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Date:      Fri, 27 Feb 1998 17:45:39 -0800
From:      Mike Smith <mike@smith.net.au>
To:        Greg Lehey <grog@lemis.com>
Cc:        FreeBSD Hackers <hackers@FreeBSD.ORG>
Subject:   Re: Kernel debugging: what's going on here? 
Message-ID:  <199802280145.RAA29930@dingo.cdrom.com>
In-Reply-To: Your message of "Sat, 28 Feb 1998 11:43:49 %2B1030." <19980228114349.01329@freebie.lemis.com> 

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> Can anybody explain this to me?  I'm writing a disk block, and am
> currently at bwrite:
>
> (kgdb) bt
> #0  bwrite (bp=0xf051ec00) at ../../kern/vfs_bio.c:364
> #1  0xf0138d6a in vop_stdbwrite (ap=0xf2a76c74) at ../../kern/vfs_default.c:283
> #2  0xf0138bb1 in vop_defaultop (ap=0xf2a76c74) at ../../kern/vfs_default.c:130
> #3  0xf0146639 in spec_vnoperate (ap=0xf2a76c74) at ../../miscfs/specfs/spec_vnops.c:127
> #4  0xf01c5679 in ufs_vnoperatespec (ap=0xf2a76c74) at ../../ufs/ufs/ufs_vnops.c:2242
> #5  0xf2aab097 in VOP_BWRITE (bp=0xf051ec00) at vnode_if.h:1117
> #6  0xf2aa95c4 in vinumstart (vol=0xf0563000, bp=0xf10f1bb0) at request.c:228
> #7  0xf2aa9189 in vinumstrategy (bp=0xf10f1bb0) at request.c:71
> #8  0xf2aa7b63 in vinum_writedisklabel (vol=0xf0563000, lp=0xf0563110) at io.c:830
> 
> I've handed a buffer header up from frame 6 (not the bp in the
> parameter list).  When it gets to bwrite, it has a different content.
> gdb tells me different contents depending on the frame it's in:

My guess would be that the bp has been translated to reflect the block 
device that it will be operating on at bwrite level rather than the 
logical device that you were operating on when you called VOP_BWRITE.

This would involve a change in vnode, as well as (maybe) offset etc.

-- 
\\  Sometimes you're ahead,       \\  Mike Smith
\\  sometimes you're behind.      \\  mike@smith.net.au
\\  The race is long, and in the  \\  msmith@freebsd.org
\\  end it's only with yourself.  \\  msmith@cdrom.com



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