/*
** 2008 October 7
**
** 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 code use to implement an in-memory rollback journal.
** The in-memory rollback journal is used to journal transactions for
** ":memory:" databases and when the journal_mode=MEMORY pragma is used.
*/
#include "sqliteInt.h"
/* Forward references to internal structures */
typedef struct MemJournal MemJournal;
typedef struct FilePoint FilePoint;
typedef struct FileChunk FileChunk;
/* Space to hold the rollback journal is allocated in increments of
** this many bytes.
**
** The size chosen is a little less than a power of two. That way,
** the FileChunk object will have a size that almost exactly fills
** a power-of-two allocation. This mimimizes wasted space in power-of-two
** memory allocators.
*/
#define JOURNAL_CHUNKSIZE ((int)(1024-sizeof(FileChunk*)))
/* Macro to find the minimum of two numeric values.
*/
#ifndef MIN
# define MIN(x,y) ((x)<(y)?(x):(y))
#endif
/*
** The rollback journal is composed of a linked list of these structures.
*/
struct FileChunk {
FileChunk *pNext; /* Next chunk in the journal */
u8 zChunk[JOURNAL_CHUNKSIZE]; /* Content of this chunk */
};
/*
** An instance of this object serves as a cursor into the rollback journal.
** The cursor can be either for reading or writing.
*/
struct FilePoint {
sqlite3_int64 iOffset; /* Offset from the beginning of the file */
FileChunk *pChunk; /* Specific chunk into which cursor points */
};
/*
** This subclass is a subclass of sqlite3_file. Each open memory-journal
** is an instance of this class.
*/
struct MemJournal {
sqlite3_io_methods *pMethod; /* Parent class. MUST BE FIRST */
FileChunk *pFirst; /* Head of in-memory chunk-list */
FilePoint endpoint; /* Pointer to the end of the file */
FilePoint readpoint; /* Pointer to the end of the last xRead() */
};
/*
** Read data from the in-memory journal file. This is the implementation
** of the sqlite3_vfs.xRead method.
*/
static int memjrnlRead(
sqlite3_file *pJfd, /* The journal file from which to read */
void *zBuf, /* Put the results here */
int iAmt, /* Number of bytes to read */
sqlite_int64 iOfst /* Begin reading at this offset */
){
MemJournal *p = (MemJournal *)pJfd;
u8 *zOut = zBuf;
int nRead = iAmt;
int iChunkOffset;
FileChunk *pChunk;
/* SQLite never tries to read past the end of a rollback journal file */
assert( iOfst+iAmt<=p->endpoint.iOffset );
if( p->readpoint.iOffset!=iOfst || iOfst==0 ){
sqlite3_int64 iOff = 0;
for(pChunk=p->pFirst;
ALWAYS(pChunk) && (iOff+JOURNAL_CHUNKSIZE)<=iOfst;
pChunk=pChunk->pNext
){
iOff += JOURNAL_CHUNKSIZE;
}
}else{
pChunk = p->readpoint.pChunk;
}
iChunkOffset = (int)(iOfst%JOURNAL_CHUNKSIZE);
do {
int iSpace = JOURNAL_CHUNKSIZE - iChunkOffset;
int nCopy = MIN(nRead, (JOURNAL_CHUNKSIZE - iChunkOffset));
memcpy(zOut, &pChunk->zChunk[iChunkOffset], nCopy);
zOut += nCopy;
nRead -= iSpace;
iChunkOffset = 0;
} while( nRead>=0 && (pChunk=pChunk->pNext)!=0 && nRead>0 );
p->readpoint.iOffset = iOfst+iAmt;
p->readpoint.pChunk = pChunk;
return SQLITE_OK;
}
/*
** Write data to the file.
*/
static int memjrnlWrite(
sqlite3_file *pJfd, /* The journal file into which to write */
const void *zBuf, /* Take data to be written from here */
int iAmt, /* Number of bytes to write */
sqlite_int64 iOfst /* Begin writing at this offset into the file */
){
MemJournal *p = (MemJournal *)pJfd;
int nWrite = iAmt;
u8 *zWrite = (u8 *)zBuf;
