src/test_journal.c

   1 /*
   2 ** 2008 Jan 22
   3 **
   4 ** The author disclaims copyright to this source code.  In place of
   5 ** a legal notice, here is a blessing:
   6 **
   7 **    May you do good and not evil.
   8 **    May you find forgiveness for yourself and forgive others.
   9 **    May you share freely, never taking more than you give.
  10 **
  11 ******************************************************************************
  12 **
  13 ** This file contains code for a VFS layer that acts as a wrapper around
  14 ** an existing VFS. The code in this file attempts to verify that SQLite
  15 ** correctly populates and syncs a journal file before writing to a
  16 ** corresponding database file.
  17 **
  18 ** INTERFACE
  19 **
  20 **   The public interface to this wrapper VFS is two functions:
  21 **
  22 **     jt_register()
  23 **     jt_unregister()
  24 **
  25 **   See header comments associated with those two functions below for
  26 **   details.
  27 **
  28 ** LIMITATIONS
  29 **
  30 **   This wrapper will not work if "PRAGMA synchronous = off" is used.
  31 **
  32 ** OPERATION
  33 **
  34 **  Starting a Transaction:
  35 **
  36 **   When a write-transaction is started, the contents of the database is
  37 **   inspected and the following data stored as part of the database file
  38 **   handle (type struct jt_file):
  39 **
  40 **     a) The page-size of the database file.
  41 **     b) The number of pages that are in the database file.
  42 **     c) The set of page numbers corresponding to free-list leaf pages.
  43 **     d) A check-sum for every page in the database file.
  44 **
  45 **   The start of a write-transaction is deemed to have occurred when a
  46 **   28-byte journal header is written to byte offset 0 of the journal
  47 **   file.
  48 **
  49 **  Syncing the Journal File:
  50 **
  51 **   Whenever the xSync method is invoked to sync a journal-file, the
  52 **   contents of the journal file are read. For each page written to
  53 **   the journal file, a check-sum is calculated and compared to the
  54 **   check-sum calculated for the corresponding database page when the
  55 **   write-transaction was initialized. The success of the comparison
  56 **   is assert()ed. So if SQLite has written something other than the
  57 **   original content to the database file, an assert() will fail.
  58 **
  59 **   Additionally, the set of page numbers for which records exist in
  60 **   the journal file is added to (unioned with) the set of page numbers
  61 **   corresponding to free-list leaf pages collected when the
  62 **   write-transaction was initialized. This set comprises the page-numbers
  63 **   corresponding to those pages that SQLite may now safely modify.
  64 **
  65 **  Writing to the Database File:
  66 **
  67 **   When a block of data is written to a database file, the following
  68 **   invariants are asserted:
  69 **
  70 **     a) That the block of data is an aligned block of page-size bytes.
  71 **
  72 **     b) That if the page being written did not exist when the
  73 **        transaction was started (i.e. the database file is growing), then
  74 **        the journal-file must have been synced at least once since
  75 **        the start of the transaction.
  76 **
  77 **     c) That if the page being written did exist when the transaction
  78 **        was started, then the page must have either been a free-list
  79 **        leaf page at the start of the transaction, or else must have
  80 **        been stored in the journal file prior to the most recent sync.
  81 **
  82 **  Closing a Transaction:
  83 **
  84 **   When a transaction is closed, all data collected at the start of
  85 **   the transaction, or following an xSync of a journal-file, is
  86 **   discarded. The end of a transaction is recognized when any one
  87 **   of the following occur:
  88 **
  89 **     a) A block of zeroes (or anything else that is not a valid
  90 **        journal-header) is written to the start of the journal file.
  91 **
  92 **     b) A journal file is truncated to zero bytes in size using xTruncate.
  93 **
  94 **     c) The journal file is deleted using xDelete.
  95 */
  96 #if SQLITE_TEST          /* This file is used for testing only */
  97
  98 #include "sqlite3.h"
  99 #include "sqliteInt.h"
 100
 101 /*
 102 ** Maximum pathname length supported by the jt backend.
 103 */
 104 #define JT_MAX_PATHNAME 512
 105
 106 /*
 107 ** Name used to identify this VFS.
