizeof(int) );
      if( aNew==0 ){
        /* If a malloc fails, just leak the file descriptor */
      }else{
        pOpen->aPending = aNew;
        pOpen->aPending[pOpen->nPending] = pFile->h;
        pOpen->nPending++;
        pFile->h = -1;
      }
    }
    releaseOpenCnt(pFile->pOpen);
    sqlite3_free(pFile->lockingContext);
    closeUnixFile(id);
    unixLeaveMutex();
  }
  return SQLITE_OK;
................................................................................
*/
static int unixRead(
  sqlite3_file *id, 
  void *pBuf, 
  int amt,
  sqlite3_int64 offset
){

  int got;
  assert( id );


  /* Never read or write any of the bytes in the locking range */
  assert( ((unixFile*)id)->isLockable==0

          || offset>=PENDING_BYTE+512
          || offset+amt<=PENDING_BYTE );


  got = seekAndRead((unixFile*)id, offset, pBuf, amt);
  if( got==amt ){
    return SQLITE_OK;
  }else if( got<0 ){
    /* lastErrno set by seekAndRead */
    return SQLITE_IOERR_READ;
  }else{
    ((unixFile*)id)->lastErrno = 0; /* not a system error */
    /* Unread parts of the buffer must be zero-filled */
    memset(&((char*)pBuf)[got], 0, amt-got);
    return SQLITE_IOERR_SHORT_READ;
  }
}

/*
................................................................................
*/
static int unixWrite(
  sqlite3_file *id, 
  const void *pBuf, 
  int amt,
  sqlite3_int64 offset 
){

  int wrote = 0;
  assert( id );
  assert( amt>0 );


  /* Never read or write any of the bytes in the locking range */
  assert( ((unixFile*)id)->isLockable==0

          || offset>=PENDING_BYTE+512
          || offset+amt<=PENDING_BYTE );


#ifndef NDEBUG
  /* If we are doing a normal write to a database file (as opposed to
  ** doing a hot-journal rollback or a write to some file other than a
  ** normal database file) then record the fact that the database
  ** has changed.  If the transaction counter is modified, record that
  ** fact too.
  */
  if( ((unixFile*)id)->inNormalWrite ){
    unixFile *pFile = (unixFile*)id;
    pFile->dbUpdate = 1;  /* The database has been modified */
    if( offset<=24 && offset+amt>=27 ){
      int rc;
      char oldCntr[4];
      SimulateIOErrorBenign(1);
      rc = seekAndRead(pFile, 24, oldCntr, 4);
      SimulateIOErrorBenign(0);
................................................................................
      if( rc!=4 || memcmp(oldCntr, &((char*)pBuf)[24-offset], 4)!=0 ){
        pFile->transCntrChng = 1;  /* The transaction counter has changed */
      }
    }
  }
#endif

  while( amt>0 && (wrote = seekAndWrite((unixFile*)id, offset, pBuf, amt))>0 ){
    amt -= wrote;
    offset += wrote;
    pBuf = &((char*)pBuf)[wrote];
  }
  SimulateIOError(( wrote=(-1), amt=1 ));
  SimulateDiskfullError(( wrote=0, amt=1 ));
  if( amt>0 ){
    if( wrote<0 ){
      /* lastErrno set by seekAndWrite */
      return SQLITE_IOERR_WRITE;
    }else{
      ((unixFile*)id)->lastErrno = 0; /* not a system error */
      return SQLITE_FULL;
    }
  }
  return SQLITE_OK;
}

#ifdef SQLITE_TEST
................................................................................
** Routine to transform a unixFile into a proxy-locking unixFile.
** Implementation in the proxy-lock division, but used by unixOpen()
** if SQLITE_PREFER_PROXY_LOCKING is defined.
*/
static int proxyTransformUnixFile(unixFile*, const char*);
#endif






















































