• Joel Becker's avatar
    ocfs2: Zero the tail cluster when extending past i_size. · 5693486b
    Joel Becker authored
    ocfs2's allocation unit is the cluster.  This can be larger than a block
    or even a memory page.  This means that a file may have many blocks in
    its last extent that are beyond the block containing i_size.  There also
    may be more unwritten extents after that.
    
    When ocfs2 grows a file, it zeros the entire cluster in order to ensure
    future i_size growth will see cleared blocks.  Unfortunately,
    block_write_full_page() drops the pages past i_size.  This means that
    ocfs2 is actually leaking garbage data into the tail end of that last
    cluster.  This is a bug.
    
    We adjust ocfs2_write_begin_nolock() and ocfs2_extend_file() to detect
    when a write or truncate is past i_size.  They will use
    ocfs2_zero_extend() to ensure the data is properly zeroed.
    
    Older versions of ocfs2_zero_extend() simply zeroed every block between
    i_size and the zeroing position.  This presumes three things:
    
    1) There is allocation for all of these blocks.
    2) The extents are not unwritten.
    3) The extents are not refcounted.
    
    (1) and (2) hold true for non-sparse filesystems, which used to be the
    only users of ocfs2_zero_extend().  (3) is another bug.
    
    Since we're now using ocfs2_zero_extend() for sparse filesystems as
    well, we teach ocfs2_zero_extend() to check every extent between
    i_size and the zeroing position.  If the extent is unwritten, it is
    ignored.  If it is refcounted, it is CoWed.  Then it is zeroed.
    Signed-off-by: default avatarJoel Becker <joel.becker@oracle.com>
    Cc: stable@kernel.org
    5693486b
file.h 2.62 KB