switch /dev/zero and /dev/full to ->read_iter()

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

drivers/char/mem.c

@@ -622,53 +622,23 @@ static ssize_t splice_write_null(struct pipe_inode_info *pipe, struct file *out,
 	return splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_null);
 }
 
-static ssize_t read_zero(struct file *file, char __user *buf,
-			 size_t count, loff_t *ppos)
+static ssize_t read_iter_zero(struct kiocb *iocb, struct iov_iter *iter)
 {
-	size_t written;
-
-	if (!count)
-		return 0;
-
-	if (!access_ok(VERIFY_WRITE, buf, count))
-		return -EFAULT;
-
-	written = 0;
-	while (count) {
-		unsigned long unwritten;
-		size_t chunk = count;
+	size_t written = 0;
 
+	while (iov_iter_count(iter)) {
+		size_t chunk = iov_iter_count(iter), n;
 		if (chunk > PAGE_SIZE)
 			chunk = PAGE_SIZE;	/* Just for latency reasons */
-		unwritten = __clear_user(buf, chunk);
-		written += chunk - unwritten;
-		if (unwritten)
-			break;
+		n = iov_iter_zero(chunk, iter);
+		if (!n && iov_iter_count(iter))
+			return written ? written : -EFAULT;
+		written += n;
 		if (signal_pending(current))
 			return written ? written : -ERESTARTSYS;
-		buf += chunk;
-		count -= chunk;
 		cond_resched();
 	}
-	return written ? written : -EFAULT;
-}
-
-static ssize_t aio_read_zero(struct kiocb *iocb, const struct iovec *iov,
-			     unsigned long nr_segs, loff_t pos)
-{
-	size_t written = 0;
-	unsigned long i;
-	ssize_t ret;
-
-	for (i = 0; i < nr_segs; i++) {
-		ret = read_zero(iocb->ki_filp, iov[i].iov_base, iov[i].iov_len,
-				&pos);
-		if (ret < 0)
-			break;
-		written += ret;
-	}
-
-	return written ? written : -EFAULT;
+	return written;
 }
 
 static int mmap_zero(struct file *file, struct vm_area_struct *vma)
@@ -738,7 +708,6 @@ 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 read_full       read_zero
 #define aio_write_zero	aio_write_null
 #define open_mem	open_port
 #define open_kmem	open_mem
@@ -783,9 +752,9 @@ static const struct file_operations port_fops = {
 
 static const struct file_operations zero_fops = {
 	.llseek		= zero_lseek,
-	.read		= read_zero,
+	.read		= new_sync_read,
 	.write		= write_zero,
-	.aio_read	= aio_read_zero,
+	.read_iter	= read_iter_zero,
 	.aio_write	= aio_write_zero,
 	.mmap		= mmap_zero,
 };
@@ -802,7 +771,8 @@ static struct backing_dev_info zero_bdi = {
 
 static const struct file_operations full_fops = {
 	.llseek		= full_lseek,
-	.read		= read_full,
+	.read		= new_sync_read,
+	.read_iter	= read_iter_zero,
 	.write		= write_full,
 };