SQLite

  sqlite3_vfs *pParent;           /* The VFS to use for file IO */
  sqlite3_vfs *pVfs;              /* The testvfs registered with SQLite */
  Tcl_Interp *interp;             /* Interpreter to run script in */
  int nScript;                    /* Number of elements in array apScript */
  Tcl_Obj **apScript;             /* Script to execute */
  TestvfsBuffer *pBuffer;         /* List of shared buffers */
  int isNoshm;

  int mask;
  int iIoerrCnt;
  int ioerr;
};

/*
** A shared-memory buffer.
*/
struct TestvfsBuffer {
  char *zFile;                    /* Associated file name */
  int n;                          /* Size of allocated buffer in bytes */
  u8 *a;                          /* Buffer allocated using ckalloc() */
  int nRef;                       /* Number of references to this object */
  TestvfsBuffer *pNext;           /* Next in linked list of all buffers */
};

#define TESTVFS_SHMOPEN_MASK    0x00000001
#define TESTVFS_SHMSIZE_MASK    0x00000002
#define TESTVFS_SHMGET_MASK     0x00000004
#define TESTVFS_SHMRELEASE_MASK 0x00000008
#define TESTVFS_SHMLOCK_MASK    0x00000010
#define TESTVFS_SHMBARRIER_MASK 0x00000020
#define TESTVFS_SHMCLOSE_MASK   0x00000040

#define TESTVFS_ALL_MASK        0x0000007F


#define PARENTVFS(x) (((Testvfs *)((x)->pAppData))->pParent)


/*
** Method declarations for TestvfsFile.

  **   SCRIPT xShmOpen FILENAME
  **
  ** If the script returns an SQLite error code other than SQLITE_OK, an
  ** error is returned to the caller. If it returns SQLITE_OK, the new
  ** connection is named "anon". Otherwise, the value returned by the
  ** script is used as the connection name.
  */
  Tcl_ResetResult(p->interp);
  if( p->mask&TESTVFS_SHMOPEN_MASK ){
    tvfsExecTcl(p, "xShmOpen", Tcl_NewStringObj(pFd->zFilename, -1), 0, 0);
  }
  if( tvfsResultCode(p, &rc) ){
    if( rc!=SQLITE_OK ) return rc;
    pId = Tcl_NewStringObj("anon", -1);
  }else{
    pId = Tcl_GetObjResult(p->interp);
  }
  Tcl_IncrRefCount(pId);

  int reqSize,
  int *pNewSize
){
  int rc = SQLITE_OK;
  TestvfsFile *pFd = (TestvfsFile *)pFile;
  Testvfs *p = (Testvfs *)(pFd->pVfs->pAppData);

  if( p->mask&TESTVFS_SHMSIZE_MASK ){
    tvfsExecTcl(p, "xShmSize", 
        Tcl_NewStringObj(pFd->pShm->zFile, -1), pFd->pShmId, 0
    );
    tvfsResultCode(p, &rc);
  }
  if( rc==SQLITE_OK ){
    tvfsGrowBuffer(pFd, reqSize, pNewSize);
  }
  return rc;
}

static int tvfsShmGet(
  sqlite3_file *pFile, 
  int reqMapSize, 
  int *pMapSize, 
  volatile void **pp
){
  int rc = SQLITE_OK;
  TestvfsFile *pFd = (TestvfsFile *)pFile;
  Testvfs *p = (Testvfs *)(pFd->pVfs->pAppData);

  if( p->mask&TESTVFS_SHMGET_MASK ){
    tvfsExecTcl(p, "xShmGet", 
        Tcl_NewStringObj(pFd->pShm->zFile, -1), pFd->pShmId, 0
    );
    tvfsResultCode(p, &rc);
  }
  if( rc==SQLITE_OK ){
    tvfsGrowBuffer(pFd, reqMapSize, pMapSize);
    *pp = pFd->pShm->a;
  }
  return rc;
}

static int tvfsShmRelease(sqlite3_file *pFile){
  int rc = SQLITE_OK;
  TestvfsFile *pFd = (TestvfsFile *)pFile;
  Testvfs *p = (Testvfs *)(pFd->pVfs->pAppData);

  if( p->mask&TESTVFS_SHMRELEASE_MASK ){
    tvfsExecTcl(p, "xShmRelease", 
        Tcl_NewStringObj(pFd->pShm->zFile, -1), pFd->pShmId, 0
    );
    tvfsResultCode(p, &rc);
  }

  return rc;
}

static int tvfsShmLock(
  sqlite3_file *pFile,
  int ofst,
  int n,
  int flags
){
  int rc = SQLITE_OK;
  TestvfsFile *pFd = (TestvfsFile *)pFile;
  Testvfs *p = (Testvfs *)(pFd->pVfs->pAppData);
  int nLock;
  char zLock[80];