 108 */
 109 #define JT_VFS_NAME "jt"
 110
 111 typedef struct jt_file jt_file;
 112 struct jt_file {
 113   sqlite3_file base;
 114   const char *zName;       /* Name of open file */
 115   int flags;               /* Flags the file was opened with */
 116
 117   /* The following are only used by database file file handles */
 118   int eLock;               /* Current lock held on the file */
 119   u32 nPage;               /* Size of file in pages when transaction started */
 120   u32 nPagesize;           /* Page size when transaction started */
 121   Bitvec *pWritable;       /* Bitvec of pages that may be written to the file */
 122   u32 *aCksum;             /* Checksum for first nPage pages */
 123   int nSync;               /* Number of times journal file has been synced */
 124
 125   /* Only used by journal file-handles */
 126   sqlite3_int64 iMaxOff;   /* Maximum offset written to this transaction */
 127
 128   jt_file *pNext;          /* All files are stored in a linked list */
 129   sqlite3_file *pReal;     /* The file handle for the underlying vfs */
 130 };
 131
 132 /*
 133 ** Method declarations for jt_file.
 134 */
 135 static int jtClose(sqlite3_file*);
 136 static int jtRead(sqlite3_file*, void*, int iAmt, sqlite3_int64 iOfst);
 137 static int jtWrite(sqlite3_file*,const void*,int iAmt, sqlite3_int64 iOfst);
 138 static int jtTruncate(sqlite3_file*, sqlite3_int64 size);
 139 static int jtSync(sqlite3_file*, int flags);
 140 static int jtFileSize(sqlite3_file*, sqlite3_int64 *pSize);
 141 static int jtLock(sqlite3_file*, int);
 142 static int jtUnlock(sqlite3_file*, int);
 143 static int jtCheckReservedLock(sqlite3_file*, int *);
 144 static int jtFileControl(sqlite3_file*, int op, void *pArg);
 145 static int jtSectorSize(sqlite3_file*);
 146 static int jtDeviceCharacteristics(sqlite3_file*);
 147
 148 /*
 149 ** Method declarations for jt_vfs.
 150 */
 151 static int jtOpen(sqlite3_vfs*, const char *, sqlite3_file*, int , int *);
 152 static int jtDelete(sqlite3_vfs*, const char *zName, int syncDir);
 153 static int jtAccess(sqlite3_vfs*, const char *zName, int flags, int *);
 154 static int jtFullPathname(sqlite3_vfs*, const char *zName, int, char *zOut);
 155 static void *jtDlOpen(sqlite3_vfs*, const char *zFilename);
 156 static void jtDlError(sqlite3_vfs*, int nByte, char *zErrMsg);
 157 static void (*jtDlSym(sqlite3_vfs*,void*, const char *zSymbol))(void);
 158 static void jtDlClose(sqlite3_vfs*, void*);
 159 static int jtRandomness(sqlite3_vfs*, int nByte, char *zOut);
 160 static int jtSleep(sqlite3_vfs*, int microseconds);
 161 static int jtCurrentTime(sqlite3_vfs*, double*);
 162 static int jtCurrentTimeInt64(sqlite3_vfs*, sqlite3_int64*);
 163 static int jtGetLastError(sqlite3_vfs*, int, char*);
 164
 165 static sqlite3_vfs jt_vfs = {
 166   2,                             /* iVersion */
 167   sizeof(jt_file),               /* szOsFile */
 168   JT_MAX_PATHNAME,               /* mxPathname */
 169   0,                             /* pNext */
 170   JT_VFS_NAME,                   /* zName */
 171   0,                             /* pAppData */
 172   jtOpen,                        /* xOpen */
 173   jtDelete,                      /* xDelete */
 174   jtAccess,                      /* xAccess */
 175   jtFullPathname,                /* xFullPathname */
 176   jtDlOpen,                      /* xDlOpen */
 177   jtDlError,                     /* xDlError */
 178   jtDlSym,                       /* xDlSym */
 179   jtDlClose,                     /* xDlClose */
 180   jtRandomness,                  /* xRandomness */
 181   jtSleep,                       /* xSleep */
 182   jtCurrentTime,                 /* xCurrentTime */
 183   jtGetLastError,                /* xGetLastError */
 184   jtCurrentTimeInt64             /* xCurrentTimeInt64 */
 185 };
 186
 187 static sqlite3_io_methods jt_io_methods = {
 188   1,                             /* iVersion */
 189   jtClose,                       /* xClose */
 190   jtRead,                        /* xRead */
 191   jtWrite,                       /* xWrite */
 192   jtTruncate,                    /* xTruncate */
 193   jtSync,                        /* xSync */
 194   jtFileSize,                    /* xFileSize */
 195   jtLock,                        /* xLock */
 196   jtUnlock,                      /* xUnlock */
 197   jtCheckReservedLock,           /* xCheckReservedLock */
 198   jtFileControl,                 /* xFileControl */
 199   jtSectorSize,                  /* xSectorSize */
 200   jtDeviceCharacteristics        /* xDeviceCharacteristics */
 201 };
 202
 203 struct JtGlobal {
 204   sqlite3_vfs *pVfs;             /* Parent VFS */
 205   jt_file *pList;                /* List of all open files */
 206 };
 207 static struct JtGlobal g = {0, 0};
 208
 209 /*
 210 ** Functions to obtain and relinquish a mutex to protect g.pList. The
 211 ** STATIC_PRNG mutex is reused, purely for the sake of convenience.
