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Overview
Comment:Changes to wal.c so that SQLite can read even if the WAL file is opened read-only, provided the wal-index (shm file) is opened read/write.
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SHA1:932d19da73c9673cdd4cc01289b17761c23d23cb
User & Date: dan 2010-07-15 18:20:54
Context
2010-07-15
18:32
Optionally support shared-memory in /dev/shm or other tmpfs directory using an unsupported compile-time option. check-in: 534aab83 user: drh tags: trunk
18:20
Changes to wal.c so that SQLite can read even if the WAL file is opened read-only, provided the wal-index (shm file) is opened read/write. check-in: 932d19da user: dan tags: trunk
17:54
Handle the case where xShmMap returns SQLITE_BUSY. check-in: 75f53548 user: dan tags: trunk
Changes
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Changes to src/wal.c.

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  int nWiData;               /* Size of array apWiData */
  volatile u32 **apWiData;   /* Pointer to wal-index content in memory */
  u16 szPage;                /* Database page size */
  i16 readLock;              /* Which read lock is being held.  -1 for none */
  u8 exclusiveMode;          /* Non-zero if connection is in exclusive mode */
  u8 writeLock;              /* True if in a write transaction */
  u8 ckptLock;               /* True if holding a checkpoint lock */

  WalIndexHdr hdr;           /* Wal-index header for current transaction */
  const char *zWalName;      /* Name of WAL file */
  u32 nCkpt;                 /* Checkpoint sequence counter in the wal-header */
#ifdef SQLITE_DEBUG
  u8 lockError;              /* True if a locking error has occurred */
#endif
};
................................................................................
  pRet->readLock = -1;
  pRet->zWalName = zWalName;

  /* Open file handle on the write-ahead log file. */
  flags = (SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE|SQLITE_OPEN_WAL);
  rc = sqlite3OsOpen(pVfs, zWalName, pRet->pWalFd, flags, &flags);
  if( rc==SQLITE_OK && flags&SQLITE_OPEN_READONLY ){
    rc = SQLITE_CANTOPEN;
  }

  if( rc!=SQLITE_OK ){
    walIndexClose(pRet, 0);
    sqlite3OsClose(pRet->pWalFd);
    sqlite3_free(pRet);
  }else{
................................................................................
*/
int sqlite3WalBeginWriteTransaction(Wal *pWal){
  int rc;

  /* Cannot start a write transaction without first holding a read
  ** transaction. */
  assert( pWal->readLock>=0 );





  /* Only one writer allowed at a time.  Get the write lock.  Return
  ** SQLITE_BUSY if unable.
  */
  rc = walLockExclusive(pWal, WAL_WRITE_LOCK, 1);
  if( rc ){
    return rc;







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  int nWiData;               /* Size of array apWiData */
  volatile u32 **apWiData;   /* Pointer to wal-index content in memory */
  u16 szPage;                /* Database page size */
  i16 readLock;              /* Which read lock is being held.  -1 for none */
  u8 exclusiveMode;          /* Non-zero if connection is in exclusive mode */
  u8 writeLock;              /* True if in a write transaction */
  u8 ckptLock;               /* True if holding a checkpoint lock */
  u8 readOnly;               /* True if the WAL file is open read-only */
  WalIndexHdr hdr;           /* Wal-index header for current transaction */
  const char *zWalName;      /* Name of WAL file */
  u32 nCkpt;                 /* Checkpoint sequence counter in the wal-header */
#ifdef SQLITE_DEBUG
  u8 lockError;              /* True if a locking error has occurred */
#endif
};
................................................................................
  pRet->readLock = -1;
  pRet->zWalName = zWalName;

  /* Open file handle on the write-ahead log file. */
  flags = (SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE|SQLITE_OPEN_WAL);
  rc = sqlite3OsOpen(pVfs, zWalName, pRet->pWalFd, flags, &flags);
  if( rc==SQLITE_OK && flags&SQLITE_OPEN_READONLY ){
    pRet->readOnly = 1;
  }

  if( rc!=SQLITE_OK ){
    walIndexClose(pRet, 0);
    sqlite3OsClose(pRet->pWalFd);
    sqlite3_free(pRet);
  }else{
................................................................................
*/
int sqlite3WalBeginWriteTransaction(Wal *pWal){
  int rc;

  /* Cannot start a write transaction without first holding a read
  ** transaction. */
  assert( pWal->readLock>=0 );

  if( pWal->readOnly ){
    return SQLITE_READONLY;
  }

  /* Only one writer allowed at a time.  Get the write lock.  Return
  ** SQLITE_BUSY if unable.
  */
  rc = walLockExclusive(pWal, WAL_WRITE_LOCK, 1);
  if( rc ){
    return rc;

Changes to test/wal2.test.

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  do_test wal2-13.1.1 {
    list [file exists test.db-shm] [file exists test.db-wal]
  } {1 1}
  faultsim_save_and_close

  foreach {tn db_perm wal_perm shm_perm can_open can_read can_write} {
    2   00644   00644   00644   1   1   1
    3   00644   00400   00644   1   0   0
    4   00644   00644   00400   1   0   0
    5   00400   00644   00644   1   1   0

    7   00644   00000   00644   1   0   0
    8   00644   00644   00000   1   0   0
    9   00000   00644   00644   0   0   0
  } {







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  do_test wal2-13.1.1 {
    list [file exists test.db-shm] [file exists test.db-wal]
  } {1 1}
  faultsim_save_and_close

  foreach {tn db_perm wal_perm shm_perm can_open can_read can_write} {
    2   00644   00644   00644   1   1   1
    3   00644   00400   00644   1   1   0
    4   00644   00644   00400   1   0   0
    5   00400   00644   00644   1   1   0

    7   00644   00000   00644   1   0   0
    8   00644   00644   00000   1   0   0
    9   00000   00644   00644   0   0   0
  } {