/* ** 2009 January 28 ** ** 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 contains the implementation of the sqlite3_backup_XXX() ** API functions and the related features. */ #include "sqliteInt.h" #include "btreeInt.h" /* Macro to find the minimum of two numeric values. */ #ifndef MIN # define MIN(x,y) ((x)<(y)?(x):(y)) #endif /* ** Structure allocated for each backup operation. */ struct sqlite3_backup { sqlite3* pDestDb; /* Destination database handle */ Btree *pDest; /* Destination b-tree file */ u32 iDestSchema; /* Original schema cookie in destination */ int bDestLocked; /* True once a write-transaction is open on pDest */ Pgno iNext; /* Page number of the next source page to copy */ sqlite3* pSrcDb; /* Source database handle */ Btree *pSrc; /* Source b-tree file */ int rc; /* Backup process error code */ /* These two variables are set by every call to backup_step(). They are ** read by calls to backup_remaining() and backup_pagecount(). */ Pgno nRemaining; /* Number of pages left to copy */ Pgno nPagecount; /* Total number of pages to copy */ int isAttached; /* True once backup has been registered with pager */ sqlite3_backup *pNext; /* Next backup associated with source pager */ }; /* ** THREAD SAFETY NOTES: ** ** Once it has been created using backup_init(), a single sqlite3_backup ** structure may be accessed via two groups of thread-safe entry points: ** ** * Via the sqlite3_backup_XXX() API function backup_step() and ** backup_finish(). Both these functions obtain the source database ** handle mutex and the mutex associated with the source BtShared ** structure, in that order. ** ** * Via the BackupUpdate() and BackupRestart() functions, which are ** invoked by the pager layer to report various state changes in ** the page cache associated with the source database. The mutex ** associated with the source database BtShared structure will always ** be held when either of these functions are invoked. ** ** The other sqlite3_backup_XXX() API functions, backup_remaining() and ** backup_pagecount() are not thread-safe functions. If they are called ** while some other thread is calling backup_step() or backup_finish(), ** the values returned may be invalid. There is no way for a call to ** BackupUpdate() or BackupRestart() to interfere with backup_remaining() ** or backup_pagecount(). ** ** Depending on the SQLite configuration, the database handles and/or ** the Btree objects may have their own mutexes that require locking. ** Non-sharable Btrees (in-memory databases for example), do not have ** associated mutexes. */ /* ** Return a pointer corresponding to database zDb (i.e. "main", "temp") ** in connection handle pDb. If such a database cannot be found, return ** a NULL pointer and write an error message to pErrorDb. ** ** If the "temp" database is requested, it may need to be opened by this ** function. If an error occurs while doing so, return 0 and write an ** error message to pErrorDb. */ static Btree *findBtree(sqlite3 *pErrorDb, sqlite3 *pDb, const char *zDb){ int i = sqlite3FindDbName(pDb, zDb); if( i==1 ){ Parse *pParse; int rc = 0; pParse = sqlite3StackAllocZero(pErrorDb, sizeof(*pParse)); if( pParse==0 ){ sqlite3Error(pErrorDb, SQLITE_NOMEM, "out of memory"); rc = SQLITE_NOMEM; }else{ pParse->db = pDb; if( sqlite3OpenTempDatabase(pParse) ){ sqlite3Error(pErrorDb, pParse->rc, "%s", pParse->zErrMsg); rc = SQLITE_ERROR; } sqlite3DbFree(pErrorDb, pParse->zErrMsg); sqlite3StackFree(pErrorDb, pParse); } if( rc ){ return 0; } } if( i<0 ){ sqlite3Error(pErrorDb, SQLITE_ERROR, "unknown database %s", zDb); return 0; } return