 212 */
 213 static void enterJtMutex(void){
 214   sqlite3_mutex_enter(sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_PRNG));
 215 }
 216 static void leaveJtMutex(void){
 217   sqlite3_mutex_leave(sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_PRNG));
 218 }
 219
 220 extern int sqlite3_io_error_pending;
 221 extern int sqlite3_io_error_hit;
 222 static void stop_ioerr_simulation(int *piSave, int *piSave2){
 223   *piSave = sqlite3_io_error_pending;
 224   *piSave2 = sqlite3_io_error_hit;
 225   sqlite3_io_error_pending = -1;
 226   sqlite3_io_error_hit = 0;
 227 }
 228 static void start_ioerr_simulation(int iSave, int iSave2){
 229   sqlite3_io_error_pending = iSave;
 230   sqlite3_io_error_hit = iSave2;
 231 }
 232
 233 /*
 234 ** The jt_file pointed to by the argument may or may not be a file-handle
 235 ** open on a main database file. If it is, and a transaction is currently
 236 ** opened on the file, then discard all transaction related data.
 237 */
 238 static void closeTransaction(jt_file *p){
 239   sqlite3BitvecDestroy(p->pWritable);
 240   sqlite3_free(p->aCksum);
 241   p->pWritable = 0;
 242   p->aCksum = 0;
 243   p->nSync = 0;
 244 }
 245
 246 /*
 247 ** Close an jt-file.
 248 */
 249 static int jtClose(sqlite3_file *pFile){
 250   jt_file **pp;
 251   jt_file *p = (jt_file *)pFile;
 252
 253   closeTransaction(p);
 254   enterJtMutex();
 255   if( p->zName ){
 256     for(pp=&g.pList; *pp!=p; pp=&(*pp)->pNext);
 257     *pp = p->pNext;
 258   }
 259   leaveJtMutex();
 260   sqlite3OsClose(p->pReal);
 261   return SQLITE_OK;
 262 }
 263
 264 /*
 265 ** Read data from an jt-file.
 266 */
 267 static int jtRead(
 268   sqlite3_file *pFile,
 269   void *zBuf,
 270   int iAmt,
 271   sqlite_int64 iOfst
 272 ){
 273   jt_file *p = (jt_file *)pFile;
 274   return sqlite3OsRead(p->pReal, zBuf, iAmt, iOfst);
 275 }
 276
 277 /*
 278 ** Parameter zJournal is the name of a journal file that is currently
 279 ** open. This function locates and returns the handle opened on the
 280 ** corresponding database file by the pager that currently has the
 281 ** journal file opened. This file-handle is identified by the
 282 ** following properties:
 283 **
 284 **   a) SQLITE_OPEN_MAIN_DB was specified when the file was opened.
 285 **
 286 **   b) The file-name specified when the file was opened matches
 287 **      all but the final 8 characters of the journal file name.
 288 **
 289 **   c) There is currently a reserved lock on the file. This
 290 **      condition is waived if the noLock argument is non-zero.
 291 **/
 292 static jt_file *locateDatabaseHandle(const char *zJournal, int noLock){
 293   jt_file *pMain = 0;
 294   enterJtMutex();
 295   for(pMain=g.pList; pMain; pMain=pMain->pNext){
 296     int nName = (int)(strlen(zJournal) - strlen("-journal"));
 297     if( (pMain->flags&SQLITE_OPEN_MAIN_DB)
 298      && ((int)strlen(pMain->zName)==nName)
 299      && 0==memcmp(pMain->zName, zJournal, nName)
 300      && ((pMain->eLock>=SQLITE_LOCK_RESERVED) || noLock)
 301     ){
 302       break;
 303     }
 304   }
 305   leaveJtMutex();
 306   return pMain;
 307 }
 308
 309 /*
 310 ** Parameter z points to a buffer of 4 bytes in size containing a
 311 ** unsigned 32-bit integer stored in big-endian format. Decode the
 312 ** integer and return its value.
 313 */
 314 static u32 decodeUint32(const unsigned char *z){
 315   return (z[0]<<24) + (z[1]<<16) + (z[2]<<8) + z[3];
 316 }
 317
 318 /*
 319 ** Calculate a checksum from the buffer of length n bytes pointed to
 320 ** by parameter z.
