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

Dave Chinner
2009-02-11T07:55:16Z

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