• Matthew Bobrowski's avatar
    ext4: introduce direct I/O write using iomap infrastructure · 378f32ba
    Matthew Bobrowski authored
    This patch introduces a new direct I/O write path which makes use of
    the iomap infrastructure.
    
    All direct I/O writes are now passed from the ->write_iter() callback
    through to the new direct I/O handler ext4_dio_write_iter(). This
    function is responsible for calling into the iomap infrastructure via
    iomap_dio_rw().
    
    Code snippets from the existing direct I/O write code within
    ext4_file_write_iter() such as, checking whether the I/O request is
    unaligned asynchronous I/O, or whether the write will result in an
    overwrite have effectively been moved out and into the new direct I/O
    ->write_iter() handler.
    The block mapping flags that are eventually passed down to
    ext4_map_blocks() from the *_get_block_*() suite of routines have been
    taken out and introduced within ext4_iomap_alloc().
    
    For inode extension cases, ext4_handle_inode_extension() is
    effectively the function responsible for performing such metadata
    updates. This is called after iomap_dio_rw() has returned so that we
    can safely determine whether we need to potentially truncate any
    allocated blocks that may have been prepared for this direct I/O
    write. We don't perform the inode extension, or truncate operations
    from the ->end_io() handler as we don't have the original I/O 'length'
    available there. The ->end_io() however is responsible fo converting
    allocated unwritten extents to written extents.
    
    In the instance of a short write, we fallback and complete the
    remainder of the I/O using buffered I/O via
    ext4_buffered_write_iter().
    
    The existing buffer_head direct I/O implementation has been removed as
    it's now redundant.
    
    [ Fix up ext4_dio_write_iter() per Jan's comments at
      https://lore.kernel.org/r/20191105135932.GN22379@quack2.suse.cz -- TYT ]
    Signed-off-by: default avatarMatthew Bobrowski <mbobrowski@mbobrowski.org>
    Reviewed-by: default avatarJan Kara <jack@suse.cz>
    Reviewed-by: default avatarRitesh Harjani <riteshh@linux.ibm.com>
    Link: https://lore.kernel.org/r/e55db6f12ae6ff017f36774135e79f3e7b0333da.1572949325.git.mbobrowski@mbobrowski.orgSigned-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
    378f32ba
file.c 19.9 KB