/*
** Open the file zPath.
** 
** Previously, the SQLite OS layer used three functions in place of this
** one:
**
................................................................................
static int unixOpen(
  sqlite3_vfs *pVfs,           /* The VFS for which this is the xOpen method */
  const char *zPath,           /* Pathname of file to be opened */
  sqlite3_file *pFile,         /* The file descriptor to be filled in */
  int flags,                   /* Input flags to control the opening */
  int *pOutFlags               /* Output flags returned to SQLite core */
){

  int fd = -1;                    /* File descriptor returned by open() */
  int dirfd = -1;                /* Directory file descriptor */
  int openFlags = 0;             /* Flags to pass to open() */
  int eType = flags&0xFFFFFF00;  /* Type of file to open */
  int noLock;                    /* True to omit locking primitives */
  int rc = SQLITE_OK;

  int isExclusive  = (flags & SQLITE_OPEN_EXCLUSIVE);
  int isDelete     = (flags & SQLITE_OPEN_DELETEONCLOSE);
  int isCreate     = (flags & SQLITE_OPEN_CREATE);
  int isReadonly   = (flags & SQLITE_OPEN_READONLY);
  int isReadWrite  = (flags & SQLITE_OPEN_READWRITE);

................................................................................
  */
  assert((isReadonly==0 || isReadWrite==0) && (isReadWrite || isReadonly));
  assert(isCreate==0 || isReadWrite);
  assert(isExclusive==0 || isCreate);
  assert(isDelete==0 || isCreate);

  /* The main DB, main journal, and master journal are never automatically
  ** deleted
  */
  assert( eType!=SQLITE_OPEN_MAIN_DB || !isDelete );
  assert( eType!=SQLITE_OPEN_MAIN_JOURNAL || !isDelete );
  assert( eType!=SQLITE_OPEN_MASTER_JOURNAL || !isDelete );

  /* Assert that the upper layer has set one of the "file-type" flags. */
  assert( eType==SQLITE_OPEN_MAIN_DB      || eType==SQLITE_OPEN_TEMP_DB 
       || eType==SQLITE_OPEN_MAIN_JOURNAL || eType==SQLITE_OPEN_TEMP_JOURNAL 
       || eType==SQLITE_OPEN_SUBJOURNAL   || eType==SQLITE_OPEN_MASTER_JOURNAL 
       || eType==SQLITE_OPEN_TRANSIENT_DB
  );

  memset(pFile, 0, sizeof(unixFile));










  if( !zName ){

    assert(isDelete && !isOpenDirectory);
    rc = getTempname(MAX_PATHNAME+1, zTmpname);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    zName = zTmpname;
  }





  if( isReadonly )  openFlags |= O_RDONLY;
  if( isReadWrite ) openFlags |= O_RDWR;
  if( isCreate )    openFlags |= O_CREAT;
  if( isExclusive ) openFlags |= (O_EXCL|O_NOFOLLOW);
  openFlags |= (O_LARGEFILE|O_BINARY);


  fd = open(zName, openFlags, isDelete?0600:SQLITE_DEFAULT_FILE_PERMISSIONS);
  OSTRACE4("OPENX   %-3d %s 0%o\n", fd, zName, openFlags);
  if( fd<0 && errno!=EISDIR && isReadWrite && !isExclusive ){
    /* Failed to open the file for read/write access. Try read-only. */
    flags &= ~(SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE);
    flags |= SQLITE_OPEN_READONLY;
    return unixOpen(pVfs, zPath, pFile, flags, pOutFlags);
  }
  if( fd<0 ){
    return SQLITE_CANTOPEN;
  }







  if( isDelete ){
#if OS_VXWORKS
    zPath = zName;
#else
    unlink(zName);
#endif
  }
#if SQLITE_ENABLE_LOCKING_STYLE
  else{
    ((unixFile*)pFile)->openFlags = openFlags;
  }
#endif
  if( pOutFlags ){
    *pOutFlags = flags;
  }

