Re: [PATCH] xfsprogs: reduce bb_numrecs in bno/cnt btrees when log consumes all agf space

[Dave Chinner <david@fromorbit.com>]

On Mon, Mar 18, 2013 at 05:38:09PM -0400, Brian Foster wrote:
> The mkfs code currently creates a single free space extent record
> for each of the bno and cnt btrees in each AG. The start block of
> the record is pushed forward on the AG that hosts an internal log.
> If the log happens to consume all available space in the AG, the
> start block becomes equal to sb->sb_agblocks and thus invalid.
> This causes xfs_repair to complain.
> 
> For example, the following sequence:
> 
> 	mkfs.xfs -d file,name=./fs.img,size=50g,agsize=16m
> 	xfs_repair ./fs.img
> 
> ... produces the following xfs_repair output:
> 
> 	Phase 1 - find and verify superblock...
> 	Phase 2 - using internal log
>         	- scan filesystem freespace and inode maps...
> 	invalid start block 4096 in record 0 of bno btree block 1600/1
> 	invalid start block 4096 in record 0 of cnt btree block 1600/2
>         	- found root inode chunk
> 	...
> 
> xfs_repair appears to correct the numrecs value such that subsequent
> checks are successful. The sequence above is pulled from xfstests
> 
> Modify mkfs.xfs such that we check the block count value of the
> free space record for the log AG after the log is accounted for. If
> no space is left for the record, reset the record count to 0.
> 
> Signed-off-by: Brian Foster <bfoster@redhat.com>
> ---
>  mkfs/xfs_mkfs.c |    6 ++++++
>  1 files changed, 6 insertions(+), 0 deletions(-)
> 
> diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
> index c84448e..c4ae15b 100644
> --- a/mkfs/xfs_mkfs.c
> +++ b/mkfs/xfs_mkfs.c
> @@ -2594,6 +2594,9 @@ an AG size that is one stripe unit smaller, for example %llu.\n"),
>  		}
>  		arec->ar_blockcount = cpu_to_be32(agsize - 
>  					be32_to_cpu(arec->ar_startblock));
> +		if (!arec->ar_blockcount)
> +			block->bb_numrecs = cpu_to_be16(0);

You don't need to endian swap zero. block->bb_numrecs = 0; is just
fine.  I'd also add a comment to explain why this is being done....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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