 321 */
 322 static u32 genCksum(const unsigned char *z, int n){
 323   int i;
 324   u32 cksum = 0;
 325   for(i=0; i<n; i++){
 326     cksum = cksum + z[i] + (cksum<<3);
 327   }
 328   return cksum;
 329 }
 330
 331 /*
 332 ** The first argument, zBuf, points to a buffer containing a 28 byte
 333 ** serialized journal header. This function deserializes four of the
 334 ** integer fields contained in the journal header and writes their
 335 ** values to the output variables.
 336 **
 337 ** SQLITE_OK is returned if the journal-header is successfully
 338 ** decoded. Otherwise, SQLITE_ERROR.
 339 */
 340 static int decodeJournalHdr(
 341   const unsigned char *zBuf,         /* Input: 28 byte journal header */
 342   u32 *pnRec,                        /* Out: Number of journalled records */
 343   u32 *pnPage,                       /* Out: Original database page count */
 344   u32 *pnSector,                     /* Out: Sector size in bytes */
 345   u32 *pnPagesize                    /* Out: Page size in bytes */
 346 ){
 347   unsigned char aMagic[] = { 0xd9, 0xd5, 0x05, 0xf9, 0x20, 0xa1, 0x63, 0xd7 };
 348   if( memcmp(aMagic, zBuf, 8) ) return SQLITE_ERROR;
 349   if( pnRec ) *pnRec = decodeUint32(&zBuf[8]);
 350   if( pnPage ) *pnPage = decodeUint32(&zBuf[16]);
 351   if( pnSector ) *pnSector = decodeUint32(&zBuf[20]);
 352   if( pnPagesize ) *pnPagesize = decodeUint32(&zBuf[24]);
 353   return SQLITE_OK;
 354 }
 355
 356 /*
 357 ** This function is called when a new transaction is opened, just after
 358 ** the first journal-header is written to the journal file.
 359 */
 360 static int openTransaction(jt_file *pMain, jt_file *pJournal){
 361   unsigned char *aData;
 362   sqlite3_file *p = pMain->pReal;
 363   int rc = SQLITE_OK;
 364
 365   closeTransaction(pMain);
 366   aData = sqlite3_malloc(pMain->nPagesize);
 367   pMain->pWritable = sqlite3BitvecCreate(pMain->nPage);
 368   pMain->aCksum = sqlite3_malloc(sizeof(u32) * (pMain->nPage + 1));
 369   pJournal->iMaxOff = 0;
 370
 371   if( !pMain->pWritable || !pMain->aCksum || !aData ){
 372     rc = SQLITE_IOERR_NOMEM;
 373   }else if( pMain->nPage>0 ){
 374     u32 iTrunk;
 375     int iSave;
 376     int iSave2;
 377
 378     stop_ioerr_simulation(&iSave, &iSave2);
 379
 380     /* Read the database free-list. Add the page-number for each free-list
 381     ** leaf to the jt_file.pWritable bitvec.
 382     */
 383     rc = sqlite3OsRead(p, aData, pMain->nPagesize, 0);
 384     if( rc==SQLITE_OK ){
 385       u32 nDbsize = decodeUint32(&aData[28]);
 386       if( nDbsize>0 && memcmp(&aData[24], &aData[92], 4)==0 ){
 387         u32 iPg;
 388         for(iPg=nDbsize+1; iPg<=pMain->nPage; iPg++){
 389           sqlite3BitvecSet(pMain->pWritable, iPg);
 390         }
 391       }
 392     }
 393     iTrunk = decodeUint32(&aData[32]);
 394     while( rc==SQLITE_OK && iTrunk>0 ){
 395       u32 nLeaf;
 396       u32 iLeaf;
 397       sqlite3_int64 iOff = (i64)(iTrunk-1)*pMain->nPagesize;
 398       rc = sqlite3OsRead(p, aData, pMain->nPagesize, iOff);
 399       nLeaf = decodeUint32(&aData[4]);
 400       for(iLeaf=0; rc==SQLITE_OK && iLeaf<nLeaf; iLeaf++){
 401         u32 pgno = decodeUint32(&aData[8+4*iLeaf]);
 402         sqlite3BitvecSet(pMain->pWritable, pgno);
 403       }
 404       iTrunk = decodeUint32(aData);
 405     }
 406
 407     /* Calculate and store a checksum for each page in the database file. */
 408     if( rc==SQLITE_OK ){
 409       int ii;
 410       for(ii=0; rc==SQLITE_OK && ii<(int)pMain->nPage; ii++){
 411         i64 iOff = (i64)(pMain->nPagesize) * (i64)ii;
 412         if( iOff==PENDING_BYTE ) continue;
 413         rc = sqlite3OsRead(pMain->pReal, aData, pMain->nPagesize, iOff);
 414         pMain->aCksum[ii] = genCksum(aData, pMain->nPagesize);
 415         if( ii+1==(int)pMain->nPage && rc==SQLITE_IOERR_SHORT_READ ){
 416           rc = SQLITE_OK;
 417         }
 418       }
 419     }
 420
 421     start_ioerr_simulation(iSave, iSave2);
 422   }
 423
 424   sqlite3_free(aData);
 425   return rc;
 426 }
 427
 428 /*
 429 ** The first argument to this function is a handle open on a journal file.
