fs: add vfs_iter_{read,write} helpers

Simple helpers that pass an arbitrary iov_iter to filesystems.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/read_write.c

@@ -333,6 +333,52 @@ SYSCALL_DEFINE5(llseek, unsigned int, fd, unsigned long, offset_high,
 }
 #endif
 
+ssize_t vfs_iter_read(struct file *file, struct iov_iter *iter, loff_t *ppos)
+{
+	struct kiocb kiocb;
+	ssize_t ret;
+
+	if (!file->f_op->read_iter)
+		return -EINVAL;
+
+	init_sync_kiocb(&kiocb, file);
+	kiocb.ki_pos = *ppos;
+	kiocb.ki_nbytes = iov_iter_count(iter);
+
+	iter->type |= READ;
+	ret = file->f_op->read_iter(&kiocb, iter);
+	if (ret == -EIOCBQUEUED)
+		ret = wait_on_sync_kiocb(&kiocb);
+
+	if (ret > 0)
+		*ppos = kiocb.ki_pos;
+	return ret;
+}
+EXPORT_SYMBOL(vfs_iter_read);
+
+ssize_t vfs_iter_write(struct file *file, struct iov_iter *iter, loff_t *ppos)
+{
+	struct kiocb kiocb;
+	ssize_t ret;
+
+	if (!file->f_op->write_iter)
+		return -EINVAL;
+
+	init_sync_kiocb(&kiocb, file);
+	kiocb.ki_pos = *ppos;
+	kiocb.ki_nbytes = iov_iter_count(iter);
+
+	iter->type |= WRITE;
+	ret = file->f_op->write_iter(&kiocb, iter);
+	if (ret == -EIOCBQUEUED)
+		ret = wait_on_sync_kiocb(&kiocb);
+
+	if (ret > 0)
+		*ppos = kiocb.ki_pos;
+	return ret;
+}
+EXPORT_SYMBOL(vfs_iter_write);
+
 /*
  * rw_verify_area doesn't like huge counts. We limit
  * them to something that fits in "int" so that others

fs/splice.c

@@ -961,7 +961,6 @@ iter_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
 	splice_from_pipe_begin(&sd);
 	while (sd.total_len) {
 		struct iov_iter from;
-		struct kiocb kiocb;
 		size_t left;
 		int n, idx;
 
@@ -1005,26 +1004,15 @@ iter_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
 			left -= this_len;
 		}
 
-		/* ... iov_iter */
 		iov_iter_bvec(&from, ITER_BVEC | WRITE, array, n,
 			      sd.total_len - left);
-
-		/* ... and iocb */
-		init_sync_kiocb(&kiocb, out);
-		kiocb.ki_pos = sd.pos;
-		kiocb.ki_nbytes = sd.total_len - left;
-
-		/* now, send it */
-		ret = out->f_op->write_iter(&kiocb, &from);
-		if (-EIOCBQUEUED == ret)
-			ret = wait_on_sync_kiocb(&kiocb);
-
+		ret = vfs_iter_write(out, &from, &sd.pos);
 		if (ret <= 0)
 			break;
 
 		sd.num_spliced += ret;
 		sd.total_len -= ret;
-		*ppos = sd.pos = kiocb.ki_pos;
+		*ppos = sd.pos;
 
 		/* dismiss the fully eaten buffers, adjust the partial one */
 		while (ret) {

include/linux/fs.h

@@ -2494,6 +2494,9 @@ extern ssize_t do_sync_write(struct file *filp, const char __user *buf, size_t l
 extern ssize_t new_sync_read(struct file *filp, char __user *buf, size_t len, loff_t *ppos);
 extern ssize_t new_sync_write(struct file *filp, const char __user *buf, size_t len, loff_t *ppos);
 
+ssize_t vfs_iter_read(struct file *file, struct iov_iter *iter, loff_t *ppos);
+ssize_t vfs_iter_write(struct file *file, struct iov_iter *iter, loff_t *ppos);
+
 /* fs/block_dev.c */
 extern ssize_t blkdev_read_iter(struct kiocb *iocb, struct iov_iter *to);
 extern ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from);