  if( p->mask&TESTVFS_SHMLOCK_MASK ){
    sqlite3_snprintf(sizeof(zLock), zLock, "%d %d", ofst, n);
    nLock = strlen(zLock);
    if( flags & SQLITE_SHM_LOCK ){
      strcpy(&zLock[nLock], " lock");
    }else{
      strcpy(&zLock[nLock], " unlock");
    }
    nLock += strlen(&zLock[nLock]);
    if( flags & SQLITE_SHM_SHARED ){
      strcpy(&zLock[nLock], " shared");
    }else{
      strcpy(&zLock[nLock], " exclusive");
    }
    tvfsExecTcl(p, "xShmLock", 
        Tcl_NewStringObj(pFd->pShm->zFile, -1), pFd->pShmId,
        Tcl_NewStringObj(zLock, -1)
    );
    tvfsResultCode(p, &rc);
  }
  return rc;
}

static void tvfsShmBarrier(sqlite3_file *pFile){

  TestvfsFile *pFd = (TestvfsFile *)pFile;
  Testvfs *p = (Testvfs *)(pFd->pVfs->pAppData);

  if( p->mask&TESTVFS_SHMBARRIER_MASK ){
    tvfsExecTcl(p, "xShmBarrier", 
        Tcl_NewStringObj(pFd->pShm->zFile, -1), pFd->pShmId, 0
    );

  }
}

static int tvfsShmClose(
  sqlite3_file *pFile,
  int deleteFlag
){
  int rc = SQLITE_OK;
  TestvfsFile *pFd = (TestvfsFile *)pFile;
  Testvfs *p = (Testvfs *)(pFd->pVfs->pAppData);
  TestvfsBuffer *pBuffer = pFd->pShm;

  assert( pFd->pShmId && pFd->pShm );
#if 0
  assert( (deleteFlag!=0)==(pBuffer->nRef==1) );
#endif

  if( p->mask&TESTVFS_SHMCLOSE_MASK ){
    tvfsExecTcl(p, "xShmClose", 
        Tcl_NewStringObj(pFd->pShm->zFile, -1), pFd->pShmId, 0
    );
    tvfsResultCode(p, &rc);
  }

  pBuffer->nRef--;
  if( pBuffer->nRef==0 ){
    TestvfsBuffer **pp;
    for(pp=&p->pBuffer; *pp!=pBuffer; pp=&((*pp)->pNext));
    *pp = (*pp)->pNext;
    ckfree((char *)pBuffer->a);

  ClientData cd,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  Testvfs *p = (Testvfs *)cd;

  static const char *CMD_strs[] = { "shm", "delete", "filter", "ioerr", 0 };
  enum DB_enum { CMD_SHM, CMD_DELETE, CMD_FILTER, CMD_IOERR };
  int i;
  
  if( objc<2 ){
    Tcl_WrongNumArgs(interp, 1, objv, "SUBCOMMAND ...");
    return TCL_ERROR;
  }
  if( Tcl_GetIndexFromObj(interp, objv[1], CMD_strs, "subcommand", 0, &i) ){

        pBuffer->a = (u8 *)ckrealloc((char *)pBuffer->a, n);
        pBuffer->n = n;
        memcpy(pBuffer->a, a, n);
      }
      Tcl_SetObjResult(interp, Tcl_NewByteArrayObj(pBuffer->a, pBuffer->n));
      break;
    }

    case CMD_FILTER: {
      static struct VfsMethod {
        char *zName;
        int mask;
      } vfsmethod [] = {
        { "xShmOpen",    TESTVFS_SHMOPEN_MASK },
        { "xShmSize",    TESTVFS_SHMSIZE_MASK },
        { "xShmGet",     TESTVFS_SHMGET_MASK },
        { "xShmRelease", TESTVFS_SHMRELEASE_MASK },
        { "xShmLock",    TESTVFS_SHMLOCK_MASK },
        { "xShmBarrier", TESTVFS_SHMBARRIER_MASK },
        { "xShmClose",   TESTVFS_SHMCLOSE_MASK },
      };
      Tcl_Obj **apElem = 0;
      int nElem = 0;
      int i;
      int mask = 0;
      if( objc!=3 ){
        Tcl_WrongNumArgs(interp, 2, objv, "LIST");
        return TCL_ERROR;
      }
      if( Tcl_ListObjGetElements(interp, objv[2], &nElem, &apElem) ){
        return TCL_ERROR;
      }
      Tcl_ResetResult(interp);
      for(i=0; i<nElem; i++){
        int iMethod;
        char *zElem = Tcl_GetString(apElem[i]);
        for(iMethod=0; iMethod<ArraySize(vfsmethod); iMethod++){
          if( strcmp(zElem, vfsmethod[iMethod].zName)==0 ){
            mask |= vfsmethod[iMethod].mask;
            break;
          }
        }
        if( iMethod==ArraySize(vfsmethod) ){
          Tcl_AppendResult(interp, "unknown method: ", zElem, 0);
          return TCL_ERROR;
        }
      }
      p->mask = mask;
      break;
    }

