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
 164 static sqlite3_vfs jt_vfs = {
 165   2,                             /* iVersion */
 166   sizeof(jt_file),               /* szOsFile */
 167   JT_MAX_PATHNAME,               /* mxPathname */
 168   0,                             /* pNext */
 169   JT_VFS_NAME,                   /* zName */
 170   0,                             /* pAppData */
 171   jtOpen,                        /* xOpen */
 172   jtDelete,                      /* xDelete */
 173   jtAccess,                      /* xAccess */
 174   jtFullPathname,                /* xFullPathname */
 175   jtDlOpen,                      /* xDlOpen */
 176   jtDlError,                     /* xDlError */
 177   jtDlSym,                       /* xDlSym */
 178   jtDlClose,                     /* xDlClose */
 179   jtRandomness,                  /* xRandomness */
 180   jtSleep,                       /* xSleep */
 181   jtCurrentTime,                 /* xCurrentTime */
 182   0,                             /* xGetLastError */
 183   jtCurrentTimeInt64             /* xCurrentTimeInt64 */
 184 };
 185
 186 static sqlite3_io_methods jt_io_methods = {
 187   1,                             /* iVersion */
 188   jtClose,                       /* xClose */
 189   jtRead,                        /* xRead */
 190   jtWrite,                       /* xWrite */
 191   jtTruncate,                    /* xTruncate */
 192   jtSync,                        /* xSync */
 193   jtFileSize,                    /* xFileSize */
 194   jtLock,                        /* xLock */
 195   jtUnlock,                      /* xUnlock */
 196   jtCheckReservedLock,           /* xCheckReservedLock */
 197   jtFileControl,                 /* xFileControl */
 198   jtSectorSize,                  /* xSectorSize */
 199   jtDeviceCharacteristics        /* xDeviceCharacteristics */
 200 };
 201
 202 struct JtGlobal {
 203   sqlite3_vfs *pVfs;             /* Parent VFS */
 204   jt_file *pList;                /* List of all open files */
 205 };
 206 static struct JtGlobal g = {0, 0};
 207
 208 /*
 209 ** Functions to obtain and relinquish a mutex to protect g.pList. The
 210 ** STATIC_PRNG mutex is reused, purely for the sake of convenience.
 211 */
 212 static void enterJtMutex(void){
 213   sqlite3_mutex_enter(sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_PRNG));
 214 }
 215 static void leaveJtMutex(void){
 216   sqlite3_mutex_leave(sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_PRNG));
 217 }
 218
 219 extern int sqlite3_io_error_pending;
 220 extern int sqlite3_io_error_hit;
 221 static void stop_ioerr_simulation(int *piSave, int *piSave2){
 222   *piSave = sqlite3_io_error_pending;
 223   *piSave2 = sqlite3_io_error_hit;
 224   sqlite3_io_error_pending = -1;
 225   sqlite3_io_error_hit = 0;
 226 }
 227 static void start_ioerr_simulation(int iSave, int iSave2){
 228   sqlite3_io_error_pending = iSave;
 229   sqlite3_io_error_hit = iSave2;
 230 }
 231
 232 /*
 233 ** The jt_file pointed to by the argument may or may not be a file-handle
 234 ** open on a main database file. If it is, and a transaction is currently
 235 ** opened on the file, then discard all transaction related data.
 236 */
 237 static void closeTransaction(jt_file *p){
 238   sqlite3BitvecDestroy(p->pWritable);
 239   sqlite3_free(p->aCksum);
 240   p->pWritable = 0;
 241   p->aCksum = 0;
 242   p->nSync = 0;
 243 }
 244
 245 /*
 246 ** Close an jt-file.
 247 */
 248 static int jtClose(sqlite3_file *pFile){
 249   jt_file **pp;
 250   jt_file *p = (jt_file *)pFile;
 251
 252   closeTransaction(p);
 253   enterJtMutex();
 254   if( p->zName ){
 255     for(pp=&g.pList; *pp!=p; pp=&(*pp)->pNext);
 256     *pp = p->pNext;
 257   }
 258   leaveJtMutex();
 259   return sqlite3OsClose(p->pReal);
 260 }
 261
 262 /*
 263 ** Read data from an jt-file.