pDb->aDb[i].pBt; } /* ** Attempt to set the page size of the destination to match the page size ** of the source. */ static int setDestPgsz(sqlite3_backup *p){ int rc; rc = sqlite3BtreeSetPageSize(p->pDest,sqlite3BtreeGetPageSize(p->pSrc),-1,0); return rc; } /* ** Create an sqlite3_backup process to copy the contents of zSrcDb from ** connection handle pSrcDb to zDestDb in pDestDb. If successful, return ** a pointer to the new sqlite3_backup object. ** ** If an error occurs, NULL is returned and an error code and error message ** stored in database handle pDestDb. */ sqlite3_backup *sqlite3_backup_init( sqlite3* pDestDb, /* Database to write to */ const char *zDestDb, /* Name of database within pDestDb */ sqlite3* pSrcDb, /* Database connection to read from */ const char *zSrcDb /* Name of database within pSrcDb */ ){ sqlite3_backup *p; /* Value to return */ /* Lock the source database handle. The destination database ** handle is not locked in this routine, but it is locked in ** sqlite3_backup_step(). The user is required to ensure that no ** other thread accesses the destination handle for the duration ** of the backup operation. Any attempt to use the destination ** database connection while a backup is in progress may cause ** a malfunction or a deadlock. */ sqlite3_mutex_enter(pSrcDb->mutex); sqlite3_mutex_enter(pDestDb->mutex); if( pSrcDb==pDestDb ){ sqlite3Error( pDestDb, SQLITE_ERROR, "source and destination must be distinct" ); p = 0; }else { /* Allocate space for a new sqlite3_backup object... ** EVIDENCE-OF: R-64852-21591 The sqlite3_backup object is created by a ** call to sqlite3_backup_init() and is destroyed by a call to ** sqlite3_backup_finish(). */ p = (sqlite3_backup *)sqlite3_malloc(sizeof(sqlite3_backup)); if( !p ){ sqlite3Error(pDestDb, SQLITE_NOMEM, 0); } } /* If the allocation succeeded, populate the new object. */ if( p ){ memset(p, 0, sizeof(sqlite3_backup)); p->pSrc = findBtree(pDestDb, pSrcDb, zSrcDb); p->pDest = findBtree(pDestDb, pDestDb, zDestDb); p->pDestDb = pDestDb; p->pSrcDb = pSrcDb; p->iNext = 1; p->isAttached = 0; if( 0==p->pSrc || 0==p->pDest || setDestPgsz(p)==SQLITE_NOMEM ){ /* One (or both) of the named databases did not exist or an OOM ** error was hit. The error has already been written into the ** pDestDb handle. All that is left to do here is free the ** sqlite3_backup structure. */ sqlite3_free(p); p = 0; } } if( p ){ p->pSrc->nBackup++; } sqlite3_mutex_leave(pDestDb->mutex); sqlite3_mutex_leave(pSrcDb->mutex); return p; } /* ** Argument rc is an SQLite error code. Return true if this error is ** considered fatal if encountered during a backup operation. All errors ** are considered fatal except for SQLITE_BUSY and SQLITE_LOCKED. */ static int isFatalError(int rc){ return (rc!=SQLITE_OK && rc!=SQLITE_BUSY && ALWAYS(rc!=SQLITE_LOCKED)); } /* ** Parameter zSrcData points to a buffer containing the data for ** page iSrcPg from the source database. Copy this data into the ** destination database. */ static int backupOnePage(sqlite3_backup *p, Pgno iSrcPg, const u8 *zSrcData){ Pager * const pDestPager = sqlite3BtreePager(p->pDest); const int nSrcPgsz = sqlite3BtreeGetPageSize(p->pSrc); int nDestPgsz = sqlite3BtreeGetPageSize(p->pDest); const int nCopy = MIN(nSrcPgsz, nDestPgsz); const i64 iEnd = (i64)iSrcPg*(i64)nSrcPgsz; #ifdef SQLITE_HAS_CODEC int nSrcReserve = sqlite3BtreeGetReserve(p->pSrc); int nDestReserve = sqlite3BtreeGetReserve(p->pDest); #endif int rc = SQLITE_OK; i64 iOff; assert( p->bDestLocked ); assert( !isFatalError(p->rc) ); assert( iSrcPg!