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Re: [PATCH] xfsprogs: reduce bb_numrecs in bno/cnt btrees when log consu

To: Brian Foster <bfoster@xxxxxxxxxx>
Subject: Re: [PATCH] xfsprogs: reduce bb_numrecs in bno/cnt btrees when log consumes all agf space
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 19 Mar 2013 10:16:57 +1100
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1363642689-17718-1-git-send-email-bfoster@xxxxxxxxxx>
References: <1363642689-17718-1-git-send-email-bfoster@xxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
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@xxxxxxxxxx>
> ---
>  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@xxxxxxxxxxxxx

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