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Date: Tue, 28 Nov 2023 22:05:06 -0800
From: Christoph Hellwig <hch@infradead.org>
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>, linux-xfs@vger.kernel.org
Subject: Re: [PATCH 1/6] xfs: check rt bitmap file geometry more thoroughly
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On Tue, Nov 28, 2023 at 03:27:40PM -0800, Darrick J. Wong wrote:
> > All these will be 0 if mp->m_sb.sb_rblocks, and rtb is zeroed allocation
> > right above, so calculating the values seems a bit odd.  Why not simply:
> > 
> > 	if (mp->m_sb.sb_rblocks) {
> > 		rtb->rextents = xfs_rtb_to_rtx(mp, mp->m_sb.sb_rblocks);
> > 		rtb->rextslog = xfs_highbit32(rtb->rextents);
> 
> Well... xfs_highbit32 returns -1 if its argument is zero, which is
> possible for the nasty edge case of (say) a 64k block device and a
> realtime extent size of 1MB, which results in rblocks > 0 and
> rextents == 0.

Eww.  How do we even allow creating a mounting that?  Such a
configuration doesn't make any sense.