=PENDING_BYTE_PAGE(p->pSrc->pBt) ); assert( zSrcData ); /* Catch the case where the destination is an in-memory database and the ** page sizes of the source and destination differ. */ if( nSrcPgsz!=nDestPgsz && sqlite3PagerIsMemdb(pDestPager) ){ rc = SQLITE_READONLY; } #ifdef SQLITE_HAS_CODEC /* Backup is not possible if the page size of the destination is changing ** and a codec is in use. */ if( nSrcPgsz!=nDestPgsz && sqlite3PagerGetCodec(pDestPager)!=0 ){ rc = SQLITE_READONLY; } /* Backup is not possible if the number of bytes of reserve space differ ** between source and destination. If there is a difference, try to ** fix the destination to agree with the source. If that is not possible, ** then the backup cannot proceed. */ if( nSrcReserve!=nDestReserve ){ u32 newPgsz = nSrcPgsz; rc = sqlite3PagerSetPagesize(pDestPager, &newPgsz, nSrcReserve); if( rc==SQLITE_OK && newPgsz!=nSrcPgsz ) rc = SQLITE_READONLY; } #endif /* This loop runs once for each destination page spanned by the source ** page. For each iteration, variable iOff is set to the byte offset ** of the destination page. */ for(iOff=iEnd-(i64)nSrcPgsz; rc==SQLITE_OK && iOff<iEnd; iOff+=nDestPgsz){ DbPage *pDestPg = 0; Pgno iDest = (Pgno)(iOff/nDestPgsz)+1; if( iDest==PENDING_BYTE_PAGE(p->pDest->pBt) ) continue; if( SQLITE_OK==(rc = sqlite3PagerGet(pDestPager, iDest, &pDestPg)) && SQLITE_OK==(rc = sqlite3PagerWrite(pDestPg)) ){ const u8 *zIn = &zSrcData[iOff%nSrcPgsz]; u8 *zDestData = sqlite3PagerGetData(pDestPg); u8 *zOut = &zDestData[iOff%nDestPgsz]; /* Copy the data from the source page into the destination page. ** Then clear the Btree layer MemPage.isInit flag. Both this module ** and the pager code use this trick (clearing the first byte ** of the page 'extra' space to invalidate the Btree layers ** cached parse of the page). MemPage.isInit is marked ** "MUST BE FIRST" for this purpose. */ memcpy(zOut, zIn, nCopy); ((u8 *)sqlite3PagerGetExtra(pDestPg))[0] = 0; } sqlite3PagerUnref(pDestPg); } return rc; } /* ** If pFile is currently larger than iSize bytes, then truncate it to ** exactly iSize bytes. If pFile is not larger than iSize bytes, then ** this function is a no-op. ** ** Return SQLITE_OK if everything is successful, or an SQLite error ** code if an error occurs. */ static int backupTruncateFile(sqlite3_file *pFile, i64 iSize){ i64 iCurrent; int rc = sqlite3OsFileSize(pFile, &iCurrent); if( rc==SQLITE_OK && iCurrent>iSize ){ rc = sqlite3OsTruncate(pFile, iSize); } return rc; } /* ** Register this backup object with the associated source pager for ** callbacks when pages are changed or the cache invalidated. */ static void attachBackupObject(sqlite3_backup *p){ sqlite3_backup **pp; assert( sqlite3BtreeHoldsMutex(p->pSrc) ); pp = sqlite3PagerBackupPtr(sqlite3BtreePager(p->pSrc)); p->pNext = *pp; *pp = p; p->isAttached = 1; } /* ** Copy nPage pages from the source b-tree to the destination. */ int sqlite3_backup_step(sqlite3_backup *p, int nPage){ int rc; int destMode; /* Destination journal mode */ int pgszSrc = 0; /* Source page size */ int pgszDest = 0; /* Destination page size */ sqlite3_mutex_enter(p->pSrcDb->mutex); sqlite3BtreeEnter(p->pSrc); if( p->pDestDb ){ sqlite3_mutex_enter(p->pDestDb->mutex); } rc = p->rc; if( !isFatalError(rc) ){ Pager * const pSrcPager = sqlite3BtreePager(p->pSrc); /* Source pager */ Pager * const pDestPager = sqlite3BtreePager(p->pDest); /* Dest pager */ int ii; /* Iterator variable */ int nSrcPage = -1; /* Size of source db in pages */ int bCloseTrans = 0; /* True if src db requires unlocking */ /* If the source pager is currently in a write-transaction, return ** SQLITE_BUSY