• Darrick J. Wong's avatar
    xfs: make struct xfs_buf_log_format have a consistent size · b7df5e92
    Darrick J. Wong authored
    Increase XFS_BLF_DATAMAP_SIZE by 1 to fill in the implied padding at the
    end of struct xfs_buf_log_format.  This makes the size consistent so
    that we can check it in xfs_ondisk.h, and will be needed once we start
    logging attribute values.
    
    On amd64 we get the following pahole:
    
    struct xfs_buf_log_format {
            short unsigned int         blf_type;       /*     0     2 */
            short unsigned int         blf_size;       /*     2     2 */
            short unsigned int         blf_flags;      /*     4     2 */
            short unsigned int         blf_len;        /*     6     2 */
            long long int              blf_blkno;      /*     8     8 */
            unsigned int               blf_map_size;   /*    16     4 */
            unsigned int               blf_data_map[16]; /*    20    64 */
            /* --- cacheline 1 boundary (64 bytes) was 20 bytes ago --- */
    
            /* size: 88, cachelines: 2, members: 7 */
            /* padding: 4 */
            /* last cacheline: 24 bytes */
    };
    
    But on i386 we get the following:
    
    struct xfs_buf_log_format {
            short unsigned int         blf_type;       /*     0     2 */
            short unsigned int         blf_size;       /*     2     2 */
            short unsigned int         blf_flags;      /*     4     2 */
            short unsigned int         blf_len;        /*     6     2 */
            long long int              blf_blkno;      /*     8     8 */
            unsigned int               blf_map_size;   /*    16     4 */
            unsigned int               blf_data_map[16]; /*    20    64 */
            /* --- cacheline 1 boundary (64 bytes) was 20 bytes ago --- */
    
            /* size: 84, cachelines: 2, members: 7 */
            /* last cacheline: 20 bytes */
    };
    
    Notice how the amd64 compiler inserts 4 bytes of padding to the end of
    the structure to ensure 8-byte alignment.  Prior to "xfs: fix memory
    corruption during remote attr value buffer invalidation" we would try to
    write to blf_data_map[17], which is harmless on amd64 but really bad on
    i386.
    
    This shouldn't cause any changes in the ondisk logging formats because
    the log code writes out the log vectors with the appropriate size for
    the log item's map_size, and log recovery treats the data_map array as a
    VLA.
    Signed-off-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
    Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
    b7df5e92
xfs_ondisk.h 7.02 KB