#ifndef NDEBUG
  if( (flags & SQLITE_OPEN_MAIN_DB)!=0 ){
    ((unixFile*)pFile)->isLockable = 1;
  }
#endif

  assert( fd>=0 );
  if( isOpenDirectory ){
    rc = openDirectory(zPath, &dirfd);
    if( rc!=SQLITE_OK ){





      close(fd); /* silently leak if fail, already in error */
      return rc;
    }
  }

#ifdef FD_CLOEXEC
  fcntl(fd, F_SETFD, fcntl(fd, F_GETFD, 0) | FD_CLOEXEC);
#endif
................................................................................
  noLock = eType!=SQLITE_OPEN_MAIN_DB;

#if SQLITE_PREFER_PROXY_LOCKING
  if( zPath!=NULL && !noLock ){
    char *envforce = getenv("SQLITE_FORCE_PROXY_LOCKING");
    int useProxy = 0;

    /* SQLITE_FORCE_PROXY_LOCKING==1 means force always use proxy, 
    ** 0 means never use proxy, NULL means use proxy for non-local files only
    */
    if( envforce!=NULL ){
      useProxy = atoi(envforce)>0;
    }else{
      struct statfs fsInfo;

      if( statfs(zPath, &fsInfo) == -1 ){
				((unixFile*)pFile)->lastErrno = errno;
        if( dirfd>=0 ) close(dirfd); /* silently leak if fail, in error */
        close(fd); /* silently leak if fail, in error */
        return SQLITE_IOERR_ACCESS;
      }
      useProxy = !(fsInfo.f_flags&MNT_LOCAL);
    }
    if( useProxy ){

  struct unixOpenCnt *pOpen;       /* Info about all open fd's on this inode */
  struct unixLockInfo *pLock;      /* Info about locks on this inode */
  int h;                           /* The file descriptor */
  int dirfd;                       /* File descriptor for the directory */
  unsigned char locktype;          /* The type of lock held on this fd */
  int lastErrno;                   /* The unix errno from the last I/O error */
  void *lockingContext;            /* Locking style specific state */
  int flags;                       /* Flags value returned by xOpen() */
#if SQLITE_ENABLE_LOCKING_STYLE
  int openFlags;                   /* The flags specified at open() */
#endif
#if SQLITE_THREADSAFE && defined(__linux__)
  pthread_t tid;                   /* The thread that "owns" this unixFile */
#endif
#if OS_VXWORKS
................................................................................
  ** occur if a file is updated without also updating the transaction
  ** counter.  This test is made to avoid new problems similar to the
  ** one described by ticket #3584. 
  */
  unsigned char transCntrChng;   /* True if the transaction counter changed */
  unsigned char dbUpdate;        /* True if any part of database file changed */
  unsigned char inNormalWrite;   /* True if in a normal write operation */





#endif
#ifdef SQLITE_TEST
  /* In test mode, increase the size of this structure a bit so that 
  ** it is larger than the struct CrashFile defined in test6.c.
  */
  char aPadding[32];
#endif
................................................................................
** using the file closes.
*/
struct unixOpenCnt {
  struct unixFileId fileId;   /* The lookup key */
  int nRef;                   /* Number of pointers to this structure */
  int nLock;                  /* Number of outstanding locks */
  int nPending;               /* Number of pending close() operations */
  struct PendingClose {
    int fd;                   /* File descriptor to close */
    int flags;                /* Flags this file descriptor was opened with */
  } *aPending;                /* Malloced space holding fds awaiting close() */
#if OS_VXWORKS
  sem_t *pSem;                     /* Named POSIX semaphore */
  char aSemName[MAX_PATHNAME+1];   /* Name of that semaphore */
#endif
  struct unixOpenCnt *pNext, *pPrev;   /* List of all unixOpenCnt objects */
};

................................................................................