 430 ** This function reads the journal file and adds the page number for each
 431 ** page in the journal to the Bitvec object passed as the second argument.
 432 */
 433 static int readJournalFile(jt_file *p, jt_file *pMain){
 434   int rc = SQLITE_OK;
 435   unsigned char zBuf[28];
 436   sqlite3_file *pReal = p->pReal;
 437   sqlite3_int64 iOff = 0;
 438   sqlite3_int64 iSize = p->iMaxOff;
 439   unsigned char *aPage;
 440   int iSave;
 441   int iSave2;
 442
 443   aPage = sqlite3_malloc(pMain->nPagesize);
 444   if( !aPage ){
 445     return SQLITE_IOERR_NOMEM;
 446   }
 447
 448   stop_ioerr_simulation(&iSave, &iSave2);
 449
 450   while( rc==SQLITE_OK && iOff<iSize ){
 451     u32 nRec, nPage, nSector, nPagesize;
 452     u32 ii;
 453
 454     /* Read and decode the next journal-header from the journal file. */
 455     rc = sqlite3OsRead(pReal, zBuf, 28, iOff);
 456     if( rc!=SQLITE_OK
 457      || decodeJournalHdr(zBuf, &nRec, &nPage, &nSector, &nPagesize)
 458     ){
 459       goto finish_rjf;
 460     }
 461     iOff += nSector;
 462
 463     if( nRec==0 ){
 464       /* A trick. There might be another journal-header immediately
 465       ** following this one. In this case, 0 records means 0 records,
 466       ** not "read until the end of the file". See also ticket #2565.
 467       */
 468       if( iSize>=(iOff+nSector) ){
 469         rc = sqlite3OsRead(pReal, zBuf, 28, iOff);
 470         if( rc!=SQLITE_OK || 0==decodeJournalHdr(zBuf, 0, 0, 0, 0) ){
 471           continue;
 472         }
 473       }
 474       nRec = (u32)((iSize-iOff) / (pMain->nPagesize+8));
 475     }
 476
 477     /* Read all the records that follow the journal-header just read. */
 478     for(ii=0; rc==SQLITE_OK && ii<nRec && iOff<iSize; ii++){
 479       u32 pgno;
 480       rc = sqlite3OsRead(pReal, zBuf, 4, iOff);
 481       if( rc==SQLITE_OK ){
 482         pgno = decodeUint32(zBuf);
 483         if( pgno>0 && pgno<=pMain->nPage ){
 484           if( 0==sqlite3BitvecTest(pMain->pWritable, pgno) ){
 485             rc = sqlite3OsRead(pReal, aPage, pMain->nPagesize, iOff+4);
 486             if( rc==SQLITE_OK ){
 487               u32 cksum = genCksum(aPage, pMain->nPagesize);
 488               assert( cksum==pMain->aCksum[pgno-1] );
 489             }
 490           }
 491           sqlite3BitvecSet(pMain->pWritable, pgno);
 492         }
 493         iOff += (8 + pMain->nPagesize);
 494       }
 495     }
 496
 497     iOff = ((iOff + (nSector-1)) / nSector) * nSector;
 498   }
 499
 500 finish_rjf:
 501   start_ioerr_simulation(iSave, iSave2);
 502   sqlite3_free(aPage);
 503   if( rc==SQLITE_IOERR_SHORT_READ ){
 504     rc = SQLITE_OK;
 505   }
 506   return rc;
 507 }
 508
 509 /*
 510 ** Write data to an jt-file.
