linux-kernel - Re: [PATCH net v2] tipc: check minimum bearer MTU

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Message-ID: <20161201175251.GA18850@unicorn.suse.cz>
Date:   Thu, 1 Dec 2016 18:52:51 +0100
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Ben Hutchings <ben@...adent.org.uk>
Cc:     Jon Maloy <jon.maloy@...csson.com>,
        Ying Xue <ying.xue@...driver.com>,
        "David S. Miller" <davem@...emloft.net>,
        tipc-discussion@...ts.sourceforge.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Qian Zhang <zhangqian-c@....cn>
Subject: Re: [PATCH net v2] tipc: check minimum bearer MTU

On Thu, Dec 01, 2016 at 04:11:18PM +0000, Ben Hutchings wrote:
> On Thu, 2016-12-01 at 12:02 +0100, Michal Kubecek wrote:
> [...] 
> > +/* check if device MTU is sufficient for tipc headers */
> > +static inline bool tipc_check_mtu(struct net_device *dev, unsigned int reserve)
> > +{
> > +	if (dev->mtu >= TIPC_MIN_BEARER_MTU + reserve)
> > +		return false;
> > +	netdev_warn(dev, "MTU too low for tipc bearer\n");
> > +	return true;
> > +}
> [...]
> 
> The comment says "check if ... sufficient" but the return value
> indicates the opposite.  Could you make these consistent?

Good point. I suppose renaming the function to e.g. tipc_mtu_bad() (and
rewording the commment accordingly) would also make the code more 
readable without looking at the definition.

I'll wait for other comments and send v3 tomorrow.

> Other than that, this looks OK to me.  I haven't tested any version as
> I don't know how to use TIPC.

I checked that the patch doesn't allow enabling a bearer on top of
device with insufficient MTU and it does for sufficient (100/128), both
in eth and udp case. I also checked that lowering MTU under 100 in eth
case disables attached bearer. I didn't run any deeper test like sending
an actual traffic but the patch shouldn't affect that.

Michal Kubecek