Hi:-)
> > As I understand it your devlinks won't point to an inode, correct?
> > That means when you access /dev/fd0 the follow_link method for the
> > inode_operations needs to be called. It is this follow_link method
> > which is then doing the parsing. Then presumably you fiddle
> > base->d_inode->i_op->default_file_ops, correct?
>
> I don't know the file system internals well enough to comment on this.
> :-/
>
> > open ("/dev/fd0", ...) works but
> > open ("/dev/fd:0,format=360") does not, even though
> > % ls -l /dev/fd0
> > lrwxrwxrwx 1 root root <date> /dev/fd0 => fd:0,format=360
> >
> > "=>" is used by ls to show a devlink, rather than "->".
>
> Good point. That is a confusing situation.
>
> > It also requires a modified ls. You may also need to modify other
> > programmes which have directory browsers. I guess GNU tar would also
> > need changes.
>
> I was trying to avoid that by implementing devlink as 'symlink +
> magic bit', so that these programs would work without changes.
Er, but then GNU tar can't back up /dev properly, because it doesn't
know about the magic bit. When you restore your FS those entries
become ordinary symlinks.
> I suggest again using a sysctl or devctl to mark "/dev" as
> "a place where drivers create entries when they initialize".
Yes, I can see why you came up with that. It's hard because /dev is
not a whole filesystem: you are trying to apply a dirrerent behaviour
to a portion of a filesystem. You can't solve it either by making /dev
a different filesystem, since you need /dev to mount a disc-based
FS. Devfs doesn't have that problem, though :-)
I think such a sysctl() would be *very* hard to implement and would be
a lot more complicated than devfs.
> > > That's true. Devfs still needs more control mechanisms. If I set up a
> > > chroot jail, I want to have /dev/null in it, but I don't want to have
> > > my insmod'd printer driver popping up in there.
> >
> > # mount -t devfs none /gaol/dev
> > # cd /gaol/dev
> > # rm -f lp* sd* hd* tty* pty* ...
>
> The problem happens when an hour later, root issues the fourth command:
>
> # insmod lp
>
> I want this to create /dev/lp0, but not create /gaol/dev/lp0.
OK, then:
# mount -t devfs none /gaol/dev
# cd /gaol/dev
# rm -f lp{0,1,2} sd{a,b,c,d,e} hd{a,b,c,d} ...
because the readdir won't show lp{0,1,2} if the module has never been
loaded. Alternatively:
# echo "null" > /tmp/exclude
# mount -t devfs none /gaol/dev
# cd /gaol/dev
# rm -f `(cd /dev; tar cvXf /tmp/exclude .)`
Removing the entry if it doesn't exist is fine: the internal table
will just mark the entries for /gaol/dev as verboten for that
superblock.
Regards,
Richard....