netdev - Re: [Patch 4/5] Network Drop Monitor: Adding drop monitor implementation & Netlink protocol

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Message-ID: <20090304114423.GA6139@hmsreliant.think-freely.org>
Date:	Wed, 4 Mar 2009 06:44:23 -0500
From:	Neil Horman <nhorman@...driver.com>
To:	David Miller <davem@...emloft.net>
Cc:	zbr@...emap.net, netdev@...r.kernel.org, kuznet@....inr.ac.ru,
	pekkas@...core.fi, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
	kaber@...sh.net
Subject: Re: [Patch 4/5] Network Drop Monitor: Adding drop monitor
	implementation & Netlink protocol

On Tue, Mar 03, 2009 at 02:16:12PM -0800, David Miller wrote:
> From: Neil Horman <nhorman@...driver.com>
> Date: Tue, 3 Mar 2009 14:21:07 -0500
> 
> > On Tue, Mar 03, 2009 at 09:19:09PM +0300, Evgeniy Polyakov wrote:
> > > > +struct net_dm_config_msg {
> > > > +	size_t entries;
> > > > +	struct net_dm_config_entry options[0];
> > > > +};
> > > 
> > > Isn't size_t have different size on different platforms?
> > > 
> > Probably, but we're only sending this data over netlink sockets, so despite the
> > platform, I don't really see this as an issue.  About the only place for concern
> > I think are cases like x86_64 and ppc64, in the event you have a 64 bit kernel
> > and 32 bit user space, and in those the app can be adjusted to compensate for
> > this.  I suppose I can fixate the size if its a real concern, but I don't think
> > it really is.
> 
> Neil, that is _THE_ concern.  You have to use portable types that
> will be both sized and aligned identically on both 32-bit and
> 64-bit variants of a given platform.
> 
> This means size_t is absolutely not usable.
> 
> We really don't have a clean way to add compat layer translators
> for netlink, so you have to get this right from the beginning.
> 

Understood, I've changed this in my local tree, and will repost when I've
collected remaining comments (I'd like to avoid my usual 30 revisions of patch
:) )
Neil

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