[PATCH 002/437] fs: add generic read/write iterator helpers

[Jens Axboe]

We already do this internally for vfs_readv() and vfs_writev(), which
need to check what method to use. Add generic helpers for this so that
drivers can do this themselves, if they haven't converted to using the
read/write iterator file_operations hooks just yet.

Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
 fs/read_write.c    | 18 ++++++++++++++++++
 include/linux/fs.h |  6 ++++++
 2 files changed, 24 insertions(+)

diff --git a/fs/read_write.c b/fs/read_write.c
index 82ec75937b08..1d035293607b 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -802,6 +802,24 @@ static ssize_t do_loop_writev(struct file *file, struct iov_iter *iter,
 	return ret;
 }
 
+/* generic read side helper for drivers converting to ->read_iter() */
+ssize_t vfs_read_iter(struct kiocb *iocb, struct iov_iter *to,
+		      ssize_t (*read)(struct file *, char __user *,
+				     size_t, loff_t *))
+{
+	return do_loop_readv(iocb->ki_filp, to, &iocb->ki_pos, 0, read);
+}
+EXPORT_SYMBOL(vfs_read_iter);
+
+/* generic write side helper for drivers converting to ->write_iter() */
+ssize_t vfs_write_iter(struct kiocb *iocb, struct iov_iter *from,
+		       ssize_t (*write)(struct file *, const char __user *,
+				       size_t, loff_t *))
+{
+	return do_loop_writev(iocb->ki_filp, from, &iocb->ki_pos, 0, write);
+}
+EXPORT_SYMBOL(vfs_write_iter);
+
 ssize_t vfs_iocb_iter_read(struct file *file, struct kiocb *iocb,
 			   struct iov_iter *iter)
 {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 8dfd53b52744..fd862985a309 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2119,6 +2119,12 @@ extern ssize_t vfs_read(struct file *, char __user *, size_t, loff_t *);
 extern ssize_t vfs_write(struct file *, const char __user *, size_t, loff_t *);
 extern ssize_t vfs_copy_file_range(struct file *, loff_t , struct file *,
 				   loff_t, size_t, unsigned int);
+ssize_t vfs_write_iter(struct kiocb *iocb, struct iov_iter *from,
+		       ssize_t (*write)(struct file *, const char __user *,
+				        size_t, loff_t *));
+ssize_t vfs_read_iter(struct kiocb *iocb, struct iov_iter *to,
+		      ssize_t (*read)(struct file *, char __user *,
+				      size_t, loff_t *));
 int __generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
 				    struct file *file_out, loff_t pos_out,
 				    loff_t *len, unsigned int remap_flags,
-- 
2.43.0