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SubjectRe: UUIDs (and devfs and major/minor numbers)
tytso@mit.edu writes:
> Explain to me how this is different from mounting devfs onto /kernel
> and using devfsd to populate a disc-based /dev.
>
> It isn't, as long as the names given by devfs are specific enough that a
> user-mode daemon knows what the device is. So if devfs is creating
> names like sda1, or c0t0d0s4, this isn't useful. Names like:
> /kernel/devices/pci/adapecc2980_0/... aren't something you'd *want* to
> appear in /dev, and indeed they don't appear in /dev under Solaris.

I don't see how a hardware-based name like
/kernel/devices/pci/adapecc2980_0/... is any better than one that
includes the host#, bus# and so on.

> But this is a straw-man argument, because it ignores the persistence
> problem with a dynamic disc-based /dev which is managed with a user
> space daemon. This is a problem that's been overlooked.
>
> Consider what happens if your daemon creates and deletes device
> entries based on information from the kernel as to what devices are
> installed (and drivers loaded). When a new device is plugged in, *what
> permissions should be given*? OK, say you get some default. So the
> sysadmin does chmod(1) to change this.
>
> What happens if a device is removed? The daemon deletes the device
> entry. Then the device is plugged back in again. *What permissions
> will be given*?
>
> What makes you think the daemon should delete the device entry? I
> wouldn't. I would keep it there, since the device entry is cheap,
> and most of the time when a device is removed it's likely to come
> back later. In the rare case where hardware is being physically
> removed and it will never come back, the system administrator can
> simply delete the device for good later.

I'd want it removed, since it's clutter if there hardware isn't there.

> Again I'll ask the question I've already asked a number of times. How
> would you cleanly support a construct like this:
> opendir ("/dev/ide/cd");
> loop;
>
> 1) I don't think this is useful.

Yes it is.

Regards,

Richard....
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