[PATCH 0/3] block: loop: switch to VFS ITER_BVEC

[Ming Lei <ming.lei@canonical.com>]

This patchset uses VFS ITER_BVEC for reading/writing
loop backing file, and basically it is a rewriting of
Christoph Hellwig's post in [1].

With this change, loop code becomes much cleaner than before,
and it is also a simplication for reading/writing backing file
inside kernel.

Another benifit is that one extra page copy is avoided for
READ in case of none_transfer. 

This patchset passes xfstest test(ext4, -g auto) over loop block
devices. 

The patch 3/3 depends a bit on Christoph's kiocb split patches
which have been in -next for a while, so tree dependency(not build
depend, just behaviour depend) should be considered if it is to
be merged to 4.0. 

The next step is to add AIO/O_DIRECT support for reading/writing
backing file against this patchset if no one objects, so that double
cache can be avoided.

[1], loop: convert to vfs_bvec_write
http://marc.info/?l=linux-fsdevel&m=142159370107007&w=2

[2], kiocb split patchset
http://marc.info/?t=142238145800004&r=1&w=2

Thanks,
Ming Lei