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Question about AGFL

To: xfs@xxxxxxxxxxx
Subject: Question about AGFL
From: Sergey Stepanov <g65434.2@xxxxxxxxx>
Date: Thu, 18 Oct 2012 19:27:09 +0400
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Hi.

I have a device with XFS on it and if I run xfs_db on it, I get the following: 

xfs_db> agf 0
xfs_db> p
magicnum = 0x58414746
versionnum = 1
seqno = 0
length = 6553344
bnoroot = 19432
cntroot = 20689
bnolevel = 1
cntlevel = 1
flfirst = 0
fllast = 3
flcount = 4
freeblks = 6529632
longest = 6522442
btreeblks = 0
xfs_db> agfl 0
xfs_db> p
bno[0-127] = 0:1 1:2 2:3 3:4

As you can see, AGFL contains block numbers 1-4.

As far as I understand, blocks 1-3 contain roots for inode and free space trees, so it seems really suspicious to me that they are listed in free list.
I  digged a bit into XFS code inside Linux kernel and did not find any code that will prevent overwriting them when B+trees will start to grow.

So, the question is did I miss something and this is a normal situation, or is this some kind of bug or corruption? 

Thanks in advance. 

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