Re: [PATCH 1/3] libnfnetlink byte alignment

[Fabian Hugelshofer <hugelshofer2006@gmx.ch>]

Patrick McHardy wrote:
> Fabian Hugelshofer wrote:
>> Aligns buffers to maximum alignment of architecture to make the cast of
>> char pointers to struct pointers more portable.
>>
>> Signed-off-by: Fabian Hugelshofer <hugelshofer2006@gmx.ch>
> 
> They all seem fine to me, but a union might make it look
> a bit nicer :)

In libnfnetlink the union does not make sense, because multiple casts 
are done from the same buffer at different locations.

For libnetfilter-(conntrack|log) the union would be possible:

Original (aligned):
<< code begin >>
char buf[...] __attribute__ ((aligned));
struct nlmsghdr *nmh = (struct nlmsghdr *) buf;

nfnl_fill_hdr(h->nfnlssh, nmh, 0, pf, queuenum, ...);
<< code end >>

Union style:
<< code begin >>
union {
	char buf[...];
	struct nlmsghdr nmh;
} u;

nfnl_fill_hdr(h->nfnlssh, &u.nmh, 0, pf, queuenum, ...);
<< code end >>

I can rewrite it like this, if desired...