    case CMD_IOERR: {
      int iRet = ((p->iIoerrCnt<0) ? (1+(p->iIoerrCnt*-1)) : 0);
      if( objc==2 ){
        p->ioerr = 0;
        p->iIoerrCnt = 0;
      }else if( objc==4 ){
        int iCnt, iPersist;
        if( TCL_OK!=Tcl_GetIntFromObj(interp, objv[2], &iCnt)
         || TCL_OK!=Tcl_GetBooleanFromObj(interp, objv[3], &iPersist)
        ){
          return TCL_ERROR;
        }
        p->ioerr = (iPersist!=0) + 1;
        p->iIoerrCnt = iCnt;
      }else{
        Tcl_AppendResult(interp, "Bad args", 0);
      }
      Tcl_SetObjResult(interp, Tcl_NewIntObj(iRet));
      break;
    }

    case CMD_DELETE: {
      Tcl_DeleteCommand(interp, Tcl_GetString(objv[0]));
      break;
    }
  }

  return TCL_OK;

  memcpy(pVfs, &tvfs_vfs, sizeof(sqlite3_vfs));
  pVfs->pAppData = (void *)p;
  pVfs->zName = p->zName;
  pVfs->mxPathname = p->pParent->mxPathname;
  pVfs->szOsFile += p->pParent->szOsFile;
  p->pVfs = pVfs;
  p->isNoshm = isNoshm;
  p->mask = TESTVFS_ALL_MASK;

  Tcl_CreateObjCommand(interp, zVfs, testvfs_obj_cmd, p, testvfs_obj_del);
  sqlite3_vfs_register(pVfs, 0);

  return TCL_OK;

 bad_args:

} {8}
do_faultsim_test walfault-2 -prep {
  faultsim_restore_and_reopen
} -body {
  execsql { SELECT count(*) FROM x }
} -test {


  faultsim_test_result {0 8}

  # Run the integrity_check to make sure nothing strange has occurred.
  #
  set ic [db eval { PRAGMA integrity_check }]
  if {$ic != "ok"} { error "Integrity check: $ic" }
}

#--------------------------------------------------------------------------
# Test fault injection while writing and checkpointing a small WAL file.
#

#   set ::shmfault_ioerr_methods(xShmOpen) 1
# 
# Faults are not injected into xShmRelease, xShmClose or xShmLock method 
# calls. The global tcl variables used are:
#
#   $::shmfault_ioerr_countdown
#   $::shmfault_ioerr_persist

#
proc shmfault_vfs_cb {method args} {

  # If ::shmfault_ioerr_countdown is not set, always return SQLITE_OK.
  #
  if {[info exists ::shmfault_ioerr_countdown]==0} { return SQLITE_OK }


  incr ::shmfault_ioerr_countdown -1
  if { ($::shmfault_ioerr_countdown==0)
    || ($::shmfault_ioerr_countdown<=0 && $::shmfault_ioerr_persist)
  } {
    return SQLITE_IOERR

  }
  return SQLITE_OK
}

# Options are:
#
#   -tclprep TCL

  set A(-sqlbody) ""
  set A(-methods) [list xShmGet xShmOpen xShmSize]
  set A(-coverageonly) 0
  array set A $args

  # Create a VFS to use:
  testvfs shmfault shmfault_vfs_cb
  shmfault filter $A(-methods)


  
  foreach mode {transient persistent} {
    set ::shmfault_ioerr_persist [expr {$mode == "persistent"}]

    for {set nDelay 1} {$nDelay < 10000} {incr nDelay} {
  
      file delete -force test.db test.db-wal test.db-journal

    INSERT INTO t1 SELECT randomblob(400) FROM t1;    /* 8192 */
    INSERT INTO t1 SELECT randomblob(400) FROM t1;    /* 16384 */
  COMMIT;
}

do_shmfault_test walfault-shm-3 -methods xShmSize -tclprep {
  sqlite3 db test.db -vfs shmfault
  shmfault filter {}
  db eval {
    PRAGMA page_size = 512;
    PRAGMA journal_mode = WAL;
    PRAGMA wal_autocheckpoint = 0;
    CREATE TABLE t1(x);
    BEGIN;
      INSERT INTO t1 VALUES(randomblob(400));           /* 1 */

      INSERT INTO t1 SELECT randomblob(400) FROM t1;    /* 4096 */
      INSERT INTO t1 SELECT randomblob(400) FROM t1;    /* 8192 */
      INSERT INTO t1 SELECT randomblob(400) FROM t1;    /* 16384 */
    COMMIT;
  }

  set ::shmfault_ioerr_countdown 1
  shmfault filter xShmGet
  db close
  shmfault filter {}
  if {[file exists test.db-wal]==0} {error "Failed to create WAL file!"}

  sqlite3 db test.db -vfs shmfault
} -sqlbody {
  SELECT count(*) FROM t1;
}

      INSERT INTO t1 VALUES(randomblob(400));           /* 1 */
      INSERT INTO t1 SELECT randomblob(400) FROM t1;    /* 2 */
      INSERT INTO t1 SELECT randomblob(400) FROM t1;    /* 4 */
    COMMIT;
  }

  set ::shmfault_ioerr_countdown 1
  shmfault filter xShmGet
  db close
  shmfault filter {}
  if {[file exists test.db-wal]==0} {error "Failed to create WAL file!"}
  sqlite3 db test.db -vfs shmfault
} -sqlbody {
  SELECT count(*) FROM t1;
}

do_shmfault_test walfault-shm-5.1 -coverageonly 1 -sqlprep {