fs: pull iov_iter use higher up the stack

Right now only callers of generic_perform_write() pack their iovec
arguments into an iov_iter structure.  All the callers higher up in the
stack work on raw iovec arguments.

This patch introduces the use of the iov_iter abstraction higher up the
stack.  Private generic path functions are changed to operation on
iov_iter instead of on raw iovecs.  Exported interfaces that take iovecs
immediately pack their arguments into an iov_iter and call into the
shared functions.

File operation struct functions are added with iov_iter as an argument
so that callers to the generic file system functions can specify
abstract memory rather than iovec arrays only.

Almost all of this patch only transforms arguments and shouldn't change
functionality.  The buffered read path is the exception.  We add a
read_actor function which uses the iov_iter helper functions instead of
operating on each individual iovec element.  This may improve
performance as the iov_iter helper can copy multiple iovec elements from
one mapped page cache page.

As always, the direct IO path is special.  Sadly, it may still be
cleanest to have it work on the underlying memory structures directly
instead of working through the iov_iter abstraction.

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Cc: Zach Brown <zab@zabbo.net>
modified for Mako from LKML reference

Signed-off-by: faux123 <reioux@gmail.com>
aio: add aio_kernel_() interface

This adds an interface that lets kernel callers submit aio iocbs without
going through the user space syscalls.  This lets kernel callers avoid
the management limits and overhead of the context.  It will also let us
integrate aio operations with other kernel apis that the user space
interface doesn't have access to.

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Cc: Zach Brown <zab@zabbo.net>
modified for Mako from LKML reference

Signed-off-by: faux123 <reioux@gmail.com>
aio: add aio support for iov_iter arguments

This adds iocb cmds which specify that memory is held in iov_iter
structures.  This lets kernel callers specify memory that can be
expressed in an iov_iter, which includes pages in bio_vec arrays.

Only kernel callers can provide an iov_iter so it doesn't make a lot of
sense to expose the IOCB_CMD values for this as part of the user space
ABI.

But kernel callers should also be able to perform the usual aio
operations which suggests using the the existing operation namespace and
support code.

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Cc: Zach Brown <zab@zabbo.net>
modified for Mako from LKML reference

Signed-off-by: faux123 <reioux@gmail.com>
bio: add bvec_length(), like iov_length()

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Cc: Zach Brown <zab@zabbo.net>
modified for Mako from LKML reference

Signed-off-by: faux123 <reioux@gmail.com>
loop: use aio to perform io on the underlying file

This uses the new kernel aio interface to process loopback IO by
submitting concurrent direct aio.  Previously loop's IO was serialized
by synchronous processing in a thread.

The aio operations specify the memory for the IO with the bio_vec arrays
directly instead of mappings of the pages.

The use of aio operations is enabled when the backing file supports the
read_iter, write_iter and direct_IO methods.

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Cc: Zach Brown <zab@zabbo.net>
modified for Mako from LKML reference

Signed-off-by: faux123 <reioux@gmail.com>
fs: create file_readable() and file_writable() functions

Create functions to simplify if file_ops contain either a read
or aio_read op, or likewise write or aio_write. We will be adding
read_iter and write_iter and don't need to be complicating the code
in multiple places.

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
modified for Mako from LKML reference

Signed-off-by: faux123 <reioux@gmail.com>
ext4: add support for read_iter and write_iter

use the generic_file_read_iter(), create ext4_file_write_iter() based on
ext4_file_write(), and make ext4_file_write() a wrapper around
ext4_file_write_iter().

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Cc: Zach Brown <zab@zabbo.net>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: linux-ext4@vger.kernel.org
modified for Mako from LKML reference

Signed-off-by: faux123 <reioux@gmail.com>
tmpfs: add support for read_iter and write_iter

Convert tmpfs do_shmem_file_read() to shmem_file_read_iter().
Make file_read_iter_actor() global so tmpfs can use it too: delete
file_read_actor(), which was made global in 2.4.4 for use by tmpfs.
Replace tmpfs generic_file_aio_write() by generic_file_write_iter().

Signed-off-by: Hugh Dickins <hughd@google.com>
modified for Mako from LKML reference

Signed-off-by: faux123 <reioux@gmail.com>
exfat_super: add AIO optimization support

Signed-off-by: Paul Reioux <reioux@gmail.com>
fs: pull iov_iter use higher up the stack

Right now only callers of generic_perform_write() pack their iovec
arguments into an iov_iter structure.  All the callers higher up in the
stack work on raw iovec arguments.

This patch introduces the use of the iov_iter abstraction higher up the
stack.  Private generic path functions are changed to operation on
iov_iter instead of on raw iovecs.  Exported interfaces that take iovecs
immediately pack their arguments into an iov_iter and call into the
shared functions.

File operation struct functions are added with iov_iter as an argument
so that callers to the generic file system functions can specify
abstract memory rather than iovec arrays only.

Almost all of this patch only transforms arguments and shouldn't change
functionality.  The buffered read path is the exception.  We add a
read_actor function which uses the iov_iter helper functions instead of
operating on each individual iovec element.  This may improve
performance as the iov_iter helper can copy multiple iovec elements from
one mapped page cache page.

As always, the direct IO path is special.  Sadly, it may still be
cleanest to have it work on the underlying memory structures directly
instead of working through the iov_iter abstraction.

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Cc: Zach Brown <zab@zabbo.net>
modified for Mako from LKML reference

Signed-off-by: faux123 <reioux@gmail.com>

Conflicts:
	mm/filemap.c