new methods: ->read_iter() and ->write_iter()

Beginning to introduce those.  Just the callers for now, and it's
clumsier than it'll eventually become; once we finish converting
aio_read and aio_write instances, the things will get nicer.

For now, these guys are in parallel to ->aio_read() and ->aio_write();
they take iocb and iov_iter, with everything in iov_iter already
validated.  File offset is passed in iocb->ki_pos, iov/nr_segs -
in iov_iter.

Main concerns in that series are stack footprint and ability to
split the damn thing cleanly.

[fix from Peter Ujfalusi <peter.ujfalusi@ti.com> folded]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 4 insertions, 2 deletions

diff --git a/fs/open.c b/fs/open.c
index 39d3d0468ee6..36662d036237 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -725,9 +725,11 @@ static int do_dentry_open(struct file *f,
         }
         if ((f->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
                 i_readcount_inc(inode);
-        if ((f->f_mode & FMODE_READ) && likely(f->f_op->read || f->f_op->aio_read))
+        if ((f->f_mode & FMODE_READ) &&
+             likely(f->f_op->read || f->f_op->aio_read || f->f_op->read_iter))
                 f->f_mode |= FMODE_CAN_READ;
-        if ((f->f_mode & FMODE_WRITE) && likely(f->f_op->write || f->f_op->aio_write))
+        if ((f->f_mode & FMODE_WRITE) &&
+             likely(f->f_op->write || f->f_op->aio_write || f->f_op->write_iter))
                 f->f_mode |= FMODE_CAN_WRITE;
 
         f->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);