SQLite

    pPager = sqlite3BtreePager(pBtree);
    assert( pPager!=0 );
    fd = sqlite3PagerFile(pPager);
    assert( fd!=0 );
    if( op==SQLITE_FCNTL_FILE_POINTER ){
      *(sqlite3_file**)pArg = fd;
      rc = SQLITE_OK;
    }else if( op==SQLITE_FCNTL_VFS_POINTER ){
      *(sqlite3_vfs**)pArg = sqlite3PagerVfs(pPager);
      rc = SQLITE_OK;
    }else if( fd->pMethods ){
      rc = sqlite3OsFileControl(fd, op, pArg);
    }else{
      rc = SQLITE_NOTFOUND;
    }
    sqlite3BtreeLeave(pBtree);
  }

const char *sqlite3PagerFilename(Pager *pPager, int nullIfMemDb){
  return (nullIfMemDb && pPager->memDb) ? "" : pPager->zFilename;
}

/*
** Return the VFS structure for the pager.
*/
sqlite3_vfs *sqlite3PagerVfs(Pager *pPager){
  return pPager->pVfs;
}

/*
** Return the file handle for the database file associated
** with the pager.  This might return NULL if the file has
** not yet been opened.

u8 sqlite3PagerIsreadonly(Pager*);
u32 sqlite3PagerDataVersion(Pager*);
#ifdef SQLITE_DEBUG
  int sqlite3PagerRefcount(Pager*);
#endif
int sqlite3PagerMemUsed(Pager*);
const char *sqlite3PagerFilename(Pager*, int);
sqlite3_vfs *sqlite3PagerVfs(Pager*);
sqlite3_file *sqlite3PagerFile(Pager*);
const char *sqlite3PagerJournalname(Pager*);
int sqlite3PagerNosync(Pager*);
void *sqlite3PagerTempSpace(Pager*);
int sqlite3PagerIsMemdb(Pager*);
void sqlite3PagerCacheStat(Pager *, int, int, int *);
void sqlite3PagerClearCache(Pager *);

  ".system CMD ARGS...    Run CMD ARGS... in a system shell\n"
  ".tables ?TABLE?        List names of tables\n"
  "                         If TABLE specified, only list tables matching\n"
  "                         LIKE pattern TABLE.\n"
  ".timeout MS            Try opening locked tables for MS milliseconds\n"
  ".timer on|off          Turn SQL timer on or off\n"
  ".trace FILE|off        Output each SQL statement as it is run\n"
  ".vfsinfo ?AUX?         Information about the top-level VFS\n"
  ".vfsname ?AUX?         Print the name of the VFS stack\n"
  ".width NUM1 NUM2 ...   Set column widths for \"column\" mode\n"
  "                         Negative values right-justify\n"
;

/* Forward reference */
static int process_input(ShellState *p, FILE *in);

  }else
#endif /* SQLITE_USER_AUTHENTICATION */

  if( c=='v' && strncmp(azArg[0], "version", n)==0 ){
    fprintf(p->out, "SQLite %s %s\n" /*extra-version-info*/,
        sqlite3_libversion(), sqlite3_sourceid());
  }else

  if( c=='v' && strncmp(azArg[0], "vfsinfo", n)==0 ){
    const char *zDbName = nArg==2 ? azArg[1] : "main";
    sqlite3_vfs *pVfs;
    if( p->db ){
      sqlite3_file_control(p->db, zDbName, SQLITE_FCNTL_VFS_POINTER, &pVfs);
      if( pVfs ){
        fprintf(p->out, "vfs.zName      = \"%s\"\n", pVfs->zName);
        fprintf(p->out, "vfs.iVersion   = %d\n", pVfs->iVersion);
        fprintf(p->out, "vfs.szOsFile   = %d\n", pVfs->szOsFile);
        fprintf(p->out, "vfs.mxPathname = %d\n", pVfs->mxPathname);
      }
    }
  }else

  if( c=='v' && strncmp(azArg[0], "vfsname", n)==0 ){
    const char *zDbName = nArg==2 ? azArg[1] : "main";
    char *zVfsName = 0;
    if( p->db ){
      sqlite3_file_control(p->db, zDbName, SQLITE_FCNTL_VFSNAME, &zVfsName);
      if( zVfsName ){

** [sqlite3_malloc()] and the result is stored in the char* variable
** that the fourth parameter of [sqlite3_file_control()] points to.
** The caller is responsible for freeing the memory when done.  As with
** all file-control actions, there is no guarantee that this will actually
** do anything.  Callers should initialize the char* variable to a NULL
** pointer in case this file-control is not implemented.  This file-control
** is intended for diagnostic use only.
**
** <li>[[SQLITE_FCNTL_VFS_POINTER]]
** ^The [SQLITE_FCNTL_VFS_POINTER] opcode finds a pointer to the top-level
** [VFSes] currently in use.  ^(The argument X in
** sqlite3_file_control(db,SQLITE_FCNTL_VFS_POINTER,X) must be
** of type "[sqlite3_vfs] **".  This opcodes will set *X
** to a pointer to the top-level VFS.^)
** ^When there are multiple VFS shims in the stack, this opcode finds the
** upper-most shim only.
**
** <li>[[SQLITE_FCNTL_PRAGMA]]
** ^Whenever a [PRAGMA] statement is parsed, an [SQLITE_FCNTL_PRAGMA] 
** file control is sent to the open [sqlite3_file] object corresponding
** to the database file to which the pragma statement refers. ^The argument
** to the [SQLITE_FCNTL_PRAGMA] file control is an array of
** pointers to strings (char**) in which the second element of the array

#define SQLITE_FCNTL_HAS_MOVED              20
#define SQLITE_FCNTL_SYNC                   21
#define SQLITE_FCNTL_COMMIT_PHASETWO        22
#define SQLITE_FCNTL_WIN32_SET_HANDLE       23
#define SQLITE_FCNTL_WAL_BLOCK              24
#define SQLITE_FCNTL_ZIPVFS                 25
#define SQLITE_FCNTL_RBU                    26
#define SQLITE_FCNTL_VFS_POINTER            27

/* deprecated names */
#define SQLITE_GET_LOCKPROXYFILE      SQLITE_FCNTL_GET_LOCKPROXYFILE
#define SQLITE_SET_LOCKPROXYFILE      SQLITE_FCNTL_SET_LOCKPROXYFILE
#define SQLITE_LAST_ERRNO             SQLITE_FCNTL_LAST_ERRNO