 511 */
 512 static int jtWrite(
 513   sqlite3_file *pFile,
 514   const void *zBuf,
 515   int iAmt,
 516   sqlite_int64 iOfst
 517 ){
 518   int rc;
 519   jt_file *p = (jt_file *)pFile;
 520   if( p->flags&SQLITE_OPEN_MAIN_JOURNAL ){
 521     if( iOfst==0 ){
 522       jt_file *pMain = locateDatabaseHandle(p->zName, 0);
 523       assert( pMain );
 524
 525       if( iAmt==28 ){
 526         /* Zeroing the first journal-file header. This is the end of a
 527         ** transaction. */
 528         closeTransaction(pMain);
 529       }else if( iAmt!=12 ){
 530         /* Writing the first journal header to a journal file. This happens
 531         ** when a transaction is first started.  */
 532         u8 *z = (u8 *)zBuf;
 533         pMain->nPage = decodeUint32(&z[16]);
 534         pMain->nPagesize = decodeUint32(&z[24]);
 535         if( SQLITE_OK!=(rc=openTransaction(pMain, p)) ){
 536           return rc;
 537         }
 538       }
 539     }
 540     if( p->iMaxOff<(iOfst + iAmt) ){
 541       p->iMaxOff = iOfst + iAmt;
 542     }
 543   }
 544
 545   if( p->flags&SQLITE_OPEN_MAIN_DB && p->pWritable ){
 546     if( iAmt<(int)p->nPagesize
 547      && p->nPagesize%iAmt==0
 548      && iOfst>=(PENDING_BYTE+512)
 549      && iOfst+iAmt<=PENDING_BYTE+p->nPagesize
 550     ){
 551       /* No-op. This special case is hit when the backup code is copying a
 552       ** to a database with a larger page-size than the source database and
 553       ** it needs to fill in the non-locking-region part of the original
 554       ** pending-byte page.
 555       */
 556     }else{
 557       u32 pgno = (u32)(iOfst/p->nPagesize + 1);
 558       assert( (iAmt==1||iAmt==(int)p->nPagesize) &&
 559               ((iOfst+iAmt)%p->nPagesize)==0 );
 560       assert( pgno<=p->nPage || p->nSync>0 );
 561       assert( pgno>p->nPage || sqlite3BitvecTest(p->pWritable, pgno) );
 562     }
 563   }
 564
 565   rc = sqlite3OsWrite(p->pReal, zBuf, iAmt, iOfst);
 566   if( (p->flags&SQLITE_OPEN_MAIN_JOURNAL) && iAmt==12 ){
 567     jt_file *pMain = locateDatabaseHandle(p->zName, 0);
 568     int rc2 = readJournalFile(p, pMain);
 569     if( rc==SQLITE_OK ) rc = rc2;
 570   }
 571   return rc;
 572 }
 573
 574 /*
 575 ** Truncate an jt-file.
 576 */
 577 static int jtTruncate(sqlite3_file *pFile, sqlite_int64 size){
 578   jt_file *p = (jt_file *)pFile;
 579   if( p->flags&SQLITE_OPEN_MAIN_JOURNAL && size==0 ){
 580     /* Truncating a journal file. This is the end of a transaction. */
 581     jt_file *pMain = locateDatabaseHandle(p->zName, 0);
 582     closeTransaction(pMain);
 583   }
 584   if( p->flags&SQLITE_OPEN_MAIN_DB && p->pWritable ){
 585     u32 pgno;
 586     u32 locking_page = (u32)(PENDING_BYTE/p->nPagesize+1);
 587     for(pgno=(u32)(size/p->nPagesize+1); pgno<=p->nPage; pgno++){
 588       assert( pgno==locking_page || sqlite3BitvecTest(p->pWritable, pgno) );
 589     }
 590   }
 591   return sqlite3OsTruncate(p->pReal, size);
 592 }
 593
 594 /*
 595 ** Sync an jt-file.
 596 */
 597 static int jtSync(sqlite3_file *pFile, int flags){
 598   jt_file *p = (jt_file *)pFile;
 599
 600   if( p->flags&SQLITE_OPEN_MAIN_JOURNAL ){
 601     int rc;
 602     jt_file *pMain;                   /* The associated database file */
 603
 604     /* The journal file is being synced. At this point, we inspect the
 605     ** contents of the file up to this point and set each bit in the
 606     ** jt_file.pWritable bitvec of the main database file associated with
 607     ** this journal file.
 608     */
 609     pMain = locateDatabaseHandle(p->zName, 0);
 610
 611     /* Set the bitvec values */
 612     if( pMain && pMain->pWritable ){
 613       pMain->nSync++;
 614       rc = readJournalFile(p, pMain);
 615       if( rc!=SQLITE_OK ){
 616         return rc;
 617       }
 618     }
 619   }
 620
 621   return sqlite3OsSync(p->pReal, flags);
 622 }
 623
 624 /*
 625 ** Return the current file-size of an jt-file.
 626 */
 627 static int jtFileSize(sqlite3_file *pFile, sqlite_int64 *pSize){
 628   jt_file *p = (jt_file *)pFile;
 629   return sqlite3OsFileSize(p->pReal, pSize);
 630 }
 631
 632 /*
 633 ** Lock an jt-file.
