kern/115572: [gbde] gbde partitions fail at 28bit/48bit LBA addressing boundary

[Graham]

The following reply was made to PR kern/115572; it has been noted by GNATS.

From: Graham <gbradley at rocketmail.com>
To: bug-followup at FreeBSD.org
Cc:  
Subject: Re: kern/115572: [gbde] gbde partitions fail at 28bit/48bit LBA addressing boundary
Date: Sat, 18 Aug 2007 13:49:13 -0700 (PDT)

 I have stripped this problem down to its simplest form, which is that a
 block read or write where the block straddles the 137gb boundary fails.
 
 Simplest reproducible form:
 1. create a single partition on a large drive, so then the first
 partition starts at a sector offset of 1.  In my case this is
 /dev/ad4s1.
 
 2. attempt (say)....
 rabbit# dd if=/dev/zero of=/dev/ad4s1 oseek=2097151 count=1 bs=64k
 and the result is....
 dd: /dev/ad4s1: Input/output error
 1+0 records in
 0+0 records out
 0 bytes transferred in 0.000325 secs (0 bytes/sec)
 
 (If dd is performed on the raw drive, /dev/ad4 then block boundary is
 always a power of 2, and blocksize a smaller power of 2.  That's always
 ok.  But we can't assume we use drives that way.)
 
 So a transfer which starts in the 28-bit zone, but extends over into
 the 48-bit region, fails.  Such transfers happen in the superblock of
 certain size drives, and that plays havoc.  The sector mapping of gbde
 can do this, but soft-update gets screwed by this happening.  It's not
 actually to do with the crypto as I first suspected.
 
 
        
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