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

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Message-ID: <20090710072841.GB19408@skywalker>
Date:	Fri, 10 Jul 2009 12:58:41 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Xiang Wang <xiangw@...gle.com>
Cc:	Theodore Tso <tytso@....edu>, 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 09, 2009 at 11:30:58AM -0700, Xiang Wang wrote:
> 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?
> 

Now that I look at commit 0390131ba84fd3f726f9e24fc4553828125700bb
if i understood correctly, that should always force a no journal 
mount to data=writeback ?

I tested it as below

 mkfs.ext4 -O ^has_journal /home/opensource/images/ext3.img
 sudo mount -o loop /home/opensource/images/ext3.img  /mnt/
[master@...ux-2.6]$ cat /proc/mounts  | grep mnt
/dev/loop0 /mnt ext4 rw,relatime,barrier=1,data=writeback 0 0

So what we really need is to update ext4_should_writeback_data
not to return 0 when we  don't have a journal. Ted already have a patch
in the patch queue that does the same. I guess that patch should get
everything working fine.  So if mke2fs have created a journal to run
in no journal mode one can say -o noload. I guess that is more or less
what we wanted.

-aneesh
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