netdev - Re: [PATCH 1/2] batman-adv: Avoid u32 overflow during gateway select

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Date:	Sun, 21 Jun 2015 20:27:45 +0200
From:	Sven Eckelmann <sven@...fation.org>
To:	antonio@...hcoding.com
Cc:	netdev@...r.kernel.org, b.a.t.m.a.n@...ts.open-mesh.org,
	ruben@...ifunk-nrw.de, ruben@...-nrw.de,
	mareklindner@...mailbox.ch, David Miller <davem@...emloft.net>
Subject: Re: [PATCH 1/2] batman-adv: Avoid u32 overflow during gateway select

On Sunday 21 June 2015 09:37:13 David Miller wrote:
> From: Antonio Quartulli <antonio@...hcoding.com>
> Date: Tue, 16 Jun 2015 21:06:23 +0200
> 
> > @@ -133,7 +133,7 @@ batadv_gw_get_best_gw_node(struct batadv_priv
> > *bat_priv)> 
> >  	struct batadv_neigh_node *router;
> >  	struct batadv_neigh_ifinfo *router_ifinfo;
> >  	struct batadv_gw_node *gw_node, *curr_gw = NULL;
> > 
> > -	uint32_t max_gw_factor = 0, tmp_gw_factor = 0;
> > +	uint64_t max_gw_factor = 0, tmp_gw_factor = 0;
> > 
> >  	uint32_t gw_divisor;
> 
> Divides are performed using these variables, so if you make
> them 64-bit the build will fail.  You have to use one of the
> routines in include/linux/math64.h in this situation, but
> realize that this operation is now going to be quite expensive.

Just a minor comment: The division is currently "max_gw_factor >> 18" which 
the compiler also outputs as such (shrd + shr on i586). This is the reason why 
it currently also works on architectures without a native 64 bit div.

Kind regards,
	Sven
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