Re: ifunit and struct ifnet/ieee80211com

From: Brooks Davis (brooks_at_one-eyed-alien.net)
Date: 09/24/04

  • Next message: Jeremie Le Hen: "Re: STRIP in /usr/share/mk/" 
    Date: Thu, 23 Sep 2004 22:49:17 -0700
To: Phillip Crumpler <listsubs@crippy.mel.crumpler.com.au>

    On Fri, Sep 24, 2004 at 03:23:21PM +1000, Phillip Crumpler wrote:
    > Hi hackers,
    >
    > A few questions re. ifunit and struct ifnet/ieee80211com, if anyone can
    > help me out:
    >
    > I assume that for a wireless interface ifunit will return a pointer to a
    > struct ieee80211com. Is there any way to tell which of these I have, so
    > I don't try to access ieee80211com members in a struct that is actually
    > the smaller infet? Both ethernet and wireless ethernet seem to use
    > if_type == 6 (IFT_ETHER) and if_physical == 0. Can I distinguish which
    > type I have or should I just make sure I know beforehand?

    You need to know that the struct ifnet is actually embeded in a struct
    ieee80211com if you want to access the members. In properly designed
    code this won't generally be ambiguious. If you some how manage to get
    into a state where it is, if_dname is probably your best bet. That sort
    of thing is discouraged though.

    > Also, what is the lifetime of the (struct ifnet *) that ifunit returns?
    > If an interface goes away is the ifnet freed, leaving me with a dangling
    > pointer, or is it kept but marked inactive in some way?

    There is currently no assurance that a pointer to a struct ifnet is
    valid. If you're going to hold a pointer over anything but trivial
    operations, don't. Hold the index and us ifnet_byindex instead.
    Currently that also dies since it returns NULL after attach, but I plan
    to look in to returning a special dead_if to avoid crashes.

    -- Brooks 

    -- 
Any statement of the form "X is the one, true Y" is FALSE.
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  • Next message: Jeremie Le Hen: "Re: STRIP in /usr/share/mk/"

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