On Sun, Feb 28, 2010 at 05:28:38PM +0100, Pablo Neira Ayuso wrote:
> >>> +struct ulogd_unixsock_option_t {
> >>> + uint16_t option_id;
> >>> + uint16_t option_length;
> >>> + char option_value[0];
> >>> +} __attribute__((packed));
> >>> +
> >>> +#define ALIGN_SIZE 8
> >> Minor question: why align this to 64 bits?
> >
> > I originally used an alignment to 32 bits, but Jan noticed it would
> > break if using options/values on 64 bits (and a test confirmed that). I
> > took 64 bits as the biggest allowed value for integers.
>
> I would need to look into this in more detail, not sure where the
> problem is. I think that you can use something like `struct nlattr' (see
> include/linux/netlink.h) and then nla_put() to add attributes in the TLV
> format (see lib/nlattr.c). Those are align-safe. I'm using something
> similar for conntrackd for the synchronization messages (src/build.c and
> src/parse.c).
>
Yes, this is very similar though NLA_ALIGNTO is set to 4 which will
cause problems with 64 bits integers.
The other way to solve this would be to read integers byte per byte,
like in [1], but I found this not very elegant (and is likely to be slow
compared to aligned access).
Or do you have any preferred solution ? Maybe using nlattr + one special
function for dealing with 64 bits variables ?
Pierre
[1] https://dev.prelude-technologies.com/projects/libprelude/repository/revisions/master/entry/src/include/prelude-extract.h
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