• O
    [PATCH] writeback: fix range handling · 111ebb6e
    OGAWA Hirofumi 提交于
    When a writeback_control's `start' and `end' fields are used to
    indicate a one-byte-range starting at file offset zero, the required
    values of .start=0,.end=0 mean that the ->writepages() implementation
    has no way of telling that it is being asked to perform a range
    request.  Because we're currently overloading (start == 0 && end == 0)
    to mean "this is not a write-a-range request".
    
    To make all this sane, the patch changes range of writeback_control.
    
    So caller does: If it is calling ->writepages() to write pages, it
    sets range (range_start/end or range_cyclic) always.
    
    And if range_cyclic is true, ->writepages() thinks the range is
    cyclic, otherwise it just uses range_start and range_end.
    
    This patch does,
    
        - Add LLONG_MAX, LLONG_MIN, ULLONG_MAX to include/linux/kernel.h
          -1 is usually ok for range_end (type is long long). But, if someone did,
    
    		range_end += val;		range_end is "val - 1"
    		u64val = range_end >> bits;	u64val is "~(0ULL)"
    
          or something, they are wrong. So, this adds LLONG_MAX to avoid nasty
          things, and uses LLONG_MAX for range_end.
    
        - All callers of ->writepages() sets range_start/end or range_cyclic.
    
        - Fix updates of ->writeback_index. It seems already bit strange.
          If it starts at 0 and ended by check of nr_to_write, this last
          index may reduce chance to scan end of file.  So, this updates
          ->writeback_index only if range_cyclic is true or whole-file is
          scanned.
    Signed-off-by: NOGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
    Cc: Nathan Scott <nathans@sgi.com>
    Cc: Anton Altaparmakov <aia21@cantab.net>
    Cc: Steven French <sfrench@us.ibm.com>
    Cc: "Vladimir V. Saveliev" <vs@namesys.com>
    Signed-off-by: NAndrew Morton <akpm@osdl.org>
    Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
    111ebb6e
kernel.h 9.8 KB