linux-ext4 - Re: How can I flush all writes before yanking the power cable?

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Message-ID: <51141CCB.9060908@redhat.com>
Date:	Thu, 07 Feb 2013 15:29:47 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	Autif Khan <autif.mlist@...il.com>
CC:	"Theodore Ts'o" <tytso@....edu>, linux-ext4@...r.kernel.org
Subject: Re: How can I flush all writes before yanking the power cable?

On 2/7/13 3:28 PM, Autif Khan wrote:
> On Thu, Feb 7, 2013 at 3:58 PM, Theodore Ts'o <tytso@....edu> wrote:
>> On Thu, Feb 07, 2013 at 02:37:02PM -0500, Autif Khan wrote:
>>>
>>> That was precisely my ignorance. I did not know about barrier. Adding
>>> it during mount ro and remount rw seems to have fixed these issues.
>>
>> You also didn't say what file system you were using.  Was it ext4?
>> ext3?  ext2?  What kernel version?  On modern kernels barrier is
>> enabled by default for both ext3 and ext4.
> 
> The filesystem is ext4. Kernel version is 3.2.0
> 
> I could not grep -i  barrier in the kernel config. How is barrier
> enabled or disabled in the kernel by default?


in ext4_fill_super():

        if ((def_mount_opts & EXT4_DEFM_NOBARRIER) == 0)
                set_opt(sb, BARRIER);

It's a mount option, not a kernel config option.

-Eric

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