end_lock:
  unixLeaveMutex();
  OSTRACE4("LOCK    %d %s %s\n", pFile->h, locktypeName(locktype), 
      rc==SQLITE_OK ? "ok" : "failed");
  return rc;
}

/*
** Close all file descriptors accumuated in the p->aPending[] array. If
** all such file descriptors are closed without error, the aPending[] 
** array is deleted and SQLITE_OK returned.
**
** Otherwise, if an error occurs, then successfully closed file descriptor
** entries in the aPending[] array are set to -1, the aPending[] array
** not deleted and SQLITE_IOERR_CLOSE returned.
*/ 
static int closePendingFds(unixFile *pFile){
  struct unixOpenCnt *pOpen = pFile->pOpen;
  struct PendingClose *aPending = pOpen->aPending;
  int i;
  int rc = SQLITE_OK;
  assert( unixMutexHeld() );
  for(i=0; i<pOpen->nPending; i++){
    if( aPending[i].fd>=0 ){
      if( close(aPending[i].fd) ){
        pFile->lastErrno = errno;
        rc = SQLITE_IOERR_CLOSE;
      }else{
        aPending[i].fd = -1;
      }
    }
  }
  if( rc==SQLITE_OK ){
    sqlite3_free(aPending);
    pOpen->nPending = 0;
    pOpen->aPending = 0;
  }
  return rc;
}

/*
** Add the file descriptor used by file handle pFile to the corresponding
** aPending[] array to be closed after some other connection releases
** a lock.
*/
static void setPendingFd(unixFile *pFile){
  struct PendingClose *aNew;
  struct unixOpenCnt *pOpen = pFile->pOpen;
  int nByte = (pOpen->nPending+1)*sizeof(pOpen->aPending[0]);
  aNew = sqlite3_realloc(pOpen->aPending, nByte);
  if( aNew==0 ){
    /* If a malloc fails, just leak the file descriptor */
  }else{
    pOpen->aPending = aNew;
    pOpen->aPending[pOpen->nPending].fd = pFile->h;
    pOpen->aPending[pOpen->nPending].flags = pFile->flags;
    pOpen->nPending++;
    pFile->h = -1;
  }
}

/*
** Lower the locking level on file descriptor pFile to locktype.  locktype
** must be either NO_LOCK or SHARED_LOCK.
**
** If the locking level of the file descriptor is already at or below
** the requested locking level, this routine is a no-op.
................................................................................
        pFile->lastErrno = tErrno;
      }
      goto end_unlock;
    }
  }
  if( locktype==NO_LOCK ){
    struct unixOpenCnt *pOpen;


    /* Decrement the shared lock counter.  Release the lock using an
    ** OS call only when all threads in this same process have released
    ** the lock.
    */
    pLock->cnt--;
    if( pLock->cnt==0 ){
................................................................................
    ** count reaches zero, close any other file descriptors whose close
    ** was deferred because of outstanding locks.
    */
    pOpen = pFile->pOpen;
    pOpen->nLock--;
    assert( pOpen->nLock>=0 );
    if( pOpen->nLock==0 && pOpen->nPending>0 ){
      int rc2 = closePendingFds(pFile);


















      if( rc==SQLITE_OK ){
        rc = rc2;
      }
    }
  }
	
end_unlock:
  unixLeaveMutex();
  if( rc==SQLITE_OK ) pFile->locktype = locktype;
  return rc;
................................................................................
    unixEnterMutex();
    if( pFile->pOpen && pFile->pOpen->nLock ){
      /* If there are outstanding locks, do not actually close the file just
      ** yet because that would clear those locks.  Instead, add the file
      ** descriptor to pOpen->aPending.  It will be automatically closed when
      ** the last lock is cleared.
      */








      setPendingFd(pFile);


    }
    releaseLockInfo(pFile->pLock);
    releaseOpenCnt(pFile->pOpen);
    rc = closeUnixFile(id);
    unixLeaveMutex();
  }
  return rc;
................................................................................

