linux-kernel - Re: [PATCH 12/13] xfs: make the calculation generic in xfs_sb_validate_fsb

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Date: Mon, 26 Feb 2024 23:47:30 +1100
From: Dave Chinner <david@...morbit.com>
To: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
Cc: linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, chandan.babu@...cle.com,
	akpm@...ux-foundation.org, mcgrof@...nel.org, ziy@...dia.com,
	hare@...e.de, djwong@...nel.org, gost.dev@...sung.com,
	linux-mm@...ck.org, willy@...radead.org,
	Pankaj Raghav <p.raghav@...sung.com>
Subject: Re: [PATCH 12/13] xfs: make the calculation generic in
 xfs_sb_validate_fsb_count()

On Mon, Feb 26, 2024 at 10:49:35AM +0100, Pankaj Raghav (Samsung) wrote:
> From: Pankaj Raghav <p.raghav@...sung.com>
> 
> Instead of assuming that PAGE_SHIFT is always higher than the blocklog,
> make the calculation generic so that page cache count can be calculated
> correctly for LBS.
> 
> Signed-off-by: Pankaj Raghav <p.raghav@...sung.com>
> ---
>  fs/xfs/xfs_mount.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> index aabb25dc3efa..69af3b06be99 100644
> --- a/fs/xfs/xfs_mount.c
> +++ b/fs/xfs/xfs_mount.c
> @@ -133,9 +133,15 @@ xfs_sb_validate_fsb_count(
>  {
>  	ASSERT(PAGE_SHIFT >= sbp->sb_blocklog);
>  	ASSERT(sbp->sb_blocklog >= BBSHIFT);
> +	uint64_t mapping_count;
> +	uint64_t bytes;
>  
> +	if (check_mul_overflow(nblocks, (1 << sbp->sb_blocklog), &bytes))
> +		return -EFBIG;
> +
> +	mapping_count = bytes >> PAGE_SHIFT;

max_index, not a "mapping count". Also, put this after this comment:

>  	/* Limited by ULONG_MAX of page cache index */

So it is obvious what the max_index we are calculating belongs to.

-Dave.
-- 
Dave Chinner
david@...morbit.com