netdev - Re: [GIT PULL] [IPV6] COMPAT: Fix SSM applications on 64bit kernels.

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Date:	Thu, 24 Apr 2008 23:23:15 -0700
From:	David Stevens <dlstevens@...ibm.com>
To:	YOSHIFUJI Hideaki / 吉藤英明 
	<yoshfuji@...ux-ipv6.org>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	netdev-owner@...r.kernel.org, yoshfuji@...ux-ipv6.org
Subject: Re: [GIT PULL] [IPV6] COMPAT: Fix SSM applications on 64bit kernels.

netdev-owner@...r.kernel.org wrote on 04/24/2008 10:38:45 PM:

> In article 
<OF3A37018B.9EFE360C-ON88257435.00614684-88257435.00622448@...ibm.
> com> (at Thu, 24 Apr 2008 11:52:01 -0600), David Stevens 
<dlstevens@...ibm.com> says:
> 
> >  #ifdef CONFIG_COMPAT
> > +
> > +struct compat_group_req {
> > +       __u32                                   gr_interface;
> > +       struct __kernel_sockaddr_storage        gr_group;
> > +} __attribute__ ((packed));
> > +
> :
> 
> I prefer __compat_sockaddr_storage{} which has definition closer to
> one on 32bit platform.  "packed" seems overkill to me.

        Yes, I saw the discussion you and Dave had. I think it ought to be
at least a local-use declaration with these, rather than in a header. For
these 32-bit ints that are being aligned in this case, the effect is
exactly the same, so I don't object.

> Unfortunately this cannot work.
> __copy_tofrom_user is not available on x86_64 etc.

        I don't know if there is a standard user-user copy
available for these. I wanted to allocate the copy on the
user stack to avoid allocating a temporary kernel buffer and
resetting the segment, but I prefer any approach where the
compatibility portion is done in the compat wrapper without
modification to non-compat code. That approach also has the
advantage of allowing the same wrapper to work with both
v6 and v4.

                                                        +-DLS

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