linux-ext4 - Re: jbd2 inside a device mapper module

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20081226161708.GC4127@blitiri.com.ar>
Date:	Fri, 26 Dec 2008 14:17:08 -0200
From:	Alberto Bertogli <albertito@...tiri.com.ar>
To:	Theodore Tso <tytso@....edu>, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org, dm-devel@...hat.com
Subject: Re: jbd2 inside a device mapper module

On Thu, Dec 25, 2008 at 10:37:36PM -0500, Theodore Tso wrote:
> On Thu, Dec 25, 2008 at 10:00:05PM -0200, Alberto Bertogli wrote:
> > 
> > I think I'm not explaining myself correctly. My code has _nothing_ to do
> > with ext2/3/4 (or any other filesystem) whatsoever. I'm not using the
> > journal as an external one for a filesystem. I want to use it to be able
> > to do atomic writes in my own, filesystem independant, device-mapper
> > code.
> 
> How many block writes are you batching into a single transaction?  If
> you're not careful you may find that performance overhead will be
> quite expensive.

At this moment I'm trying to keep it simple, so I plan to batch two for
each sector written to the device: one for the metadata and one for the
data.


> > After what you told me (both this and the deprecation of
> > jbd2_journal_create()), I took a look at e2fsprogs' source. From what I
> > could see, "mke2fs -O journal_dev" creates the external journal inside
> > some ext2/3/4 structures, which caused my journal-loading code to fail
> > (because it doesn't know about ext stuff).
> 
> Yes, this is necessary because in a production system you need to be
> able to identify the external journal by UUID, and the ext2/3/4
> superblock makes it easy to add a label, UUID, et. al.  It also
> significantly lowers the chance that an external journal will get
> misidentified as some other filesystem based on the data stored in the
> journal.

Yes, it makes sense. I've reserved the first sector for that purpose.

Thanks a lot,
		Alberto

--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html