From mboxrd@z Thu Jan  1 00:00:00 1970
From: liubo <liubo2009@cn.fujitsu.com>
Subject: Re: [RFC PATCH 2/5 v3] Btrfs: avoid transaction stuff when btrfs
 is readonly
Date: Wed, 15 Dec 2010 17:12:14 +0800
Message-ID: <4D08866E.6080501@cn.fujitsu.com>
References: <4CF8A74F.2010306@cn.fujitsu.com> <AANLkTikgAj1sFPr==ruot50Bq3oJ_v0ZG8Wy_QLdL+aG@mail.gmail.com>
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Cc: Linux Btrfs <linux-btrfs@vger.kernel.org>,
	Josef Bacik <josef@redhat.com>,
	Tsutomu Itoh <t-itoh@jp.fujitsu.com>,
	"Yan, Zheng" <zheng.yan@oracle.com>,
	Wenyi Liu <qingshenlwy@gmail.com>,
	Mike Fedyk <mfedyk@mikefedyk.com>
To: "Yan, Zheng" <zheng.z.yan@linux.intel.com>
Return-path: <linux-btrfs-owner@vger.kernel.org>
In-Reply-To: <AANLkTikgAj1sFPr==ruot50Bq3oJ_v0ZG8Wy_QLdL+aG@mail.gmail.com>
List-ID: <linux-btrfs.vger.kernel.org>

On 12/15/2010 04:45 PM, Yan, Zheng wrote:
> On Fri, Dec 3, 2010 at 4:16 PM, liubo <liubo2009@cn.fujitsu.com> wrote:
>> When the filesystem is readonly, avoid transaction stuff by checking MS_RDONLY
>> at start transaction time.
>>
>> Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
>> ---
>>  fs/btrfs/transaction.c |    3 +++
>>  1 files changed, 3 insertions(+), 0 deletions(-)
>>
>> diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
>> index 1fffbc0..14a597d 100644
>> --- a/fs/btrfs/transaction.c
>> +++ b/fs/btrfs/transaction.c
>> @@ -181,6 +181,9 @@ static struct btrfs_trans_handle *start_transaction(struct btrfs_root *root,
>>        struct btrfs_trans_handle *h;
>>        struct btrfs_transaction *cur_trans;
>>        int ret;
>> +
>> +       if (root->fs_info->sb->s_flags & MS_RDONLY)
>> +               return ERR_PTR(-EROFS);
>>  again:
>>        h = kmem_cache_alloc(btrfs_trans_handle_cachep, GFP_NOFS);
>>        if (!h)
> 
> There are cases that we need to start transaction when MS_RDONLY flag is set.
> For example, remount FS into read-only mode and log replay.

However, is it weird to make changes to disk as fs is in readonly state?
IMO, btrfs needs to limit the use of these "disk-change while readonly" cases,
as it is not what readonly means.

Since it has been here, we can bypass readonly in those cases(as I did in the 5th patch):

...
flags = sb->s_flags;
if (sb->s_flags & MS_RDONLY)
	sb->s_flags &= ~MS_RDONLY

remount()

sb->s_flags = flags;
...

thanks,
Liu Bo

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