sl@0: /*
sl@0: ** 2007 August 22
sl@0: **
sl@0: ** The author disclaims copyright to this source code.  In place of
sl@0: ** a legal notice, here is a blessing:
sl@0: **
sl@0: **    May you do good and not evil.
sl@0: **    May you find forgiveness for yourself and forgive others.
sl@0: **    May you share freely, never taking more than you give.
sl@0: **
sl@0: *************************************************************************
sl@0: **
sl@0: ** @(#) $Id: journal.c,v 1.8 2008/05/01 18:01:47 drh Exp $
sl@0: */
sl@0: 
sl@0: #ifdef SQLITE_ENABLE_ATOMIC_WRITE
sl@0: 
sl@0: /*
sl@0: ** This file implements a special kind of sqlite3_file object used
sl@0: ** by SQLite to create journal files if the atomic-write optimization
sl@0: ** is enabled.
sl@0: **
sl@0: ** The distinctive characteristic of this sqlite3_file is that the
sl@0: ** actual on disk file is created lazily. When the file is created,
sl@0: ** the caller specifies a buffer size for an in-memory buffer to
sl@0: ** be used to service read() and write() requests. The actual file
sl@0: ** on disk is not created or populated until either:
sl@0: **
sl@0: **   1) The in-memory representation grows too large for the allocated 
sl@0: **      buffer, or
sl@0: **   2) The xSync() method is called.
sl@0: */
sl@0: 
sl@0: #include "sqliteInt.h"
sl@0: 
sl@0: 
sl@0: /*
sl@0: ** A JournalFile object is a subclass of sqlite3_file used by
sl@0: ** as an open file handle for journal files.
sl@0: */
sl@0: struct JournalFile {
sl@0:   sqlite3_io_methods *pMethod;    /* I/O methods on journal files */
sl@0:   int nBuf;                       /* Size of zBuf[] in bytes */
sl@0:   char *zBuf;                     /* Space to buffer journal writes */
sl@0:   int iSize;                      /* Amount of zBuf[] currently used */
sl@0:   int flags;                      /* xOpen flags */
sl@0:   sqlite3_vfs *pVfs;              /* The "real" underlying VFS */
sl@0:   sqlite3_file *pReal;            /* The "real" underlying file descriptor */
sl@0:   const char *zJournal;           /* Name of the journal file */
sl@0: };
sl@0: typedef struct JournalFile JournalFile;
sl@0: 
sl@0: /*
sl@0: ** If it does not already exists, create and populate the on-disk file 
sl@0: ** for JournalFile p.
sl@0: */
sl@0: static int createFile(JournalFile *p){
sl@0:   int rc = SQLITE_OK;
sl@0:   if( !p->pReal ){
sl@0:     sqlite3_file *pReal = (sqlite3_file *)&p[1];
sl@0:     rc = sqlite3OsOpen(p->pVfs, p->zJournal, pReal, p->flags, 0);
sl@0:     if( rc==SQLITE_OK ){
sl@0:       p->pReal = pReal;
sl@0:       if( p->iSize>0 ){
sl@0:         assert(p->iSize<=p->nBuf);
sl@0:         rc = sqlite3OsWrite(p->pReal, p->zBuf, p->iSize, 0);
sl@0:       }
sl@0:     }
sl@0:   }
sl@0:   return rc;
sl@0: }
sl@0: 
sl@0: /*
sl@0: ** Close the file.
sl@0: */
sl@0: static int jrnlClose(sqlite3_file *pJfd){
sl@0:   JournalFile *p = (JournalFile *)pJfd;
sl@0:   if( p->pReal ){
sl@0:     sqlite3OsClose(p->pReal);
sl@0:   }
sl@0:   sqlite3_free(p->zBuf);
sl@0:   return SQLITE_OK;
sl@0: }
sl@0: 
sl@0: /*
sl@0: ** Read data from the file.
sl@0: */
sl@0: static int jrnlRead(
sl@0:   sqlite3_file *pJfd,    /* The journal file from which to read */
sl@0:   void *zBuf,            /* Put the results here */
sl@0:   int iAmt,              /* Number of bytes to read */
sl@0:   sqlite_int64 iOfst     /* Begin reading at this offset */
sl@0: ){
sl@0:   int rc = SQLITE_OK;
sl@0:   JournalFile *p = (JournalFile *)pJfd;
sl@0:   if( p->pReal ){
sl@0:     rc = sqlite3OsRead(p->pReal, zBuf, iAmt, iOfst);
sl@0:   }else{
sl@0:     assert( iAmt+iOfst<=p->iSize );
sl@0:     memcpy(zBuf, &p->zBuf[iOfst], iAmt);
sl@0:   }
sl@0:   return rc;
sl@0: }
sl@0: 
sl@0: /*
sl@0: ** Write data to the file.
