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Comment:On unix, if the *-shm file cannot be opened for read/write access, open it read-only and proceed as if the readonly_shm=1 URI option were specified.
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SHA3-256:ba718754fa5ab8596cb84b751051de98afa2706fe6c5df39ad6d925d790719ee
User & Date: dan 2017-11-07 15:43:52
Context
2017-11-07
21:15
Handle the race condition that may occur if another process connects and then checkpoints and truncates the wal file while a readonly-shm client is building its heap-memory wal-index. check-in: 5a6703fc user: dan tags: readonly-wal-recovery
15:43
On unix, if the *-shm file cannot be opened for read/write access, open it read-only and proceed as if the readonly_shm=1 URI option were specified. check-in: ba718754 user: dan tags: readonly-wal-recovery
09:08
Add fault-injection tests for the code on this branch. check-in: a7d949fb user: dan tags: readonly-wal-recovery
Changes
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Changes to src/os_unix.c.

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** file is created.  The shared memory will be simulated with heap memory.
*/
static int unixOpenSharedMemory(unixFile *pDbFd){
  struct unixShm *p = 0;          /* The connection to be opened */
  struct unixShmNode *pShmNode;   /* The underlying mmapped file */
  int rc = SQLITE_OK;             /* Result code */
  unixInodeInfo *pInode;          /* The inode of fd */
  char *zShmFilename;             /* Name of the file used for SHM */
  int nShmFilename;               /* Size of the SHM filename in bytes */

  /* Allocate space for the new unixShm object. */
  p = sqlite3_malloc64( sizeof(*p) );
  if( p==0 ) return SQLITE_NOMEM_BKPT;
  memset(p, 0, sizeof(*p));
  assert( pDbFd->pShm==0 );
................................................................................
#endif
    pShmNode = sqlite3_malloc64( sizeof(*pShmNode) + nShmFilename );
    if( pShmNode==0 ){
      rc = SQLITE_NOMEM_BKPT;
      goto shm_open_err;
    }
    memset(pShmNode, 0, sizeof(*pShmNode)+nShmFilename);
    zShmFilename = pShmNode->zFilename = (char*)&pShmNode[1];
#ifdef SQLITE_SHM_DIRECTORY
    sqlite3_snprintf(nShmFilename, zShmFilename, 
                     SQLITE_SHM_DIRECTORY "/sqlite-shm-%x-%x",
                     (u32)sStat.st_ino, (u32)sStat.st_dev);
#else
    sqlite3_snprintf(nShmFilename, zShmFilename, "%s-shm", zBasePath);
    sqlite3FileSuffix3(pDbFd->zPath, zShmFilename);
#endif
    pShmNode->h = -1;
    pDbFd->pInode->pShmNode = pShmNode;
    pShmNode->pInode = pDbFd->pInode;
    if( sqlite3GlobalConfig.bCoreMutex ){
      pShmNode->mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_FAST);
      if( pShmNode->mutex==0 ){
        rc = SQLITE_NOMEM_BKPT;
        goto shm_open_err;
      }
    }

    if( pInode->bProcessLock==0 ){
      int openFlags = O_RDWR | O_CREAT;
      if( sqlite3_uri_boolean(pDbFd->zPath, "readonly_shm", 0) ){
        openFlags = O_RDONLY;
        pShmNode->isReadonly = 1;

      }

      pShmNode->h = robust_open(zShmFilename, openFlags, (sStat.st_mode&0777));
      if( pShmNode->h<0 ){
        rc = unixLogError(SQLITE_CANTOPEN_BKPT, "open", zShmFilename);
        goto shm_open_err;


      }

      /* If this process is running as root, make sure that the SHM file
      ** is owned by the same user that owns the original database.  Otherwise,
      ** the original owner will not be able to connect.
      */
      robustFchown(pShmNode->h, sStat.st_uid, sStat.st_gid);







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** file is created.  The shared memory will be simulated with heap memory.
*/
static int unixOpenSharedMemory(unixFile *pDbFd){
  struct unixShm *p = 0;          /* The connection to be opened */
  struct unixShmNode *pShmNode;   /* The underlying mmapped file */
  int rc = SQLITE_OK;             /* Result code */
  unixInodeInfo *pInode;          /* The inode of fd */
  char *zShm;             /* Name of the file used for SHM */
  int nShmFilename;               /* Size of the SHM filename in bytes */

