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    SubjectRe: LANANA: To Pending Device Number Registrants

    On Tue, 15 May 2001, James Simmons wrote:
    > >
    > > Static devices like /dev/fbN are no different. They were just plugged in
    > > before the OS booted.
    > Actually their are hotplug video cards. High end servers have hot swapable
    > graphcis cards. Would you want to take down a very important server
    > because the graphics card went dead. You pull it out and you plug a new
    > one in. Also their are PCMCIA video cards. I have seen them for the hand
    > held ipaqs. It is only a matter of time before all devices are hot
    > swappable.

    True, but not really necessarily important.

    The thing is, even if the device happens to be soldered down, inside a
    computer that is locked in a safe, the question boils down to a fairly
    simple one: "how do we approach devices?".

    Do we approach devices as something static, or do we approach them as more
    dynamic entities? Do we consider soldered-down devices to be fundamentally
    different from the ones that can be hot-plugged?

    And my opinion is that the "hot-plugged" approach works for devices even
    if they are soldered down - the "plugging" event just always happens
    before the OS is booted, and people just don't unplug it. So we might as
    well consider devices to always be hot-pluggable, whether that is actually
    physically true or not. Because that will always work, and that way we
    don't create any artificial distinctions (and they often really _are_
    artifical: historically soldered-down devices tend to eventually move in a
    more hot-pluggable direction, as you point out).

    Now, if we just fundamentally try to think about any device as being
    hot-pluggable, you realize that things like "which PCI slot is this device
    in" are completely _worthless_ as device identification, because they
    fundamentally take the wrong approach, and they don't fit the generic
    approach at all.

    But this is also why I don't think static device numbers make any
    sense. It's silly to have the same disk show up as different devices just
    because it is connected to a different kind of controller. And it is
    _really_ silly to statically pre-allocate device numbers based on the
    "location" of a device.

    We should strive for a setup where device plugin causes that device to
    show up in /dev, and everywhere else it is needed. And the logical
    extension of such a setup is to consider built-in devices to be plugged in
    at bootup.

    This is true to the point that I would not actually think that it is a bad
    idea to call /sbin/hotplug when we enumerate the motherboard devices. In
    fact, if you look at the current network drivers, this is exactly what
    will happen: when we auto-detect the motherboard devices, we _will_
    actually call /sbin/hotplug to tell that we've "inserted" a network

    It's just that we haven't really mounted the root filesystem yet, so
    user-land never actually "sees" this fact. But I think it's the right
    approach to take, and realizing that even static devices are just a
    sub-case of the problem of dynamic allocation means that you tend to
    automatically also see that static device number allocation is just

    [ The biggest silliness is this "let's try to make the disks appear in the
    same order that the BIOS probes them". Now THAT is really stupid, and it
    goes on a lot more than I'd ever like to see. ]


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