immediately. */ if( p->pDestDb && p->pSrc->pBt->inTransaction==TRANS_WRITE ){ rc = SQLITE_BUSY; }else{ rc = SQLITE_OK; } /* Lock the destination database, if it is not locked already. */ if( SQLITE_OK==rc && p->bDestLocked==0 && SQLITE_OK==(rc = sqlite3BtreeBeginTrans(p->pDest, 2)) ){ p->bDestLocked = 1; sqlite3BtreeGetMeta(p->pDest, BTREE_SCHEMA_VERSION, &p->iDestSchema); } /* If there is no open read-transaction on the source database, open ** one now. If a transaction is opened here, then it will be closed ** before this function exits. */ if( rc==SQLITE_OK && 0==sqlite3BtreeIsInReadTrans(p->pSrc) ){ rc = sqlite3BtreeBeginTrans(p->pSrc, 0); bCloseTrans = 1; } /* Do not allow backup if the destination database is in WAL mode ** and the page sizes are different between source and destination */ pgszSrc = sqlite3BtreeGetPageSize(p->pSrc); pgszDest = sqlite3BtreeGetPageSize(p->pDest); destMode = sqlite3PagerGetJournalMode(sqlite3BtreePager(p->pDest)); if( SQLITE_OK==rc && destMode==PAGER_JOURNALMODE_WAL && pgszSrc!=pgszDest ){ rc = SQLITE_READONLY; } /* Now that there is a read-lock on the source database, query the ** source pager for the number of pages in the database. */ nSrcPage = (int)sqlite3BtreeLastPage(p->pSrc); assert( nSrcPage>=0 ); for(ii=0; (nPage<0 || ii<nPage) && p->iNext<=(Pgno)nSrcPage && !rc; ii++){ const Pgno iSrcPg = p->iNext; /* Source page number */ if( iSrcPg!=PENDING_BYTE_PAGE(p->pSrc->pBt) ){ DbPage *pSrcPg; /* Source page object */ rc = sqlite3PagerGet(pSrcPager, iSrcPg, &pSrcPg); if( rc==SQLITE_OK ){ rc = backupOnePage(p, iSrcPg, sqlite3PagerGetData(pSrcPg)); sqlite3PagerUnref(pSrcPg); } } p->iNext++; } if( rc==SQLITE_OK ){ p->nPagecount = nSrcPage; p->nRemaining = nSrcPage+1-p->iNext; if( p->iNext>(Pgno)nSrcPage ){ rc = SQLITE_DONE; }else if( !p->isAttached ){ attachBackupObject(p); } } /* Update the schema version field in the destination database. This ** is to make sure that the schema-version really does change in ** the case where the source and destination databases have the ** same schema version. */ if( rc==SQLITE_DONE && (rc = sqlite3BtreeUpdateMeta(p->pDest,1,p->iDestSchema+1))==SQLITE_OK ){ int nDestTruncate; if( p->pDestDb ){ sqlite3ResetInternalSchema(p->pDestDb, -1); } /* Set nDestTruncate to the final number of pages in the destination ** database. The complication here is that the destination page ** size may be different to the source page size. ** ** If the source page size is smaller than the destination page size, ** round up. In this case the call to sqlite3OsTruncate() below will ** fix the size of the file. However it is important to call ** sqlite3PagerTruncateImage() here so that any pages in the ** destination file that lie beyond the nDestTruncate page mark are ** journalled by PagerCommitPhaseOne() before they are destroyed ** by the file truncation. */ assert( pgszSrc==sqlite3BtreeGetPageSize(p->pSrc) ); assert( pgszDest==sqlite3BtreeGetPageSize(p->pDest) ); if( pgszSrc<pgszDest ){ int ratio = pgszDest/pgszSrc; nDestTruncate = (nSrcPage+ratio-1)/ratio; if( nDestTruncate==(int)PENDING_BYTE_PAGE(p->pDest->pBt) ){ nDestTruncate--; } }else{ nDestTruncate = nSrcPage * (pgszSrc/pgszDest); } sqlite3PagerTruncateImage(pDestPager, nDestTruncate); if( pgszSrc<pgszDest ){ /* If the source page-size is smaller than the destination page-size, ** two extra things may need to happen: ** ** * The destination may need to be truncated, and ** ** * Data stored on the pages immediately following the ** pending-byte page in the source database may need to be ** copied into the destination database. */ const i64 iSize = (i64)pgszSrc * (i64)nSrcPage; sqlite3_file * const pFile = sqlite3PagerFile(pDestPager); i64 iOff; i64 iEnd; assert( pFile ); assert( (i64)nDestTruncate*(i64)pgszDest >= iSize || ( nDestTruncate==(int)(PENDING_BYTE_PAGE(p->pDest->pBt)-1) && iSize>=PENDING_BYTE && iSize<=PENDING_BYTE+pgszDest )); /* This call ensures that all data required to recreate the original ** database has been stored in the journal for pDestPager and the ** journal synced to disk. So at this point we may safely modify ** the database file in any way, knowing that if a power failure ** occurs, the original database will be reconstructed from the ** journal file. */ rc = sqlite3PagerCommitPhaseOne(pDestPager, 0, 1); /* Write the extra pages and truncate the database file as required. */ iEnd = MIN(PENDING_BYTE + pgszDest, iSize); for( iOff=PENDING_BYTE+pgszSrc; rc==SQLITE_OK && iOff<iEnd; iOff+=pgszSrc ){ PgHdr *pSrcPg = 0; const Pgno iSrcPg = (Pgno)((iOff/pgszSrc)+1); rc = sqlite3PagerGet(pSrcPager, iSrcPg, &pSrcPg); if( rc==SQLITE_OK ){ u8 *zData = sqlite3PagerGetData(pSrcPg); rc = sqlite3OsWrite(pFile, zData, pgszSrc, iOff); } sqlite3PagerUnref(pSrcPg); } if( rc==SQLITE_OK ){ rc = backupTruncateFile(pFile, iSize); } /* Sync the database file to disk. */ if( rc==SQLITE_OK ){ rc = sqlite3PagerSync(pDestPager); } }else{ rc = sqlite3PagerCommitPhaseOne(pDestPager, 0, 0); } /* Finish committing the transaction to the destination database. */ if( SQLITE_OK==rc && SQLITE_OK==(rc = sqlite3BtreeCommitPhaseTwo(p->pDest, 0)) ){ rc = SQLITE_DONE; } } /* If bCloseTrans is true, then this function opened a read transaction ** on the source database. Close the read transaction here. There is ** no need to check the return values of the btree methods here, as ** "committing" a read-only transaction cannot fail. */ if( bCloseTrans ){ TESTONLY( int rc2 ); TESTONLY( rc2 = ) sqlite3BtreeCommitPhaseOne(p->pSrc, 0); TESTONLY( rc2 |= ) sqlite3BtreeCommitPhaseTwo(p->pSrc, 0); assert( rc2==SQLITE_OK ); } if( rc==SQLITE_IOERR_NOMEM ){ rc = SQLITE_NOMEM; } p->rc = rc; } if( p->pDestDb ){ sqlite3_mutex_leave(p->pDestDb->mutex); } sqlite3BtreeLeave(p->pSrc); sqlite3_mutex_leave(p->pSrcDb->mutex); return rc; } /* ** Release all resources associated with an sqlite3_backup* handle. */ int sqlite3_backup_finish(sqlite3_backup *p){ sqlite3_backup **pp; /* Ptr to head of pagers backup list */ sqlite3_mutex *mutex; /* Mutex to protect source database */ int rc; /* Value to return */ /* Enter the mutexes */ if( p==0 ) return SQLITE_OK; sqlite3_mutex_enter(p->pSrcDb->mutex); sqlite3BtreeEnter(p->pSrc); mutex = p->pSrcDb->mutex; if( p->pDestDb ){ sqlite3_mutex_enter(p->pDestDb->mutex); } /* Detach this backup from the source pager. */ if( p->pDestDb ){ p->pSrc->nBackup--; } if( p->isAttached ){ pp = sqlite3PagerBackupPtr(sqlite3BtreePager(p->pSrc)); while( *pp!=p ){ pp = &(*pp)->pNext; } *pp = p->pNext; } /* If a transaction is still open on the Btree, roll it back. */ sqlite3BtreeRollback(p->pDest); /* Set the error code of the destination database handle. */ rc = (p->rc==SQLITE_DONE) ? SQLITE_OK : p->rc; sqlite3Error(p->pDestDb, rc, 0); /* Exit the mutexes and free the backup context structure. */ if( p->pDestDb ){ sqlite3_mutex_leave(p->pDestDb->mutex); } sqlite3BtreeLeave(p->pSrc); if( p->pDestDb ){ /* EVIDENCE-OF: R-64852-21591 The sqlite3_backup object is created by a ** call to sqlite3_backup_init() and is destroyed by a call to ** sqlite3_backup_finish(). */ sqlite3_free(p); } sqlite3_mutex_leave(mutex); return rc; } /* ** Return the number of pages still to be backed up as