From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [RFC] should we care of COMPAT mode in bridge ?
Date: Mon, 06 Jun 2011 22:12:54 +0200
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To: Arnd Bergmann <arnd@arndb.de>
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Le lundi 06 juin 2011 =C3=A0 22:06 +0200, Arnd Bergmann a =C3=A9crit :
> On Monday 06 June 2011 21:45:40 Eric Dumazet wrote:
> > While trying Alexander Holler patch, I found a 32bit brctl program =
was
> > not able to work on a 64bit kernel. So I had to switch to another
> > machine for my tests.
> >=20
> > brctl addbr mybridge
> > ->
> > socket(PF_FILE, SOCK_STREAM, 0)         =3D 3
> > ioctl(3, SIOCSIFBR, 0xffd509c0)         =3D -1 EINVAL (Invalid argu=
ment)
> >=20
> > Should we care or not ?
> >=20
>=20
> Generally, we try to make all ioctls work in compat mode. For the old
> bridge ioctls, this is currently impossible because it uses SIOCPRIVA=
TE
> ioctls, but it would be easy to add an ndo_do_compat_ioctl.=20
>=20
> The solution that is documented in net/socket.c is to return=20
> an invalid version number for BRCTL_VERSION, in the hope that
> brctl would switch to the newer interfaces. The new style bridge
> ioctls (SIOCBRADDBR, SIOCBRADDIF, ...) are actually supposed to work,
> but I've never tried that.
>=20


I see... problem is brctl does :

int br_add_bridge(const char *brname)
{
        int ret;

#ifdef SIOCBRADDBR
        ret =3D ioctl(br_socket_fd, SIOCBRADDBR, brname);
        if (ret < 0)
#endif
        {
                char _br[IFNAMSIZ];
                unsigned long arg[3]
                        =3D { BRCTL_ADD_BRIDGE, (unsigned long) _br };

                strncpy(_br, brname, IFNAMSIZ);
                ret =3D ioctl(br_socket_fd, SIOCSIFBR, arg);
        }

        return ret < 0 ? errno : 0;
}


So for an old binary, compiled at the time SIOCBRADDBR wasnt there (in
include file I mean), we ended doing :

        {
                char _br[IFNAMSIZ];
                unsigned long arg[3]
                        =3D { BRCTL_ADD_BRIDGE, (unsigned long) _br };

                strncpy(_br, brname, IFNAMSIZ);
                ret =3D ioctl(br_socket_fd, SIOCSIFBR, arg);
        }

And this breaks on 64bit kernel

I guess we shall add some logic in kernel to support SIOCSIFBR
afterall ;)

Thanks !

BTW: I confirm that compiling an up2date 32bit brctl with an up2date
include files is OK on 64bit kernel.