/* An in-memory journal file should only ever be appended to. Random
** access writes are not required by sqlite.
*/
assert( iOfst==p->endpoint.iOffset );
UNUSED_PARAMETER(iOfst);
while( nWrite>0 ){
FileChunk *pChunk = p->endpoint.pChunk;
int iChunkOffset = (int)(p->endpoint.iOffset%JOURNAL_CHUNKSIZE);
int iSpace = MIN(nWrite, JOURNAL_CHUNKSIZE - iChunkOffset);
if( iChunkOffset==0 ){
/* New chunk is required to extend the file. */
FileChunk *pNew = sqlite3_malloc(sizeof(FileChunk));
if( !pNew ){
return SQLITE_IOERR_NOMEM;
}
pNew->pNext = 0;
if( pChunk ){
assert( p->pFirst );
pChunk->pNext = pNew;
}else{
assert( !p->pFirst );
p->pFirst = pNew;
}
p->endpoint.pChunk = pNew;
}
memcpy(&p->endpoint.pChunk->zChunk[iChunkOffset], zWrite, iSpace);
zWrite += iSpace;
nWrite -= iSpace;
p->endpoint.iOffset += iSpace;
}
return SQLITE_OK;
}
/*
** Truncate the file.
*/
static int memjrnlTruncate(sqlite3_file *pJfd, sqlite_int64 size){
MemJournal *p = (MemJournal *)pJfd;
FileChunk *pChunk;
assert(size==0);
UNUSED_PARAMETER(size);
pChunk = p->pFirst;
while( pChunk ){
FileChunk *pTmp = pChunk;
pChunk = pChunk->pNext;
sqlite3_free(pTmp);
}
sqlite3MemJournalOpen(pJfd);
return SQLITE_OK;
}
/*
** Close the file.
*/
static int memjrnlClose(sqlite3_file *pJfd){
memjrnlTruncate(pJfd, 0);
return SQLITE_OK;
}
/*
** Sync the file.
**
** Syncing an in-memory journal is a no-op. And, in fact, this routine
** is never called in a working implementation. This implementation
** exists purely as a contingency, in case some malfunction in some other
** part of SQLite causes Sync to be called by mistake.
*/
static int memjrnlSync(sqlite3_file *NotUsed, int NotUsed2){
UNUSED_PARAMETER2(NotUsed, NotUsed2);
return SQLITE_OK;
}
/*
** Query the size of the file in bytes.
*/
static int memjrnlFileSize(sqlite3_file *pJfd, sqlite_int64 *pSize){
MemJournal *p = (MemJournal *)pJfd;
*pSize = (sqlite_int64) p->endpoint.iOffset;
return SQLITE_OK;
}
/*
** Table of methods for MemJournal sqlite3_file object.
*/
static const struct sqlite3_io_methods MemJournalMethods = {
1, /* iVersion */
memjrnlClose, /* xClose */
memjrnlRead, /* xRead */
memjrnlWrite, /* xWrite */
memjrnlTruncate, /* xTruncate */
memjrnlSync, /* xSync */
memjrnlFileSize, /* xFileSize */
0, /* xLock */
0, /* xUnlock */
0, /* xCheckReservedLock */
0, /* xFileControl */
0, /* xSectorSize */
0, /* xDeviceCharacteristics */
0, /* xShmMap */
0, /* xShmLock */
0, /* xShmBarrier */
0 /* xShmUnlock */
};
/*
** Open a journal file.
*/
void sqlite3MemJournalOpen(sqlite3_file *pJfd){
MemJournal *p = (MemJournal *)pJfd;
assert( EIGHT_BYTE_ALIGNMENT(p) );
memset(p, 0, sqlite3MemJournalSize());
p->pMethod = (sqlite3_io_methods*)&MemJournalMethods;
}
/*
** Return true if the file-handle passed as an argument is
** an in-memory journal
*/
int sqlite3IsMemJournal(sqlite3_file *pJfd){
return pJfd->pMethods==&MemJournalMethods;
}
/*
** Return the number of bytes required to store a MemJournal file descriptor.
*/
int sqlite3MemJournalSize(void){
return sizeof(MemJournal);
}