On Mon, 2011-09-19 at 16:45 -0500, Eric Sandeen wrote:
> RH QA discovered this bug:
>
> Steps to Reproduce:
> 1. Create 4 TB - 1 B partition
> dd if=/dev/zero of=x.img bs=1 count=0 seek=4398046511103
> 2. Create xfs fs with 512 B block size on the partition
> mkfs.xfs -b size=512 xfs.img
>
> Actual results:
> Agsize is computed incorrectly resulting in fs creation fail:
> agsize (2147483648b) too big, maximum is 2147483647 blocks
>
> This is due to the "rounding up" at the very end of the calculations;
> there may be other places to alleviate the problem, but it seems
> most obvious to simply skip the rounding up if it would create too
> many blocks in the AG. Worst case, we lose 1 block per AG.
>
> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
> ---
The fix is the right way about it.
This may seem petty, but I think this would be better:
blocks = dblocks >> shift
if (blocks & xfs_mask32lo(shift)) {
if (blocks < XFS_AG_MAX_BLOCKS(blocklog))
blocks++;
}
It emphasizes more why we'd be doing the increment,
plus I'd rather see a "real" increment rather than
adding a Boolean value.
Either way:
Reviewed-by: Alex Elder <aelder@xxxxxxx>
> diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
> index 5b3b9a7..856a261 100644
> --- a/mkfs/xfs_mkfs.c
> +++ b/mkfs/xfs_mkfs.c
> @@ -658,7 +659,9 @@ calc_default_ag_geometry(
> * last bit of the filesystem. The same principle applies
> * to the AG count, so we don't lose the last AG!
> */
> - blocks = (dblocks >> shift) + ((dblocks & xfs_mask32lo(shift)) != 0);
> + blocks = (dblocks >> shift);
> + if (blocks < XFS_AG_MAX_BLOCKS(blocklog))
> + blocks += ((dblocks & xfs_mask32lo(shift)) != 0);
>
> done:
> *agsize = blocks;
>
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