Re: adding if_dev member to struct ifnet

From: John Baldwin (jhb_at_FreeBSD.org)
Date: 09/30/03

  • Next message: Doug Rabson: "Re: finishing the if.h/if_var.h split" 
    Date: Tue, 30 Sep 2003 13:14:39 -0400 (EDT)
To: Poul-Henning Kamp <phk@phk.freebsd.dk>

    On 30-Sep-2003 Poul-Henning Kamp wrote:
    > In message <XFMail.20030930103348.jhb@FreeBSD.org>, John Baldwin writes:
    >
    >>>>Yes, if it helps to remove if_name/if_unit, it is a thing to do. Moreover it
    >>>>sounds a good idea to have the if_dev field into the ifnet structure.
    >>>
    >>> Somebody please explain how this would work for non-hardware
    >>> interfaces like if_loop, if_tun, if_tap etc ?
    >>>
    >>> device_t is what we use to hitch drivers to hardware.
    >>>
    >>> ifnet is what we use to hitch drivers to the netstack.
    >>>
    >>> They should not be tangled.
    >>
    >>You mean like dev_t and device_t shouldn't be tangled like we do
    >>with si_drv1? Oh, wait...
    >
    > I don't think any correctly written driver stores it's device_t in
    > a dev_t. It should store it's softc structure, which should contain
    > pointers to both. Even if there is a driver which does do that,
    > it happens inside the device driver, and it does not handicap the
    > remaining device drivers with its choice.

    Fair enough. I think that Brooks planned to use a NULL device_t for
    interfaces w/o a backing new-bus device. However, that means you
    still need if_name for all the non-newbus devices, so this seems
    somewhat pointless if if_name is the only reason. Another counterpoint
    is that the new-bus namespace and the netif namespace aren't the same
    anyway and that seemed to be the point of this linkage. The
    dev_t <> softc <> device_t linkages aren't about unifying namespaces.

    > There is nothing in the "data-model" of the kernel that says that
    > a network interface corresponds to exactly one hardware device
    > and more importantly: there shouldn't be either.

    Agreed.

    > If all you want is an extra field in "struct ifnet" to hang driver
    > information on, then by all means add that field. As long as you
    > give it type "void *" and make it private to the driver I have no
    > problem with that.

    Fair enough, though I don't think this is what Brooks was after. 

    -- 
John Baldwin <jhb@FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve!"  -  http://www.FreeBSD.org/
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