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To: fs@freebsd.org
From: Brian Bergstrand <brian@classicalguitar.net>
Date: Fri, 11 Jun 2004 11:31:47 -0500
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Subject: Ext2 vs UFS getlbns
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I just noticed something in ext2_getlbns() (ext2_bmap.c, v1.57) vs. 
ufs_getlbns() (ufs_bmap.c, v1.60)

In the last loop to setup the indir array,

UFS does:

{
...
blockcnt /= MNINDIR(ump);
off = (bn / blockcnt) % MNINDIR(ump);

++numlevels;
ap->in_lbn = metalbn;
ap->in_off = off;
ap->in_exists = 0;
++ap;

metalbn -= -1 + off * blockcnt;
}

While Ext2 does:

{
...
off = (bn / blockcnt) % MNINDIR(ump);

++numlevels;
ap->in_lbn = metalbn;
ap->in_off = off;
ap->in_exists = 0;
++ap;

metalbn -= -1 + off * blockcnt;
blockcnt /= MNINDIR(ump);
}

Notice that blockcnt is changed AFTER offset/metalbn in Ext2 and BEFORE 
those in UFS.

Was this change in Ext2 done on purpose for some reason? It makes a 
difference in calculating in_off and metalbn for some block #'s.

Thanks.

Brian Bergstrand <http://www.bergstrand.org/brian/>, AIM: triryche206
PGP Key: <http://www.bergstrand.org/brian/misc/public_key.txt>
If all else fails, lower your standards.
As of 11:31:08 AM, iTunes is playing "Tristessa" from "Gish" by 
"Smashing Pumpkins"

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