btrfs: refactor btrfs_dio_iomap_end()

That function has the following problems:

- Read/write handling scattered across different locations
  E.g. At the beginning there is a dedicated hole read handling, but
  later short read handling is at an if() branch.

- Modifying of @pos and @length parameter for short read
  Although it's completely fine to modify those parameters as they are
  passed by value, but it can still be confusing to read.  As normally
  we would assume @pos and @length to be the original range.

  But for short IO handling we modify @pos/@length, and completely
  ignore @written.

- Unnecessary split for ordered extent and changeset handling
  Both OE and changeset are only for writes, but they are handled in two
  different if (write) {} blocks.

Refactor the function so that:

- Handling of reads and writes are concentrated in their code block
  Now the handling of reads are in its own small if () branch.

  Leaving the more complex writes handling to take the remaining
  function, and reduce the indent level.

  This also removes all unnecessary "if (write)" checks.

- Do not modify @pos and @length
  Let short IO handling to manually calculate the remaining range.

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

0 files changed, 0 insertions, 0 deletions