net/9p: switch p9_fd_read to kernel_write

Instead of playing with the addressing limits.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

net/9p/trans_fd.c

@@ -422,8 +422,7 @@ static void p9_read_work(struct work_struct *work)
 
 static int p9_fd_write(struct p9_client *client, void *v, int len)
 {
-	int ret;
-	mm_segment_t oldfs;
+	ssize_t ret;
 	struct p9_trans_fd *ts = NULL;
 
 	if (client && client->status != Disconnected)
@@ -435,12 +434,7 @@ static int p9_fd_write(struct p9_client *client, void *v, int len)
 	if (!(ts->wr->f_flags & O_NONBLOCK))
 		p9_debug(P9_DEBUG_ERROR, "blocking write ...\n");
 
-	oldfs = get_fs();
-	set_fs(get_ds());
-	/* The cast to a user pointer is valid due to the set_fs() */
-	ret = vfs_write(ts->wr, (__force void __user *)v, len, &ts->wr->f_pos);
-	set_fs(oldfs);
-
+	ret = kernel_write(ts->wr, v, len, &ts->wr->f_pos);
 	if (ret <= 0 && ret != -ERESTARTSYS && ret != -EAGAIN)
 		client->status = Disconnected;
 	return ret;