journal.c
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上传日期:2022-01-25
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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.
- **
- *************************************************************************
- **
- ** @(#) $Id: journal.c,v 1.7 2007/09/06 13:49:37 drh Exp $
- */
- #ifdef SQLITE_ENABLE_ATOMIC_WRITE
- /*
- ** 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 xSync() method is called.
- */
- #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);
- }
- }
- }
- 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{
- assert( iAmt+iOfst<=p->iSize );
- 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;
- rc = createFile(p);
- if( rc==SQLITE_OK ){
- rc = sqlite3OsSync(p->pReal, flags);
- }
- 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 */
- };
- /*
- ** 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);
- }
- /*
- ** 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