From: Li Zefan <lizf@cn.fujitsu.com>
Date: Mon, 28 Nov 2011 08:43:00 +0000 (+0800)
Subject: Btrfs: fix oops when calling statfs on readonly device
X-Git-Tag: v3.2-rc4~3^2~6
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b772a86ea6d932ac29d5e50e67c977653c832f8a;p=pandora-kernel.git

Btrfs: fix oops when calling statfs on readonly device

To reproduce this bug:

  # dd if=/dev/zero of=img bs=1M count=256
  # mkfs.btrfs img
  # losetup -r /dev/loop1 img
  # mount /dev/loop1 /mnt
  OOPS!!

It triggered BUG_ON(!nr_devices) in btrfs_calc_avail_data_space().

To fix this, instead of checking write-only devices, we check all open
deivces:

  # df -h /dev/loop1
  Filesystem            Size  Used Avail Use% Mounted on
  /dev/loop1            250M   28K  238M   1% /mnt

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
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