Locking a file backed mdconfig into memory

[Jeremy Chadwick]

On Mon, May 31, 2010 at 11:25:51AM -0700, Dave Hayes wrote:
> Jeremy Chadwick <freebsd at jdc.parodius.com> writes:
> > Is the mfsroot file compressed (.gz extension)?  Reason I ask is that
> > the OP states he's using RELENG_7...
> 
> Yes it is compressed. 
> 
> > http://jdc.parodius.com/freebsd/pxeboot_serial_install_7.html#step7
> 
> Thanks much for this. I did a simple test, I rebuilt a DVD that wasn't
> booting to use a lower level of compression (gzip -9 to gzip -6) on
> mfsroot without changing anything else. This caused it to boot normally.
> 
> I'm not sure it's conclusive evidence, but it certainly looks like a
> weak datapoint supporting this kernel bug being the source of my
> problem.
> 
> Is this problem fixed in 8.0 or by a patch?

With regards to said bug, gzip compression seems to work fine on
RELENG_8, at least in my experiences:

http://jdc.parodius.com/freebsd/pxeboot_serial_install_8.html

I'm not sure the level of compression is what triggers the bug though;
I haven't tested all levels (1 through 9).

CC'ing jhb@ since he last updated PR kern/120127 (which I would say is
still a problem on RELENG_7 :-) ).  John, are you aware of any gzip
decompression / mfsroot changes which might explain the problem on
RELENG_7?  I haven't done a "thorough" series of tests, but on my
testbed boxes RELENG_8 works fine with a gzip'd mfsroot.

-- 
| Jeremy Chadwick                                   jdc at parodius.com |
| Parodius Networking                       http://www.parodius.com/ |
| UNIX Systems Administrator                  Mountain View, CA, USA |
| Making life hard for others since 1977.              PGP: 4BD6C0CB |