• Allison Henderson's avatar
    ext4: Add new ext4_discard_partial_page_buffers routines · 4e96b2db
    Allison Henderson authored
    This patch adds two new routines: ext4_discard_partial_page_buffers
    and ext4_discard_partial_page_buffers_no_lock.
    
    The ext4_discard_partial_page_buffers routine is a wrapper
    function to ext4_discard_partial_page_buffers_no_lock.
    The wrapper function locks the page and passes it to
    ext4_discard_partial_page_buffers_no_lock.
    Calling functions that already have the page locked can call
    ext4_discard_partial_page_buffers_no_lock directly.
    
    The ext4_discard_partial_page_buffers_no_lock function
    zeros a specified range in a page, and unmaps the
    corresponding buffer heads.  Only block aligned regions of the
    page will have their buffer heads unmapped.  Unblock aligned regions
    will be mapped if needed so that they can be updated with the
    partial zero out.  This function is meant to
    be used to update a page and its buffer heads to be zeroed
    and unmapped when the corresponding blocks have been released
    or will be released.
    
    This routine is used in the following scenarios:
    * A hole is punched and the non page aligned regions
      of the head and tail of the hole need to be discarded
    
    * The file is truncated and the partial page beyond EOF needs
      to be discarded
    
    * The end of a hole is in the same page as EOF.  After the
      page is flushed, the partial page beyond EOF needs to be
      discarded.
    
    * A write operation begins or ends inside a hole and the partial
      page appearing before or after the write needs to be discarded
    
    * A write operation extends EOF and the partial page beyond EOF
      needs to be discarded
    
    This function takes a flag EXT4_DISCARD_PARTIAL_PG_ZERO_UNMAPPED
    which is used when a write operation begins or ends in a hole.
    When the EXT4_DISCARD_PARTIAL_PG_ZERO_UNMAPPED flag is used, only
    buffer heads that are already unmapped will have the corresponding
    regions of the page zeroed.
    Signed-off-by: default avatarAllison Henderson <achender@linux.vnet.ibm.com>
    Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
    4e96b2db
ext4.h 79.7 KB