 264 */
 265 static int jtRead(
 266   sqlite3_file *pFile,
 267   void *zBuf,
 268   int iAmt,
 269   sqlite_int64 iOfst
 270 ){
 271   jt_file *p = (jt_file *)pFile;
 272   return sqlite3OsRead(p->pReal, zBuf, iAmt, iOfst);
 273 }
 274
 275 /*
 276 ** Parameter zJournal is the name of a journal file that is currently
 277 ** open. This function locates and returns the handle opened on the
 278 ** corresponding database file by the pager that currently has the
 279 ** journal file opened. This file-handle is identified by the
 280 ** following properties:
 281 **
 282 **   a) SQLITE_OPEN_MAIN_DB was specified when the file was opened.
 283 **
 284 **   b) The file-name specified when the file was opened matches
 285 **      all but the final 8 characters of the journal file name.
 286 **
 287 **   c) There is currently a reserved lock on the file.
 288 **/
 289 static jt_file *locateDatabaseHandle(const char *zJournal){
 290   jt_file *pMain = 0;
 291   enterJtMutex();
 292   for(pMain=g.pList; pMain; pMain=pMain->pNext){
 293     int nName = (int)(strlen(zJournal) - strlen("-journal"));
 294     if( (pMain->flags&SQLITE_OPEN_MAIN_DB)
 295      && ((int)strlen(pMain->zName)==nName)
 296      && 0==memcmp(pMain->zName, zJournal, nName)
 297      && (pMain->eLock>=SQLITE_LOCK_RESERVED)
 298     ){
 299       break;
 300     }
 301   }
 302   leaveJtMutex();
 303   return pMain;
 304 }
 305
 306 /*
 307 ** Parameter z points to a buffer of 4 bytes in size containing a
 308 ** unsigned 32-bit integer stored in big-endian format. Decode the
 309 ** integer and return its value.
 310 */
 311 static u32 decodeUint32(const unsigned char *z){
 312   return (z[0]<<24) + (z[1]<<16) + (z[2]<<8) + z[3];
 313 }
 314
 315 /*
 316 ** Calculate a checksum from the buffer of length n bytes pointed to
 317 ** by parameter z.
 318 */
 319 static u32 genCksum(const unsigned char *z, int n){
 320   int i;
 321   u32 cksum = 0;
 322   for(i=0; i<n; i++){
 323     cksum = cksum + z[i] + (cksum<<3);
 324   }
 325   return cksum;
 326 }
 327
 328 /*
 329 ** The first argument, zBuf, points to a buffer containing a 28 byte
 330 ** serialized journal header. This function deserializes four of the
 331 ** integer fields contained in the journal header and writes their
 332 ** values to the output variables.
 333 **
 334 ** SQLITE_OK is returned if the journal-header is successfully
 335 ** decoded. Otherwise, SQLITE_ERROR.
 336 */
 337 static int decodeJournalHdr(
 338   const unsigned char *zBuf,         /* Input: 28 byte journal header */
 339   u32 *pnRec,                        /* Out: Number of journalled records */
 340   u32 *pnPage,                       /* Out: Original database page count */
 341   u32 *pnSector,                     /* Out: Sector size in bytes */
 342   u32 *pnPagesize                    /* Out: Page size in bytes */
 343 ){
 344   unsigned char aMagic[] = { 0xd9, 0xd5, 0x05, 0xf9, 0x20, 0xa1, 0x63, 0xd7 };
 345   if( memcmp(aMagic, zBuf, 8) ) return SQLITE_ERROR;
 346   if( pnRec ) *pnRec = decodeUint32(&zBuf[8]);
 347   if( pnPage ) *pnPage = decodeUint32(&zBuf[16]);
 348   if( pnSector ) *pnSector = decodeUint32(&zBuf[20]);
 349   if( pnPagesize ) *pnPagesize = decodeUint32(&zBuf[24]);
 350   return SQLITE_OK;
 351 }
 352
 353 /*
 354 ** This function is called when a new transaction is opened, just after
 355 ** the first journal-header is written to the journal file.
