/*+
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** 2007 August 22+
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**+
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** The author disclaims copyright to this source code.  In place of+
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** a legal notice, here is a blessing:+
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**+
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**    May you do good and not evil.+
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**    May you find forgiveness for yourself and forgive others.+
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**    May you share freely, never taking more than you give.+
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**+
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*************************************************************************+
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**+
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** @(#) $Id: journal.cpp 1282 2008-11-13 09:31:33Z LarsPson $+
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*/+
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+
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#ifdef SQLITE_ENABLE_ATOMIC_WRITE+
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+
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/*+
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** This file implements a special kind of sqlite3_file object used+
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** by SQLite to create journal files if the atomic-write optimization+
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** is enabled.+
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**+
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** The distinctive characteristic of this sqlite3_file is that the+
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** actual on disk file is created lazily. When the file is created,+
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** the caller specifies a buffer size for an in-memory buffer to+
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** be used to service read() and write() requests. The actual file+
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** on disk is not created or populated until either:+
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**+
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**   1) The in-memory representation grows too large for the allocated +
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**      buffer, or+
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**   2) The xSync() method is called.+
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*/+
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+
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#include "sqliteInt.h"+
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+
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+
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/*+
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** A JournalFile object is a subclass of sqlite3_file used by+
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** as an open file handle for journal files.+
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*/+
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struct JournalFile {+
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  sqlite3_io_methods *pMethod;    /* I/O methods on journal files */+
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  int nBuf;                       /* Size of zBuf[] in bytes */+
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  char *zBuf;                     /* Space to buffer journal writes */+
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  int iSize;                      /* Amount of zBuf[] currently used */+
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  int flags;                      /* xOpen flags */+
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  sqlite3_vfs *pVfs;              /* The "real" underlying VFS */+
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  sqlite3_file *pReal;            /* The "real" underlying file descriptor */+
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  const char *zJournal;           /* Name of the journal file */+
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};+
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typedef struct JournalFile JournalFile;+
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+
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/*+
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** If it does not already exists, create and populate the on-disk file +
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** for JournalFile p.+
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*/+
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static int createFile(JournalFile *p){+
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  int rc = SQLITE_OK;+
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  if( !p->pReal ){+
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    sqlite3_file *pReal = (sqlite3_file *)&p[1];+
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    rc = sqlite3OsOpen(p->pVfs, p->zJournal, pReal, p->flags, 0);+
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    if( rc==SQLITE_OK ){+
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      p->pReal = pReal;+
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      if( p->iSize>0 ){+
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        assert(p->iSize<=p->nBuf);+
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        rc = sqlite3OsWrite(p->pReal, p->zBuf, p->iSize, 0);+
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      }+
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    }+
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  }+
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  return rc;+
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}+
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+
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/*+
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** Close the file.+
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*/+
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static int jrnlClose(sqlite3_file *pJfd){+
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  JournalFile *p = (JournalFile *)pJfd;+
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  if( p->pReal ){+
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    sqlite3OsClose(p->pReal);+
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  }+
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  sqlite3_free(p->zBuf);+
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  return SQLITE_OK;+
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}+
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+
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/*+
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** Read data from the file.+
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*/+
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static int jrnlRead(+
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  sqlite3_file *pJfd,    /* The journal file from which to read */+
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  void *zBuf,            /* Put the results here */+
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  int iAmt,              /* Number of bytes to read */+
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  sqlite_int64 iOfst     /* Begin reading at this offset */+
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){+
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  int rc = SQLITE_OK;+
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  JournalFile *p = (JournalFile *)pJfd;+
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  if( p->pReal ){+
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    rc = sqlite3OsRead(p->pReal, zBuf, iAmt, iOfst);+
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  }else{+
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    assert( iAmt+iOfst<=p->iSize );+
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    memcpy(zBuf, &p->zBuf[iOfst], iAmt);+
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  }+
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  return rc;+
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}+
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+
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/*+
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** Write data to the file.+
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*/+
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static int jrnlWrite(+
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  sqlite3_file *pJfd,    /* The journal file into which to write */+
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  const void *zBuf,      /* Take data to be written from here */+
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  int iAmt,              /* Number of bytes to write */+
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  sqlite_int64 iOfst     /* Begin writing at this offset into the file */+
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){+
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  int rc = SQLITE_OK;+
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  JournalFile *p = (JournalFile *)pJfd;+