  if( rc==SQLITE_OK ){
    if( locktype==NO_LOCK ){
      struct unixOpenCnt *pOpen = pFile->pOpen;
      pOpen->nLock--;
      assert( pOpen->nLock>=0 );
      if( pOpen->nLock==0 && pOpen->nPending>0 ){
        rc = closePendingFds(pFile);














      }
    }
  }
  unixLeaveMutex();
  if( rc==SQLITE_OK ){
    pFile->locktype = locktype;
  }
  return rc;
}

/*
** Close a file & cleanup AFP specific locking context 
*/
static int afpClose(sqlite3_file *id) {
................................................................................
    unixEnterMutex();
    if( pFile->pOpen && pFile->pOpen->nLock ){
      /* If there are outstanding locks, do not actually close the file just
      ** yet because that would clear those locks.  Instead, add the file
      ** descriptor to pOpen->aPending.  It will be automatically closed when
      ** the last lock is cleared.
      */








      setPendingFd(pFile);


    }
    releaseOpenCnt(pFile->pOpen);
    sqlite3_free(pFile->lockingContext);
    closeUnixFile(id);
    unixLeaveMutex();
  }
  return SQLITE_OK;
................................................................................
*/
static int unixRead(
  sqlite3_file *id, 
  void *pBuf, 
  int amt,
  sqlite3_int64 offset
){
  unixFile *pFile = (unixFile *)id;
  int got;
  assert( id );

  /* If this is a database file (not a journal, master-journal or temp
  ** file), the bytes in the locking range should never be read or written. */

  assert( (pFile->flags&SQLITE_OPEN_MAIN_DB)==0
       || offset>=PENDING_BYTE+512
       || offset+amt<=PENDING_BYTE 
  );

  got = seekAndRead(pFile, offset, pBuf, amt);
  if( got==amt ){
    return SQLITE_OK;
  }else if( got<0 ){
    /* lastErrno set by seekAndRead */
    return SQLITE_IOERR_READ;
  }else{
    pFile->lastErrno = 0; /* not a system error */
    /* Unread parts of the buffer must be zero-filled */
    memset(&((char*)pBuf)[got], 0, amt-got);
    return SQLITE_IOERR_SHORT_READ;
  }
}

/*
................................................................................
*/
static int unixWrite(
  sqlite3_file *id, 
  const void *pBuf, 
  int amt,
  sqlite3_int64 offset 
){
  unixFile *pFile = (unixFile*)id;
  int wrote = 0;
  assert( id );
  assert( amt>0 );

  /* If this is a database file (not a journal, master-journal or temp
  ** file), the bytes in the locking range should never be read or written. */

  assert( (pFile->flags&SQLITE_OPEN_MAIN_DB)==0
       || offset>=PENDING_BYTE+512
       || offset+amt<=PENDING_BYTE 
  );

#ifndef NDEBUG
  /* If we are doing a normal write to a database file (as opposed to
  ** doing a hot-journal rollback or a write to some file other than a
  ** normal database file) then record the fact that the database
  ** has changed.  If the transaction counter is modified, record that
  ** fact too.
  */
  if( pFile->inNormalWrite ){

    pFile->dbUpdate = 1;  /* The database has been modified */
    if( offset<=24 && offset+amt>=27 ){
      int rc;
      char oldCntr[4];
      SimulateIOErrorBenign(1);
      rc = seekAndRead(pFile, 24, oldCntr, 4);
      SimulateIOErrorBenign(0);
................................................................................
      if( rc!=4 || memcmp(oldCntr, &((char*)pBuf)[24-offset], 4)!=0 ){
        pFile->transCntrChng = 1;  /* The transaction counter has changed */
      }
    }
  }
#endif

  while( amt>0 && (wrote = seekAndWrite(pFile, offset, pBuf, amt))>0 ){
    amt -= wrote;
    offset += wrote;
    pBuf = &((char*)pBuf)[wrote];
  }
  SimulateIOError(( wrote=(-1), amt=1 ));
  SimulateDiskfullError(( wrote=0, amt=1 ));
  if( amt>0 ){
    if( wrote<0 ){
      /* lastErrno set by seekAndWrite */
      return SQLITE_IOERR_WRITE;
    }else{
      pFile->lastErrno = 0; /* not a system error */
      return SQLITE_FULL;
    }
  }
  return SQLITE_OK;
}

