linux-ext4 - Re: [PATCH 2/2] ext4: journal superblock modifications in ext4

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Date:	Mon, 23 Nov 2009 14:40:52 +0000
From:	Duane Griffin <duaneg@...da.com>
To:	tytso@....edu
Cc:	Andreas Dilger <andreas.dilger@...tre.org>,
	Eric Sandeen <sandeen@...hat.com>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 2/2] ext4: journal superblock modifications in 
	ext4_statfs()

2009/11/23  <tytso@....edu>:
> On Mon, Nov 23, 2009 at 11:57:44AM +0000, Duane Griffin wrote:
>> Unfortunately you can't just blindly give back the journalled block:
>> it may have been escaped. So you need to read in the block from the
>> journal, unescape it if required, then give it back.
>
> Good point; this is going to make supporting a read-only mount that
> doesn't replay the journal very difficult to implement for
> data=journal mode, since it would mean intercepting the actual block
> I/O read functions for data reads, which is outside of fs/ext4 in the
> generic fs/ and mm/ functions.  Doing it for metadata blocks will be
> annoying, but at least it's all inside fs/ext4.

Yes, that is the sticking point I got to with my last attempt at this :(

I was kinda hoping that someone would have a bright idea that doesn't
involve hacking an IO completion callback into get_block_t...

>                                        - Ted

Cheers,
Duane.

-- 
"I never could learn to drink that blood and call it wine" - Bob Dylan
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