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SubjectRe: Larger dev_t
On Tue, 27 Mar 2001, Dan Hollis wrote:

> On Tue, 27 Mar 2001, H. Peter Anvin wrote:
> > c) Make sure chown/chmod/link/symlink/rename/rm etc does the right thing,
> > without the need for "tar hacks" or anything equivalently gross.
> write-through filesystem, like overlaying a r/w ext2 on top of an iso9660
> fs.

functionality to do this is in devfs and devfsd already.

there are 2 ways:

1. devfs on /dev, maintain state in /dev-state.
2. regular ext2 (devfs naming style) /dev and devfs mounted on, eg,
/devfs for hotplug and module load/unload updates


/dev-state -> regular ext2
/dev -> devfs

use the CREATE, CHANGE and REGISTER hooks that devfs has to
allow devfsd to transparently copy changes in /dev to the ext2
/dev-state. See the example devfsd.conf for appropriate entries, eg:

REGISTER .* COPY /dev-state/$devname $devpath
CHANGE .* COPY $devpath /dev-state/$devname
CREATE .* COPY $devpath /dev-state/$devname


/dev -> regular ext2
/devfs -> devfs

use the devfs hooks for REGISTER and UNREGISTER to have devfsd update
the static /dev whenever hotplug events occur. Eg:

REGISTER .* COPY ${mntpnt}/$devname /dev/$devname
UNREGISTER .* CFUNCTION GLOBAL unlink /dev/$devname

seems to work for me:

[root@fogarty /devfs]# ls -l /dev{,fs}/misc/nvram
ls: /dev/misc/nvram: No such file or directory
ls: /devfs/misc/nvram: No such file or directory
[root@fogarty /devfs]# modprobe nvram
[root@fogarty /devfs]# ls -l /dev{,fs}/misc/nvram
crw-r----- 1 root root 10, 144 Jan 1 1970 /devfs/misc/nvram
crw-r----- 1 root root 10, 144 Mar 28 01:56 /dev/misc/nvram
[root@fogarty /devfs]# rmmod nvram
[root@fogarty /devfs]# ls -l /dev{,fs}/misc/nvram
ls: /dev/misc/nvram: No such file or directory
ls: /devfs/misc/nvram: No such file or directory

> -Dan

i prefer option 2 as /dev state is then not dependent on devfsd being
there and it just sidesteps the whole permissions issue. if devfsd
doesn't start then i still have a fully functional /dev.

but anyway... there seems to be loads of scope to do lots of
different things with devfsd, plus NIS support. :)

Paul Jakma
PGP5 key:
Premature optimization is the root of all evil.
-- D.E. Knuth

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