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, 12 insertions, 2 deletions

diff --git a/fs/aio.c b/fs/aio.c
index a0ed6c7d2cd2..56b28607c32d 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1241,6 +1241,7 @@ SYSCALL_DEFINE1(io_destroy, aio_context_t, ctx)
 
 typedef ssize_t (aio_rw_op)(struct kiocb *, const struct iovec *,
                             unsigned long, loff_t);
+typedef ssize_t (rw_iter_op)(struct kiocb *, struct iov_iter *);
 
 static ssize_t aio_setup_vectored_rw(struct kiocb *kiocb,
                                      int rw, char __user *buf,
@@ -1298,7 +1299,9 @@ static ssize_t aio_run_iocb(struct kiocb *req, unsigned opcode,
         int rw;
         fmode_t mode;
         aio_rw_op *rw_op;
+        rw_iter_op *iter_op;
         struct iovec inline_vec, *iovec = &inline_vec;
+        struct iov_iter iter;
 
         switch (opcode) {
         case IOCB_CMD_PREAD:
@@ -1306,6 +1309,7 @@ static ssize_t aio_run_iocb(struct kiocb *req, unsigned opcode,
                 mode    = FMODE_READ;
                 rw      = READ;
                 rw_op   = file->f_op->aio_read;
+                iter_op = file->f_op->read_iter;
                 goto rw_common;
 
         case IOCB_CMD_PWRITE:
@@ -1313,12 +1317,13 @@ static ssize_t aio_run_iocb(struct kiocb *req, unsigned opcode,
                 mode    = FMODE_WRITE;
                 rw      = WRITE;
                 rw_op   = file->f_op->aio_write;
+                iter_op = file->f_op->write_iter;
                 goto rw_common;
 rw_common:
                 if (unlikely(!(file->f_mode & mode)))
                         return -EBADF;
 
-                if (!rw_op)
+                if (!rw_op && !iter_op)
                         return -EINVAL;
 
                 ret = (opcode == IOCB_CMD_PREADV ||
@@ -1347,7 +1352,12 @@ rw_common:
                 if (rw == WRITE)
                         file_start_write(file);
 
-                ret = rw_op(req, iovec, nr_segs, req->ki_pos);
+                if (iter_op) {
+                        iov_iter_init(&iter, rw, iovec, nr_segs, req->ki_nbytes);
+                        ret = iter_op(req, &iter);
+                } else {
+                        ret = rw_op(req, iovec, nr_segs, req->ki_pos);
+                }
 
                 if (rw == WRITE)
                         file_end_write(file);