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Comment:When available, use posix_fallocate() rather than ftruncate() to allocate space for mmap()ed -shm files, since posix_fallocate() gives an error if no disk space is available whereas ftruncate() is silent and leaves the system vulnerable to a SIGBUS upon first write to the mmap()ed region. Ticket [5eaa61ea1881040b17449ca043b6f8fd9ca55dc3]
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SHA1: 356259617cfad04492a02912fdf781f54a2b4494
User & Date: drh 2012-11-13 10:54:12
Context
2012-11-13
11:08
Use preprocessor macros to automatically detect whether or not posix_allocate() is available. (It is generally available on Linux but not on Mac.) Ticket [5eaa61ea1881040b17449ca043b6f8fd9ca55dc3] (Closed-Leaf check-in: 597333f1 user: drh tags: tkt-5eaa61ea18)
10:54
When available, use posix_fallocate() rather than ftruncate() to allocate space for mmap()ed -shm files, since posix_fallocate() gives an error if no disk space is available whereas ftruncate() is silent and leaves the system vulnerable to a SIGBUS upon first write to the mmap()ed region. Ticket [5eaa61ea1881040b17449ca043b6f8fd9ca55dc3] (check-in: 35625961 user: drh tags: tkt-5eaa61ea18)
2012-11-09
21:40
Only log unlink() errors if the error is something other than SQLITE_IOERR_DELETE_NOENT. The error is still reported up the stack, it is simply not added to the sqlite3_log(). (check-in: 5a3b07f0 user: drh tags: trunk)
Changes
Unified Diff Ignore Whitespace Patch
Changes to src/os_unix.c.
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        /* The requested memory region does not exist. If bExtend is set to
        ** false, exit early. *pp will be set to NULL and SQLITE_OK returned.
        **
        ** Alternatively, if bExtend is true, use ftruncate() to allocate
        ** the requested memory region.
        */
        if( !bExtend ) goto shmpage_out;







        if( robust_ftruncate(pShmNode->h, nByte) ){
          rc = unixLogError(SQLITE_IOERR_SHMSIZE, "ftruncate",
                            pShmNode->zFilename);
          goto shmpage_out;
        }

      }
    }

    /* Map the requested memory region into this processes address space. */
    apNew = (char **)sqlite3_realloc(
        pShmNode->apRegion, (iRegion+1)*sizeof(char *)
    );








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        /* The requested memory region does not exist. If bExtend is set to
        ** false, exit early. *pp will be set to NULL and SQLITE_OK returned.
        **
        ** Alternatively, if bExtend is true, use ftruncate() to allocate
        ** the requested memory region.
        */
        if( !bExtend ) goto shmpage_out;
#if defined(HAVE_POSIX_FALLOCATE) && HAVE_POSIX_FALLOCATE
        if( osFallocate(pShmNode->h, sStat.st_size, nByte)!=0 ){
          rc = unixLogError(SQLITE_IOERR_SHMSIZE, "fallocate",
                            pShmNode->zFilename);
          goto shmpage_out;
        }
#else
        if( robust_ftruncate(pShmNode->h, nByte) ){
          rc = unixLogError(SQLITE_IOERR_SHMSIZE, "ftruncate",
                            pShmNode->zFilename);
          goto shmpage_out;
        }
#endif
      }
    }

    /* Map the requested memory region into this processes address space. */
    apNew = (char **)sqlite3_realloc(
        pShmNode->apRegion, (iRegion+1)*sizeof(char *)
    );
︙︙
Changes to test/wal9.test.
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  COMMIT;
} {}

# Check file sizes are as expected. The real requirement here is that 
# the *shm file is now more than one chunk (>32KiB).
do_test 1.3 { file size test.db     } {1024}
do_test 1.4 { file size test.db-wal } {15421352}
do_test 1.5 { file size test.db-shm } {131072}

do_execsql_test 1.6 { PRAGMA wal_checkpoint } {0 14715 14715}

# At this point connection [db2] has mapped the first 32KB of the *shm file
# only. Because the entire WAL file has been checkpointed, it is not 
# necessary to map any more of the *-shm file to read or write the database
# (since all data will be read directly from the db file). 








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  COMMIT;
} {}

# Check file sizes are as expected. The real requirement here is that 
# the *shm file is now more than one chunk (>32KiB).
do_test 1.3 { file size test.db     } {1024}
do_test 1.4 { file size test.db-wal } {15421352}
do_test 1.5 { expr {[file size test.db-shm]>32768} } {1}

do_execsql_test 1.6 { PRAGMA wal_checkpoint } {0 14715 14715}

# At this point connection [db2] has mapped the first 32KB of the *shm file
# only. Because the entire WAL file has been checkpointed, it is not 
# necessary to map any more of the *-shm file to read or write the database
# (since all data will be read directly from the db file).
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      INSERT INTO t VALUES('hello');
    ROLLBACK;
  } db2
} {}
db2 close

finish_test









<

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      INSERT INTO t VALUES('hello');
    ROLLBACK;
  } db2
} {}
db2 close

finish_test