of the most recent ** call to sqlite3_backup_step(). */ int sqlite3_backup_remaining(sqlite3_backup *p){ return p->nRemaining; } /* ** Return the total number of pages in the source database as of the most ** recent call to sqlite3_backup_step(). */ int sqlite3_backup_pagecount(sqlite3_backup *p){ return p->nPagecount; } /* ** This function is called after the contents of page iPage of the ** source database have been modified. If page iPage has already been ** copied into the destination database, then the data written to the ** destination is now invalidated. The destination copy of iPage needs ** to be updated with the new data before the backup operation is ** complete. ** ** It is assumed that the mutex associated with the BtShared object ** corresponding to the source database is held when this function is ** called. */ void sqlite3BackupUpdate(sqlite3_backup *pBackup, Pgno iPage, const u8 *aData){ sqlite3_backup *p; /* Iterator variable */ for(p=pBackup; p; p=p->pNext){ assert( sqlite3_mutex_held(p->pSrc->pBt->mutex) ); if( !isFatalError(p->rc) && iPage<p->iNext ){ /* The backup process p has already copied page iPage. But now it ** has been modified by a transaction on the source pager. Copy ** the new data into the backup. */ int rc; assert( p->pDestDb ); sqlite3_mutex_enter(p->pDestDb->mutex); rc = backupOnePage(p, iPage, aData); sqlite3_mutex_leave(p->pDestDb->mutex); assert( rc!=SQLITE_BUSY && rc!=SQLITE_LOCKED ); if( rc!=SQLITE_OK ){ p->rc = rc; } } } } /* ** Restart the backup process. This is called when the pager layer ** detects that the database has been modified by an external database ** connection. In this case there is no way of knowing which of the ** pages that have been copied into the destination database are still ** valid and which are not, so the entire process needs to be restarted. ** ** It is assumed that the mutex associated with the BtShared object ** corresponding to the source database is held when this function is ** called. */ void sqlite3BackupRestart(sqlite3_backup *pBackup){ sqlite3_backup *p; /* Iterator variable */ for(p=pBackup; p; p=p->pNext){ assert( sqlite3_mutex_held(p->pSrc->pBt->mutex) ); p->iNext = 1; } } #ifndef SQLITE_OMIT_VACUUM /* ** Copy the complete content of pBtFrom into pBtTo. A transaction ** must be active for both files. ** ** The size of file pTo may be reduced by this operation. If anything ** goes wrong, the transaction on pTo is rolled back. If successful, the ** transaction is committed before returning. */ int sqlite3BtreeCopyFile(Btree *pTo, Btree *pFrom){ int rc; sqlite3_backup b; sqlite3BtreeEnter(pTo); sqlite3BtreeEnter(pFrom); /* Set up an sqlite3_backup object. sqlite3_backup.pDestDb must be set ** to 0. This is used by the implementations of sqlite3_backup_step() ** and sqlite3_backup_finish() to detect that they are being called ** from this function, not directly by the user. */ memset(&b, 0, sizeof(b)); b.pSrcDb = pFrom->db; b.pSrc = pFrom; b.pDest = pTo; b.iNext = 1; /* 0x7FFFFFFF is the hard limit for the number of pages in a database ** file. By passing this as the number of pages to copy to ** sqlite3_backup_step(), we can guarantee that the copy finishes ** within a single call (unless an error occurs). The assert() statement ** checks this assumption - (p->rc) should be set to either SQLITE_DONE ** or an error code. */ sqlite3_backup_step(&b, 0x7FFFFFFF); assert( b.rc!=SQLITE_OK ); rc = sqlite3_backup_finish(&b); if( rc==SQLITE_OK ){ pTo->pBt->pageSizeFixed = 0; } sqlite3BtreeLeave(pFrom); sqlite3BtreeLeave(pTo); return rc; } #endif /* SQLITE_OMIT_VACUUM */