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Date:      Tue, 7 Jul 1998 10:38:58 -0400 (EDT)
From:      Erick Engelke <erick@dark.uwaterloo.ca>
To:        "Alton, Matthew" <Matthew.Alton@anheuser-busch.com>
Cc:        "'hackers@freebsd.org'" <hackers@FreeBSD.ORG>, "'freebsd-fs@freebsd.org'" <freebsd-fs@FreeBSD.ORG>, "Smallie, Scott" <Scott.Smallie@anheuser-busch.com>
Subject:   RE: lfs
Message-ID:  <Pine.BSF.3.96.980707090119.16293B-100000@dark.uwaterloo.ca>
In-Reply-To: <31B3F0BF1C40D11192A700805FD48BF901776600@STLABCEXG011>

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On Mon, 6 Jul 1998, Alton, Matthew wrote:
> erick wrote:
> > I see that a newlfs'd partition shows up nicely with the ifile log
> > file and lost+found.  But as soon as sync happens, whether timed or
> > due to a umount or file i/o, we have a panic.
 
> 	[Alton, Matthew]  
> 	Are you getting a core dump for kgdb?  I don't have a scratch
>       box running this code right now.  I've got a nasty old 486/33
>       almost up for testing purposes...

Now that I'm more up to speed on kdb (thanks for the tips), I got a bit
farther.  My scratch pc is a 486/50... not much better, eh? 

The actual error is in the lfs_writeseg() of lfs_segment.c
where lfs is copying individual bufs into contiguous memory
for a big long write.  (called from lfs_segwrite, from lfs_sync)

It looks like I'm dying at ++cbp->b_vp->v_numoutput...  and a quick look
suggests it is possible the vnode points to garbage.  I'll have to verify
that with kdb and experiment some more. 

While on the topic, LFS has a lot of hacks, many specifically about
bufferring.  Some other PC OS's simply manipulate the page tables to map
buffers into contiguous RAM... (and then instruct 3rd parties to never do
the same).  I don't imagine that pagetable fiddling practice is ever used
with FreeBSD, is it?  


> > Hmmm, where do printfs send their output... nowhere I happen to be
> > looking?

> 	[Alton, Matthew]  
> 	I thought they went to /dev/console 

They do.  My mistake.  

Thanks for the hints.



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