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

Christoph Hellwig
2009-02-15T18:24:31Z

On Wed, Feb 11, 2009 at 06:54:33PM +1100, Dave Chinner wrote:
> 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))

Yeah. Either that, or dividing the sizeof by four.

> > 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.

Yeah, two slots was the very first implementation, I'll fix up the
comment too.