 634 */
 635 static int jtLock(sqlite3_file *pFile, int eLock){
 636   int rc;
 637   jt_file *p = (jt_file *)pFile;
 638   rc = sqlite3OsLock(p->pReal, eLock);
 639   if( rc==SQLITE_OK && eLock>p->eLock ){
 640     p->eLock = eLock;
 641   }
 642   return rc;
 643 }
 644
 645 /*
 646 ** Unlock an jt-file.
 647 */
 648 static int jtUnlock(sqlite3_file *pFile, int eLock){
 649   int rc;
 650   jt_file *p = (jt_file *)pFile;
 651   rc = sqlite3OsUnlock(p->pReal, eLock);
 652   if( rc==SQLITE_OK && eLock<p->eLock ){
 653     p->eLock = eLock;
 654   }
 655   return rc;
 656 }
 657
 658 /*
 659 ** Check if another file-handle holds a RESERVED lock on an jt-file.
 660 */
 661 static int jtCheckReservedLock(sqlite3_file *pFile, int *pResOut){
 662   jt_file *p = (jt_file *)pFile;
 663   return sqlite3OsCheckReservedLock(p->pReal, pResOut);
 664 }
 665
 666 /*
 667 ** File control method. For custom operations on an jt-file.
 668 */
 669 static int jtFileControl(sqlite3_file *pFile, int op, void *pArg){
 670   jt_file *p = (jt_file *)pFile;
 671   return p->pReal->pMethods->xFileControl(p->pReal, op, pArg);
 672 }
 673
 674 /*
 675 ** Return the sector-size in bytes for an jt-file.
 676 */
 677 static int jtSectorSize(sqlite3_file *pFile){
 678   jt_file *p = (jt_file *)pFile;
 679   return sqlite3OsSectorSize(p->pReal);
 680 }
 681
 682 /*
 683 ** Return the device characteristic flags supported by an jt-file.
 684 */
 685 static int jtDeviceCharacteristics(sqlite3_file *pFile){
 686   jt_file *p = (jt_file *)pFile;
 687   return sqlite3OsDeviceCharacteristics(p->pReal);
 688 }
 689
 690 /*
 691 ** Open an jt file handle.
 692 */
 693 static int jtOpen(
 694   sqlite3_vfs *pVfs,
 695   const char *zName,
 696   sqlite3_file *pFile,
 697   int flags,
 698   int *pOutFlags
 699 ){
 700   int rc;
 701   jt_file *p = (jt_file *)pFile;
 702   pFile->pMethods = 0;
 703   p->pReal = (sqlite3_file *)&p[1];
 704   p->pReal->pMethods = 0;
 705   rc = sqlite3OsOpen(g.pVfs, zName, p->pReal, flags, pOutFlags);
 706   assert( rc==SQLITE_OK || p->pReal->pMethods==0 );
 707   if( rc==SQLITE_OK ){
 708     pFile->pMethods = &jt_io_methods;
 709     p->eLock = 0;
 710     p->zName = zName;
 711     p->flags = flags;
 712     p->pNext = 0;
 713     p->pWritable = 0;
 714     p->aCksum = 0;
 715     enterJtMutex();
 716     if( zName ){
 717       p->pNext = g.pList;
 718       g.pList = p;
 719     }
 720     leaveJtMutex();
 721   }
 722   return rc;
 723 }
 724
 725 /*
 726 ** Delete the file located at zPath. If the dirSync argument is true,
 727 ** ensure the file-system modifications are synced to disk before
 728 ** returning.
 729 */
 730 static int jtDelete(sqlite3_vfs *pVfs, const char *zPath, int dirSync){
 731   int nPath = (int)strlen(zPath);
 732   if( nPath>8 && 0==strcmp("-journal", &zPath[nPath-8]) ){
 733     /* Deleting a journal file. The end of a transaction. */
 734     jt_file *pMain = locateDatabaseHandle(zPath, 0);
 735     if( pMain ){
 736       closeTransaction(pMain);
 737     }
 738   }
 739
 740   return sqlite3OsDelete(g.pVfs, zPath, dirSync);
 741 }
 742
 743 /*
 744 ** Test for access permissions. Return true if the requested permission
 745 ** is available, or false otherwise.
 746 */
 747 static int jtAccess(
 748   sqlite3_vfs *pVfs,
 749   const char *zPath,
 750   int flags,
 751   int *pResOut
 752 ){
 753   return sqlite3OsAccess(g.pVfs, zPath, flags, pResOut);
 754 }
 755
 756 /*
 757 ** Populate buffer zOut with the full canonical pathname corresponding
 758 ** to the pathname in zPath. zOut is guaranteed to point to a buffer
 759 ** of at least (JT_MAX_PATHNAME+1) bytes.
