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Date:      Fri, 29 May 1998 19:58:10 -0700
From:      Julian Elischer <julian@whistle.com>
To:        "Jordan K. Hubbard" <jkh@time.cdrom.com>
Cc:        current@FreeBSD.ORG
Subject:   Re: I see one major problem with DEVFS...
Message-ID:  <356F75C2.7566F4CF@whistle.com>
References:  <199805300108.SAA16711@time.cdrom.com>

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Jordan K. Hubbard wrote:
> 
> bash# ls -l bpf*
> crw-------  1 root  wheel   23,   0 May 29 08:03 bpf0
> crw-------  1 root  wheel   23,   1 May 29 08:03 bpf1
> crw-------  1 root  wheel   23,   2 May 29 08:03 bpf2
> crw-------  1 root  wheel   23,   3 May 29 08:03 bpf4
> bash# rm bpf4
> bash# ls -l bpf*
> crw-------  1 root  wheel   23,   0 May 29 08:03 bpf0
> crw-------  1 root  wheel   23,   1 May 29 08:03 bpf1
> crw-------  1 root  wheel   23,   2 May 29 08:03 bpf2
> bash# mknod bpf4 c 23 3
> 
> E.g. I can shoot my foot off, but I can't sew it back on. :-)
> 
> Also, while I'm on this topic, what is the purpose served by
> DEVFS auto-mounting itself on "dummy_mount"?  I'm only going to
> mount it as /dev later, so I don't really get the idea behind
> the first instance of it.  Is it for "cloning" purposes or
> something?
> 
> - Jordan
> 
> To Unsubscribe: send mail to majordomo@FreeBSD.org
> with "unsubscribe freebsd-current" in the body of the message

dummy_mount is a hack
the trouble is that the root fs is mounted before
/dev so the device has to come out of the kernel's internel /de
blueprint
(from which it makes the user alterable versions that people mount)

trouble with this is that SYNC only writes back superblocks on
devices that are mounted from filesysytems in the mount list,
which the internal copy is  not (or it was not).
to ge tthe root superblock SYNC'd I needed to add that internal copy
to the mount list..
I've since decided that in the DEVFS/SLICE case, a better answer 
would be to special-case that and just do it and the mount list as well

julian

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