 356 */
 357 static int openTransaction(jt_file *pMain, jt_file *pJournal){
 358   unsigned char *aData;
 359   sqlite3_file *p = pMain->pReal;
 360   int rc = SQLITE_OK;
 361
 362   closeTransaction(pMain);
 363   aData = sqlite3_malloc(pMain->nPagesize);
 364   pMain->pWritable = sqlite3BitvecCreate(pMain->nPage);
 365   pMain->aCksum = sqlite3_malloc(sizeof(u32) * (pMain->nPage + 1));
 366   pJournal->iMaxOff = 0;
 367
 368   if( !pMain->pWritable || !pMain->aCksum || !aData ){
 369     rc = SQLITE_IOERR_NOMEM;
 370   }else if( pMain->nPage>0 ){
 371     u32 iTrunk;
 372     int iSave;
 373     int iSave2;
 374
 375     stop_ioerr_simulation(&iSave, &iSave2);
 376
 377     /* Read the database free-list. Add the page-number for each free-list
 378     ** leaf to the jt_file.pWritable bitvec.
 379     */
 380     rc = sqlite3OsRead(p, aData, pMain->nPagesize, 0);
 381     if( rc==SQLITE_OK ){
 382       u32 nDbsize = decodeUint32(&aData[28]);
 383       if( nDbsize>0 && memcmp(&aData[24], &aData[92], 4)==0 ){
 384         u32 iPg;
 385         for(iPg=nDbsize+1; iPg<=pMain->nPage; iPg++){
 386           sqlite3BitvecSet(pMain->pWritable, iPg);
 387         }
 388       }
 389     }
 390     iTrunk = decodeUint32(&aData[32]);
 391     while( rc==SQLITE_OK && iTrunk>0 ){
 392       u32 nLeaf;
 393       u32 iLeaf;
 394       sqlite3_int64 iOff = (i64)(iTrunk-1)*pMain->nPagesize;
 395       rc = sqlite3OsRead(p, aData, pMain->nPagesize, iOff);
 396       nLeaf = decodeUint32(&aData[4]);
 397       for(iLeaf=0; rc==SQLITE_OK && iLeaf<nLeaf; iLeaf++){
 398         u32 pgno = decodeUint32(&aData[8+4*iLeaf]);
 399         sqlite3BitvecSet(pMain->pWritable, pgno);
 400       }
 401       iTrunk = decodeUint32(aData);
 402     }
 403
 404     /* Calculate and store a checksum for each page in the database file. */
 405     if( rc==SQLITE_OK ){
 406       int ii;
 407       for(ii=0; rc==SQLITE_OK && ii<(int)pMain->nPage; ii++){
 408         i64 iOff = (i64)(pMain->nPagesize) * (i64)ii;
 409         if( iOff==PENDING_BYTE ) continue;
 410         rc = sqlite3OsRead(pMain->pReal, aData, pMain->nPagesize, iOff);
 411         pMain->aCksum[ii] = genCksum(aData, pMain->nPagesize);
 412         if( ii+1==pMain->nPage && rc==SQLITE_IOERR_SHORT_READ ) rc = SQLITE_OK;
 413       }
 414     }
 415
 416     start_ioerr_simulation(iSave, iSave2);
 417   }
 418
 419   sqlite3_free(aData);
 420   return rc;
 421 }
 422
 423 /*
 424 ** The first argument to this function is a handle open on a journal file.
 425 ** This function reads the journal file and adds the page number for each
 426 ** page in the journal to the Bitvec object passed as the second argument.
 427 */
 428 static int readJournalFile(jt_file *p, jt_file *pMain){
 429   int rc = SQLITE_OK;
 430   unsigned char zBuf[28];
 431   sqlite3_file *pReal = p->pReal;
 432   sqlite3_int64 iOff = 0;
 433   sqlite3_int64 iSize = p->iMaxOff;
 434   unsigned char *aPage;
 435   int iSave;
 436   int iSave2;
 437
 438   aPage = sqlite3_malloc(pMain->nPagesize);
 439   if( !aPage ){
 440     return SQLITE_IOERR_NOMEM;
 441   }
 442
 443   stop_ioerr_simulation(&iSave, &iSave2);
 444
 445   while( rc==SQLITE_OK && iOff<iSize ){
 446     u32 nRec, nPage, nSector, nPagesize;
 447     u32 ii;
 448
 449     /* Read and decode the next journal-header from the journal file. */
 450     rc = sqlite3OsRead(pReal, zBuf, 28, iOff);
 451     if( rc!=SQLITE_OK
 452      || decodeJournalHdr(zBuf, &nRec, &nPage, &nSector, &nPagesize)
 453     ){
 454       goto finish_rjf;
 455     }
 456     iOff += nSector;
 457
 458     if( nRec==0 ){
 459       /* A trick. There might be another journal-header immediately
 460       ** following this one. In this case, 0 records means 0 records,
 461       ** not "read until the end of the file". See also ticket #2565.