 760 */
 761 static int jtFullPathname(
 762   sqlite3_vfs *pVfs,
 763   const char *zPath,
 764   int nOut,
 765   char *zOut
 766 ){
 767   return sqlite3OsFullPathname(g.pVfs, zPath, nOut, zOut);
 768 }
 769
 770 /*
 771 ** Open the dynamic library located at zPath and return a handle.
 772 */
 773 static void *jtDlOpen(sqlite3_vfs *pVfs, const char *zPath){
 774   return g.pVfs->xDlOpen(g.pVfs, zPath);
 775 }
 776
 777 /*
 778 ** Populate the buffer zErrMsg (size nByte bytes) with a human readable
 779 ** utf-8 string describing the most recent error encountered associated
 780 ** with dynamic libraries.
 781 */
 782 static void jtDlError(sqlite3_vfs *pVfs, int nByte, char *zErrMsg){
 783   g.pVfs->xDlError(g.pVfs, nByte, zErrMsg);
 784 }
 785
 786 /*
 787 ** Return a pointer to the symbol zSymbol in the dynamic library pHandle.
 788 */
 789 static void (*jtDlSym(sqlite3_vfs *pVfs, void *p, const char *zSym))(void){
 790   return g.pVfs->xDlSym(g.pVfs, p, zSym);
 791 }
 792
 793 /*
 794 ** Close the dynamic library handle pHandle.
 795 */
 796 static void jtDlClose(sqlite3_vfs *pVfs, void *pHandle){
 797   g.pVfs->xDlClose(g.pVfs, pHandle);
 798 }
 799
 800 /*
 801 ** Populate the buffer pointed to by zBufOut with nByte bytes of
 802 ** random data.
 803 */
 804 static int jtRandomness(sqlite3_vfs *pVfs, int nByte, char *zBufOut){
 805   return sqlite3OsRandomness(g.pVfs, nByte, zBufOut);
 806 }
 807
 808 /*
 809 ** Sleep for nMicro microseconds. Return the number of microseconds
 810 ** actually slept.
 811 */
 812 static int jtSleep(sqlite3_vfs *pVfs, int nMicro){
 813   return sqlite3OsSleep(g.pVfs, nMicro);
 814 }
 815
 816 /*
 817 ** Return the current time as a Julian Day number in *pTimeOut.
 818 */
 819 static int jtCurrentTime(sqlite3_vfs *pVfs, double *pTimeOut){
 820   return g.pVfs->xCurrentTime(g.pVfs, pTimeOut);
 821 }
 822 /*
 823 ** Return the current time as a Julian Day number in *pTimeOut.
 824 */
 825 static int jtCurrentTimeInt64(sqlite3_vfs *pVfs, sqlite3_int64 *pTimeOut){
 826   return g.pVfs->xCurrentTimeInt64(g.pVfs, pTimeOut);
 827 }
 828
 829 static int jtGetLastError(sqlite3_vfs *pVfs, int n, char *z){
 830   return g.pVfs->xGetLastError(g.pVfs, n, z);
 831 }
 832
 833 /**************************************************************************
 834 ** Start of public API.
 835 */
 836
 837 /*
 838 ** Configure the jt VFS as a wrapper around the VFS named by parameter
 839 ** zWrap. If the isDefault parameter is true, then the jt VFS is installed
 840 ** as the new default VFS for SQLite connections. If isDefault is not
 841 ** true, then the jt VFS is installed as non-default. In this case it
 842 ** is available via its name, "jt".
 843 */
 844 int jt_register(char *zWrap, int isDefault){
 845   g.pVfs = sqlite3_vfs_find(zWrap);
 846   if( g.pVfs==0 ){
 847     return SQLITE_ERROR;
 848   }
 849   jt_vfs.szOsFile = sizeof(jt_file) + g.pVfs->szOsFile;
 850   if( g.pVfs->iVersion==1 ){
 851     jt_vfs.iVersion = 1;
 852   }else if( g.pVfs->xCurrentTimeInt64==0 ){
 853     jt_vfs.xCurrentTimeInt64 = 0;
 854   }
 855   sqlite3_vfs_register(&jt_vfs, isDefault);
 856   return SQLITE_OK;
 857 }
 858
 859 /*
 860 ** Uninstall the jt VFS, if it is installed.
 861 */
 862 void jt_unregister(void){
 863   sqlite3_vfs_unregister(&jt_vfs);
 864 }
 865
 866 #endif