#ifdef SQLITE_TEST
................................................................................
** Routine to transform a unixFile into a proxy-locking unixFile.
** Implementation in the proxy-lock division, but used by unixOpen()
** if SQLITE_PREFER_PROXY_LOCKING is defined.
*/
static int proxyTransformUnixFile(unixFile*, const char*);
#endif

/*
** Search for an unused file descriptor that was opened on the database 
** file (not a journal or master-journal file) identified by pathname
** zPath with SQLITE_OPEN_XXX flags matching those passed as the second
** argument to this function.
**
** Such a file descriptor may exist if a database connection was closed
** but the associated file descriptor could not be closed because some
** other file descriptor open on the same file is holding a file-lock.
** Refer to comments in the unixClose() function and the lengthy comment
** describing "Posix Advisory Locking" at the start of this file for 
** further details. Also, ticket #4018.
**
** If a suitable file descriptor is found, then it is returned. If no
** such file descriptor is located, -1 is returned.
*/
static int findReusableFd(const char *zPath, int flags){
  int fd = -1;                         /* Return value */
  struct stat sStat;                   /* Results of stat() call */

  /* A stat() call may fail for various reasons. If this happens, it is
  ** almost certain that an open() call on the same path will also fail.
  ** For this reason, if an error occurs in the stat() call here, it is
  ** ignored and -1 is returned. The caller will try to open a new file
  ** descriptor on the same path, fail, and return an error to SQLite.
  **
  ** Even if a subsequent open() call does succeed, the consequences of
  ** not searching for a resusable file descriptor are not dire.  */
  if( 0==stat(zPath, &sStat) ){
    struct unixOpenCnt *p;
    struct unixFileId id;
    id.dev = sStat.st_dev;
    id.ino = sStat.st_ino;

    unixEnterMutex();
    for(p=openList; p&& memcmp(&id, &p->fileId, sizeof(id)); p=p->pNext);
    if( p && p->aPending ){
      int i;
      struct PendingClose *aPending = p->aPending;
      for(i=0; i<p->nPending; i++){
        if( aPending[i].fd>=0 && flags==aPending[i].flags ){
          fd = aPending[i].fd;
          aPending[i].fd = -1;
          break;
        }
      }
    }
    unixLeaveMutex();
  }

  return fd;
}

/*
** Open the file zPath.
** 
** Previously, the SQLite OS layer used three functions in place of this
** one:
**
................................................................................
static int unixOpen(
  sqlite3_vfs *pVfs,           /* The VFS for which this is the xOpen method */
  const char *zPath,           /* Pathname of file to be opened */
  sqlite3_file *pFile,         /* The file descriptor to be filled in */
  int flags,                   /* Input flags to control the opening */
  int *pOutFlags               /* Output flags returned to SQLite core */
){
  unixFile *p = (unixFile *)pFile;
  int fd = -1;                   /* File descriptor returned by open() */
  int dirfd = -1;                /* Directory file descriptor */
  int openFlags = 0;             /* Flags to pass to open() */
  int eType = flags&0xFFFFFF00;  /* Type of file to open */
  int noLock;                    /* True to omit locking primitives */
  int rc = SQLITE_OK;            /* Function Return Code */

  int isExclusive  = (flags & SQLITE_OPEN_EXCLUSIVE);
  int isDelete     = (flags & SQLITE_OPEN_DELETEONCLOSE);
  int isCreate     = (flags & SQLITE_OPEN_CREATE);
  int isReadonly   = (flags & SQLITE_OPEN_READONLY);
  int isReadWrite  = (flags & SQLITE_OPEN_READWRITE);

