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256 lines (242 loc) · 7.11 KB
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/*
** 2007 August 22
**
** 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 implements a special kind of sqlite3_file object used
** by SQLite to create journal files if the atomic-write optimization
** is enabled.
**
** The distinctive characteristic of this sqlite3_file is that the
** actual on disk file is created lazily. When the file is created,
** the caller specifies a buffer size for an in-memory buffer to
** be used to service read() and write() requests. The actual file
** on disk is not created or populated until either:
**
** 1) The in-memory representation grows too large for the allocated
** buffer, or
** 2) The sqlite3JournalCreate() function is called.
*/
#ifdef SQLITE_ENABLE_ATOMIC_WRITE
#include "sqliteInt.h"
/*
** A JournalFile object is a subclass of sqlite3_file used by
** as an open file handle for journal files.
*/
struct JournalFile {
sqlite3_io_methods *pMethod; /* I/O methods on journal files */
int nBuf; /* Size of zBuf[] in bytes */
char *zBuf; /* Space to buffer journal writes */
int iSize; /* Amount of zBuf[] currently used */
int flags; /* xOpen flags */
sqlite3_vfs *pVfs; /* The "real" underlying VFS */
sqlite3_file *pReal; /* The "real" underlying file descriptor */
const char *zJournal; /* Name of the journal file */
};
typedef struct JournalFile JournalFile;
/*
** If it does not already exists, create and populate the on-disk file
** for JournalFile p.
*/
static int createFile(JournalFile *p){
int rc = SQLITE_OK;
if( !p->pReal ){
sqlite3_file *pReal = (sqlite3_file *)&p[1];
rc = sqlite3OsOpen(p->pVfs, p->zJournal, pReal, p->flags, 0);
if( rc==SQLITE_OK ){
p->pReal = pReal;
if( p->iSize>0 ){
assert(p->iSize<=p->nBuf);
rc = sqlite3OsWrite(p->pReal, p->zBuf, p->iSize, 0);
}
if( rc!=SQLITE_OK ){
/* If an error occurred while writing to the file, close it before
** returning. This way, SQLite uses the in-memory journal data to
** roll back changes made to the internal page-cache before this
** function was called. */
sqlite3OsClose(pReal);
p->pReal = 0;
}
}
}
return rc;
}
/*
** Close the file.
*/
static int jrnlClose(sqlite3_file *pJfd){
JournalFile *p = (JournalFile *)pJfd;
if( p->pReal ){
sqlite3OsClose(p->pReal);
}
sqlite3_free(p->zBuf);
return SQLITE_OK;
}
/*
** Read data from the file.
*/
static int jrnlRead(
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 */
){
int rc = SQLITE_OK;
JournalFile *p = (JournalFile *)pJfd;
if( p->pReal ){
rc = sqlite3OsRead(p->pReal, zBuf, iAmt, iOfst);
}else if( (iAmt+iOfst)>p->iSize ){
rc = SQLITE_IOERR_SHORT_READ;
}else{
memcpy(zBuf, &p->zBuf[iOfst], iAmt);
}
return rc;
}
/*
** Write data to the file.
*/
static int jrnlWrite(
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 */
){
int rc = SQLITE_OK;
JournalFile *p = (JournalFile *)pJfd;
if( !p->pReal && (iOfst+iAmt)>p->nBuf ){
rc = createFile(p);
}
if( rc==SQLITE_OK ){
if( p->pReal ){
rc = sqlite3OsWrite(p->pReal, zBuf, iAmt, iOfst);
}else{
memcpy(&p->zBuf[iOfst], zBuf, iAmt);
if( p->iSize<(iOfst+iAmt) ){
p->iSize = (iOfst+iAmt);
}
}
}
return rc;
}
/*
** Truncate the file.
*/
static int jrnlTruncate(sqlite3_file *pJfd, sqlite_int64 size){
int rc = SQLITE_OK;
JournalFile *p = (JournalFile *)pJfd;
if( p->pReal ){
rc = sqlite3OsTruncate(p->pReal, size);
}else if( size<p->iSize ){
p->iSize = size;
}
return rc;
}
/*
** Sync the file.
*/
static int jrnlSync(sqlite3_file *pJfd, int flags){
int rc;
JournalFile *p = (JournalFile *)pJfd;
if( p->pReal ){
rc = sqlite3OsSync(p->pReal, flags);
}else{
rc = SQLITE_OK;
}
return rc;
}
/*
** Query the size of the file in bytes.
*/
static int jrnlFileSize(sqlite3_file *pJfd, sqlite_int64 *pSize){
int rc = SQLITE_OK;
JournalFile *p = (JournalFile *)pJfd;
if( p->pReal ){
rc = sqlite3OsFileSize(p->pReal, pSize);
}else{
*pSize = (sqlite_int64) p->iSize;
}
return rc;
}
/*
** Table of methods for JournalFile sqlite3_file object.
*/
static struct sqlite3_io_methods JournalFileMethods = {
1, /* iVersion */
jrnlClose, /* xClose */
jrnlRead, /* xRead */
jrnlWrite, /* xWrite */
jrnlTruncate, /* xTruncate */
jrnlSync, /* xSync */
jrnlFileSize, /* xFileSize */
0, /* xLock */
0, /* xUnlock */
0, /* xCheckReservedLock */
0, /* xFileControl */
0, /* xSectorSize */
0, /* xDeviceCharacteristics */
0, /* xShmMap */
0, /* xShmLock */
0, /* xShmBarrier */
0 /* xShmUnmap */
};
/*
** Open a journal file.
*/
int sqlite3JournalOpen(
sqlite3_vfs *pVfs, /* The VFS to use for actual file I/O */
const char *zName, /* Name of the journal file */
sqlite3_file *pJfd, /* Preallocated, blank file handle */
int flags, /* Opening flags */
int nBuf /* Bytes buffered before opening the file */
){
JournalFile *p = (JournalFile *)pJfd;
memset(p, 0, sqlite3JournalSize(pVfs));
if( nBuf>0 ){
p->zBuf = sqlite3MallocZero(nBuf);
if( !p->zBuf ){
return SQLITE_NOMEM;
}
}else{
return sqlite3OsOpen(pVfs, zName, pJfd, flags, 0);
}
p->pMethod = &JournalFileMethods;
p->nBuf = nBuf;
p->flags = flags;
p->zJournal = zName;
p->pVfs = pVfs;
return SQLITE_OK;
}
/*
** If the argument p points to a JournalFile structure, and the underlying
** file has not yet been created, create it now.
*/
int sqlite3JournalCreate(sqlite3_file *p){
if( p->pMethods!=&JournalFileMethods ){
return SQLITE_OK;
}
return createFile((JournalFile *)p);
}
/*
** The file-handle passed as the only argument is guaranteed to be an open
** file. It may or may not be of class JournalFile. If the file is a
** JournalFile, and the underlying file on disk has not yet been opened,
** return 0. Otherwise, return 1.
*/
int sqlite3JournalExists(sqlite3_file *p){
return (p->pMethods!=&JournalFileMethods || ((JournalFile *)p)->pReal!=0);
}
/*
** Return the number of bytes required to store a JournalFile that uses vfs
** pVfs to create the underlying on-disk files.
*/
int sqlite3JournalSize(sqlite3_vfs *pVfs){
return (pVfs->szOsFile+sizeof(JournalFile));
}
#endif