 462       */
 463       if( iSize>=(iOff+nSector) ){
 464         rc = sqlite3OsRead(pReal, zBuf, 28, iOff);
 465         if( rc!=SQLITE_OK || 0==decodeJournalHdr(zBuf, 0, 0, 0, 0) ){
 466           continue;
 467         }
 468       }
 469       nRec = (u32)((iSize-iOff) / (pMain->nPagesize+8));
 470     }
 471
 472     /* Read all the records that follow the journal-header just read. */
 473     for(ii=0; rc==SQLITE_OK && ii<nRec && iOff<iSize; ii++){
 474       u32 pgno;
 475       rc = sqlite3OsRead(pReal, zBuf, 4, iOff);
 476       if( rc==SQLITE_OK ){
 477         pgno = decodeUint32(zBuf);
 478         if( pgno>0 && pgno<=pMain->nPage ){
 479           if( 0==sqlite3BitvecTest(pMain->pWritable, pgno) ){
 480             rc = sqlite3OsRead(pReal, aPage, pMain->nPagesize, iOff+4);
 481             if( rc==SQLITE_OK ){
 482               u32 cksum = genCksum(aPage, pMain->nPagesize);
 483               assert( cksum==pMain->aCksum[pgno-1] );
 484             }
 485           }
 486           sqlite3BitvecSet(pMain->pWritable, pgno);
 487         }
 488         iOff += (8 + pMain->nPagesize);
 489       }
 490     }
 491
 492     iOff = ((iOff + (nSector-1)) / nSector) * nSector;
 493   }
 494
 495 finish_rjf:
 496   start_ioerr_simulation(iSave, iSave2);
 497   sqlite3_free(aPage);
 498   if( rc==SQLITE_IOERR_SHORT_READ ){
 499     rc = SQLITE_OK;
 500   }
 501   return rc;
 502 }
 503
 504 /*
 505 ** Write data to an jt-file.
 506 */
 507 static int jtWrite(
 508   sqlite3_file *pFile,
 509   const void *zBuf,
 510   int iAmt,
 511   sqlite_int64 iOfst
 512 ){
 513   int rc;
 514   jt_file *p = (jt_file *)pFile;
 515   if( p->flags&SQLITE_OPEN_MAIN_JOURNAL ){
 516     if( iOfst==0 ){
 517       jt_file *pMain = locateDatabaseHandle(p->zName);
 518       assert( pMain );
 519
 520       if( iAmt==28 ){
 521         /* Zeroing the first journal-file header. This is the end of a
 522         ** transaction. */
 523         closeTransaction(pMain);
 524       }else if( iAmt!=12 ){
 525         /* Writing the first journal header to a journal file. This happens
 526         ** when a transaction is first started.  */
 527         u8 *z = (u8 *)zBuf;
 528         pMain->nPage = decodeUint32(&z[16]);
 529         pMain->nPagesize = decodeUint32(&z[24]);
 530         if( SQLITE_OK!=(rc=openTransaction(pMain, p)) ){
 531           return rc;
 532         }
 533       }
 534     }
 535     if( p->iMaxOff<(iOfst + iAmt) ){
 536       p->iMaxOff = iOfst + iAmt;
 537     }
 538   }
 539
 540   if( p->flags&SQLITE_OPEN_MAIN_DB && p->pWritable ){
 541     if( iAmt<(int)p->nPagesize
 542      && p->nPagesize%iAmt==0
 543      && iOfst>=(PENDING_BYTE+512)
 544      && iOfst+iAmt<=PENDING_BYTE+p->nPagesize
 545     ){
 546       /* No-op. This special case is hit when the backup code is copying a
 547       ** to a database with a larger page-size than the source database and
 548       ** it needs to fill in the non-locking-region part of the original
 549       ** pending-byte page.
