On Tue, Apr 05, 2016 at 04:05:07PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> Commit 96f859d ("libxfs: pack the agfl header structure so
> XFS_AGFL_SIZE is correct") allowed the freelist to use the empty
> slot at the end of the freelist on 64 bit systems that was not
> being used due to sizeof() rounding up the structure size.
>
> This has caused versions of xfs_repair prior to 4.5.0 (which also
> has the fix) to report this as a corruption once the filesystem has
> been grown. Older kernels can also have problems (seen from a whacky
> container/vm management environment) mounting filesystems grown on a
> system with a newer kernel than the vm/container it is deployed on.
>
> To avoid this problem, change the initial free list indexes not to
> wrap across the end of the AGFL, hence avoiding the initialisation
> of agf_fllast to the last index in the AGFL.
I have to admit that it's been a while that I looked at the AGFL
code, but I simply don't understand what's happening in this patch.
Diff slightly reorder:
> - agf->agf_flfirst = 0;
> + agf->agf_flfirst = cpu_to_be32(1);
So flfirst moves from 0 to 1.
> - agf->agf_fllast = cpu_to_be32(XFS_AGFL_SIZE(mp) - 1);
> + agf->agf_fllast = 0;
And last from size - 1 to 0. In my naive reading this introduces
wrapping and doesn't remove it. What do I miss?
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