Re: [B.A.T.M.A.N.] [PATCHv2 3/4] batman-adv: improved roaming mechanism

[Antonio Quartulli <ordex@autistici.org>]

On Wed, May 04, 2011 at 03:52:23PM +0200, Andrew Lunn wrote:
> On Wed, May 04, 2011 at 03:36:37PM +0200, Antonio Quartulli wrote:
> > On Wed, May 04, 2011 at 01:22:34PM +0200, Andrew Lunn wrote:
> > > > +struct roam_adv_packet {
> > > > +	uint8_t  packet_type;
> > > > +	uint8_t  version;
> > > > +	uint8_t  dst[6];
> > > > +	uint8_t  ttl;
> > > > +	uint8_t  src[6];
> > > > +	uint8_t  client[6];
> > > > +} __packed;
> > > > +
> > > 
> > > Maybe put ttl at the end, to help with alignment? 
> > 
> > As I did for the tt_query packet, the initial four fields are the same as the
> > unicast_packet so that I can exploit route_unicast_packet() instead of writing
> > routing function.
> > 
> > Is that a major issue?
> 
> No. It just that gcc might optimize accesses to src and client as a
> word read + 1/2 word read, if they where 1/2 word aligned. With ttl
> where it is, src and client are in strange alignments, so gcc will
> have to do byte access. 

Understood. Thanks for the explanation.

> But this is not the fast path, so it does not
> matter much.
> 

Exactly..So I think we can leave as it is in this case

> > > > +	tt_global_add(bat_priv, orig_node, roam_adv_packet->client,
> > > > +		      atomic_read(&orig_node->last_ttvn) + 1, true);
> > > > +
> > > > +	/* Roaming phase starts: I have a new information but the ttvn has been
> > > > +	 * incremented yet. This flag will make me check all the incoming
> > > > +	 * packets for the correct destination. */
> > > 
> > > The grammar in that comment could be better:
> > > 
> > > 	/* Roaming phase starts: I have new information but the ttvn has not 
> > > 	 * been incremented yet. This flag will make me check all the incoming
> > > 	 * packets for the correct destination. */
> > > 
> > 
> > Thanks and sorry for my poor grammar :)
> 
> Actually, it is mostly very good....
> 
> > Ok..I got the point. Maybe I will not be so drastic but I will follow
> > your suggestion
> 
> Lots of small functions is my style. However, the Linux coding style
> documentation says something similar:
> 
>                 Chapter 6: Functions
> 
> Functions should be short and sweet, and do just one thing.  They should
> fit on one or two screenfuls of text (the ISO/ANSI screen size is 80x24,
> as we all know), and do one thing and do that well.
> 
> It is well worth reading Documentation/CodingStyle
> 


Mh, thank you for showing me this document. I'll deeply read it as soon as
possible! :)

Regards,

-- 
Antonio Quartulli

..each of us alone is worth nothing..
Ernesto "Che" Guevara