switch drivers/char/mem.c to ->read_iter/->write_iter

Note that _these_ guys have ->read() and ->write() left in place - they are
eqiuvalent to what we'd get if we replaced those with NULL, but we are
talking about hot paths here.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

drivers/char/mem.c

@@ -607,16 +607,16 @@ static ssize_t write_null(struct file *file, const char __user *buf,
 	return count;
 }
 
-static ssize_t aio_read_null(struct kiocb *iocb, const struct iovec *iov,
-			     unsigned long nr_segs, loff_t pos)
+static ssize_t read_iter_null(struct kiocb *iocb, struct iov_iter *to)
 {
 	return 0;
 }
 
-static ssize_t aio_write_null(struct kiocb *iocb, const struct iovec *iov,
-			      unsigned long nr_segs, loff_t pos)
+static ssize_t write_iter_null(struct kiocb *iocb, struct iov_iter *from)
 {
-	return iov_length(iov, nr_segs);
+	size_t count = iov_iter_count(from);
+	iov_iter_advance(from, count);
+	return count;
 }
 
 static int pipe_to_null(struct pipe_inode_info *info, struct pipe_buffer *buf,
@@ -718,7 +718,7 @@ static int open_port(struct inode *inode, struct file *filp)
 #define zero_lseek	null_lseek
 #define full_lseek      null_lseek
 #define write_zero	write_null
-#define aio_write_zero	aio_write_null
+#define write_iter_zero	write_iter_null
 #define open_mem	open_port
 #define open_kmem	open_mem
 
@@ -750,8 +750,8 @@ static const struct file_operations null_fops = {
 	.llseek		= null_lseek,
 	.read		= read_null,
 	.write		= write_null,
-	.aio_read	= aio_read_null,
-	.aio_write	= aio_write_null,
+	.read_iter	= read_iter_null,
+	.write_iter	= write_iter_null,
 	.splice_write	= splice_write_null,
 };
 
@@ -766,7 +766,7 @@ static const struct file_operations zero_fops = {
 	.llseek		= zero_lseek,
 	.write		= write_zero,
 	.read_iter	= read_iter_zero,
-	.aio_write	= aio_write_zero,
+	.write_iter	= write_iter_zero,
 	.mmap		= mmap_zero,
 #ifndef CONFIG_MMU
 	.mmap_capabilities = zero_mmap_capabilities,