 550       */
 551     }else{
 552       u32 pgno = (u32)(iOfst/p->nPagesize + 1);
 553       assert( (iAmt==1||iAmt==p->nPagesize) && ((iOfst+iAmt)%p->nPagesize)==0 );
 554       assert( pgno<=p->nPage || p->nSync>0 );
 555       assert( pgno>p->nPage || sqlite3BitvecTest(p->pWritable, pgno) );
 556     }
 557   }
 558
 559   rc = sqlite3OsWrite(p->pReal, zBuf, iAmt, iOfst);
 560   if( (p->flags&SQLITE_OPEN_MAIN_JOURNAL) && iAmt==12 ){
 561     jt_file *pMain = locateDatabaseHandle(p->zName);
 562     int rc2 = readJournalFile(p, pMain);
 563     if( rc==SQLITE_OK ) rc = rc2;
 564   }
 565   return rc;
 566 }
 567
 568 /*
 569 ** Truncate an jt-file.
 570 */
 571 static int jtTruncate(sqlite3_file *pFile, sqlite_int64 size){
 572   jt_file *p = (jt_file *)pFile;
 573   if( p->flags&SQLITE_OPEN_MAIN_JOURNAL && size==0 ){
 574     /* Truncating a journal file. This is the end of a transaction. */
 575     jt_file *pMain = locateDatabaseHandle(p->zName);
 576     closeTransaction(pMain);
 577   }
 578   if( p->flags&SQLITE_OPEN_MAIN_DB && p->pWritable ){
 579     u32 pgno;
 580     u32 locking_page = (u32)(PENDING_BYTE/p->nPagesize+1);
 581     for(pgno=(u32)(size/p->nPagesize+1); pgno<=p->nPage; pgno++){
 582       assert( pgno==locking_page || sqlite3BitvecTest(p->pWritable, pgno) );
 583     }
 584   }
 585   return sqlite3OsTruncate(p->pReal, size);
 586 }
 587
 588 /*
 589 ** Sync an jt-file.
 590 */
 591 static int jtSync(sqlite3_file *pFile, int flags){
 592   jt_file *p = (jt_file *)pFile;
 593
 594   if( p->flags&SQLITE_OPEN_MAIN_JOURNAL ){
 595     int rc;
 596     jt_file *pMain;                   /* The associated database file */
 597
 598     /* The journal file is being synced. At this point, we inspect the
 599     ** contents of the file up to this point and set each bit in the
 600     ** jt_file.pWritable bitvec of the main database file associated with
 601     ** this journal file.
 602     */
 603     pMain = locateDatabaseHandle(p->zName);
 604     assert(pMain);
 605
 606     /* Set the bitvec values */
 607     if( pMain->pWritable ){
 608       pMain->nSync++;
 609       rc = readJournalFile(p, pMain);
 610       if( rc!=SQLITE_OK ){
 611         return rc;
 612       }
 613     }
 614   }
 615
 616   return sqlite3OsSync(p->pReal, flags);
 617 }
 618
 619 /*
 620 ** Return the current file-size of an jt-file.
 621 */
 622 static int jtFileSize(sqlite3_file *pFile, sqlite_int64 *pSize){
 623   jt_file *p = (jt_file *)pFile;
 624   return sqlite3OsFileSize(p->pReal, pSize);
 625 }
 626
 627 /*
 628 ** Lock an jt-file.
 629 */
 630 static int jtLock(sqlite3_file *pFile, int eLock){
 631   int rc;
 632   jt_file *p = (jt_file *)pFile;
 633   rc = sqlite3OsLock(p->pReal, eLock);
 634   if( rc==SQLITE_OK && eLock>p->eLock ){
 635     p->eLock = eLock;
 636   }
 637   return rc;
 638 }
 639
 640 /*
 641 ** Unlock an jt-file.
