linux-ext4 - Re: RFC PATCH: ext4 no journal corruption with locale-gen

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Message-ID: <d5ca277e0907091130y5182debakc86d1f390396b92c@mail.gmail.com>
Date:	Thu, 9 Jul 2009 11:30:58 -0700
From:	Xiang Wang <xiangw@...gle.com>
To:	Theodore Tso <tytso@....edu>
Cc:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Curt Wohlgemuth <curtw@...gle.com>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: RFC PATCH: ext4 no journal corruption with locale-gen

When working on the patch of adding the data=nojournal mount option,
I start to wonder whether this mount option is actually needed.

When we mount a filesystem that was mkfs'ed with journal, using the
"noload" mount option
can help specify we do not load the journal.

When we mount a filesystem that was mkfs'ed without journal, we simply
go into the
nojournal mode.

That said, I do not really feel this data=nojournal option is necessary.
But I am still working on the patch to print appropriate messages when
people mount a filesystem
created without a journal but explicitly specify the "data=" option.
Any comments?

Thanks,
Xiang

On Mon, Jul 6, 2009 at 9:21 AM, Xiang Wang<xiangw@...gle.com> wrote:
> On Sun, Jul 5, 2009 at 8:41 PM, Theodore Tso<tytso@....edu> wrote:
>> On Thu, Jul 02, 2009 at 12:01:30AM +0530, Aneesh Kumar K.V wrote:
>>>
>>> I looked at the patch in detail and  I guess we should instead force
>>> a data=writeback mode if the filesystem is created without a journal.
>>> I am not sure what whould be the meaning of data=ordered/data=journal
>>> without a journal. So if we find that file system doesn't have a journal
>>> then either we should update the default mount option in the filesystem
>>> to be of data=writeback.
>>
>> Here's a patch which takes your approach to solving the problem.  What
>> do you think?
>>
>> I haven't messed with dealing with the data= mount options in
>> fs/ext4/super.c.  That's important from a UI point of view, but we
>> needed to fix ext4_jbd2.h since it was unconditionally returning 0 if
>> there was no journal for all of the ext4_should_*_data() functions.
>>
>> I believe this should DTRT with the -o nobh mount option, but I'd
>> appreciate another pair of eyes taking a look at this.
>
> This patch looks good to us.
>
> In the long run, we still think adding the data=nojournal mount option
> is useful and we are working on this patch.
>
> Thanks,
> Xiang
>
>>
>>                                         - Ted
>>
>> commit 2a73eff8ba80095a871a6b402dfd24bc454e5bdc
>> Author: Theodore Ts'o <tytso@....edu>
>> Date:   Sun Jul 5 23:37:13 2009 -0400
>>
>>    ext4: fix no journal corruption with locale-gen
>>
>>    If there is no journal, ext4_should_writeback_data() should return
>>    TRUE.  This will fix ext4_set_aops() to set ext4_da_ops in the case of
>>    delayed allocation; otherwise ext4_journaled_aops gets used by
>>    default, which doesn't handle delayed allocation properly.
>>
>>    The advantage of using ext4_should_writeback_data() approach is that
>>    it should handle nobh better as well.
>>
>>    Thanks to Curt Wohlgemuth for investigating this problem, and Aneesh
>>    Kumar for suggesting this approach.
>>
>>    Signed-off-by: "Theodore Ts'o" <tytso@....edu>
>>
>> diff --git a/fs/ext4/ext4_jbd2.h b/fs/ext4/ext4_jbd2.h
>> index be2f426..f800134 100644
>> --- a/fs/ext4/ext4_jbd2.h
>> +++ b/fs/ext4/ext4_jbd2.h
>> @@ -282,7 +282,7 @@ static inline int ext4_should_order_data(struct inode *inode)
>>  static inline int ext4_should_writeback_data(struct inode *inode)
>>  {
>>        if (EXT4_JOURNAL(inode) == NULL)
>> -               return 0;
>> +               return 1;
>>        if (!S_ISREG(inode->i_mode))
>>                return 0;
>>        if (EXT4_I(inode)->i_flags & EXT4_JOURNAL_DATA_FL)
>> --
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>
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