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    SubjectRe: [PATCH] ioctl SIOCGIFNETMASK: ip alias bug 2.4.9 and 2.2.19
    On Mon, 10 Sep 2001, David Weinehall wrote:

    > "[snip] old and the new stuff, please name precisely the objections
    > against portability and compatibility with FreeBSD 4.x aliasing."
    > ^^^^^^^^^^^^^^^^^^^^
    > This is what lead me to my conclusion. Care to clarify? If you simply
    > meant SIOCGIFNETMASK, why not write that instead instead of involving
    > FreeBSD 4.x?!

    Dave, I came up with that because the same piece of code I looked at
    choked on Linux 2.4, but not on FreeBSD 4.4-RC. I tracked this down,
    fixed it and sent the patch. This can all be read from my posts to the

    The issue here is:

    1/ Linux returns ALL addresses to SIOCGIFCONF, no matter if these are visible
    to SIOCGIFNETMASK or not. Invisible addresses are the second and
    subsequent addresses added with ip addr add without using a distinct
    label. This means the innocent application that just feeds the
    SIOCGIFCONF results into SIOCGIFNETMASK will get the netmask for the
    first address. Of course, you can "filter" the addresses through
    SIOCGIFADDR and drop the duplicates after that, but why not fix it for
    the better?

    2/ FreeBSD also uses IP aliases without "logical" interface names such
    as eth0:0

    3/ FreeBSD returns the netmask for the requested address, Linux returns
    the netmask for the first address of the interface.

    4/ I sent a patch to enhance the compatibility with "nameless" IP

    If you talk about NOT fixing the SIOCG* ioctl API, then fix SIOCGIFCONF
    to just return one address per interface regardless how many IPs it
    listens to.

    But this has all been through. Reread my mails, please.
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