 642 */
 643 static int jtUnlock(sqlite3_file *pFile, int eLock){
 644   int rc;
 645   jt_file *p = (jt_file *)pFile;
 646   rc = sqlite3OsUnlock(p->pReal, eLock);
 647   if( rc==SQLITE_OK && eLock<p->eLock ){
 648     p->eLock = eLock;
 649   }
 650   return rc;
 651 }
 652
 653 /*
 654 ** Check if another file-handle holds a RESERVED lock on an jt-file.
 655 */
 656 static int jtCheckReservedLock(sqlite3_file *pFile, int *pResOut){
 657   jt_file *p = (jt_file *)pFile;
 658   return sqlite3OsCheckReservedLock(p->pReal, pResOut);
 659 }
 660
 661 /*
 662 ** File control method. For custom operations on an jt-file.
 663 */
 664 static int jtFileControl(sqlite3_file *pFile, int op, void *pArg){
 665   jt_file *p = (jt_file *)pFile;
 666   return p->pReal->pMethods->xFileControl(p->pReal, op, pArg);
 667 }
 668
 669 /*
 670 ** Return the sector-size in bytes for an jt-file.
 671 */
 672 static int jtSectorSize(sqlite3_file *pFile){
 673   jt_file *p = (jt_file *)pFile;
 674   return sqlite3OsSectorSize(p->pReal);
 675 }
 676
 677 /*
 678 ** Return the device characteristic flags supported by an jt-file.
 679 */
 680 static int jtDeviceCharacteristics(sqlite3_file *pFile){
 681   jt_file *p = (jt_file *)pFile;
 682   return sqlite3OsDeviceCharacteristics(p->pReal);
 683 }
 684
 685 /*
 686 ** Open an jt file handle.
 687 */
 688 static int jtOpen(
 689   sqlite3_vfs *pVfs,
 690   const char *zName,
 691   sqlite3_file *pFile,
 692   int flags,
 693   int *pOutFlags
 694 ){
 695   int rc;
 696   jt_file *p = (jt_file *)pFile;
 697   pFile->pMethods = 0;
 698   p->pReal = (sqlite3_file *)&p[1];
 699   p->pReal->pMethods = 0;
 700   rc = sqlite3OsOpen(g.pVfs, zName, p->pReal, flags, pOutFlags);
 701   assert( rc==SQLITE_OK || p->pReal->pMethods==0 );
 702   if( rc==SQLITE_OK ){
 703     pFile->pMethods = &jt_io_methods;
 704     p->eLock = 0;
 705     p->zName = zName;
 706     p->flags = flags;
 707     p->pNext = 0;
 708     p->pWritable = 0;
 709     p->aCksum = 0;
 710     enterJtMutex();
 711     if( zName ){
 712       p->pNext = g.pList;
 713       g.pList = p;
 714     }
 715     leaveJtMutex();
 716   }
 717   return rc;
 718 }
 719
 720 /*
 721 ** Delete the file located at zPath. If the dirSync argument is true,
 722 ** ensure the file-system modifications are synced to disk before
 723 ** returning.
 724 */
 725 static int jtDelete(sqlite3_vfs *pVfs, const char *zPath, int dirSync){
 726   int nPath = (int)strlen(zPath);
 727   if( nPath>8 && 0==strcmp("-journal", &zPath[nPath-8]) ){
 728     /* Deleting a journal file. The end of a transaction. */
 729     jt_file *pMain = locateDatabaseHandle(zPath);
 730     if( pMain ){
 731       closeTransaction(pMain);
 732     }
 733   }
 734
 735   return sqlite3OsDelete(g.pVfs, zPath, dirSync);
 736 }
 737
 738 /*
 739 ** Test for access permissions. Return true if the requested permission
 740 ** is available, or false otherwise.
 741 */
 742 static int jtAccess(
 743   sqlite3_vfs *pVfs,
 744   const char *zPath,
 745   int flags,
 746   int *pResOut
 747 ){
 748   return sqlite3OsAccess(g.pVfs, zPath, flags, pResOut);
 749 }
 750
 751 /*
 752 ** Populate buffer zOut with the full canonical pathname corresponding
 753 ** to the pathname in zPath. zOut is guaranteed to point to a buffer
 754 ** of at least (JT_MAX_PATHNAME+1) bytes.