sl@0: */
sl@0: static int jrnlWrite(
sl@0:   sqlite3_file *pJfd,    /* The journal file into which to write */
sl@0:   const void *zBuf,      /* Take data to be written from here */
sl@0:   int iAmt,              /* Number of bytes to write */
sl@0:   sqlite_int64 iOfst     /* Begin writing at this offset into the file */
sl@0: ){
sl@0:   int rc = SQLITE_OK;
sl@0:   JournalFile *p = (JournalFile *)pJfd;
sl@0:   if( !p->pReal && (iOfst+iAmt)>p->nBuf ){
sl@0:     rc = createFile(p);
sl@0:   }
sl@0:   if( rc==SQLITE_OK ){
sl@0:     if( p->pReal ){
sl@0:       rc = sqlite3OsWrite(p->pReal, zBuf, iAmt, iOfst);
sl@0:     }else{
sl@0:       memcpy(&p->zBuf[iOfst], zBuf, iAmt);
sl@0:       if( p->iSize<(iOfst+iAmt) ){
sl@0:         p->iSize = (iOfst+iAmt);
sl@0:       }
sl@0:     }
sl@0:   }
sl@0:   return rc;
sl@0: }
sl@0: 
sl@0: /*
sl@0: ** Truncate the file.
sl@0: */
sl@0: static int jrnlTruncate(sqlite3_file *pJfd, sqlite_int64 size){
sl@0:   int rc = SQLITE_OK;
sl@0:   JournalFile *p = (JournalFile *)pJfd;
sl@0:   if( p->pReal ){
sl@0:     rc = sqlite3OsTruncate(p->pReal, size);
sl@0:   }else if( size<p->iSize ){
sl@0:     p->iSize = size;
sl@0:   }
sl@0:   return rc;
sl@0: }
sl@0: 
sl@0: /*
sl@0: ** Sync the file.
sl@0: */
sl@0: static int jrnlSync(sqlite3_file *pJfd, int flags){
sl@0:   int rc;
sl@0:   JournalFile *p = (JournalFile *)pJfd;
sl@0:   if( p->pReal ){
sl@0:     rc = sqlite3OsSync(p->pReal, flags);
sl@0:   }else{
sl@0:     rc = SQLITE_OK;
sl@0:   }
sl@0:   return rc;
sl@0: }
sl@0: 
sl@0: /*
sl@0: ** Query the size of the file in bytes.
sl@0: */
sl@0: static int jrnlFileSize(sqlite3_file *pJfd, sqlite_int64 *pSize){
sl@0:   int rc = SQLITE_OK;
sl@0:   JournalFile *p = (JournalFile *)pJfd;
sl@0:   if( p->pReal ){
sl@0:     rc = sqlite3OsFileSize(p->pReal, pSize);
sl@0:   }else{
sl@0:     *pSize = (sqlite_int64) p->iSize;
sl@0:   }
sl@0:   return rc;
sl@0: }
sl@0: 
sl@0: /*
sl@0: ** Table of methods for JournalFile sqlite3_file object.
sl@0: */
sl@0: static struct sqlite3_io_methods JournalFileMethods = {
sl@0:   1,             /* iVersion */
sl@0:   jrnlClose,     /* xClose */
sl@0:   jrnlRead,      /* xRead */
sl@0:   jrnlWrite,     /* xWrite */
sl@0:   jrnlTruncate,  /* xTruncate */
sl@0:   jrnlSync,      /* xSync */
sl@0:   jrnlFileSize,  /* xFileSize */
sl@0:   0,             /* xLock */
sl@0:   0,             /* xUnlock */
sl@0:   0,             /* xCheckReservedLock */
sl@0:   0,             /* xFileControl */
sl@0:   0,             /* xSectorSize */
sl@0:   0              /* xDeviceCharacteristics */
sl@0: };
sl@0: 
sl@0: /* 
sl@0: ** Open a journal file.
sl@0: */
sl@0: int sqlite3JournalOpen(
sl@0:   sqlite3_vfs *pVfs,         /* The VFS to use for actual file I/O */
sl@0:   const char *zName,         /* Name of the journal file */
sl@0:   sqlite3_file *pJfd,        /* Preallocated, blank file handle */
sl@0:   int flags,                 /* Opening flags */
sl@0:   int nBuf                   /* Bytes buffered before opening the file */
sl@0: ){
sl@0:   JournalFile *p = (JournalFile *)pJfd;
sl@0:   memset(p, 0, sqlite3JournalSize(pVfs));
sl@0:   if( nBuf>0 ){
sl@0:     p->zBuf = sqlite3MallocZero(nBuf);
sl@0:     if( !p->zBuf ){
sl@0:       return SQLITE_NOMEM;
sl@0:     }
sl@0:   }else{
sl@0:     return sqlite3OsOpen(pVfs, zName, pJfd, flags, 0);
sl@0:   }
sl@0:   p->pMethod = &JournalFileMethods;
sl@0:   p->nBuf = nBuf;
sl@0:   p->flags = flags;
sl@0:   p->zJournal = zName;
sl@0:   p->pVfs = pVfs;
sl@0:   return SQLITE_OK;
sl@0: }
sl@0: 
sl@0: /*
sl@0: ** If the argument p points to a JournalFile structure, and the underlying
sl@0: ** file has not yet been created, create it now.
sl@0: */
sl@0: int sqlite3JournalCreate(sqlite3_file *p){
sl@0:   if( p->pMethods!=&JournalFileMethods ){
sl@0:     return SQLITE_OK;
sl@0:   }
sl@0:   return createFile((JournalFile *)p);
sl@0: }
sl@0: 
sl@0: /* 
sl@0: ** Return the number of bytes required to store a JournalFile that uses vfs
sl@0: ** pVfs to create the underlying on-disk files.
sl@0: */
sl@0: int sqlite3JournalSize(sqlite3_vfs *pVfs){
sl@0:   return (pVfs->szOsFile+sizeof(JournalFile));
sl@0: }
sl@0: #endif