linux-ext4 - Re: Journal under-reservation bug on first >2G file

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Message-ID: <20141001224325.GE2903@thunk.org>
Date:	Wed, 1 Oct 2014 18:43:25 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	Andreas Dilger <adilger@...ger.ca>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: Journal under-reservation bug on first >2G file

On Wed, Oct 01, 2014 at 03:37:17PM -0500, Eric Sandeen wrote:
> 
> Ok.  I guess this is only an issue for ext4 - well, at least this specific
> issue.  Delalloc makes it much different than ext2 & ext3, which reserve quite a
> lot more.  Whether there's a corner case over there which breaks, I dunno...
> 
> So it seems like the simplest test is simply: Are we RW mounted with delalloc?
> And if so, update the feature.  Seems simpler than mucking with "which features
> are unique to ext4"

I'd do "are we RW mounted with the extents feature".  That way we
don't need to worry about someone accidentally mounting a partition
meant for Hurd using ext4, which would imply delalloc, and then
causing Hurd to no longer be able to deal with the file system.  That
*shouldn't* happen, but if someone accidentally mounts the file system
with -t ext4, but it seems safer to gate it on the existence of the
extents feature.

						- Ted
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