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  if( !p->pReal && (iOfst+iAmt)>p->nBuf ){+
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    rc = createFile(p);+
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  }+
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  if( rc==SQLITE_OK ){+
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    if( p->pReal ){+
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      rc = sqlite3OsWrite(p->pReal, zBuf, iAmt, iOfst);+
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    }else{+
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      memcpy(&p->zBuf[iOfst], zBuf, iAmt);+
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      if( p->iSize<(iOfst+iAmt) ){+
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        p->iSize = (iOfst+iAmt);+
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      }+
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    }+
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  }+
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  return rc;+
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}+
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+
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/*+
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** Truncate the file.+
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*/+
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static int jrnlTruncate(sqlite3_file *pJfd, sqlite_int64 size){+
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  int rc = SQLITE_OK;+
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  JournalFile *p = (JournalFile *)pJfd;+
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  if( p->pReal ){+
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    rc = sqlite3OsTruncate(p->pReal, size);+
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  }else if( size<p->iSize ){+
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    p->iSize = size;+
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  }+
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  return rc;+
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}+
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+
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/*+
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** Sync the file.+
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*/+
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static int jrnlSync(sqlite3_file *pJfd, int flags){+
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  int rc;+
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  JournalFile *p = (JournalFile *)pJfd;+
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  rc = createFile(p);+
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  if( rc==SQLITE_OK ){+
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    rc = sqlite3OsSync(p->pReal, flags);+
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  }+
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  return rc;+
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}+
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+
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/*+
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** Query the size of the file in bytes.+
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*/+
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static int jrnlFileSize(sqlite3_file *pJfd, sqlite_int64 *pSize){+
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  int rc = SQLITE_OK;+
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  JournalFile *p = (JournalFile *)pJfd;+
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  if( p->pReal ){+
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    rc = sqlite3OsFileSize(p->pReal, pSize);+
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  }else{+
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    *pSize = (sqlite_int64) p->iSize;+
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  }+
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  return rc;+
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}+
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+
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/*+
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** Table of methods for JournalFile sqlite3_file object.+
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*/+
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static struct sqlite3_io_methods JournalFileMethods = {+
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  1,             /* iVersion */+
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  jrnlClose,     /* xClose */+
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  jrnlRead,      /* xRead */+
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  jrnlWrite,     /* xWrite */+
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  jrnlTruncate,  /* xTruncate */+
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  jrnlSync,      /* xSync */+
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  jrnlFileSize,  /* xFileSize */+
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  0,             /* xLock */+
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  0,             /* xUnlock */+
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  0,             /* xCheckReservedLock */+
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  0,             /* xFileControl */+
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  0,             /* xSectorSize */+
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  0              /* xDeviceCharacteristics */+
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};+
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+
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/* +
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** Open a journal file.+
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*/+
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int sqlite3JournalOpen(+
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  sqlite3_vfs *pVfs,         /* The VFS to use for actual file I/O */+
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  const char *zName,         /* Name of the journal file */+
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  sqlite3_file *pJfd,        /* Preallocated, blank file handle */+
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  int flags,                 /* Opening flags */+
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  int nBuf                   /* Bytes buffered before opening the file */+
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){+
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  JournalFile *p = (JournalFile *)pJfd;+
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  memset(p, 0, sqlite3JournalSize(pVfs));+
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  if( nBuf>0 ){+
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    p->zBuf = sqlite3MallocZero(nBuf);+
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    if( !p->zBuf ){+
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      return SQLITE_NOMEM;+
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    }+
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  }else{+
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    return sqlite3OsOpen(pVfs, zName, pJfd, flags, 0);+
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  }+
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  p->pMethod = &JournalFileMethods;+
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  p->nBuf = nBuf;+
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  p->flags = flags;+
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  p->zJournal = zName;+
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  p->pVfs = pVfs;+
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  return SQLITE_OK;+
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}+
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+
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/*+
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** If the argument p points to a JournalFile structure, and the underlying+
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** file has not yet been created, create it now.+
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*/+
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int sqlite3JournalCreate(sqlite3_file *p){+
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  if( p->pMethods!=&JournalFileMethods ){+
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    return SQLITE_OK;+
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  }+
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  return createFile((JournalFile *)p);+
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}+
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+
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/* +
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** Return the number of bytes required to store a JournalFile that uses vfs+
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** pVfs to create the underlying on-disk files.+
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*/+
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int sqlite3JournalSize(sqlite3_vfs *pVfs){+
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  return (pVfs->szOsFile+sizeof(JournalFile));+
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}+
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#endif+
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