From 9ba1f6e44ed7a1fa52d3f292508bf921b5054172 Mon Sep 17 00:00:00 2001
From: Liu Bo <liubo2009@cn.fujitsu.com>
Date: Fri, 11 May 2012 18:11:26 +0800
Subject: [PATCH] Btrfs: do not do balance in readonly mode

In normal cases, we would not be allowed to do balance in RO mode.
However, when we're using a seeding device and adding another device to sprout,
things will change:

$ mkfs.btrfs /dev/sdb7
$ btrfstune -S 1 /dev/sdb7
$ mount /dev/sdb7 /mnt/btrfs -o ro
$ btrfs fi bal /mnt/btrfs   -----------------------> fail.
$ btrfs dev add /dev/sdb8 /mnt/btrfs
$ btrfs fi bal /mnt/btrfs   -----------------------> works!

It should not be designed as an exception, and we'd better add another check for
mnt flags.

Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
Reviewed-by: Josef Bacik <josef@redhat.com>
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