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Re: Possible small bug in xfsprogs-dev/db/metadump.c

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: Possible small bug in xfsprogs-dev/db/metadump.c
From: Richard Sharpe <realrichardsharpe@xxxxxxxxx>
Date: Mon, 28 Sep 2009 10:36:13 -0700
Cc: Dave Chinner <david@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
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References: <46b8a8850909271220w372d60c3s18a543ed00825082@xxxxxxxxxxxxxx> <20090928172137.GA21868@xxxxxxxxxxxxx>
On Mon, Sep 28, 2009 at 10:21 AM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
> [Cc'ed to the list, where people including the most active person on the
>  userspace side hang out]
>
> On Sun, Sep 27, 2009 at 12:20:33PM -0700, Richard Sharpe wrote:
>> Hi folks,
>>
>> There seems to be a small bug in
>> xfsprogs-dev/db/metadump.c:scanfunc_freesp (although I think the same
>> problem exists in other functions).
>>
>> It has a check to see if the number of records is invalid:
>>
>>         numrecs = be16_to_cpu(block->bb_numrecs);
>>         if (numrecs > mp->m_alloc_mxr[1]) {
>>                 if (show_warnings)
>>                         print_warning("invalid numrecs (%u) in %s block 
>> %u/%u",
>>                                 numrecs, typtab[btype].name, agno, agbno);
>>                 return 1;
>>         }
>>
>> However, it seems to me that you should pay attention to bb_level in
>> the node when using that test, because leaf nodes can appear at
>> multiple levels in the tree.
>
> Before that code there is a
>
>        if (level == 0)
>                return 1;
>
> which should take care of the leaf nodes by exiting early.

Well, yes there is, but that is the problem I encountered. It is level
as passed in when starting at the top of the tree, which is obtained
from the levels value in the AGF, and is decremented by one on each
recursion:

        if (!(*func)(iocur_top->data, agno, agbno, level - 1, btype, arg))

However, what should really be looked at is the value bb_level in the
header in each free-space Btree node.

After I made that change to my changes, I started being able to
properly count all leaf nodes and free extents, and the numbers came
out where I expected them to be (instead of not seeing many leaf nodes
and vastly undercounting free extents).





-- 
Regards,
Richard Sharpe

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