  /* Allocate space for the new unixShm object. */
  p = sqlite3_malloc64( sizeof(*p) );
  if( p==0 ) return SQLITE_NOMEM_BKPT;
  memset(p, 0, sizeof(*p));
  assert( pDbFd->pShm==0 );
................................................................................
#endif
    pShmNode = sqlite3_malloc64( sizeof(*pShmNode) + nShmFilename );
    if( pShmNode==0 ){
      rc = SQLITE_NOMEM_BKPT;
      goto shm_open_err;
    }
    memset(pShmNode, 0, sizeof(*pShmNode)+nShmFilename);
    zShm = pShmNode->zFilename = (char*)&pShmNode[1];
#ifdef SQLITE_SHM_DIRECTORY
    sqlite3_snprintf(nShmFilename, zShm, 
                     SQLITE_SHM_DIRECTORY "/sqlite-shm-%x-%x",
                     (u32)sStat.st_ino, (u32)sStat.st_dev);
#else
    sqlite3_snprintf(nShmFilename, zShm, "%s-shm", zBasePath);
    sqlite3FileSuffix3(pDbFd->zPath, zShm);
#endif
    pShmNode->h = -1;
    pDbFd->pInode->pShmNode = pShmNode;
    pShmNode->pInode = pDbFd->pInode;
    if( sqlite3GlobalConfig.bCoreMutex ){
      pShmNode->mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_FAST);
      if( pShmNode->mutex==0 ){
        rc = SQLITE_NOMEM_BKPT;
        goto shm_open_err;
      }
    }

    if( pInode->bProcessLock==0 ){

      if( 0==sqlite3_uri_boolean(pDbFd->zPath, "readonly_shm", 0) ){


        pShmNode->h = robust_open(zShm, O_RDWR|O_CREAT, (sStat.st_mode&0777));
      }
      if( pShmNode->h<0 ){
        pShmNode->h = robust_open(zShm, O_RDONLY, (sStat.st_mode&0777));
        if( pShmNode->h<0 ){
          rc = unixLogError(SQLITE_CANTOPEN_BKPT, "open", zShm);
          goto shm_open_err;
        }
        pShmNode->isReadonly = 1;
      }

      /* If this process is running as root, make sure that the SHM file
      ** is owned by the same user that owns the original database.  Otherwise,
      ** the original owner will not be able to connect.
      */
      robustFchown(pShmNode->h, sStat.st_uid, sStat.st_gid);

Changes to test/wal2.test.

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    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
  } {
    faultsim_restore







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    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   1   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
  } {
    faultsim_restore

Changes to test/walro.test.

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    set {} {}
  } {}
  do_test 1.2.8 { sql1 "SELECT * FROM t1" } {a b c d e f g h i j k l}

  # Now check that if the readonly_shm option is not supplied, or if it
  # is set to zero, it is not possible to connect to the database without
  # read-write access to the shm.




  do_test 1.3.1 {
    code1 { db close }
    code1 { sqlite3 db test.db }
    csql1 { SELECT * FROM t1 }
  } {1 {unable to open database file}}

  # Also test that if the -shm file can be opened for read/write access,
  # it is not if readonly_shm=1 is present in the URI.
  do_test 1.3.2.1 {
    code1 { db close }
    code2 { db2 close }
    file exists test.db-shm







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    set {} {}
  } {}
  do_test 1.2.8 { sql1 "SELECT * FROM t1" } {a b c d e f g h i j k l}

  # Now check that if the readonly_shm option is not supplied, or if it
  # is set to zero, it is not possible to connect to the database without
  # read-write access to the shm.
  # 
  # UPDATE: os_unix.c now opens the *-shm file in readonly mode 
  # automatically.
  #
  do_test 1.3.1 {
    code1 { db close }
    code1 { sqlite3 db test.db }
    csql1 { SELECT * FROM t1 }
  } {0 {a b c d e f g h i j k l}}

  # Also test that if the -shm file can be opened for read/write access,
  # it is not if readonly_shm=1 is present in the URI.
  do_test 1.3.2.1 {
    code1 { db close }
    code2 { db2 close }
    file exists test.db-shm