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

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Message-ID: <20090706034144.GB31532@mit.edu>
Date:	Sun, 5 Jul 2009 23:41:44 -0400
From:	Theodore Tso <tytso@....edu>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	Curt Wohlgemuth <curtw@...gle.com>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: RFC PATCH: ext4 no journal corruption with locale-gen

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.

	   	   	   	       	 - 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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