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[PATCH] mkfs.xfs: don't increase agblocks past maximum

To: xfs-oss <xfs@xxxxxxxxxxx>
Subject: [PATCH] mkfs.xfs: don't increase agblocks past maximum
From: Eric Sandeen <sandeen@xxxxxxxxxx>
Date: Mon, 19 Sep 2011 16:45:06 -0500
Cc: Boris Ranto <branto@xxxxxxxxxx>
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:6.0.2) Gecko/20110902 Thunderbird/6.0.2
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>

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);
        *agsize = blocks;

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