................................................................................
  */
  assert((isReadonly==0 || isReadWrite==0) && (isReadWrite || isReadonly));
  assert(isCreate==0 || isReadWrite);
  assert(isExclusive==0 || isCreate);
  assert(isDelete==0 || isCreate);

  /* The main DB, main journal, and master journal are never automatically
  ** deleted. Nor are they ever temporary files.  */

  assert( (!isDelete && zName) || eType!=SQLITE_OPEN_MAIN_DB );
  assert( (!isDelete && zName) || eType!=SQLITE_OPEN_MAIN_JOURNAL );
  assert( (!isDelete && zName) || eType!=SQLITE_OPEN_MASTER_JOURNAL );

  /* Assert that the upper layer has set one of the "file-type" flags. */
  assert( eType==SQLITE_OPEN_MAIN_DB      || eType==SQLITE_OPEN_TEMP_DB 
       || eType==SQLITE_OPEN_MAIN_JOURNAL || eType==SQLITE_OPEN_TEMP_JOURNAL 
       || eType==SQLITE_OPEN_SUBJOURNAL   || eType==SQLITE_OPEN_MASTER_JOURNAL 
       || eType==SQLITE_OPEN_TRANSIENT_DB
  );

  memset(p, 0, sizeof(unixFile));

  if( eType==SQLITE_OPEN_MAIN_DB ){
    /* Try to find an unused file descriptor to reuse. This is not done
    ** for vxworks. Not because vxworks would not benefit from the change
    ** (it might, we're not sure), but because no way to test it is
    ** currently available. It is better not to risk breaking vxworks for 
    ** the sake of such an obscure feature.   */
#if !OS_VXWORKS
    fd = findReusableFd(zName, flags);
#endif
  }else if( !zName ){
    /* If zName is NULL, the upper layer is requesting a temp file. */
    assert(isDelete && !isOpenDirectory);
    rc = getTempname(MAX_PATHNAME+1, zTmpname);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    zName = zTmpname;
  }

  /* Determine the value of the flags parameter passed to POSIX function
  ** open(). These must be calculated even if open() is not called, as
  ** they may be stored as part of the file handle and used by the 
  ** 'conch file' locking functions later on.  */
  if( isReadonly )  openFlags |= O_RDONLY;
  if( isReadWrite ) openFlags |= O_RDWR;
  if( isCreate )    openFlags |= O_CREAT;
  if( isExclusive ) openFlags |= (O_EXCL|O_NOFOLLOW);
  openFlags |= (O_LARGEFILE|O_BINARY);

  if( fd<0 ){
    fd = open(zName, openFlags, isDelete?0600:SQLITE_DEFAULT_FILE_PERMISSIONS);
    OSTRACE4("OPENX   %-3d %s 0%o\n", fd, zName, openFlags);
    if( fd<0 && errno!=EISDIR && isReadWrite && !isExclusive ){
      /* Failed to open the file for read/write access. Try read-only. */
      flags &= ~(SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE);
      flags |= SQLITE_OPEN_READONLY;
      return unixOpen(pVfs, zPath, pFile, flags, pOutFlags);
    }
    if( fd<0 ){
      return SQLITE_CANTOPEN;
    }
  }
  assert( fd>=0 );
  p->flags = flags;
  if( pOutFlags ){
    *pOutFlags = flags;
  }

  if( isDelete ){
#if OS_VXWORKS
    zPath = zName;
#else
    unlink(zName);
#endif
  }
#if SQLITE_ENABLE_LOCKING_STYLE
  else{
    p->openFlags = openFlags;









