Re: [PATCH 10/13] xfs: add CRC checks to the AGFL

[Dave Chinner <david@fromorbit.com>]

On Tue, Feb 10, 2009 at 03:22:51PM -0500, Christoph Hellwig wrote:
> Add CRC checks, location information and a magic number to the AGFL.
> Previously the AGFL was just a block containing nothing but the
> free block pointers.  The new AGFL has a real header with the usual
> boilerplate instead, so that we can verify it's not corrupted and
> written into the right place.

I haven't had a chance to look over any of this series in detail - just
a quick glance really - but this popped out as looking wrong:

> +/*
> + * Size of the AGFL.  For CRC-enabled filesystes we steal the last two slots
> + * for location information (agno) and the crc.
> + */
> +#define XFS_AGFL_SIZE(mp) \
> +	((mp)->m_sb.sb_sectsize / sizeof(xfs_agblock_t) - \
> +	 (xfs_sb_version_hascrc(&((mp)->m_sb)) ? sizeof(struct xfs_agfl) : 0))

sb_sectsize is in bytes, sizeof(xfs_agblock_t) is in bytes, which
means that the numerator is a count of the number of agblocks that
will fit in the AGFL. sizeof(struct xfs_agfl) is also in bytes,
so your subtracting a number of bytes from a count of agblocks....

I think you mean:

#define XFS_AGFL_SIZE(mp) \
	(((mp)->m_sb.sb_sectsize - (xfs_sb_version_hascrc(&((mp)->m_sb)) ? \
						sizeof(struct xfs_agfl) : 0)) \
	  / sizeof(xfs_agblock_t))

>  typedef struct xfs_agfl {
> -	__be32		agfl_bno[1];	/* actually XFS_AGFL_SIZE(mp) */
> +	__be32		agfl_magicnum;
> +	__be32		agfl_seqno;
> +	uuid_t		agfl_uuid;
> +	__be32		agfl_crc;
> +	__be32		agfl_bno[];	/* actually XFS_AGFL_SIZE(mp) */
>  } xfs_agfl_t;

And judging by that you are stealing more than 2 slots - more like
8 slots.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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