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Copy pathbackup.c
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747 lines (687 loc) · 26.1 KB
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/*
** 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"
/*
** 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 *)sqlite3MallocZero(sizeof(sqlite3_backup));
if( !p ){
sqlite3Error(pDestDb, SQLITE_NOMEM, 0);
}
}
/* If the allocation succeeded, populate the new object. */
if( p ){
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, /* Backup handle */
Pgno iSrcPg, /* Source database page to backup */
const u8 *zSrcData, /* Source database page data */
int bUpdate /* True for an update, false otherwise */
){
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
/* Use BtreeGetReserveNoMutex() for the source b-tree, as although it is
** guaranteed that the shared-mutex is held by this thread, handle
** p->pSrc may not actually be the owner. */
int nSrcReserve = sqlite3BtreeGetReserveNoMutex(p->pSrc);
int nDestReserve = sqlite3BtreeGetReserve(p->pDest);
#endif
int rc = SQLITE_OK;
i64 iOff;
assert( sqlite3BtreeGetReserveNoMutex(p->pSrc)>=0 );
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;
if( iOff==0 && bUpdate==0 ){
sqlite3Put4byte(&zOut[28], sqlite3BtreeLastPage(p->pSrc));
}
}
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 = sqlite3PagerAcquire(pSrcPager, iSrcPg, &pSrcPg,
PAGER_GET_READONLY);
if( rc==SQLITE_OK ){
rc = backupOnePage(p, iSrcPg, sqlite3PagerGetData(pSrcPg), 0);
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 ){
if( nSrcPage==0 ){
rc = sqlite3BtreeNewDb(p->pDest);
nSrcPage = 1;
}
if( rc==SQLITE_OK || rc==SQLITE_DONE ){
rc = sqlite3BtreeUpdateMeta(p->pDest,1,p->iDestSchema+1);
}
if( rc==SQLITE_OK ){
if( p->pDestDb ){
sqlite3ResetAllSchemasOfConnection(p->pDestDb);
}
if( destMode==PAGER_JOURNALMODE_WAL ){
rc = sqlite3BtreeSetVersion(p->pDest, 2);
}
}
if( rc==SQLITE_OK ){
int nDestTruncate;
/* 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);
}
assert( nDestTruncate>0 );
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);
Pgno iPg;
int nDstPage;
i64 iOff;
i64 iEnd;
assert( pFile );
assert( nDestTruncate==0
|| (i64)nDestTruncate*(i64)pgszDest >= iSize || (
nDestTruncate==(int)(PENDING_BYTE_PAGE(p->pDest->pBt)-1)
&& iSize>=PENDING_BYTE && iSize<=PENDING_BYTE+pgszDest
));
/* This block 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. */
sqlite3PagerPagecount(pDestPager, &nDstPage);
for(iPg=nDestTruncate; rc==SQLITE_OK && iPg<=(Pgno)nDstPage; iPg++){
if( iPg!=PENDING_BYTE_PAGE(p->pDest->pBt) ){
DbPage *pPg;
rc = sqlite3PagerGet(pDestPager, iPg, &pPg);
if( rc==SQLITE_OK ){
rc = sqlite3PagerWrite(pPg);
sqlite3PagerUnref(pPg);
}
}
}
if( rc==SQLITE_OK ){
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{
sqlite3PagerTruncateImage(pDestPager, nDestTruncate);
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 *pSrcDb; /* Source database connection */
int rc; /* Value to return */
/* Enter the mutexes */
if( p==0 ) return SQLITE_OK;
pSrcDb = p->pSrcDb;
sqlite3_mutex_enter(pSrcDb->mutex);
sqlite3BtreeEnter(p->pSrc);
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, SQLITE_OK);
/* 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 ){
sqlite3LeaveMutexAndCloseZombie(p->pDestDb);
}
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);
}
sqlite3LeaveMutexAndCloseZombie(pSrcDb);
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, 1);
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_file *pFd; /* File descriptor for database pTo */
sqlite3_backup b;
sqlite3BtreeEnter(pTo);
sqlite3BtreeEnter(pFrom);
assert( sqlite3BtreeIsInTrans(pTo) );
pFd = sqlite3PagerFile(sqlite3BtreePager(pTo));
if( pFd->pMethods ){
i64 nByte = sqlite3BtreeGetPageSize(pFrom)*(i64)sqlite3BtreeLastPage(pFrom);
rc = sqlite3OsFileControl(pFd, SQLITE_FCNTL_OVERWRITE, &nByte);
if( rc==SQLITE_NOTFOUND ) rc = SQLITE_OK;
if( rc ) goto copy_finished;
}
/* 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->btsFlags &= ~BTS_PAGESIZE_FIXED;
}else{
sqlite3PagerClearCache(sqlite3BtreePager(b.pDest));
}
assert( sqlite3BtreeIsInTrans(pTo)==0 );
copy_finished:
sqlite3BtreeLeave(pFrom);
sqlite3BtreeLeave(pTo);
return rc;
}
#endif /* SQLITE_OMIT_VACUUM */