 755 */
 756 static int jtFullPathname(
 757   sqlite3_vfs *pVfs,
 758   const char *zPath,
 759   int nOut,
 760   char *zOut
 761 ){
 762   return sqlite3OsFullPathname(g.pVfs, zPath, nOut, zOut);
 763 }
 764
 765 /*
 766 ** Open the dynamic library located at zPath and return a handle.
 767 */
 768 static void *jtDlOpen(sqlite3_vfs *pVfs, const char *zPath){
 769   return g.pVfs->xDlOpen(g.pVfs, zPath);
 770 }
 771
 772 /*
 773 ** Populate the buffer zErrMsg (size nByte bytes) with a human readable
 774 ** utf-8 string describing the most recent error encountered associated
 775 ** with dynamic libraries.
 776 */
 777 static void jtDlError(sqlite3_vfs *pVfs, int nByte, char *zErrMsg){
 778   g.pVfs->xDlError(g.pVfs, nByte, zErrMsg);
 779 }
 780
 781 /*
 782 ** Return a pointer to the symbol zSymbol in the dynamic library pHandle.
 783 */
 784 static void (*jtDlSym(sqlite3_vfs *pVfs, void *p, const char *zSym))(void){
 785   return g.pVfs->xDlSym(g.pVfs, p, zSym);
 786 }
 787
 788 /*
 789 ** Close the dynamic library handle pHandle.
 790 */
 791 static void jtDlClose(sqlite3_vfs *pVfs, void *pHandle){
 792   g.pVfs->xDlClose(g.pVfs, pHandle);
 793 }
 794
 795 /*
 796 ** Populate the buffer pointed to by zBufOut with nByte bytes of
 797 ** random data.
 798 */
 799 static int jtRandomness(sqlite3_vfs *pVfs, int nByte, char *zBufOut){
 800   return sqlite3OsRandomness(g.pVfs, nByte, zBufOut);
 801 }
 802
 803 /*
 804 ** Sleep for nMicro microseconds. Return the number of microseconds
 805 ** actually slept.
 806 */
 807 static int jtSleep(sqlite3_vfs *pVfs, int nMicro){
 808   return sqlite3OsSleep(g.pVfs, nMicro);
 809 }
 810
 811 /*
 812 ** Return the current time as a Julian Day number in *pTimeOut.
 813 */
 814 static int jtCurrentTime(sqlite3_vfs *pVfs, double *pTimeOut){
 815   return g.pVfs->xCurrentTime(g.pVfs, pTimeOut);
 816 }
 817 /*
 818 ** Return the current time as a Julian Day number in *pTimeOut.
 819 */
 820 static int jtCurrentTimeInt64(sqlite3_vfs *pVfs, sqlite3_int64 *pTimeOut){
 821   return g.pVfs->xCurrentTimeInt64(g.pVfs, pTimeOut);
 822 }
 823
 824 /**************************************************************************
 825 ** Start of public API.
 826 */
 827
 828 /*
 829 ** Configure the jt VFS as a wrapper around the VFS named by parameter
 830 ** zWrap. If the isDefault parameter is true, then the jt VFS is installed
 831 ** as the new default VFS for SQLite connections. If isDefault is not
 832 ** true, then the jt VFS is installed as non-default. In this case it
 833 ** is available via its name, "jt".
 834 */
 835 int jt_register(char *zWrap, int isDefault){
 836   g.pVfs = sqlite3_vfs_find(zWrap);
 837   if( g.pVfs==0 ){
 838     return SQLITE_ERROR;
 839   }
 840   jt_vfs.szOsFile = sizeof(jt_file) + g.pVfs->szOsFile;
 841   if( g.pVfs->iVersion==1 ){
 842     jt_vfs.iVersion = 1;
 843   }else if( g.pVfs->xCurrentTimeInt64==0 ){
 844     jt_vfs.xCurrentTimeInt64 = 0;
 845   }
 846   sqlite3_vfs_register(&jt_vfs, isDefault);
 847   return SQLITE_OK;
 848 }
 849
 850 /*
 851 ** Uninstall the jt VFS, if it is installed.
 852 */
 853 void jt_unregister(void){
 854   sqlite3_vfs_unregister(&jt_vfs);
 855 }
 856
 857 #endif