  }
#endif


  if( isOpenDirectory ){
    rc = openDirectory(zPath, &dirfd);
    if( rc!=SQLITE_OK ){
      /* It is safe to close fd at this point, because it is guaranteed not
      ** to be open on a database file. If it were open on a database file,
      ** it would not be safe to close as this would cause any locks held
      ** on the file by this process to be released.  */
      assert( eType!=SQLITE_OPEN_MAIN_DB );
      close(fd);             /* silently leak if fail, already in error */
      return rc;
    }
  }

#ifdef FD_CLOEXEC
  fcntl(fd, F_SETFD, fcntl(fd, F_GETFD, 0) | FD_CLOEXEC);
#endif
................................................................................
  noLock = eType!=SQLITE_OPEN_MAIN_DB;

#if SQLITE_PREFER_PROXY_LOCKING
  if( zPath!=NULL && !noLock ){
    char *envforce = getenv("SQLITE_FORCE_PROXY_LOCKING");
    int useProxy = 0;

    /* SQLITE_FORCE_PROXY_LOCKING==1 means force always use proxy, 0 means 
    ** never use proxy, NULL means use proxy for non-local files only.  */

    if( envforce!=NULL ){
      useProxy = atoi(envforce)>0;
    }else{
      struct statfs fsInfo;

      if( statfs(zPath, &fsInfo) == -1 ){
        ((unixFile*)pFile)->lastErrno = errno;
        if( dirfd>=0 ) close(dirfd); /* silently leak if fail, in error */
        close(fd); /* silently leak if fail, in error */
        return SQLITE_IOERR_ACCESS;
      }
      useProxy = !(fsInfo.f_flags&MNT_LOCAL);
    }
    if( useProxy ){

# 2009 August 20
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
# This file implements regression tests for SQLite library.
#
# This file implements tests to verify that ticket #4018 has been
# fixed.  
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl

proc testsql {sql} {
  set fd [open tf_main.tcl w]
  puts $fd [subst -nocommands {
    sqlite3_test_control_pending_byte 0x0010000
    sqlite3 db test.db
    set rc [catch { db eval {$sql} } msg]
    puts -nonewline "[set rc] {[set msg]}"
    flush stdout
    exit
  }]
  close $fd
  set fd [open "| [info nameofexec] ./tf_main.tcl" r] 
  set res [read $fd]
  close $fd
  return $res
}

do_test tkt4018-1.1 {
  execsql {
    CREATE TABLE t1(a, b);
    BEGIN;
    SELECT * FROM t1;
  }
} {}

# The database is locked by connection [db]. Open and close a second
# connection to test.db 20000 times. If file-descriptors are not being
# reused, then the process will quickly exceed its maximum number of
# file descriptors (1024 by default on linux).
do_test tkt4018-1.2 {
  for {set i 0} {$i < 10000} {incr i} {
    sqlite3 db2 test.db
    db2 close
  }
} {}

# Now check that connection [db] is still holding a SHARED lock by
# having a second process try to write the db.
do_test tkt4018-1.3 {
  testsql {INSERT INTO t1 VALUES(3, 4)}
} {1 {database is locked}}

# Sanity checking. Have [db] release the lock and then retry the
# INSERT from the previous test case.
do_test tkt4018-1.4 {
  db eval COMMIT
  testsql {INSERT INTO t1 VALUES(3, 4)}
} {0 {}}

# Check that reusing a file descriptor cannot change a read-only 
# connection into a read-write connection.
do_test tkt4018-2.1 {
  sqlite3 db2 test.db
  execsql {INSERT INTO t1 VALUES(1, 2)} db2
} {}
do_test tkt4018-2.2 {
  execsql {
    BEGIN;
    SELECT * FROM t1 ORDER BY a;
  }
} {1 2 3 4}
do_test tkt4018-2.3 {
  db2 close
  sqlite3 db2 test.db -readonly 1
  execsql COMMIT
  catchsql {INSERT INTO t1 VALUES(5, 6)} db2
} {1 {attempt to write a readonly database}}
db2 close

finish_test