fat: switch to ->iterate_shared()

... and make that weird ioctl lock directory only shared.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/fat/dir.c

@@ -769,7 +769,7 @@ static int fat_ioctl_readdir(struct inode *inode, struct file *file,
 
 	buf.dirent = dirent;
 	buf.result = 0;
-	inode_lock(inode);
+	inode_lock_shared(inode);
 	buf.ctx.pos = file->f_pos;
 	ret = -ENOENT;
 	if (!IS_DEADDIR(inode)) {
@@ -777,7 +777,7 @@ static int fat_ioctl_readdir(struct inode *inode, struct file *file,
 				    short_only, both ? &buf : NULL);
 		file->f_pos = buf.ctx.pos;
 	}
-	inode_unlock(inode);
+	inode_unlock_shared(inode);
 	if (ret >= 0)
 		ret = buf.result;
 	return ret;
@@ -861,7 +861,7 @@ static long fat_compat_dir_ioctl(struct file *filp, unsigned cmd,
 const struct file_operations fat_dir_operations = {
 	.llseek		= generic_file_llseek,
 	.read		= generic_read_dir,
-	.iterate	= fat_readdir,
+	.iterate_shared	= fat_readdir,
 	.unlocked_ioctl	= fat_dir_ioctl,
 #ifdef CONFIG_COMPAT
 	.compat_ioctl	= fat_compat_dir_ioctl,