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Date: Thu, 17 Jan 2008 16:01:48 -0500
From: David Schultz <das@FreeBSD.ORG>
To: Adam <urbansnap@gmail.com>
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Cc: freebsd-current@FreeBSD.ORG
Subject: Re: Reading and Writing to Block from di_spare
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On Thu, Jan 17, 2008, Adam wrote:
> David,
> I understand that there is no routine to read and write specifically  
> to an address contained in the di_spare.   I also understand that  
> di_spare is currently unused and has no specific manipulators.
> 
> Allow me to clarify.  I am looking for a way to take a ufs2_daddr_t  
> (which is neither a direct nor indirect block of a di_node) and read/ 
> write to that address.

To do it cleanly you'd probably need to hack ufs_bmap and
ffs_balloc to map your 'extra' block to a particular LBN (or at
least that's the only way I know how to do it easily.)  But as I
said before, if you just need to store a small amount of
information, extended attributes are most likely a much simpler
alternative.